Eobrolgus Spinosus Class: Multicrustacea, Malacostraca, Eumalacostraca

Phylum: Arthropoda, Crustacea

Eobrolgus spinosus Class: Multicrustacea, Malacostraca, Eumalacostraca

Order: Peracarida, Amphipoda, Amphilochidea, A gammarid amphipod Lysianassida, Haustoriidira Family: Haustorioidea, Phoxocephalidae, Brolginae

Taxonomy: The genera Eobrolgus and as long as pereonites one through three Foxiphalus were designated in 1979 by Bar- (Barnard 1975) (Fig. 1). nard and included species formerly in the Rostrum: Rostrum well developed and genus Paraphoxus, including E. spinosus not constricted (Eobrolgus, Barnard 1979) (e.g. Paraphoxus spinosus) (Barnard and (Fig. 1). Barnard 1982). Eyes: Large, black and about same size in females (Figs. 1, 2) and immature Description males, but is much larger in mature males Size: Individuals to 4.5 mm in length (Puget (not figured). Sound, Barnard 1960). The largest Oregon Antenna 1: Female first antenna equal specimens were 3.5 mm (Coos Bay) and 2.4 in length to second antenna. Flagellum has mm (Yaquina Bay) (Kemp et al. 1985). Ovi- about seven articles (Fig. 3a) and accessory gerous females are not longer than 5 mm flagellum (in both sexes) is with about five ar- (Barnard 1975). ticles. Color: White, with black eyes. Antenna 2: The peduncle of the General Morphology: The body of amphi- second antenna in females is with some pod crustaceans can be divided into three heavy spines and setae (Fig. 3b). The major regions. The cephalon (head) or flagellum has about seven slender articles, cephalothorax includes antennules, anten- and is shorter than the peduncle (Barnard nae, mandibles, maxillae and maxillipeds 1960). The male flagellum is longer than the (collectively the mouthparts). Posterior to body in mature males and can have sensory the cephalon is the pereon (thorax) with clubs on proximal flagellal articles and on fifth seven pairs of pereopods attached to pere- peduncle articles (not figured). Immature onites followed by the pleon (abdomen) with males have flagella a little longer than six pairs of pleopods. The first three sets of peduncle. pleopods are generally used for swimming, Mouthparts: Epistome (a part of the while the last three are simpler and surround lip) is not produced into cusp (Fig. 1a) the telson at the animal posterior. Members (Barnard 1960). The Phoxocephalidae is one of the gammarid family Phoxocephalidae are of few groups in which epistome is of taxo- referred to as “spiny heads” due to their nomic importance. For a lateral view, push shield-like pointed rostrums. They are also antennae and mandibular palps aside one the most abundant and diverse group of (Barnard 1960). Mandible with tri-articled crustaceans in this size range (1–10 mm, palp, feeble molar and no large process. Right Chapman 2007). Unlike many amphipod female mandible is with simple lacinia mobilis groups, taxonomic keys tend to favor female (Barnard and Barnard 1981) (Fig. 4). The first specimens in the Phoxocephalidae maxilla is with biarticulate palp and an outer (Chapman 2007). plate with nine spines (Barnard and Barnard Cephalon: Head tapers evenly and is not 1981). Maxilliped palp of article four is with- abruptly narrowed (Fig. 2) with length about

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. 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.

out large distal setae (not figured). inner ramus is more than half as long as the Pereon: outer and is quite setose in mature specimens Coxae: Coxal plate one almost as (Fig. 9c) (Barnard 1960). large as two. The fourth coxa is broad and Epimera: The third epimeron is not the fifth rounded (Fig. 1). Coxal margins produced into a tooth and is naked (i.e. bears bear simple setae. no setae) (Barnard and Barnard 1981) (Fig. Gnathopod 1: Small. Similar in size 1). and shape to the second gnathopods Telson: Teslon, with cleft, is thin, lamellar and (Eobrolgus, Barnard 1979). Article six is each lobe is with one short spine and one fine broad. seta (Fig. 8). Gnathopod 2: Much like first gnatho- Sexual Dimorphism: Not as strong as in pods. The first article is not pronounced (i.e. some amphipod families. Males have larger with even margins) and the sixth article is eyes, much longer second antennae and spi- broad. nose uropods (uropod three). Usual amphi- Pereopods 3 through 7: Pereopods pod gnathopod sexual dimorphism is not ob- with stout spines (Figs. 1, 6, 7). Pereopod served in this genus (Barnard 1960; Chapman four "normal" in orientation, not reversed like 2007). pereopods 5–7 (Barnard 1975) (see Possible Misidentifications Eohaustorius estuarius). Pereopod five with Phoxocephalids can be distinguished second article broad, articles 4–5 expanded primarily by their sixth and seventh pereo- but narrower than article two (Fig. 1). pods, which are greatly different from each Pereopod six is longer and more slender other. They also have distinctive multiarticu- and with narrower article two than pereopod late accessory flagellae (on antenna one), seven (Fig. 6). Pereopod seven is shorter, and long rostrums (Barnard 1960). Hyalidae stouter and with article two broader than and Dogielinotidae are also estuarine families, pereopod six and has rounded posterior but they lack mandibular palps and inner rami edge with fine spines, no large spur (Fig. 7). on the third uropods. The Pleustidae have Pleon: uncleft telsons and only vestigial antennal ac- Pleonites: Fourth pleonite with proxi- cessory flagella (Barnard 1975). Both the mal edge strongly depressed in males, while Gammaridae and Haustoriidae have pereo- the edge is almost flush with segment three pods that are similar in size and shape (not in females (Eobrolgus, Barnard 1960). like the Phoxocephalidae) and in these fami- Urosomites: First urosomite pedun- lies, pereopod four is reversed. Gammaridae cle with at least one dorsal margin, with only have a telson with connected lobes (see one or no spines and two spines on inner Eogammarus confervicolus), while the telson peduncle margin. Inner and outer branches lobes of Haustoriidae are disjunct (see similar, with one apical and one margin Eohaustorius estuarius), and are much spine (Fig. 9a). Second uropods in females heavier than those of Eobrolgus. with four stout spines on peduncle margin, The Phoxocephalidae is a diverse and rami shorter than peduncle and without mar- abundant group of amphipods with 13 genera ginal spines (Fig. 9b) (Barnard 1960). In (comprising 30–45 species) represented lo- males, there are more spines on peduncle cally including, Mandibulophoxus (one local (not figured). The third uropods in females species), Cephalophoxoides (one local spe- is with inner ramus half as long as (or sligh- cies), Heterophoxus, (five local species), Ma- tly less than) outer (Fig. 9d). In males, the joxiphalus (one local species), Metaphoxus 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]

(one local species), and Parametaphoxus Adults are larger than those of E. spinosus (one local species). Most phoxocephalid and ovigerous females are over 6 mm in len- species formerly in Paraphoxus have been gth, but not under 5 mm. Foxiphalus major placed (by Barnard 1979) into one of six amphipods have longer heads and smaller genera including Metharpinia (two local spe- eyes than do E. spinosus and their fifth pereo- cies), Eyakia (one local species), Foxiphalus pod is slender, not stout. The inner ramus of (seven local species), Grandifoxus (three the female third uropod is more than ½ the local species), Rhepoxynius (19 local length of the outer ramus (not less than ½, species), and Eobrolgus (two local species). Fig. 9d). The third pleonal epimeron is conca- Mandibulophoxus is distinguished ve or straight on its posterior edge and seto- from Eobrolgus by its sickle-shaped mandi- se. Foxiphalus major was found under its old bular palp borne on a large process. It has name (Pontharpinia obtusidens) on Oregon's a biarticulate palp on the first maxilla (like outer coast (Barnard 1954, 1979). Eobrolgus). Mandibulophoxus gilesi is an Rhepoxynius tridentatus and others of eyeless, long-rostrumed species that has this genus have an abruptly narrowing, unta- been found subtidally (to 14 meters depth) in pered rostrum and the second article of pere- Yaquina Bay and other Oregon estuaries opod seven has three large teeth on the pos- (Chapman 2007). terior edge (Barnard 1954, 1979). Eobrolgus chumashi is an endemic Rhepoxynius abronius, with a broad head and oceanic species whose range probably narrow, short rostrum, has a long, sharp epis- extends only south of Oregon (Barnard and tomal process. This species has large teeth Barnard 1981). Its body is dwarfed and the on the posterior edge of pereopod seven. It head and eyes are large. The pleonal has been reported from Yaquina Bay, Ore- epimeron are not naked as in E. spinosus, gon. but have 1–2 ventral setae. The lacinia Grandifoxus grandis (= Grandifoxus mobilis (on the right mandible of the female) milleri and Paraphosux milleri) is found in the is bifid, not simple. Some hybridization Columbia River estuary. This closely related between these two species of Eobrolgus species has a narrow gnathopod hand (sixth may occur (Barnard and Barnard 1981; article) and an abruptly narrowing rostrum Chapman 2007). (Barnard 1960, 1979). The genera Foxiphalus and Eobrol- Ecological Information gus are morphologically similar. Female Range: Type locality is New England (Homes Eobrolgus have a short second article on 1905; Barnard and Barnard 1982). Known antenna one with a ventral surface that is range includes the western Atlantic, from continually covered with setae. Female which it may have been introduced to the Foxiphalus, on the other hand, have a gap eastern Pacific. Distribution along the west on the ventral side of antenna one. Confus- coast of North America now includes Puget ingly, Eobrolgus males exhibit similar mor- Sound, Washington to Newport Bay, Califor- phology of antenna one to Foxiphalus fe- nia (Barnard and Barnard 1981). males and, thus, cannot be differentiated Local Distribution: Coos Bay sites in South (Barnard and Barnard 1982) and, further- Slough, at Jordan Cove and at Pigeon Point more, Foxiphalus species are difficult to dis- (Barnard 1975). Other Oregon estuaries inclu- tinguish from Majoxiphalus (Chapman de Yaquina Bay. 2007). Foxiphalus major is probably the Habitat: A burrower in sandy and muddy bot- species most similar to Eobrolgus spinosus.

toms of estuaries that also tolerates sub- Kemp et al. 1985) and proceeds with few, strates mixed with wood chips (e.g. Jordan large eggs per brood (e.g. 5–12 eggs per Cove, Coos Bay). Phoxocepahlid amphi- brood, Slattery 1985 and 4–16, Kemp et al. pods are sensitive to a variety of pollutants 1985). Individuals of R. abronius breed in and are common subjects of toxicity tests winter months and females are ovigerous in (e.g. Rhepoxynius abronius, Robinson et al. late winter and early spring in Monterey, Cali- 1988). fornia and beginning in October in Yaquina Salinity: Collected at salinities of 30 (Coos Bay, Oregon (Kemp et al. 1985). Egg size is Bay). approximately 460 µm and, upon hatching, Temperature: are approximately 1.0 mm (Slattery 1985). Tidal Level: High and mid intertidal (Coos Larva: Since most amphipods are direct de- Bay) (Chapman 2007). veloping, they lack a definite larval stage. In- Associates: In beds of the ghost shrimp, stead this young developmental stage resem- Neotrypaea, and with the polychaetes, bles small adults (e.g. Fig. 39.1, Wolff 2014). Pygospio elegans and Pseudopolydora Juvenile: Sexual maturity is reached after 2– kempi, outside of shrimp beds (Coos Bay, 3 molts in the phoxocephalid species, South Slough) (Posey 1985). Rhepoxynius fatigans, and R. abronius Abundance: Phoxocephalid amphipods are (Slattery 1985), which, in R. abronius, is when highly abundant, reaching densities up to individuals are approximately 2.7 mm in 700 individuals per square meter in Califor- length (Kemp et al. 1985). nia (Oakden 1984). Dominant invertebrate Longevity: Up to one year (Slattery 1985; at Jordan Cove, Coos Bay. Recorded June Chapman 2007). abundances: lower intertidal (+0.9 meters Growth Rate: Amphipod growth occurs in MLLW) 60–162 individuals per 13 x 15 cm conjunction with molting where the exoskele- core; mid intertidal (+1.0 meters MLLW) 92– ton is shed and replaced. Post-molt individu- 174 individuals; high intertidal (+1.1 meters als will have soft shells as the cuticle gradual- M LLW) 37–58 individuals (Posey 1985). ly hardens (Ruppert et al. 2004). Generally not as abundant as its close rela- Growth rate of Rhepoxynius abronius tive, Foxiphalus major (Barnard 1960). new recruits was 0.3 mm per month (Kemp et al. 1985). Life-History Information Food: Many phoxocephalids are detritivores, Reproduction: Most amphipods have sepa- but some are also predators of larval poly- rate sexes with some sex determination cor- chaetes, and their grazing may affect commu- related with environmental conditions nity structure (Kemp et al. 1985). Eobrolgus (Straude 1987). Females brood embryos in spinosus is a common predator of small meio- an external thoracic brood chamber and cre- faunal invertebrate taxa (e.g. larval, juvenile ate a water flow by moving their pleopods to and adult polychaetes, nematodes, Oliver et irrigate embryos. Development within this al. 1982; Oakden 1984; Chapman 2007). brood chamber is direct and individuals Predators: Fish, shorebirds. hatch as juveniles that resemble small Behavior: Males positively phototropic and adults, with no larval stage. Little is known attracted to night light, a trait that may be cor- about the reproduction and development of related with very large eyes. E. spinosus, but the development of another phoxocephalid species, Rhepoxynius abro- Bibliography nius, has been described (Slattery 1985; 1. BARNARD, J. L. 1954. Marine amphipoda

of Oregon. Oregon State Monographs, strate preference in five species of Phoxo- Studies in Zoology. No. 8:1-103. cephalid amphipods from central Califor- 2. —. 1960. The amphipod family Phoxo- nia. Journal of Crustacean Biology. 4:233- cephalidae in the eastern Pacific ocean, 247. with analyses of other species and notes 11. OLIVER, J. S., J. M. OAKDEN, and P. N. for a revision of the family. Allan Han- SLATTERY. 1982. Phoxocephalid amphi- cock Pacific Expedition. 18:171-376. pod crustaceans as predators on larvae 3. —. 1975. Phylum Anthropoda: Crusta- and juveniles in marine soft-bottom com- cea, Amphipoda: Gammaridea, p. 313- munities. Marine Ecology Progress Series. 366. In: Light's manual: intertidal inverte- 7:179-184. brates of the central California coast. S. 12. POSEY, M. H. 1985. The Effects upon the F. Light, R. I. Smith, and J. T. Carlton macrofaunal community of a dominant (eds.). University of California Press, burrowing deposit feeder, Callianassa cali- Berkeley. forniensis, and the role of predation in de- 4. —. 1979. Revision of American species termining its intertidal distribution. Ph.D. of the marine amphipod genus University of Oregon. Paraphoxus (Gemmaridea: Phoxocepha- 13. ROBINSON, A. M., J. O. LAMBERSON, F. lidae). Proceedings of the Biological So- A. COLE, and R. C. SWARTZ. 1988. Ef- ciety of Washington. 92:368-379. fects of culture conditions on the sensitivity 5. BARNARD, J. L., and C. M. BARNARD. of a Phoxocephalid amphipod, 1981. The amphipod genera Eobrolgus Rhepoxynius abronius, to cadmium sedi- and Eyakia (Crustacea: Phoxocepha- ment. Environmental Toxicology and lidae) in the Pacific Ocean. Proceedings Chemistry. 7:953-959. of the Biological Society of Washington. 14. RUPPERT, E.E., R.S. FOX, and R.D 94:295-313. BARNES. 2004. Invertebrate zoology: a 6. —. 1982. Revision of Foxiphalus and Eu- functional evolutionary approach, 7th Edi- brolgus (Crustacea: Amphipoda: Phoxo- tion. Thomson Brooks/Cole, Belmont, cephalidae) from American oceans. CA. Smithsonian Contributions to Zoology:I- 15. SLATTERY, P. N. 1985. Life histories of IV, 1-35. infaunal amphipods from subtidal sands of 7. CHAPMAN, J. W. 2007. Amphipoda: Monterey Bay, California. Journal of Crus- Gammaridea, p. 545-611. In: The Light tacean Biology. 5:635-649. and Smith manual: intertidal inverte- 16. STRAUD, C. P. 1987. Phylum or Subphy- brates from central California to Oregon. lum Crustacea, Class Malacostraca, Order J. T. Carlton (ed.). University of Califor- Amphipoda, p. 424-431. In: Reproduction nia Press, Berkeley, CA. and development of marine invertebrates 8. HOLMES, S. J. 1905. The amphipoda of of the northern Pacific coast. M. F. Strath- southern New England. US Government man (ed.). University of Washington Printing Office. Press, Seattle, WA. 9. KEMP, P. F., F. A. COLE, and R. C. 17. WOLFF, C. 2014. Amphipoda, p. 206-209. SWARTZ. 1985. Life history and produc- In: Atlas of crustacean larvae. J.W. Martin, tivity of the phoxocephalid amphipod J. Olesen, and J. T. Høeg (eds.). Johns Rhepoxynius abronius (Barnard). Journal Hopkins University Press, Baltimore. of Crustacean Biology. 5:449-464. Updated 2015 10. OAKDEN, J. M. 1984. Feeding and sub- T.C. Hiebert 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.