Americorophium Brevis Class: Multicrustacea, Malacostraca, Eumalacostraca

Phylum: Arthropoda, Crustacea

Americorophium brevis Class: Multicrustacea, Malacostraca, Eumalacostraca

Order: Peracarida, Amphipoda, Senticaudata, Corophiida, Corophiidira Family: Corophioidea, Corophiidae, Corophiinae, Corophiini

Taxonomy: Corophium brevis was de- Cephalon: scribed in 1949 by Shoemaker and was Rostrum: Small central triangle is transferred to the genus Americorophium in shorter than sharp ocular runes (Fig. 1). 1997 based on morphological characters Eyes: (Bousfield and Hoover 1997) (see Possible Antenna 1: Reaches a little beyond Misidentifications). Not all researchers fourth article of second antenna in males and have followed this transition in other Ameri- the flagellum ranges from approximately 11 corophium species (e.g. A. spinicorne, joints (Siuslaw Estuary specimens) to 9-14 Lester and Clark 2002; Sakamaki and Rich- (Coos Bay specimens, Fig. 1) (Shoemaker ardson 2009), but we follow the nomencla- 1949). Antenna base is not expanded lateral- ture used in other current local intertidal ly. The female flagellum consists of 7–8 joints guides (Chapman 2007). and is almost as long as second antenna (Shoemaker 1949) (Fig. 6). Description Antenna 2: Male antenna large, al- Size: Males range in size from 3.5 most as long as body and is with groups of (Shoemaker 1949) to 8 mm (South Slough setae. The fourth article is a large, distal of Coos Bay). Females are 4 (Siuslaw Estu- tooth forming a half-moon with an accessory ary) to 4.5 mm (Shoemaker 1949). tooth within (Fig. 2). The fifth article has two Color: Transparent, with brown mottled small teeth: one distal and one proximal (Fig. markings, especially on large second anten- 2). The second antenna in females is not as na. large as in males, and instead of a half-moon General Morphology: The body of amphi- tooth and an accessory tooth, there are three pod crustaceans can be divided into three pairs of equally spaced, heavy spines on the major regions. The cephalon (head) in- lower margin (Shoemaker 1949) (Fig. 5). cludes antennules, antennae, mandibles, Mouthparts: maxillae and maxillipeds (collectively the Pereon: mouthparts). Posterior to the cephalon is Coxae: the pereon (thorax) with seven pairs of Gnathopod 1: pereopods attached to pereonites followed Gnathopod 2: Filtering type, with fine by the pleon (abdomen) with six segments long setae, present in both sexes (Fig. 3). comprising three pleonites (together the Pereopods 3 through 7: Quite setose. pleosome), three urosomites (together the Pleon: urosome), and finally a telson at the animal Pleonites: posterior (see Plate 254, Chapman 2007). Urosomites: Three segments of uro- In members of the genus Americorophium, some separate and distinguishable (Fig. 4) in the body is flattened dorso-ventrally and both sexes. The lateral edge of peduncle with rarely exceeds 1 cm in total length (including about eight short, blunt spines on first uro- antennae) in local specimens (see Fig 46, pods (Fig. 4). Third uropods with few fine se- Kozloff 1993).

A publication of the University of Oregon Libraries and the Oregon Institute of Marine Biology Individual species: https://oimb.uoregon.edu/oregon-estuarine-invertebrates and full 3rd edition: http://hdl.handle.net/1794/18839 Email corrections to: [email protected]

Hiebert, T.C. 2015. Americorophium brevis. In: Oregon Estuarine Invertebrates: Rudys' Illustrated Guide to Common Species, 3rd ed. T.C. Hiebert, B.A. Butler and A.L. Shanks (eds.). University of Oregon Libraries and Oregon Institute of Marine Biology, Charleston, OR.

tae, on distal end only, in both sexes (Fig. include first antenna, telson, first uropods 4). and third uropods. Epimera: Americorophium stimpsoni, principally Telson: Posterior rounded and convex with a northern California species, does not seem parallel rows of spines (Fig. 4). to occur in Oregon. Its chief key characteris- Sexual Dimorphism: Males and females tic is a prominent male rostrum, almost as exhibit differing morphology in characters of long as the ocular lobes. The females are Antenna 1 and 2 as well as overall body much like those of A. salmonis. size. Americorophium spinicorne, another prominent northwest species, has less Possible Misidentifications sexual dimorphism than other The gammarid family Corophiidae is Americorophium species. Both males and characterized by individuals that build U- females have a half-moon tooth on the fourth shaped tubes in both soft sediments and on article of the second antenna, but without the hard surfaces, sometimes forming dense small accessory tooth. Americorophium aggregations. Species can be dramatically spinicorne is also strongly euryhaline and sexually dimorphic and, although males often found in fresh-water habitats. may be easier to identify with taxonomically Segments of urosome are separate and not relevant characters including the rostrum fused in A. spinicorne and males and and peduncle of second antennae, most females can be distinguished by the second females can be reliably identified to species antennal features and by the presence of as well (Chapman 2007). Five corophiid lamellae and/or eggs in females. genera occur locally, Americorophium, Males: Of the Americorophium spe- Corophium, Crassicorophium, Laticoro- cies in which males have urosome segments phium and Monocorophium. The three dissimilar to females, A. stimpsoni, A. brevis, common estuarine species in this guide (A. and A. salmonis all have a half-moon and brevis, A. salmonis, A. spinicorne) were accessory tooth on the fourth article of the previously members of the genus Coro- second antenna. Americorophium brevis phium (see Shoemaker 1949), but were and A. salmonis often have similar rostrums, transferred to the genus Americorophium in but that of A. stimpsoni has a prominent cen- 1997 (Bousfield and Hoover 1997). tral lobe nearly as long as the ocular lobes. All Americorophium species have In A. salmonis the first antenna reaches only filtering-type second gnathopods and long to the middle of the fourth article. Americoro- setae on the third uropods. Of the four phium brevis does not have the flat ex- local Americorophium species, sexual panded first articles of the first antenna and dimorphism is strong in the three species A. A. salmonis usually has 14–16 articles in the brevis, A. salmonis, and A. stimpsoni. In flagellum, (though occasional specimens will particular, the second antenna and fourth have 11–12). In A. brevis, the males have segment differ between males and females about 11 articles in the flagellum of the first (Shoemaker 1949). This is not the case, antenna. The uropods of A. salmonis and A. however, for the fourth Americorophium brevis are quite dissimilar. In A. salmonis, species, A. spinicorne, where male and the peduncle of the first uropod is armed on female morphologies are similar. Additional the outside edge with three to six long, characteristics that differ between species slender spines and at the distal edge with (particularly A. brevis and A. salmonis) two to three short, blunt spines.

Americorophium brevis has instead only are frequently used in tests of sediment toxici- eight short, blunt spines. The third uropods ty and/or water quality (e.g. fluoranthene, of A. salmonis have many more and longer Swartz et al. 1990). setae than those of A. brevis. The telson Salinity: shape and spination of the two species are Temperature: also quite different (compare Figs. 4, A. Tidal Level: A high intertidal species. brevis, and Fig. 5, A. salmonis). Associates: Known associates include tanai- Females: A. salmonis and A. stimp- daceans, small polychaetes and other Coro- soni females are very much alike, with no phiidae. strong distinguishing characteristics, so the Abundance: Populations are often very species should not be differentiated solely dense and easily observed or collected in the by female specimens. The only Americoro- field. The abundance of Americorophium phium female of this group to have the half- species measured in the Campbell River Es- moon hook is A. spinicorne, so this species tuary ranged from zero to ~15,000–31,000 is easily distinguished from others. per square meter in July (Raymond et al. Americorophium brevis has three pairs of 1985). spines, as well as a spine on the gland Life-History Information cone, instead of having two single spines Reproduction: Development in most amphi- on the underside of the fourth article of the pods is direct, lacking a larval stage, and little second antenna. The first antenna has is known about the reproduction and develop- eight joints in the flagellum, while that of A. ment in A. brevis. Ovigerous A. brevis fe- salmonis has ten. males have been observed in summer Ecological Information months whereas ovigerous A. spinicorne fe- Range: Type locality is Puget Sound, Wash- males have been observed in February, ington. Known range includes Alaska to March, May and December (Eriksen 1968). San Francisco Bay (Shoemaker 1949; Coyle In the European species, Corophium volula- and Müller 1981). tor, breeding occurs in February (over- Local Distribution: Coos Bay estuarine dis- wintering population) and again in July– tribution including South Slough. Distribu- August. Young remain in brood pouch four tion also known in other Oregon estuaries weeks and females produce up to four broods (e.g. Siuslaw Estuary, Barnard 1954). per year (Green 1968). Habitat: Members of the Corophiidae inhab- Larva: Since most amphipods develop direct- it small U-shaped tubes in soft sediments, or ly, they lack a definite larval stage. Instead on hard surfaces (Chapman 2007). Occurs the young developmental stage resembles in muddy habitats (e.g. South Slough) and small adults (e.g. Fig. 39.1, Wolff 2014). sometimes in a mud and wood chip mix. Juvenile: Especially abundant in brackish estuaries Longevity: with a high degree of silt and mud Growth Rate: Amphipod growth occurs in (Raymond et al. 1985; Kozloff 1993). Com- conjunction with molting where the exoskele- parisons of macrofaunal communities within ton is shed and replaced. Post-molt individu- and outside of Dendraster excentricus beds als will have soft shells as the cuticle gradual- found Americorophium species to be more ly hardens (Ruppert et al. 2004). prevalent where sand dollars were not pre- Food: A detritovore, Americorophium brevis sent (Smith 1981). Corophiid amphipods sorts material with filtering gnathopods. Ab-

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J.W. Olesen, J.T. (ed.). Johns Hopkins University Press, Baltimore. Updated 2015 T.C. Hiebert