Eobrolgus Spinosus Class: Malacostraca Order: Amphipoda, Gammaridea a Gammarid Amphipod Family: Phoxocephalidae

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Phylum: Arthropoda, Crustacea Eobrolgus spinosus Class: Malacostraca Order: Amphipoda, Gammaridea A gammarid amphipod Family: Phoxocephalidae

Taxonomy: The genera Eobrolgus and Eyes: Large, black and about same Foxiphalus were designated in 1979 by size in females (Figs. 1, 2) and immature Barnard and included species formerly in the males, but is much larger in mature males genus Paraphoxus, including E. spinosus (not figured). (e.g. Paraphoxus spinosus) (Barnard and Antenna 1: Female first antenna Barnard 1982). equal in length to second antenna. Flagellum has about seven articles (Fig. 3a) and Description accessory flagellum (in both sexes) is with Size: Individuals to 4.5 mm in length (Puget about five articles. Sound, Barnard 1960). The largest Oregon Antenna 2: The peduncle of the specimens were 3.5 mm (Coos Bay) and 2.4 second antenna in females is with some mm (Yaquina Bay) (Kemp et al. 1985). heavy spines and setae (Fig. 3b). The Ovigerous females are not longer than 5 mm flagellum has about seven slender articles, (Barnard 1975). and is shorter than the peduncle (Barnard Color: White, with black eyes. 1960). The male flagellum is longer than the General Morphology: The body of body in mature males and can have sensory amphipod crustaceans can be divided into clubs on proximal flagellal articles and on fifth three major regions. The cephalon (head) or peduncle articles (not figured). Immature cephalothorax includes antennules, antennae, males have flagella a little longer than mandibles, maxillae and maxillipeds peduncle. (collectively the mouthparts). Posterior to Mouthparts: Epistome (a part of the the cephalon is the pereon (thorax) with lip) is not produced into cusp (Fig. 1a) seven pairs of pereopods attached to (Barnard 1960). The Phoxocephalidae is one pereonites followed by the pleon (abdomen) of few groups in which epistome is of with six pairs of pleopods. The first three sets taxonomic importance. For a lateral view, of pleopods are generally used for swimming, push antennae and mandibular palps aside while the last three are simpler and surround (Barnard 1960). Mandible with tri-articled the telson at the animal posterior. Members palp, feeble molar and no large process. of the gammarid family Phoxocephalidae are Right female mandible is with simple lacinia referred to as “spiny heads” due to their mobilis (Barnard and Barnard 1981) (Fig. 4). shield-like pointed rostrums. They are also The first maxilla is with biarticulate palp and one the most abundant and diverse group of an outer plate with nine spines (Barnard and crustaceans in this size range (1–10 mm, Barnard 1981). Maxilliped palp of article four Chapman 2007). Unlike many amphipod is without large distal setae (not figured). groups, taxonomic keys tend to favor female Pereon: specimens in the Phoxocephalidae (Chapman Coxae: Coxal plate one almost as 2007). large as two. The fourth coxa is broad and Cephalon: Head tapers evenly and is not the fifth rounded (Fig. 1). Coxal margins bear abruptly narrowed (Fig. 2) with length about simple setae. as long as pereonites one through three Gnathopod 1: Small. Similar in size (Barnard 1975) (Fig. 1). and shape to the second gnathopods Rostrum: Rostrum well developed (Eobrolgus, Barnard 1979). Article six is and not constricted (Eobrolgus, Barnard broad. 1979) (Fig. 1).

A publication of the University of Oregon Libraries and the Oregon Institute of Marine Biology Individual species: http://hdl.handle.net/1794/12705 and full 3rd edition: http://hdl.handle.net/1794/18839 Email corrections to: [email protected] Gnathopod 2: Much like first Possible Misidentifications gnathopods. The first article is not Phoxocephalids can be distinguished pronounced (i.e. with even margins) and the primarily by their sixth and seventh sixth article is broad. pereopods, which are greatly different from Pereopods 3 through 7: Pereopods each other. They also have distinctive with stout spines (Figs. 1, 6, 7). Pereopod multiarticulate accessory flagellae (on four "normal" in orientation, not reversed like antenna one), and long rostrums (Barnard pereopods 5–7 (Barnard 1975) (see 1960). Hyalidae and Dogielinotidae are also Eohaustorius estuarius). Pereopod five with estuarine families, but they lack mandibular second article broad, articles 4–5 expanded palps and inner rami on the third uropods. but narrower than article two (Fig. 1). The Pleustidae have uncleft telsons and only Pereopod six is longer and more slender and vestigial antennal accessory flagella (Barnard with narrower article two than pereopod 1975). Both the Gammaridae and seven (Fig. 6). Pereopod seven is shorter, Haustoriidae have pereopods that are similar stouter and with article two broader than in size and shape (not like the pereopod six and has rounded posterior edge Phoxocephalidae) and in these families, with fine spines, no large spur (Fig. 7). pereopod four is reversed. Gammaridae Pleon: have a telson with connected lobes (see Pleonites: Fourth pleonite with Eogammarus confervicolus), while the telson proximal edge strongly depressed in males, lobes of Haustoriidae are disjunct (see while the edge is almost flush with segment Eohaustorius estuarius), and are much three in females (Eobrolgus, Barnard 1960). heavier than those of Eobrolgus. Urosomites: First urosomite The Phoxocephalidae is a diverse and peduncle with at least one dorsal margin, with abundant group of amphipods with 13 genera only one or no spines and two spines on inner (comprising 30–45 species) represented peduncle margin. Inner and outer branches locally including, Mandibulophoxus (one local similar, with one apical and one margin spine species), Cephalophoxoides (one local (Fig. 9a). Second uropods in females with species), Heterophoxus, (five local species), four stout spines on peduncle margin, rami Majoxiphalus (one local species), shorter than peduncle and without marginal Metaphoxus (one local species), and spines (Fig. 9b) (Barnard 1960). In males, Parametaphoxus (one local species). Most there are more spines on peduncle (not phoxocephalid species formerly in figured). The third uropods in females is with Paraphoxus have been placed (by Barnard inner ramus half as long as (or slightly less 1979) into one of six genera including than) outer (Fig. 9d). In males, the inner Metharpinia (two local species), Eyakia (one ramus is more than half as long as the outer local species), Foxiphalus (seven local and is quite setose in mature specimens (Fig. species), Grandifoxus (three local species), 9c) (Barnard 1960). Rhepoxynius (19 local species), and Epimera: The third epimeron is not Eobrolgus (two local species). produced into a tooth and is naked (i.e. bears Mandibulophoxus is distinguished no setae) (Barnard and Barnard 1981) (Fig. from Eobrolgus by its sickle-shaped 1). mandibular palp borne on a large process. It Telson: Teslon, with cleft, is thin, lamellar has a biarticulate palp on the first maxilla (like and each lobe is with one short spine and one Eobrolgus). Mandibulophoxus gilesi is an fine seta (Fig. 8). eyeless, long-rostrumed species that has Sexual Dimorphism: Not as strong as in been found subtidally (to 14 meters depth) in some amphipod families. Males have larger Yaquina Bay and other Oregon estuaries eyes, much longer second antennae and (Chapman 2007). spinose uropods (uropod three). Usual Eobrolgus chumashi is an endemic amphipod gnathopod sexual dimorphism is oceanic species whose range probably not observed in this genus (Barnard 1960; extends only south of Oregon (Barnard and Chapman 2007). Barnard 1981). Its body is dwarfed and the head and eyes are large. The pleonal

Hiebert, T.C. 2015. Eobrolgus spinosus. 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. epimeron are not naked as in E. spinosus, but Ecological Information have 1–2 ventral setae. The lacinia mobilis Range: Type locality is New England (on the right mandible of the female) is bifid, (Homes 1905; Barnard and Barnard 1982). not simple. Some hybridization between Known range includes the western Atlantic, these two species of Eobrolgus may occur from which it may have been introduced to (Barnard and Barnard 1981; Chapman 2007). the eastern Pacific. Distribution along the The genera Foxiphalus and Eobrolgus west coast of North America now includes are morphologically similar. Female Puget Sound, Washington to Newport Bay, Eobrolgus have a short second article on California (Barnard and Barnard 1981). antenna one with a ventral surface that is Local Distribution: Coos Bay sites in South continually covered with setae. Female Slough, at Jordan Cove and at Pigeon Point Foxiphalus, on the other hand, have a gap on (Barnard 1975). Other Oregon estuaries the ventral side of antenna one. Confusingly, include Yaquina Bay. Eobrolgus males exhibit similar morphology of Habitat: A burrower in sandy and muddy antenna one to Foxiphalus females and, thus, bottoms of estuaries that also tolerates cannot be differentiated (Barnard and Barnard substrates mixed with wood chips (e.g. 1982) and, furthermore, Foxiphalus species Jordan Cove, Coos Bay). Phoxocepahlid are difficult to distinguish from Majoxiphalus amphipods are sensitive to a variety of (Chapman 2007). Foxiphalus major is pollutants and are common subjects of probably the species most similar to toxicity tests (e.g. Rhepoxynius abronius, Eobrolgus spinosus. Adults are larger than Robinson et al. 1988). those of E. spinosus and ovigerous females Salinity: Collected at salinities of 30 (Coos are over 6 mm in length, but not under 5 mm. Bay). Foxiphalus major amphipods have longer Temperature: heads and smaller eyes than do E. spinosus Tidal Level: High and mid intertidal (Coos and their fifth pereopod is slender, not stout. Bay) (Chapman 2007). The inner ramus of the female third uropod is Associates: In beds of the ghost shrimp, more than ½ the length of the outer ramus Neotrypaea, and with the polychaetes, (not less than ½, Fig. 9d). The third pleonal Pygospio elegans and Pseudopolydora epimeron is concave or straight on its kempi, outside of shrimp beds (Coos Bay, posterior edge and setose. Foxiphalus major South Slough) (Posey 1985). was found under its old name (Pontharpinia Abundance: Phoxocephalid amphipods are obtusidens) on Oregon's outer coast (Barnard highly abundant, reaching densities up to 700 1954, 1979). individuals per square meter in California Rhepoxynius tridentatus and others of (Oakden 1984). Dominant invertebrate at this genus have an abruptly narrowing, Jordan Cove, Coos Bay. Recorded June untapered rostrum and the second article of abundances: lower intertidal (+0.9 meters pereopod seven has three large teeth on the MLLW) 60–162 individuals per 13 x 15 cm posterior edge (Barnard 1954, 1979). core; mid intertidal (+1.0 meters MLLW) 92– Rhepoxynius abronius, with a broad head and 174 individuals; high intertidal (+1.1 meters M narrow, short rostrum, has a long, sharp LLW) 37–58 individuals (Posey 1985). epistomal process. This species has large Generally not as abundant as its close teeth on the posterior edge of pereopod relative, Foxiphalus major (Barnard 1960). seven. It has been reported from Yaquina Bay, Oregon. Life-History Information Grandifoxus grandis (= Grandifoxus Reproduction: Most amphipods have milleri and Paraphosux milleri) is found in the separate sexes with some sex determination Columbia River estuary. This closely related correlated with environmental conditions species has a narrow gnathopod hand (sixth (Straude 1987). Females brood embryos in article) and an abruptly narrowing rostrum an external thoracic brood chamber and (Barnard 1960, 1979). create a water flow by moving their pleopods to irrigate embryos. Development within this brood chamber is direct and individuals hatch

A publication of the University of Oregon Libraries and the Oregon Institute of Marine Biology Individual species: http://hdl.handle.net/1794/12705 and full 3rd edition: http://hdl.handle.net/1794/18839 Email corrections to: [email protected] as juveniles that resemble small adults, with Bibliography no larval stage. Little is known about the reproduction and development of E. spinosus, 1. BARNARD, J. L. 1954. Marine but the development of another amphipoda of Oregon. Oregon State phoxocephalid species, Rhepoxynius Monographs, Studies in Zoology. No. abronius, has been described (Slattery 1985; 8:1-103. Kemp et al. 1985) and proceeds with few, 2. —. 1960. The amphipod family large eggs per brood (e.g. 5–12 eggs per Phoxocephalidae in the eastern brood, Slattery 1985 and 4–16, Kemp et al. Pacific ocean, with analyses of other 1985). Individuals of R. abronius breed in species and notes for a revision of the winter months and females are ovigerous in family. Allan Hancock Pacific late winter and early spring in Monterey, Expedition. 18:171-376. California and beginning in October in 3. —. 1975. Phylum Anthropoda: Yaquina Bay, Oregon (Kemp et al. 1985). Crustacea, Amphipoda: Gammaridea, Egg size is approximately 460 µm and, upon p. 313-366. In: Light's manual: hatching, are approximately 1.0 mm (Slattery intertidal invertebrates of the central 1985). California coast. S. F. Light, R. I. Larva: Since most amphipods are direct Smith, and J. T. Carlton (eds.). developing, they lack a definite larval stage. University of California Press, Instead this young developmental stage Berkeley. resembles small adults (e.g. Fig. 39.1, Wolff 4. —. 1979. Revision of American 2014). species of the marine amphipod genus Juvenile: Sexual maturity is reached after 2– Paraphoxus (Gemmaridea: 3 molts in the phoxocephalid species, Phoxocephalidae). Proceedings of the Rhepoxynius fatigans, and R. abronius Biological Society of Washington. (Slattery 1985), which, in R. abronius, is when 92:368-379. individuals are approximately 2.7 mm in 5. BARNARD, J. L., and C. M. length (Kemp et al. 1985). BARNARD. 1981. The amphipod Longevity: Up to one year (Slattery 1985; genera Eobrolgus and Eyakia Chapman 2007). (Crustacea: Phoxocephalidae) in the Growth Rate: Amphipod growth occurs in Pacific Ocean. Proceedings of the conjunction with molting where the Biological Society of Washington. exoskeleton is shed and replaced. Post-molt 94:295-313. individuals will have soft shells as the cuticle 6. —. 1982. Revision of Foxiphalus and gradually hardens (Ruppert et al. 2004). Eubrolgus (Crustacea: Amphipoda: Growth rate of Rhepoxynius abronius new Phoxocephalidae) from American recruits was 0.3 mm per month (Kemp et al. oceans. Smithsonian Contributions to 1985). Zoology:I-IV, 1-35. Food: Many phoxocephalids are detritivores, 7. CHAPMAN, J. W. 2007. Amphipoda: but some are also predators of larval Gammaridea, p. 545-611. In: The polychaetes, and their grazing may affect Light and Smith manual: intertidal community structure (Kemp et al. 1985). invertebrates from central California to Eobrolgus spinosus is a common predator of Oregon. J. T. Carlton (ed.). University small meiofaunal invertebrate taxa (e.g. larval, of California Press, Berkeley, CA. juvenile and adult polychaetes, nematodes, 8. HOLMES, S. J. 1905. The amphipoda Oliver et al. 1982; Oakden 1984; Chapman of southern New England. US 2007). Government Printing Office. Predators: Fish, shorebirds. 9. KEMP, P. F., F. A. COLE, and R. C. Behavior: Males positively phototropic and SWARTZ. 1985. Life history and attracted to night light, a trait that may be productivity of the phoxocephalid correlated with very large eyes. amphipod Rhepoxynius abronius (Barnard). Journal of Crustacean Biology. 5:449-464.

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