Eogammarus Confervicolus Class: Multicrustacea, Malacostraca, Eumalacostraca
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Phylum: Arthropoda, Crustacea Eogammarus confervicolus Class: Multicrustacea, Malacostraca, Eumalacostraca Order: Peracarida, Amphipoda, Senticaudata, Gammarida, Gammaridira Family: Gammaroidea, Anisogammaridae Taxonomy: Originally described as Maera Cephalon: confervicolus, E. confervicolus has under- Rostrum: Rostrum vestigial. gone various generic designations including Eyes: Gammarus and, most recently, Anisogam- Antenna 1: Almost equal to ½ body marus. In 1979, Bousfield revised the family length and with an accessory flagellum of five Anisogammaridae and promoted Eogam- articles (Fig. 1). Longer than (or equal to) sec- marus to generic rank comprising 10 species ond antenna and with posterodistal spine on (including E. confervicolus, Tomikawa et al. peduncle (Fig. 1) (Eogammarus, Bousfield 2006). Species within this genus remain dif- 1979). Posterodistal setae on article one ficult to identify, however, because original spiniform (Tomikawa et al. 2006). descriptions often lack sufficient detail. Antenna 2: Stout, shorter than first and with 14 articles (Fig. 1). Peduncles four Description and five with two (rarely three) posterior Size: Individuals up to 19 mm. Male speci- marginal groups of setae (in addition to mens range locally from 12 mm (South terminal group) (Bousfield 1979; Tomikawa et Slough of Coos Bay) to 16 mm in length al. 2006). (Siuslaw Estuary). Mouthparts: Mandible with palp, molar Color: White with dark brown mottling and large and bears rasping surface. No palp se- brown stripes on the first and second anten- tae on the first article of maxilla one nae. (Tomikawa et al. 2006). General Morphology: The body of amphi- Pereon: pod crustaceans can be divided into three Coxae: First four coxal plates become major regions. The cephalon (head) or gradually larger and the fourth is rounded cephalothorax includes antennules, anten- (Fig. 1) while plates 5–7 are quite small. nae, mandibles, maxillae and maxillipeds Gnathopod 1: Slightly smaller than (collectively the mouthparts). Posterior to second gnathopod. Article six with palm the cephalon is the pereon (thorax) with oblique, nine peg-like teeth and dactyl curved seven pairs of pereopods attached to pere- (Fig. 2a). onites followed by the pleon (abdomen) with Gnathopod 2: Much like the first six pairs of pleopods. The first three sets of gnathopod, but larger and palm with seven pleopods are generally used for swimming, stout pegs (Fig. 2b). while the last three are simpler and surround Pereopods 3 through 7: Strong, be- the telson at the animal posterior. Amphi- coming larger posteriorly and spinous but pods in the Gammaroidea (including Gam- without plumose setae on margins of basis maridae and Anisogammaridae) display and carpus (Tomikawa et al. 2006). weak sexual dimorphism (Chapman 2007). Pleon: (For detailed key and description of E. con- Pleonites: No dorsal spines and only 0 fervicolus see Figs. 14–17 Tomikawa et al. –2 posterior marginal setae (Fig. 1). 2006). 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. Eogammarus confervicolus. 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, Charles- ton, OR. Urosomites: Urosome one with four cally subsimilar, have palms with margins ver- dorsal groups of three spines each. Uro- tical and lined with blunt spines and massive some two with dorsal spines in two groups dactyls with posterior accessory blades. They and no prominent median tooth (Fig. 3) (key also have coxal gills with accessory lobes and taxonomic character, Bousfield 1979). urosome segments with posterodorsal spines Uropods one and two with 2–4 groups of in clusters of two or four (Bousfield 1979, spines. Uropod two with rami extending 2001). The Gammaridae includes three spe- beyond peduncle of uropod three (Fig. 1) cies in the genus Gammarus locally, none of (Bousfield 1979). The inner margin of the which are certain to be native (Chapman outer ramus in uropod three usually with four 2007). The Anisogammaridae includes seven groups of strong spines, but less than 10 local species including one in the genus Ani- isolated plumose setae. The inner ramus is sogammarus, four in the genus Ramellogam- less than ½ length outer ramus (Fig. 4) marus and two in Eogammarus (Chapman (Bousfield 1979). 2007). Epimera: The genus Eogammarus is character- Telson: Split, with connected lobes each ized by uropods one and two with rami linear with two spines, and only one spine is apical and with apical margins spinose, urosome (at the tip) (Fig. 3). Eogammarus confervi- segments one and two with 2–4 groups of colus and E. oclairi can be differentiated by spines and peduncular segments one and two telson characters, as the latter species only with 2–3 groups of posterior marginal setae has one spine on each lobe. However, it is (Bousfield 1979). The only other species of currently unclear whether this feature is rep- Eogammarus in the northeastern Pacific resentative of two species, or if E. oclairi is region is Eogammarus oclairi, a pelagic simply large E. confervicolus (Bousfield estuarine form very like E. confervicolus. 1979; Chapman 2007). Both have robust setae on article one of Sexual Dimorphism: Sexual dimorphism is antenna two and no marginal setae on the relatively weak among the Gammaroidea palp of article one on maxilla one. They can compared to other amphipod families. Fe- be differentiated by each telson lobe, which male and male E. confervicolus differ very has two terminal setae, in E. oclairi, not one little, if at all. Females can be smaller, have as in E. confervicolus (Bousfield 1979). smaller gnathopods, and shorter antenna Additional characters include the following than do the males. (see Tomikawa et al. 2006): aesthetasc of flagellum on antenna one is equal to setae in Possible Misidentifications E. confervicolus and longer in E. oclairi; Gammaroidea comprises the two female calceoli on antenna two are absent in amphipod families Anisogammaridae and the former species and present in the latter; Gammaridae. The Gammaridae is charac- the longest setae on pereopod six is half the terized by gnathopods of dissimilar size width of the ischium in the former and shorter (males), palms oblique and with simple in the latter species; and the robust telson spines and slender simple dactyls. They al- setae are equal to or shorter than the slender so have simple coxal gills without accessory setae in E. confervicolus, but longer in E. lobes and urosome segments with postero- oclairi (Tomikawa et al. 2006). Despite these dorsal spines in groups of three (Bousfield characters, it remains a possibility that E. 1979). The Anisogammaridae, on the other confervicolus and E. oclairi are the same hand, have gnathopods that are morphologi- species and the above variations are simply 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] due to individual size (Chapman 2007). Slough, Siltcoos River, Siuslaw Estuary) Members of the closely related genus (Barnard 1954). Anisogammarus have first antenna shorter Habitat: Muddy substrates. Eogammarus than the second (the most distinctive confervicolus gets name from the "conferva" character) (Bousfield 1979). In or long green algae on which it lives. Also oc- Anisogammarus, each of the urosomites has curs with Salicornia, Carex and Fucus a prominent median tooth and a smaller pair (Straude 1987). Growth of E. confervicolus of dorsolateral teeth, not 2–4 groups of was compared between three habitats and spines as in Eogammarus. Finally, on ranked as follows: highest in an embankment uropod three, the rami are subequal, not along the perimeter of a marsh, medium along disparate in size as in Eogammarus. the edge of a Fucus community and lowest in Anisogammarus pugettensis has a habitat dominated by woody debris (Stanhope prominent fixed median spine on its second and Levings 1985). Little migration occurs urosomite and no rows of spines (Bousfield between different adjacent substrates, and 2001). can result in genetically different races Another closely related genus is (Stanhope et al. 1992; Stanhope et al. 1993). Ramellogammarus, characterized by dorsal Salinity: Full salt water to brackish water groups of spines on its pleon segments: (range 5–25, Stanhope et al. 1993). groups of 1–3 on urosomes one and two; Temperature: urosome three with 1–2 posterodorsal Tidal Level: Intertidal to 30 meter depths groups of spines; and 1–4 groups of poste- (Bousfield 1979; Chapman 2007). Occurs in rior marginal setae on peduncle segments of drainage channels in South Slough of Coos both first and second antennae (Bousfield Bay (+1.4 meters). 1979; Bousfield and Morino 1992; Chapman Associates: Associates include the isopod, 2007). Ramellogammarus oregonensis and Gnorimosphaeroma insulare, (South Slough R. ramellus were both previously members of Coos Bay) and the amphipod, Corophium of Gammarus, Anisogammarus and Eogam- slamonis (Siuslaw Estuary). marus. Ramellogammarus oregonensis is Abundance: Often occurs in great numbers