KEYS TO THE FRESHWATER MACROINVERTEBRATES OF MASSACHUSETTS

NO.3 : CRUSTACEA MALACOSTRACA ( Crayfish , lsopods , Amphipods )

Massachusetts Department of Environmental Quality Engineering DIVISION of WATER POLLUTION CONTROL Thomas C. McMahon, Director KEYS TO THE FRESHWATER MACROINVERTEBRATES

OF MASSACHUSETTS (No. 3): Crustacea Malacostraca

(crayfish, isopods, amphipods)

Douglas G. Smith Museum of Zoology University of Massachusetts Amherst, Massachusetts and Museum of Comparative Zoology Harvard University Cambridge, Massachusetts

In Cooperation With

The Commonwealth of Massachusetts Technical Services Branch Division of Water Pollution control Westborough, Massachusetts

Executive Office of Environmental Affairs James s. Hoyte, secretary Massachusetts Department Environmental Quality Engineering s. Russell Sylva, Commissioner

Division Water Pollution Control Thomas c. McMahon, Director

January, 1988

PUBLICATION: #15,236-61-250-2-88-CR Approved by Ric Murphy, State Purchasing Agent TABLE OF CONTENTS

ITEM PAGE PREFACE iii INTRODUCTION 1 CLASSIFICATION OF MASSACHUSETTSFRESHWATER MALACOSTRACANS 13 HOWTO USE THE KEY ...... 16 GENERAL KEY TO THE FRESHWATERMALACOSTRACA OF MASSSACHUSETTS 20

CRAYFISH HYBRIDS 40 DISTRIBUTION OF MASSSACHUSETTSFRESHWATER MALACOSTRACANS 43 GLOSSARY OF TERMS USED IN KEY 49

BIBLIOGRAPHY 50

ii PREFACE The present work, concerning the identification of freshwater malacostracan crustaceans occurring in Massachusetts, represents a continuation of a series of guides dealing with the identification of benthic macroscopic invertebrates of the inland freshwaters of Massachusetts (Smith, 1986b, 1987a). The goal of this and other guides or handbooks is to introduce various groups of freshwater invertebrates to persons working in any of several areas of the freshwater ecology of Massachusetts. Although the guides are limited in their geographic scope to areas within the political boundaries of Massachusetts, many of the organisms treated, and information regarding their ecology and biology, will be applicable to neighboring regions. To increase the usefulness of this and other guidebooks, complete regional bibliographies of the distribution of included species are provided. Also, general information discussing the usefulness of the particular species covered in this manual as biological indicators of water quality is provided. An attempt has been made to be as complete and thorough as possible in the coverage of the species of each group living in Massachusetts. Additionally, all the known published accounts relevant to each discussed invertebrate group as it occurs in the state has been presented. Nevertheless, omissions will become evident and the author will always be interested in acquiring new or overlooked information regarding these animals, particularly previously undocumented occurrences of species within the state. The author accepts responsibility for any and all mistakes of fact or interpretation appearing hereafter. Over the years, a number of people have assisted this project by providing data or acquiring specimens in the field for study or allowing access to museum collections containing material relevant to the present document. These people are (in alphabetical order): Thomas Andrews, Randall Chambers, David Halliwell, Karsten Hartel, Allen Launer, Herb Levi, Stuart Ludlam, Lawrence Master, Betty Anne McGuire, Mark Mello, Ann Pratt, Alan Richmond, Tim Simmons, William Wall, Kirk Wright, and the students of the Biology of Higher Invertebrates course at the University of Massachusetts in Amherst. The author gratefully acknowledges Dr. Horton H. Hobbs, Jr., and Dr. John R. Holsinger for providing helpful comments on specific sections of the key. The author also thanks Michael Bilger, u.s.E.P.A., Lexington, Massachusetts, for providing many useful comments. The drawings appearing in the following key are based on specimens collected in Massachusetts. Figure 35 is redrawn from Smith (1983b). Other figures have been adapted from Smith (1984).

iii INTRODUCTION The use of benthic macroinvertebrates as both indicators of various forms of pollution and as test organisms for determining the presence of toxic substances is well established (Mackenthun and Ingram, 1.967; Myslinski and Ginsburg, 1.977; cairns, 1.979; James, 1.979). Early studies on the changes in the diversity of macro invertebrates in large North American (Forbes and Richardson, 1.91.3; Richardson, 1921) and European rivers (see Hawkes, 1979, for review) first illuminated the importance of community structure of benthic invertebrates in determining the presence and degree of pollution. Later studies in North America which employed quantification methods and added chemical parameters (Mason et al., 1.971.; Starrett, 1.971.) reiterated what was previously observed and further evidenced the value of invertebrates as biological indicators of changing water quality. As a result of the earliest observations, and subsequent refinement of sampling and measurement procedures, increasingly diverse and complex methods for analyzing invertebrate community structure have been developed. Hynes' (1974) pioneering treatise includes one of the first attempts to synthesize these methods. Additional discussions and reviews of methods for analyzing invertebrates as indicators of pollution have been prepared by the United states Department of the Interior (USDI, 1.969), Goodnight (1973), Wilhm (1.975), Hawkes (1979), and Lenat et al. (1.980), and many others. The effects of toxins and ways of measuring toxins in macroinvertebrates has emerged recently as an important area of research. Information gathered from such studies adds to the usefulness of macroinvertebrates as pollution indicators by establishing lethal limits of various substances in particular species. Furthermore, assessing the ability of macro invertebrates to bioaccumulate and biomagnify toxic substances can provide a means to monitor the health of the aquatic environment. Recent syntheses which have brought together much of the data on the effects and measurement of toxicity in invertebrates (Schultz and Klement, 1.963; Polikarpov, 1966; Hart and Fuller, 1.974; Buikema and cairns, 1.980; Buikema et al., 1.981.) provide the foundation for further study, particularly in areas of heavy metal, pesticide, and radiation contamination. Concerning Massachusetts, the application of certain toxicity tests which utilize macroinvertebrate species has been discussed by Szal (1.984). A necessary requirement in pollution indicator selection or toxic substance assessment is the proper identification of the animal utilized. Improper identification of a particular species used in analysis can lead to erroneous interpretations and consequently, dubious conclusions. Additionally, the inability, due to the lack of sufficient documentation, to confidently identify an organism to species limits investigators to genus or family level identification upon which they must base their

1 conclusions. On a regional basis, assessments based on limited taxonomic information are reduced in value. For those who are engaged in the study of organisms inhabiting Massachusetts, this and other existing (Smith, 1986a, 1987a) or planned manuals are an attempt to alleviate some of the problems associated with inaccurate taxonomic identification. Animals covered in this volume include the freshwater malacostracan Crustacea. Besides demonstrating enormous value in the study of physiology and natural history, malacostracans play an important role in research on pollution and its effects on biological systems. The broad use of malacostracans in looking at specific problems of pollution (e.g., Pederson and Perkins, 1986) and in evaluating methods determining pollution effects in general (Nebeker et al., 1984) is well founded. The importance of malacostracans to such investigations is due to the wide range of tolerance exhibited by the many taxa included in the group. Whereas several species, such as upland stream-inhabiting crayfish and spring-dwelling amphipods, are clearly clean water forms, isopods have been shown to be somewhat pollution tolerant and have been useful as recovery zone indicators (Bartsch and Ingram, 1959; Hynes, 1974). Certain crayfish species are apparently also somewhat pollution tolerant as indicated by their presence in and around untreated outflows of waterside industries (D.G. Smith, personal observation). Among the principal groups of North American malacostracans, the crayfishes have been probably the most studied with respect to their tolerance to pollutants and their potential use as indicator organisms. The popularity of crayfish in pollution related investigations is likely due to their large size and the relative ease in identifying and maintaining them. Hobbs and Hall (In Hart and Fuller, 1974) have reviewed much of the literature concerning the effects of several types of pollution on crayfish. In recent years, technical advances in both the measurement of levels of toxicity and in electron microscopy have enabled more detailed analyses of toxins in crayfish and other malacostracans as well (e.g., Doughtie and Rao, 1984; Pinkney et al., 1985; Roldman and Shivers, 1987). Wastewater treatment has been a welcome outcome of many years of study which showed a direct relationship between increased pollution and a decline in biotic diversity. More recent and as yet unresolved threats to the health of aquatic systems include the increased use of pesticides and the rapid acidification of inland waters. Sanders (1969) surveyed most of the known pesticides in use at the time, and still in use, and measured their toxicity to a freshwater amphipod species. Other studies, using malacostracans as test organisms, have looked at specific pesticides, such as DDT (Dimond et al., 1968) and PCP (Spehar et al., 1985). Acidification due to acid precipitation and loss of buffering capacity in many ponds and lakes in northeastern North

2 America has led to several investigations on the effects of increased acidity on organisms, especially malacostracans. crayfish are particularly sensitive to decreased pH (Wood and Rogano, 1986), particularly while in the juvenile stage (France, 1984), although there seems to be some variation in the degree of tolerance among species (Berrill et al., 1985). Thus crayfish appear to be good indicators of acidification in freshwater environments. Another possible indicator of increasing acidity is Hyalella azteca, a widely distributed amphipod common in Massachusetts. As shown by Stephenson and Mackie (1986), this species seems to be eliminated in acidified lakes. Hyalella azteca could prove to be a valuable indicator of similar conditions locally as its environmental parameters in unpolluted Massachusetts freshwaters have been already determined (Travis, 1978).

3 THE MALACOSTRACA

The class Malacostraca is one of several classes of the Crustacea, a super group of arthropod-like organisms characterized by a chitonous exoskeleton which is periodically shed, biramous appendages, and a head with five pairs of appendages consisting of two pairs of antennae, a pair of mandibles, and two pairs of maxillae which are involved with feeding functions. Al though the Crustacea has for a long time been considered a class of the phylum Arthropoda, recent works (e.g., Clarkson, 1986; Schram, 1986) treat the Crustacea, and other major arthropod divisions, as separate and distinct phyla. This reassessment is in response to the long held contention that the Arthropoda actually comprises several discrete groups of organisms with possibly separate phylogenetic origins. The Malacostraca is one of the largest and most diverse groups of crustaceans. Members of the class also attain the greatest size among the Crustacea, though the real giant species are restricted to marine environments. Malacostracans are distinguished from other crustacean classes on the basis of the relatively constant number of body segments (15 or 16, exclusive of the head) and the presence in some groups of a one-piece covering or carapace, which encloses the head and one or several fused segments of the thorax. The biramous character of the appendages is retained only in the head region and the abdomen. The appendages of the thorax are uniramous and are adapted primarily for ambulatory locomotion and, to a lesser extent, behavioral and feeding functions. In malacostracans, the sexes are always separate and sexual dimorphism is often exhibited by certain appendages. The great majority of malacostracan species are found in brackish water and saltwater but certain groups have invaded and become successful in freshwater. The orders with freshwater representatives living in Massachusetts are the Decapoda, Isopoda, and Amphipoda. The following discussion of these three orders employs the terminology of McLaughlin (1980), except for the use of the terms thoracopod and gnathopod, which, for purposes of this manual, are not used. Instead, the term pereopod is used to describe all the larger walking legs. DECAPODA Decapods, or crayfish, are the largest malacostracans living in Massachusetts' freshwaters. They are, by virtue of their size, the most easily recognizable as well. Other decapods, including shrimps and crabs, occur in freshwater, however, no freshwater species of the latter two forms are known to inhabit Massachusetts. The Decapoda are characterized by having the head and thoracic segments combined, though not necessarily fused, into a cephalothorax which is covered by a carapace (Fig. la) . The head portion of the cephalothorax contains a median rostrum and a pair of stalked eyes (Fig. la). The thoracic segments bear

4 five pairs of large walking legs or pereopods. The legs of the first pair are modified into claws (Figs. 2a, 8). The claw itself is composed of the two distal segments of the appendage, the propod and the dactyl (Fig. 2a) and is used by the animal for various behavioral and feeding activities. Segments of the abdomen (Fig. la) are not fused and bear uniramous or biramous appendages called pleopods. The telson is flattened and lies between two similarly flattened abdominal uropods (Fig. la). Only one family of decapods, the Cambaridae, occurs in Massachusetts. Cambarid crayfish are found exclusively in North America east of the Rocky Mountains, though a few species have been introduced into other parts of North America and elsewhere. Crayfish in the family Cambaridae are diagnosed from species of other families by a number of subtle morphological characteristics including the structure of certain secondary sexual organs. However, a single biological phenomenon exhibited by cambarids not only distinguishes them from other crayfish families, but is unique among animals. Adult cambarid crayfish undergo a cyclic dimorphism which affects the appearance and activity of the primary and secondary sexual organs. During the sexually active phase, the first pleopods of the male, which are located at the abdomen-cephalothorax juncture (Fig. 3), contain sharp tips (Fig. 4a) and transmit sperm to the annulus ventralis of the female. At the conclusion of the reproductively active period the animals enter an inactive phase which is expressed physiologically by a molt which produces among other changes a pleopod incapable of sperm transport (Fig. 4b). Males in the active phase are referred to as first form males while those in the inactive phase are called second form males. The first pleopodia of second form males are curiously identical with those of juvenile males. Readers interested in learning more about this phenomenon are referred to Crocker and Barr (1968). Females of cambarid crayfish do not possess a specialized first pleopod but instead have a ventral and medially placed annulus ventralis which receives and stores sperm. Prior to laying eggs females seek a secluded place to hide. Once in seclusion, eggs are oviposited into a secreted envelope which encloses the flexed abdomen. During oviposition, the eggs are fertilized by the stored sperm. After all the eggs have been deposited and fertilized, the adhesive excretion dries, adhering the eggs to the abdominal appendages. Development through the larval stages occurs within the egg. After a few weeks, or possibly longer in some species, the young crayfish hatch. The Cambaridae are widely distributed throughout central and eastern North America. In the Appalachian Mountain region and southward the family reaches its greatest diversity. However, in more northern areas affected by Pleistocene Period glaciations, crayfish diversity is low, particularly in New England. Because of New England's remoteness with respect to its drainage systems and drainage history, very few species were able to colonize the region following the recession of the ice sheet. Nonetheless,

5 several species are presently known to occur in Massachusetts, but most of these species are present as a result of artificial introductions. As can be determined by museum records and literature documentations these introductions commenced in the early 1900 1 s and were probably carried out by visiting fishermen, aquaculturists, aquarium enthusiasts, and scientific researchers. Introductions have been most successful for species which have already adapted to cold climatic conditions existing in their natural range outside of New England, and a few of these introduced forms are presently the most widely distributed crayfish species in Massachusetts. Because the crayfish fauna of Massachusetts is dominated by species introduced from other parts of North America, no specific zoogeographic pattern can be determined. The few species which appear to be native suggest that, at best, New England lies at the extreme periphery of crayfish dispersal and has come to be inhabited (naturally) only by species which have extensive ranges throughout eastern North America. ISOPODA The freshwater Isopoda are relatively small malacostracans, rarely exceeding 15 millimeters in length. Freshwater isopods are sometimes referred to as water slaters. This name is most likely an adaptation of the term slater which is a common name for the terrestrial isopods, also called sow bugs. Freshwater isopods have a very distinctive flattened appearance. When viewed dorsally, the body segments are quite wide (Fig. lb). The head is fused with the first thoracic segment and contains two sessile eyes (Fig. lb). The remaining thorax is comprised of distinct segments (2-8) which bear the walking legs or pereopods. There is no carapace. The first pair of pereopods (pereopod 1) are subchelate, meaning that each leg of the first pair, especially in males, possesses a large propod and an opposable nail-like dactyl (Fig. 2b). The abdomen is composed of both separate and fused segments, and is fused with the telson. The fused portion, including the telson, is usually called the pleotelson (Fig. lb) . Some of the paired appendages of the abdomen are modified to function as gills. A pair of terminal uropods (Fig. lb) extends from the posterior margin of the pleotelson. The first two abdominal segments are not fused and are partially obscured by the last thoracic segment (Fig. lb). In the male, the appendages associated with the first abdominal segments (Fig. 5), particularly pleopod 2, assist in the transmittal of sperm to the female. In females, the first pleopodia are absent, while the second pair are never biramous (lack two rami). Females typically lay eggs during the spring and early summer. Eggs are deposited into a marsupium which is located on the ventral side of the animal between the pereopods. The marsupium

6 R E

__,,,------

.---·····-. ('

lilt'-- ;,-} \_.._.-~-;.._/ t"-' ' u u

T la lb le

p

/i'('(I I

I I p D D ~~~ 2a 26 2c

Fig. 1. Dorsal view of representative malacostracans: (a) decapod, (b) isopod, (c) amphipod. Fig. 2. Distal six segments of the first or second pereopod of representative malacostracans: (a) decapod first pereopod, (b) isopod first pereopod, (c) amphipod second pereopod. Not to scale.

7 Glossary of structures in Figures la-c and 2a-c.

A-A'= separation of thorax and abdomen

C = carapace D = dactyl

E = eye H = head P = propod PT= pleotelson R = rostrum T = telson U = uropod

8 is formed by several overlapping oostegi tes which are lamellar appendages arising from the bases of the pereopods. Following a short developmental period, the juvenile isopods hatch but remain within the marsupium for a brief time before being liberated. The Isopoda are represented in freshwaters of Massachusetts by a single family, the Asellidae. Asellids are, for the most part, freshwater inhabiting isopods found throughout the Northern Hemisphere. The family is very large and several generic and subgeneric categories have been proposed, though not universally accepted, to accommodate a vast array of described species. In North America, the family has achieved great success and species are known from virtually all types of aquatic habitats, including temporary and subterranean. The species living in Massachusetts are not specialists for any habitat, but are apparently not known to invade subterranean or temporary environments in Massachusetts. As is the case with non-introduced decapods, the New England isopod fauna appears to be depauperate. AMPHIPODA The amphipoda are small malacostracans, similar in size to isopods. Some species reach 15 millimeters in length, others are quite minute and never exceed five or six millimeters. Freshwater amphipods do not have widely accepted common epithets, other than the terms "scud" or "sideswimmer." Often times it is simply convenient to attach the term amphipod to some other descriptive word when referring to a specific species. Amphipods, though somewhat similar to isopods, are quite distinct organisms. Unlike isopods, which are broadest when viewed dorsally, amphipods are narrower when viewed from the same perspective (Fig. l.c). Amphipods do share with isopods a head {Fig. le) that is fused with the first thoracic segment. Sessil.e eyes may or may not be present, depending upon the species. Each free segment (2-8) of the thorax contains a pair of pereopods. The first and second pair of pereopods are subchelate and often called gnathopods. The second pair (Figs. 2c, 7a) of subchelate pereopods is usually, but not always, larger and more developed than the first pair in Massachusetts species. As in decapods and isopods, the propod and dactyl of the subchelate pereopods {Fig. 2c) are opposed. Some sexual dimorphism exists in the degree of development of the subchelate pereopods in amphipod species. The remaining pereopods are not modified and are primarily locomotor in function. Amphipods are distinct from isopods in that the abdominal segments are usually not fused {none fused in any Massachusetts species) nor are any abdominal segments fused with the telson (Fig. le) • The tel son exhibits wide variation among Massachusetts species of amphipods. The abdominal appendages, or pleopods, are separated into two distinct morphological groups. The anterior three pairs are birarnous swimmerets while the posterior three pairs are called uropods (Fig. 7a). The uropods are numbered 1. through 3 and correspond to the last three

9 abdominal segments. Uropods 1 and 2 are always biramous whereas uropod 3 is either biramous (Fig. le) or uniramous (Fig. 7c), depending upon the species. The morphology of the rami of uropod 3 also varies among Massachusetts species and is an important taxonomic tool in distinguishing different genera and species. Male amphipods, unlike decapods and isopods, do not possess highly modified appendages, abdominal or otherwise, that are involved with sperm transfer. Following copulation, usually in the spring of the year in Massachusetts species, females lay eggs. The females deposit eggs into a marsupium, which is very similar in morphology to the marsupium of isopods and occupies most of the ventral side of the thorax. Development through early larval stages occurs within the egg. Upon hatching, the young amphipod, similar in morphology to the adult, remains in the marsupium for a short time before leaving the parent. Several families of amphipods are known to occur in North American freshwaters. Freshwater amphipods rival isopods and decapods in their success in invading freshwater habitats. Species are found in virtually every kind of aquatic habitat and probably exceed isopods and decapods in total taxonomic diversity. In Massachusetts, three families are represented, containing anywhere from one to several species. The Gammaridae in Massachusetts freshwaters comprises a small group of somewhat homogeneous species that are fairly restricted in distribution. One species has an isolated inland distribution while the remaining three are confined to coastal regions and two of these are characteristically brackish water species, only occasionally being found in freshwaters. The second family, the Crangonyctidae, is the most taxonomically diverse of freshwater amphipod families in Massachusetts. It includes the only two troglobitic species of animals known to occur in the state. Other species in the Crangonyctidae are found in habitats ranging from small wetlands to large rivers. The third amphipod family found in Massachusetts freshwaters is the Hyalellidae. The group is largely tropical in its distribution and has only one representative, Hyalella azteca, living in Massachusetts. Nonetheless, the species is the most widespread amphipod in the state and is found in practically all permanent aquatic habitats.

10 Pl

8mm 3 4a 4b

:r---~/ ------~-Il .....J PII

3mm 5 6 Fig. 3. ventral view of the thoracic-abdominal region of a male decapod, Orconectes limosus; PI=first abdominal pleopod. Fig. 4. Left first pleopod in (a) first and (b) second form male Q. limosus, Xl0; CP=central projection, CPL=central projection length, PL=pleopod length. Fig. 5. ventral view of thoracic­ abdominal region of a male isopod; PII=second abdominal pleopod. Fig. 6, The second pleopod of a male isopod, Xl00; E=endopod.

11 -d

UROPOD I

PEREOPOD 7

PEREOPOD 2 ANTENNA 2 la Imm

lb le ld

Fig. 7. An amphipod, Hyalella azteca: ( a) adult male, (b) tel son, (c) uropod 3, (d) uropod 2; 7b, 7c, and 7d xlOO and correspond to b, c, and din 7a.

12 CLASSIFICATION OF MASSACHUSETTSFRESHWATER MALACOSTRACANS The classification of freshwater malacostracans in Massachusetts is shown in Tables 1 and 2. The higher classification (above family) of malacostracans covered in this key is after Bowman and Abele (In Abele, 1982). Within the Decapoda, the arrangement of genera under the family Cambaridae follows Hobbs (1974a). Subgenera have been designated for the genera Cambarus (Hobbs, In Holt et al., 1969), Procambarus (Hobbs, 1972a), and designated or revised for Orconectes (Fitzpatrick, 1987). However, subgeneric characters do not provide additional characters for the recognition of Massachusetts species and are not listed. The taxonomy of species of freshwater decapods inhabiting Massachusetts is stable with a few exceptions. Species names and their arrangement within genera are listed following Hobbs (1974b). Early works that listed occurrences of crayfish in Massachusetts placed all under the species Cambarus bartonii (Gould, 1841; Rathbun, 1905). Such accounts, though of historical value, are not reliable in the sense of modern systematics. The first comprehensive treatment of crayfish in which specific Massachusetts records are listed is Faxon (1914). Other, subsequent, works containing Massachusetts records from which Table 1 was developed include Hobbs (1972b), Crocker and Barr (1968), and crocker (1979). Additional studies, detailing the distribution of certain species in the state, are found in Smith (1982b, 1984). The occurrence of Procambarus clarkii in Massachusetts is based on an unpublished museum record (Museum of Zoology, University of Massachusetts at Amherst). The classification of Massachusetts freshwater isopod species follows Williams (1970) and incorporates the generic revision of Bowman (1975). As with the Decapoda, early accounts listing the occurrence of freshwater isopods in Massachusetts (Gould, 1841; Rathbun, 1905) are unreliable because of outdated taxonomy. The species list (Table 1) is derived from records discussed by Williams (1970, 1972) and Smith (1983a). The families and genera of the freshwater Amphipoda represented in Massachusetts (Table 2) is from Holsinger (1972) as amended by Karaman (1974) and Holsinger (1977). Subgenera, though proposed in the past for many genera, are not widely accepted and are not adopted here. The taxonomy of species occurring in Massachusetts is reasonably stable. General systematic and zoogeographical studies relevant to species covered in this manual include a few historical accounts (Rathbun, 1905; Kunkel, 1918), but now somewhat dated taxonomically, and Bousfield (1958) and Bell (1971). Other recent accounts providing specific information on the taxonomy and distribution of Massachusetts freshwater amphipods are for the Crangonyctidae, Bousfield (1973), Smith (1977b, 1981c, 1982a, 1983b, 1984, 1986a, 1987b), and Holsinger (1978), and for the Gammaridae, Bousfield (1973) and Smith ( 1982a, 1984) .

13 Table 1 The classification and species of freshwater decapod and isopod malacostracans found in Massachusetts.

Class Malacostraca

Order Decapoda

Family Cambaridae

Cambarus bartonii (Fab. 1798)

Cambarus robustus Girard 1852

Orconectes immunis (Hagen 1870)

Orconectes limosus (Raf. 1817)

Orconectes obscurus (Hagen 1870)

Orconectes propinguus (Girard 1852)

Orconectes rusticus (Girard 1852)

Orconectes virilis (Hagen 1870)

Procambarus acutus acutus (Girard 1852)

Procambarus clarkii (Girard 1852)

Order Isopoda

Family Asellidae

Caecidotea communis (Say 1818)

Caecidotea racovitzai racovitzai (Williams 1970)

14 Table 2. The classification and species of freshwater amphipod malacostracans found in Massachusetts.

Order Amphipoda

Family Crangonyctidae

Crangonyx aberrans Smith 1983

Crangonyx richmondensis richmondensis Ellis 1940 1

Crangonyx pseudogracilis Bousfield 1958

Stygobromus borealis Holsinger 1978

stygobromus tenuis tenuis (Smith 1874)

Synurella chamberlaini (Ellis 1941)

Family Gammaridae

Gammarus deubeni Liljeborg 1851

Gammarus fasciatus Say 1818

Gammarus pseudolimnaeus Bousfield 1958

Gammarus tigrinus Sexton 1939

Hyalellidae

Hyalella azteca Saussure 1857

1rn Massachusetts, this subspecies intergrades with Q. ~­ laurentianus Bousfield 1958 in central and western parts of the state. See "Notes in key."

15 HOW TO USE THE KEY The general key is designed to accomodate as many useful characters as are available to maximize the chance for a correct identification. In addition to the general key, a table is provided (Table 3) which can be used as a short cut method for the identification of the families and genera of freshwater amphipods occurring in Massachusetts. Where time is a factor, Table 3 can streamline the identification process. However, the general key should be used in all other situations as it provides a greater number of characteristics of the specimen to choose from. In order to correctly determine malacostracan species from one another it is necessary to have adult specimens represented in the collection. The presence of adults varies with the season depending upon which malacostracan group is being surveyed. Adult decapods and isopods can be found almost year around, with the possible exception of late spring and early summer. Most amphipods, including those species in the family Gammaridae, Hyalella azteca, and a few crangonyctids, can be found as adults during most months of the year. However, some species or genera of the Crangonyctidae (a few species of Cranqonyx and the genus synurella) are adult only in the spring, rarely into early summer. During the remainder of the year, these crangonyctid species are represented by juveniles and do not demonstrate sufficient characters to guarantee identification. Unlike many other invertebrate groups, positive identification can be made with only a few adult specimens available, although it is desirable to have a larger sample to work with.

Specimens should be preserved in the field. This is accomplished by placing specimens directly into a 10 percent formalin solution buffered with borax powder or marble chips. In the case of isopods and amphipods, an equal volume of 70 percent ethyl or isopropyl alcohol should be added to initiate clearing, a process which will prove useful during the latter stages of preparation. It should be noted that decapods (crayfish) have a tendency to dismember the claws (first pair of pereopods or legs) during preservation. This must be kept in mind when mixed species collections are made. Fixation in formalin takes from a few hours (smallest amphipods) to a few days (largest decapods). Once fixation is completed, the specimens should be washed in several changes of tap water. (Skin contact with formalin is not advised because of formalin's toxic nature.) Following washing with water, decapods can be left in a sealed container without fluid and allowed to drain for a few days. This will allow the tissues to dehydrate a bit thus preventing excessive dilution of the final preservative. Drained decapods can then be placed into 70 percent ethyl or 50 percent isopropyl alcohol for permanent storage. A change of alcohols is recommended for decapods, particularly large specimens, after the first few weeks. Arnphipods and isopods can be transferred to similar strength

16 alcohol solutions directly from water. Specimens with collection data should be offered to established museums or placed in an actively curated reference collection when investigations are completed. When identifying specimens of decapods, it is necessary that the adult males be in the first form stage to insure certain identification of species. One of the most important characters in crayfish taxonomy and identification is the morphology of the first pleopod of the first form male. To examine this appendage it is customary to orient the animal so that the ventral surface is facing the investigator (Fig. 3) • Once so positioned, the first pleopod, preferably the animal's left, can be dislodged and viewed separately or simply examined while still attached. While the entire organ is utilized in the key in different circumstances, the distal portion of the pleopod contains structures which are of great importance in the identification process. The tip of the pleopod (in Massachusetts species) has either two or four processes, each demonstrating various shapes depending on the genus and species being examined. Measurements of the pleopod and its components will occasionally be required as well. In this manual, the measurements involve only the total length of the pleopod (following Hobbs, 1972b) and the length of the central projection (Fig. 4). Measurements should be taken using a micrometer with accuracy to tenths of a millimeter, and with the assistance of magnification of up to l0x. All measurements used to determine ratios in the key are based on Massachusetts specimens and all figures are of the first form male and all those of the pleopod show the medial (inner) surface of the animal's left member. Once in a while it will be found that a particular specimen or two will not key out or seem intermediate between others of the same genus in the sample. There are two possible causes for this problem. Crayfish are widely dispersed by humans and there might be additional species not covered in this manual that have been recently introduced into certain locations. Alternatively, the specimen or specimens might be hybrids. (See the special section on crayfish hybrids following the key.) Methods required for the proper identification of isopods and amphipods are similar and include mounting specific appendages on slides for viewing under a compound microscope. Regarding isopods, adult males are necessary as the morphology of the second pleopod of the male provides the critical characters for separating the two species occurring in Massachusetts. Preserved specimens should be placed under a dissecting microscope with the ventral surface facing the investigator (Fig. 5). The second pleopod (Pll in Fig. 5) can be removed intact using forceps. The entire structure (Fig. 6) is then mounted on a slide using glycerin or glycerin jelly as a mounting medium. The preparation is then covered with a cover slip. These mounts are temporary only. The important component of the pleopod is the endopod (Fig. 6), which, at its tip, contains the structures necessary for distinguishing the Massachusetts species. Mount several

17 endopods, if available, in opposite positions to vary the view of the structure. To see all the details referred to in the key, the structures must be viewed at about 400x. The identification of amphipod species requires having only adult females, but having both adult males and females can help considerably in separating species of crangonyx and stygobromus. The characters used to differentiate amphipod genera and species are more plentiful and diversified than in isopods and include morphological attributes of several appendages. The appendages utilized in the key are shown in Figures 2c and 7. In addition to the appendages, the appearance and ornamentation of certain abdominal segments {Fig. le) is important in distinguishing both genera and species. The preparation and examination procedures for amphipod appendages are identical to those described for isopods. For all preparations, the animal should be immersed in fluid and oriented as in Figure 7a. Probably more important to the identification of amphipods than either isopods or decapods is distribution data. Several amphipod species have very restricted distributions in Massachusetts.

18 P3 P5 P4 8

/; 2 ~J 2 y 3 3 4

~ I/ 5 5

9 10

Fig. 8. Adult male decapod, Cambarus bartonii; Pl-5=pereopods 1 through 5. Fig. 9. Proximal segments of pereopods 2 through 5 of Procambarus Ja. acutus. Fig. 10. Proximal segments of pereopods 2 through 5 of Orconectes limosus. Arrows indicate hooks. Scale lines equal 10 mm.

19 GENERAL KEY TO THE FRESHWATERMALACOSTRACANS OF MASSACHUSETTS la Largest specimens well over 30 mm in total length; head and thorax covered by a carapace, eyes stalked, first pereopod modified into a claw (Figs. la,2a,8) ...... DECAPODA(CAMBARIDAE) ..•...... 2 lb Largest specimens under 20 mm in total length; head and thorax not covered by a carapace, eyes sessile, first or first and second pereopods subchelate (Figs.lb,c,2b,c) ...... •.....•...... 11

2a (1) Third and fourth pereopods with hooks on third segment (Fig. 9); tips of male first pleopod with more than two processes, subterminal setae present (Fig. 14a,b) (see note 1) ••• genus Procambarus ..... 3

2b Only third thoracic legs with hook (Fig. 10) (see note 2); tips of male first pleopod with only two processes, subterminal setae absent (Figs. 17b, 20, 22-24,28,30a,b) ...... •••••••.•••...... •...... 4

3a (2) First pleopod of male without shoulder on shaft, cephalic process narrowly pointed and partially obscured by setae (Fig. 14a); claw narrow in shape with low tubercles, carapace with darkly pigmented stripe (Fig. 16).Procambarus £• acutus (see note 3)

3b First pleopod of male with shoulder on shaft, cephalic process broadly truncate and not obscured by setae (Fig. 14b); claw broad in shape with raised tubercles, especially along mesial border (Fig. 15); carapace without stripe .•....•...... •.•...... •. Procambarus clarkii (see note 4)

4a (2) Margins of rostrum broadly curving towards tip, angles of margin without spines (Figs. ll,17a,18a); central projection of male first pleopod with a subterminal notch (Figs. 17b, 18b) ...... •.•.•..•. . . . . • . • ...... • . . . genus Cambarus .•...... •..... 5

20 4b Margins of rostrum forming a distinct angle towards tip, angles usually provided with spines (Figs. la,12,13) (see note 5); central projection of male first pleopod produced to a fine point, no subterminal notch (Figs. 4a,20, 22-24, 28,30a,b) •••...... genus Orconectes ••••.•...... ••...... 6

5a (4) Apical portion of rostral margin forming a nearly 90 degree angle with basal portion (Fig. 17a) , propod of claw with a single row of low tubercles along mesial margin (Fig.17c) •...• Cambarus bartonii

5b Apical portion of rostral margin forming an angle decidedly less than 90 degrees with basal portion (Fig. 18a), propod of claw with a distinct depression along lateral margin and two distinct rows of tubercles along mesial margin (Fig. 18c) ••..•••...... ••••... Cambarus robust us

6a (4) Central projection length 13 to 19 percent of pleopod length, tips of pleopod divergent (Figs. 4a,20); anterior side of carapace with a patch of spines (Fig. 19) •...... Orconectes limosus

6b Central projection length greater than 19 percent of the pleopod length, tips of pleopod either parallel or convergent; anterior side of carapace with low tubercles, but never with spines other than cervical spine (Fig. 21) ....•.•..•.....••.... 7

7a (6) Pleopod tips straight or slightly convergent, with or without a distinct shoulder on the shaft (Figs. 22-24) •...... •.•...... •..... 8

7b Pleopod tips distinctly curved in same direction, shaft without a distinct shoulder (Figs. 28, J0a,b) ••••••••••••••••••••••••••••••••••••••••••• 10

8a (7) Central projection length 20 to 28 percent of the pleopod length, pleopod shaft with or without a distinct shoulder (Figs. 22, 23) ; rostral margins not concave (Figs. 13, 26) ••...... ••...... 9

21 8b central projection length 34 to 41 percent of the pleopod length, pleopod shaft with a distinct shoulder (Fig. 24); rostral margins slightly concave (Fig. 25) ••...... Orconectes rusticus

9a ( 8) Pleopod shaft with a distinct shoulder, pleopod tips abutting each other (Fig. 22); rostrum without a low median carina (Fig. 13) ...... •...... • • • • • ...... • • • . . • • • • . . Orconectes obscurus

9b Pleopod shaft without a distinct shoulder, pleopod tips clearly separated and somewhat convergent at the tips (Fig. 23); rostrum with a low median carina (Fig. 26) ...... •...... •.•...... •... •...••...•••••••• Orconectes propinguus (see note 6)

10a (7) Proximal apposable portion of dactyl of claw with a distinct incision (Fig. 27), pleopod tips strongly curved throughout their length (Fig.. 2~) ... ,, ...... Orconectes 1mmun1s

10b Proximal apposable portion of dactyl of claw without a distinct incision (Fig. 29), only distal half of pleopod tips curved (Fig. 30a,b) ...••••...•...... Orconectes virilis (see note 7) lla (1) Body broad in dorsal view, abdomen fused with telson (Fig. lb); only first pereopod subchelate (Fig. 2b) (see note 8) ...• ISOPODA (ASELLIDAE) .... 12 llb Body narrow in dorsal view, abdomen and telson not fused (Fig. le); first and second pereopods subchelate (Figs. 2c,7a) ...•.•• AMPHIPODA.•...... 13

12a (11) Tip of endopod (Fig. 6) with two processes, a long tubular cannula and a broad caudal process (Fig. 31a,b) ••...•...... • Caecidotea communis

12b Tip of endopod (Fig. 6) with three processes, a short tubular cannula, a broad caudal process, and a hook shaped mesial process (Fig. 32a,b) •••...... Caecidotea .i;:. racovitzai

22 r r

11 12 13

E E

s \ m

14a 146 15 p

16

Fig. 11. Carapace of Cambarus bartonii. Fig. 12. Carapace of Orconectes immunis. Fig. 13. Carapace of Q. obscurus. Fig. 14. Tip of first pleopod of (a) Procambarus f!.. acutus and (b) £. clarkii. Fig. 15. Claw of £. clarkii. Fig. 16. Claw and carapace of£. _g_. acutus; cp=cephalic process, m=mesial margin, p=pigment stripe, r=rostral margin, s=shoulder. Scale lines equal 10 mm except Fig. 14. 23 ·I7a 17b 17c

cp \

' ,1 ~

I t ~ " ' 1 ,,0 '~ 't. ,;, IO ~ f' ~ i./.o ; I O" (! t"I lli\ 0 d :v--,_)1} ,~ ',.., ,] ..

,)

118a 18b 18c

Fig. 17. Cambarus bartonii: (a) rostrum, (b) first pleopod, (c) claw. Fig. 18. .Q. robustus: (a) rostrum, (b) first pleopod, (c) claw. Arrows in Figs. 17a and 18c indicate apical margin of rostrum, arrows in Figs. 17c and 18c indicate mesial margin of propod; cp=central projection, d=depression, n=notch. Scale lines equal 5 mm. 24 s

,.,,.

cp 19 \ 20 cs [i !) cp_ ' ,,I''"

21 \

cp 22 23

24 25 26

Fig. 19. Carapace of O. limosus. Fig. 20. First pleopod of Q. limosus. Fig 21. Carapace of Q. obscurus. Fig. 22. First pleopod of Q. obscurus. Fig. 23. First pleopod of Q. propinguus. Fig. 24. First pleopod of Q. rusticus. Fig. 25. Rostrum of Q. rusticus. Fig. 26. Rostrum of Q. propinguus; c=carina, cp=central projection, cs=cervical spine, s=spines. Scale lines equal 5 mm. 25 E E 0

E E I.()

27 28 / .. 1·: '' , , : " I I I S ,1 ;, ' ,. ' ~~ .t' .... ' ' ~ jl l)]l.'/

29 30a 306 Fig. 27. Claw of Orconectes irnrnunis. Arrow indicates incision on dactyl. Fig. 28. First pleopod of Q. irnrnunis. Fig. 29. Claw of Q. virilis. Fig. 30. First pleopod of Q. virilis, a and b show range of variation in pleopod. Scales in Figs. 27 and 28 apply to Figs. 29 and 30a, b, respectively.

26 C cp 0);

31a cp 316

mp

32a 32b

2 2 2

3 3 3 E E 4 5 6

33a 336 33c

Fig. 31. Tip of the endopod of the second pleopod of a male caecidotea communis, a and bare reverse views. Fig. 32. Tip of the endopod of the s~cond pleopod of a male g. ~- racovitzai, a and b are reverse views. Figs. 31 and 32 are X400 c=cannula, cp=caudal process, mp=mesial process. Fig. 33. Dorsal view of abdominal segments 1 through 6 in three amphipod families: (a) Hyalellidae, (b) Crangonyctidae, (c) Gammaridae.

27 13a (11) Dorso-posterior margins of abdominal segments 1 and 2 produced into sharp points (Figs. 7a,33a}, telson not cleft and with only a few terminal slender spines (Fig. 7b), uropod 3 uniramous (Fig. 7c) ..• HYALELLIDAE•..••.•.. Hyalella azteca (see note 9)

13b Dorso-posterior margin of abdominal segments not produced (Figs. lc,33b,c), telson cleft or not but always with several terminal spines (Figs. 34,35), uropod 3 uniramous or biramous (Fig. 38a-d) ...... 14

14a (13) Dorsal surface of abdominal segments without spines or setae (Fig. 33b), outer (longer) ramus of uropod 3 single segmented and with marginal spines only (Fig. 38a-c) •.•.•..... CRANGONYCTIDAE...•.••.....• 15

14b Dorsal surface of abdominal segments 4 through 6 with spines and setae (Figs. lc,33c), outer (longer) ramus of uropod 3 two segmented and with marginal spines and setae (Fig. 38d) .•...... • • • • • • • • • GAMMARIDAE .. ••••••••••••••....••••••••.. 20

15a (14) Eyes absent (Fig. 34) and animal without pigment, telson not cleft (Fig. 34); known only from springs in southwestern Massachusetts .....••...... ••...... • • . • • . . • . . genus stygobromus ••••...... •....•. 16

15b Eyes present (Fig. 35) and animal pigmented, telson cleft (Fig. 35); occurring in surface waters, including springs .•••..•••...... ••...... 17

16a (15) Adults ranging between 5.5 and 9.5 mm in length; propod of pereopod 2 of both sexes with several heavy, notched spines along distal margin (Fig. 36) •...... ••••••••.••. Stygobromus _t. tenuis

16b Adults rarely exceeding 4 mm in length; propod of pereopod 2 of both sexes with few unnotched spines along distal margin (Fig. 37) ...... • . . • . . • . . Stygobromus boreal is

28 17a (15) Uropod 3 uniramous (Fig. 38a), dactyl (terminal segment) of pereopod 7 with several setae along upper margin (Fig. 39a), telson usually with about six spines per lobe (Fig. 40a); found only in the southeastern most part of Massachusetts .••...... •...•..•..••...... •••••••.•.. synurella chamberlaini

17b Uropod 3 biramous (Fig. 38b,c), dactyl (terminal segment) of pereopod 7 with only one seta on upper margin (Fig. 39b), telson usually with less than six spines per lobe (Fig. 40b); distribution not restricted to southeastern most parts of the state ...... 18

18a (17) Propod of pereopod 2 with groups of two to four setae on the upper inner surface (Fig. 41), uropod 2 of male without comb-like spines on inner margin of outer ramus (Fig. 44a), telson with only two or three, rarely four, spines on each lobe (Fig. 40b) ...•••. crangonyx r. richmondensis (see note 10)

18b Propod of pereopod 2 with setae arranged singly on upper inner surface (Figs. 42,43), uropod 2 of male with comb-like spines on inner margin of outer ramus (Fig. 44b,c), telson with from two to six spines per lobe (Fig. 45a,b) •.....•...... •...... 19

19a (18) Propod of pereopod 2 with unnotched spines along middle portion of distal margin, opposable margin of dactyl with several long setae (Fig. 42); comb­ like spines on outer ramus of male uropod 2 closely set, extending less than one-half the ramus length (Fig. 44b), telson without subterminal spines (Fig. 45a) ...••...•••••....•..... Crangonyx pseudogracilis

19b Propod of pereopod 2 with notched spines all along distal margin, opposable margin of dactyl with one or more spines and setae (Fig. 43); comb-like spines on outer ramus of male uropod 2 spaced apart, covering well over one-half the ramus length (Fig. 44c), telson with subterminal spines (Figs. 35,45b) ....•••••••. crangonyx aberrans (see note 11)

20a (14) Upper corner of interantennal lobe acute, forming a distinct angle (Fig. 46a) i distal posterior corner of basis of pereopod 7 with several long setae and a few spines (Fig. 47a,b) .....•...... •...... 21

29 20b Upper corner of interantennal lobe somewhat rounded, not acute (Fig. 46b); distal posterior corner of basis of pereopod 7 with only a few short setae (Fig. 47c,d) .••...... •...... 22

21a (20) First three abdominal segments with several long marginal and submarginal setae on the pleonal plates, only a few spines present submarginally on segment 2 (Fig. 48a); coastal and inland freshwater ...... •...... •..••• Gammarus fasciatus

21b Only first abdominal segment with long marginal setae along ventral border, segments 2 and 3 with only a few setae but with several marginal and submarginal spines (Fig. 48b); upper most brackish and tidal freshwater, occasionally landlocked •...... •....•... Gammarus tigrinus (see note 12)

22a (20) First three abdominal segments with several long marginal and submarginal setae on pleonal plates, spines present marginally only on segment 3 (Fig. 48c); restricted to large springs and spring-fed streams in extreme southwestern parts of the state ...•...•...... Gammarus pseudolimnaeus

22b First three abdominal segments with a few to several long marginal and submarginal setae on pleonal plates, submarginal spines present on segment 2 (Fig. 48d) ; in freshwater pools above high tide mark in extreme northeastern Massachusetts ...•...•••...... Gammarus deubeni

30 t

34

e

t 35

Fig. 34. Adult male Stvqobromus t. tenuis; t=telson (enlarged lower right). Fig. 35. Adult male Crangonyx aberrans; t=telson (enlarged lower right), e=eye. Scale lines equal 2 mm.

31 36

s

37

Fig. 36. Propod of pereopod 2 of male Stygobromus !,_. tenuis, XlOO; s=spine (enlarged at right), n=notch. Fig. 37. Propod of pereopod 2 of male §_. borealis, X250; s=spine ( enlarged at right) . 32 Notes in key

1. Views of the male first pleopod of these and remaining species of crayfish are of the mesial side of the animal's left pleopod.

2. Occasional specimens of Orconectes propinguus will have hooks on pereopods 2 and 3, however, this condition is rare and a series of Q. propinguus will have at most only a few specimens with hooks on pereopods 2 and 3.

3. To see the pigment stripe clearly, particularly in older specimens, the carapace should be brushed clean of deposits and dirt. After extended periods of being in alcohol, the stripe, and all other pigments, will fade.

4. Large adults of Procambarus clarkii tend to be quite red in color, whereas£. g. acutus is typically mottled with browns, greens and other lighter hues.

5. In a few species, including Orconectes virilis and Q. immunis, the spines on the rostral margin are reduced or absent, particularly in older specimens. The angle of the rostral margin in these specimens might appear somewhat rounded.

6. The shaft of the pleopod of Orconectes propinguus often contains a slight notch in the place where a shoulder would occur in other species. A shoulder constitutes a distinct shelf or ledge on the organ (arrows, Figs. 22, 24). Detection of the rostral carina sometimes requires cleaning the structure and then gently brushing a probe from side to side across the surface. The often small and low carina can be felt during this procedure.

7. In Massachusetts, the taxon Orconectes virilis includes at least two of several closely related species with native distributions also occurring in mid and southwestern parts of the country. Besides typical Q. virilis, many populations will contain individuals approaching or clearly indicative of Q. nais, a very similar form whose taxonomic status remains to be resolved (Hobbs, 1972b, 1974b; Smith, 1979b; Phillips, 1980).

33 8. Terrestrial isopod species belonging to the isopod suborder Oniscoidea are often washed into water during storms or spring snow melt. Terrestrial oniscoid isopods differ from the freshwater forms inhabiting Massachusetts (suborder Asellota} by the presence of a non-subchelate first pereopod (all the pereopods are alike) and by the absence of any fusion of the abdominal segments. Investigators interested in determining local species of terrestrial isopods are referred to Bell (1971).

9 . In addition to the first two abdominal segments, the last thoracic segment will sometimes have the dorsal posterior margin produced.

10. Although populations in eastern Massachusetts are typical of Crangonyx ~- richmondensis, populations occurring in central and western parts of the state are intermediate between g. ~­ richmondensis and g. ~. laurentianus, a subspecies widespread in the Great lakes and the st. Lawrence River system. The two subspecies are distinguished primarily by individual maximum size, 12 to 14 mm in g. ~- richmondensis females, 14 to 18 mm in g. ~- laurentianus females, and the number of spines per telson lobe. Crangonyx ~- richmondensis has three spines per lobe while g. ~- laurentianus has two spines per lobe (Bousfield, 1958). 11. Crangonyx aberrans exhibits some degree of variability with regard to the extent of spination on the dactyl of pereopod 2 and the presence of subterminal spines on the telson. Often, the spines on each structure will be few in number and in subadult specimens absent altogether. It is important that breeding or post-breeding females and or males be available to insure accurate identification.

12. Gammarus fasciatus and~- tigrinus are sometimes found living together. Collections containing gammarid amphipods taken in upper oligohaline conditions can be expected to contain both species. In order to avoid incorrect lumping of the collection under one species, each specimen should be examined. Additional, though more subtle, characters useful in distinguishing the two species can be found in Bousfield (1958, 1973}.

34 38a 386 38c 38d ----

--40a

39a 39b LJ 40b Fig. 38. Uropod 3 of (a) Synurella chamberlaini, (b) Crangonyx :i;:. richmondensis, (c) .Q. aberrans, and (d) Gammarus fasciatus; r=ramus, s=second segment. Fig. 39. Distal segments of pereopod 7 of (a) 2 . chamberlaini and (b) .Q. pseudogracilis; arrows denote upper margin of dactyl. Fig. 40. Telson of (a)£• chamberlaini and (b) .Q. !:• richmondensis; arrows indicate terminal spines of a lobe. All figures X80.

35 ~~#~~/ SETAE

41

UNNOTCHED SPINE

\ SETA

42

NOTCHED SPINE

SPINE\

43

Fig. 41. Propod and dactyl of pereopod 2 of Crangonyx 1:. richmondensis showing setae groups on inner surface. Fig. 42. Similar view of ~- pseudogracilis with portion of dactyl and propod margin enlarged at left. Fig. 43. Similar view of ~­ aberrans with portion of dactyl and propod margin enlarged at left. All figures xso.

36 or cs cs

~ ~

\ \ 6 y j J I ) d

44a 44b 44c

E 45a 46a E

-

45b 46b

Fig. 44. Uropod 2 of male of (a) Crangonyx ~- richmondensis, (b) £. pseudogracilis, and (c) £. aberrans; or=outer ramus, cs=comb­ like spines. Fig. 45. Telson of (a) £. pseudogracilis and (b) £. aberrans; arrows indicate subterminal spines. Fig. 46. Head of (a) Gammarus fasciatus and (b) §_. pseudolimnaeus ; arrows point to upper angle of interantennal lobe. Figs. 44 and 45 xso.

37 BASIS \

47a 47b 47c 47d

1 \ \ 2 3 \ \

48a 48b PLEONAL 1mm PLATE \ \ \ \ \

48c 48d

Fig. 4 7. Basis of pereopod 7 of (a) Gammarus fasciatus, (b) Q. tigrinus, (c) Q. · pseudolimnaeus, and (d) Q. deubeni; distal posterior corner indicated by arrow. Fig. 48. Lateral view of first three abdominal segments of (a) Q. fasciatus, (b) Q. tigrinus, (c) Q. pseudolimnaeus, and (d) Q. deubeni.

38 Table 3. General characteristics of the families and genera of freshwater amphipods inhabiting Massachusetts. Figures 7, 34, 35, and 38 illustrate characters used in the table.

FAMILY eyes uropod 3 telson Genus/Genera

HYALELLIDAE Hyalella present uniramous entire (spines only) (2 terminal spines) CRANGONYCTIDAE Styggbromus absent uniramous entire (spines only) (several spines) synurella present uniramous cleft (spines only) (several spines) Crangonyx present biramous cleft (spines only) (several spines) GAMMARIDAE Gammarus present biramous cleft (spines and setae) (several spines)

39 CRAYFISH HYBRIDS Within the last decade hybridization has been reported in certain North American cambarid crayfish (Capelli and Capelli, 1980; Smith, 1979a, 1981a). Prior to reports recording specific occurrences of the phenomenon, hybridization was suspected as being responsible for variation in species-specific characters in crayfish species existing sympatrically (Crocker, 1957; Crocker and Barr, 1968). All of these accounts, describing or suggesting hybridization, have been reviewed and discussed by Butler and Stein (1985). The evidence upon which assumed hybridization has been based is usually the occurrence of morphological intermediacy in mixed species populations. It has also been observed that at least one of the involved species is not native to the geographical area under study. Biogeographical studies undertaken during the first part of this century and earlier dealt with populations presumed to be native and none of these investigations documented or suggested instances of hybridization. The mechanism of species recognition during mate selection in crayfish is probably based on species-specific "pheromones," chemicals used in communication, and in species which have evolved in sympatry this mechanism has most likely prevented hybridization. The process of distinguishing between like and unlike individuals is probably disrupted, however, by artificially introducing an exotic species into an established crayfish community. The inability to recognize and avoid an individual of an exotic species is a possible cause for the occurrence of hybridization (Smith, 1981a; Tierney and Dunham, 1982) . All the species undergoing hybridization in Massachusetts belong to the genus Orconectes. With existing information pointing to an artificial origin for nearly all orconectine species occurring in Massachusetts, hybridization can be expected to occur in most species pairings. The author has examined hybrid specimens which have been produced by the following combinations (with localities of hybrids in parentheses): Q. limosus and Q. rusticus (Gunn Brook, Sunderland, see Smith, 1981a), Q. limosus and Q. obscurus (Greenwater Pond, Becket), Q. limosus and Q. propinguus (Williams River, West Stockbridge), and Q. obscurus and Q. virilis (Konkapot Brook, Stockbridge). Hybrids are generally rare, except in the case involving Q. limosus and Q. obscurus (Greenwater Pond, Becket) in which most of the specimens examined have been hybrids of these two species. Figure 49 provides characteristic appearances of the first pleopod of the first form male of hybrid specimens and that of the two parental species for comparison. Hybrids of other species combinations have been observed or suggested to occur elsewhere and it is not unlikely that similar hybrids could be encountered in Massachusetts. These other hybrid producing combinations are (with state where observed):

40 Q. rusticus and Q. propinquus (Wisconsin; Capelli and Capelli, 1980), Q. rusticus and 0. virilis (Connecticut; Smith, Personal observation), and Q. bartonii and Q. robustus (New York; Crocker, 1957; Smith, 1979a).

41 0. limosus HYBRID 0. rusticus

0. limosus HYBRID 0. obscurus

0. limosus HYBRID 0. propinquus

0. obscurus HYBRID 0. virilis

Fig. 49. First pleopod of apparent hybrid specimens of crayfish found in Massachusetts with pleopods of parental species provided for comparison. All pleopods approximately XlO.

42 DISTRIBUTION OF MASSACHUSETTSFRESHWATER MALACOSTRACANS (Special Concern listings are from the Code of Massachusetts Regulations, Chapter 321, Section 8.00 (1986).)

DECAPODA

Cambarus bartonii One of the few crayfish species apparently native to Massachusetts, .Q. bartonii is confined to tributaries flowing into the Hoosic River basin in the Hudson River drainage system. Relicts of pre-industrial populations still live in the main stem of the Hoosic River in Adams (Smith, 1984). The species typically prefers well-oxygenated running waters in which it tunnels under large well-imbricated rocks. Cambarus bartonii has been collected in streams up to 470 meters (1550 feet) in altitude. A few imprecise historical records exist outside the Hoosic River in Massachusetts, but are probably the result of introduction. Cambarus bartonii is currently listed under Special Concern in Massachusetts. Cambarus robustus This species' native distribution probably does not extend east of the middle Hudson River drainage system in New York. The earliest records for New England are from the Thames River drainage system in Connecticut (1950 1 s). Successful introductions have subsequently occurred in Massachusetts in the Connecticut River, Thames River, and Mount Hope Bay drainage systems. Known populations are in the West Branch of the Farmington River, Otis; Slocum Brook, Tolland; Dickinson Brook, Granville; Sawmill Brook, Monson; and Sucker Brook, Fall River. Cambarus robustus prefers large rocky streams with moderate current. Orconectes immunis Orconectes immunis was first noticed in Massachusetts by Faxon (1914) who considered it as introduced in eastern parts, but native in western parts of the state. Crocker (1979) tends to favor a natural distribution of this species in Massachusetts. As with several crayfish species inhabiting Massachusetts, this species has a wide range extending throughout the Great Lakes region and south and west, areas largely remote from New England with respect to drainage history. Its occurrence in New England was not known until about 1900 (Faxon, 1914), yet has since been found in several localities. It is considered here to be an introduced species like the one preceding and most of the species following. In Massachusetts, Q. immunis is widespread but localized. Scattered, but occasionally large, populations are known from every major drainage system except the eastern Coastal

43 drainage system. Orconectes irorounis generally prefers either moving or stagnant water provided with abundant aquatic vegetation. Orconectes liroosus This is one of the few species of Orconectes possibly, but not certainly, native to at least parts of Massachusetts. Faxon (1914) considered it to be introduced into the few localities in Massachusetts of which he was aware. The native populations, if indeed native, are confined to major south flowing river systems in the state, including the Housatonic River, Connecticut River, where it is common, and the Thames River drainages. East of these drainages, it is less frequently encountered and probably introduced. scattered populations are known from the Merrimack River, Boston Harbor, Narragansett Bay, Mount Hope Bay, and Coastal drainage systems. The species has not been collected in the Hudson River drainage system in Massachusetts. The species is roost frequently found in large rivers and streams with weak to moderate current, but also does well in large and small lakes and impoundments. Orconectes obscurus

An introduced species, Q. obscurus has been established in the North Branch of the Hoosic River and some of its tributaries (Hudson River drainage system); and in Goose Pond in Lee, Greenwater Pond in Becket, Konkapot Brook in Stockbridge (all Housatonic River drainage system), and in the Housatonic River in Stockbridge. Orconectes propinguus This species is found in the Hoosic River basin where it is possibly native. Outside of the Hudson River drainage system in Massachusetts it has been introduced into the Housatonic River drainage system where several disjunct populations have been established. Two small populations are known from the Connecticut River drainage system: Mill Brook, Plainfield, and Swift River, Ashfield, both in the Westfield River basin. Orconectes rusticus

A recently introduced species in Massachusetts, Q. rusticus is known from only four sites: Stony Brook in South Hadley, Beaver Brook in Ware, Gunn Brook in Sunderland (each Connecticut River basin) and the Connecticut River in Montague. However, the species is rapidly spreading throughout New England and is expected to eventually turn up in other areas. Orconectes virilis

Based on museum records, Q. virilis has been known in Massachusetts since about 1935. Since then the species has been

44 widely introduced throughout the state to such an extent that presently only the southeastern coastal drainage areas (South Shore, Buzzards Bay, Cape Cod and the Islands) are still free of it. Orconectes virilis is probably the most common species in the state and lives in practically all types of permanent aquatic habitats. Procambarus g. acutus Procambarus g. acutus is another crayfish which can be argued as being native in Massachusetts. Procambarus g. acutus is restricted to an area extending from the Narragansett Bay drainage system eastward through the Boston Harbor (excluding the Mystic River basin), Mount Hope Bay and Coastal drainage system south of Boston Harbor (Smith, 1982b). Within its natural range in Massachusetts, the species occurs continuously and is common, particularly in dystrophic waterways rich in vegetation and with weak, rarely moderate, current. outside of these drainages, local populations have been established in the Spicket River, Methuen (Merrimack River drainage system), a few tributaries in the Northampton and Amherst vicinity in the Connecticut River basin and the Millers River in Ashburnham (Connecticut River drainage system).

Procambarus clarkii Discarded by researchers into the campus pond, University of Massachusetts at Amherst, around 1971, £. clarkii was observed to be breeding and common in the pond through to the present decade. Recently, only occasional adults have been seen. The species has a southern distribution and its survival during cold months in this New England pond is probably due to thermal input from steam drains on the campus. The species might be present in similar environments on other school campuses as it is a very popular and readily available research animal.

ISOPODA

Caecidotea communis Caecidotea communis is very common and widespread throughout the mainland of Massachusetts and many of the islands. The species is found in most permanent aquatic habitats where decaying vegetative debris is present.

Caecidotea ~- racovitzai Unlike the preceding isopod species, g. ~- racovitzai is somewhat restricted to western parts of the state where it is common only in the Connecticut River and Housatonic River basins. In the Connecticut River, g. ~- racovitzai and g. communis are often syntopic. The only eastern records are in the Merrimack River

45 drainage system where the specie:1 appears to be localized and much less common than .Q. commun1s. Caecidotea :i;:. racovitzai apparently prefers cooler water than .Q. communis and is often found in streams which are fed by seepage or springs.

AMPHIPODA

Crangonyx aberrans

A species endemic to New England (Smith, 1983b), _Q. aberrans is found in the eastern half of Massachusetts from the Merrimack River and Narragansett Bay drainage systems to the coast, except Cape Cod and the islands. Crangonyx aberrans is an inhabitant of freshwater wetlands, primarily red maple and white cedar swamps, marshes, and the streams draining them. Close to the coast, the species also occupies swampy margins of ponds and streams. This species is listed as Special Concern in Massachusetts. Crangonyx pseudogracilis

Available records indicate that .Q. pseudogracilis is, for the most part, restricted to the larger river basins in the state. In western sections this species is confined to the main stream, oxbows, and backwaters of the Housatonic and Connecticut Rivers, rarely is it found in larger tributaries of these rivers. In eastern Massachusetts, .Q. pseudogracilis ranges throughout the Merrimack River drainage system, often extending into small tributaries. Other known occurrences are in the Blackstone River (Narragansett Bay drainage system) and the Charles River basin. The species is typically found along the margins of slow, rarely moderate, velocity rivers and large streams where it lives among organic debris.

Crangonyx :i;:. richmondensis This species ranges throughout Massachusetts from eastern coastal freshwaters, including those on larger islands, to hill ponds in the extreme western parts of the state. Populations which are typical of .Q. :i;:. richmondensis are found only in the Coastal drainage system. All other populations in the state consist of intergrades with .Q. :i;:. laurentianus. This species is ecologically limited in its distribution in Massachusetts by its strict habitat preferences: specifically, cool natural ponds of glacial origin, usually associated with glacial deposits (till), and provided with dense aquatic vegetation and an abundance of leaf litter.

46 stygobromus borealis Stygobromus borealis is a rare troglobitic amphipod known only from subterranean waters in the Taconic Mountains (Holsinger, 1978). The species has been recorded from only a single locality in Massachusetts, a spring (springhouse) in New Marlborough. Stygobromus borealis is presently listed under Special Concern in Massachusetts. Stygobromus t. tenuis

As with the preceding species, 2 • t- tenuis is troglobitic and does not occur outside of small springs in the state. Two records exist for this species in Massachusetts and both are small springs in New Marlborough (Smith, 1986a). This species is also listed under Special Concern in Massachusetts. Synurella chamberlaini This species was recently discovered in Massachusetts (Smith, 1987b) and is as yet known only from a small red maple swamp in Dartmouth (Buzzards Bay drainage area) • It might occur in similar habitats on the Buzzards Bay moraine elsewhere along the coast. Gammarus deubeni Gammarus duebeni is a brackish water species that can seasonally survive in coastal strand pools above the high tide mark that become fresh in the summer months. The species ranges along the coast from Nahant northwards (Bousfield, 1973). Gammarus fasciatus The northern range limit of this species along the Atlantic coast has been listed as Cape Cod in Massachusetts (Holsinger, 1972; Bousfield, 1973). The species is actually distributed throughout eastern Massachusetts in the Coastal, Mount Hope Bay, Boston Harbor, and eastern Merrimack River drainage systems. It does not seem to occur much west of a line drawn NNW from the northeast corner of Rhode Island. Gammarus fasciatus exists in a variety of freshwater habitats where aquatic vegetation is present.

47 Gammarus pseudolimnaeus Gammarus pseudolimnaeus is found in Massachusetts only in the Schenob Brook drainage and a few other scattered springs in Sheffield (Housatonic River basin) (Smith, 1982a, 1984). The species lives in organic debris in large springs and their outlet streams. The species is currently listed under Special Concern in Massachusetts. Gammarus tigrinus This species is primarily an inhabitant of upper brackish (mesohaline to oligohaline) water, but often moves into freshwater for periods of time. Populations occasionally become landlocked by dam construction but it is not known if they can persist during long periods of exposure to freshwater. Gammarus tigrinus is known to occur along the entire coast of Massachusetts (Bousfield, 1973). Hyalella azteca Certainly the most common and widespread freshwater malacostracan species in Massachusetts, fi. azteca occurs in all permanent aquatic habitats from tidal fresh ponds along the coast and on islands to the highest hill ponds in western parts of the state.

48 GLOSSARY OF TERMS USED IN KEY

Abdomen. In Massachusetts freshwater malacostracans, the terminal six body segments.

Basis. On the last three pereopods in amphipods, the large and expanded segment appearing closest to the body. Biramous. An appendage having two parts, each typically called a ramus.

Carapace. The single piece covering of the anterior half of a decapod.

Cleft. Meaning that the structure, usually the telson, has a deep excision in the dorsal margin.

Dactyl. The terminal segment of a thoracic appendage.

Entire. Meaning that the structure, usually the telson, has no excision of the dorsal margin.

Head. The anterior most part of the animal, usually fused with at least the first thoracic segment and containing feeding structures, antennae, and eyes (if present).

Pereopod. A segmented appendage on each thoracic segment, typically a walking leg.

Pleopod. A segmented appendage, usually biramous, on each abdominal segment.

Propod. The second to last segment on a thoracic appendage.

Seta. Generally, a pliable and elongate filament-like structure.

Spine. Generally, a stiff and short spike-like structure. Subchelate. The two terminal structures (propod and dactyl) of a pereopod appearing as a claw-like structure, but not a true claw.

Telson. The terminal unit of the abdomen, but not treated as a true segment in this manual.

Thorax. The body segments between the head and the abdomen, variously fused in different taxa.

Uniramous. An appendage containing a single part or ramus.

Uropod. Usually a specialized appendage of the terminal or last: three abdominal segments, depending upon the taxon.

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