Americorophium Salmonis Class: Malacostraca Order: Amphipoda, Gammaridea Family: Corophiidae
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Phylum: Arthropoda, Crustacea Americorophium salmonis Class: Malacostraca Order: Amphipoda, Gammaridea Family: Corophiidae Taxonomy: Corophium salmonis was among Cephalon: the first corophiid amphipods described in Rostrum: The male rostrum is North America (Stimpson 1857). It was straight, slightly convex or with low central transferred to the genus Americorophium in projection (Fig. 1) (Shoemaker 1949). The 1997 based on morphological characters female rostrum, on the other hand, is a broad (Bousfield and Hoover 1997) (see Possible and low triangle (Fig. 7). Misidentifications). Researchers have not Eyes: always followed this transition in other Antenna 1: Reaches to middle of Americorophium species (e.g. A. spinicorne, article four of second antenna in males. Their Lester and Clark 2002; Sakamaki and flagellum comprises 14–16 articles Richardson 2009), but we follow the (occasionally 11–12) and the first article of the nomenclature used in other current local peduncle is flat and greatly expanded laterally intertidal guides (Chapman 2007). (Fig. 1) (Shoemaker 1949). First antenna about as long as the second in females. The Description female flagellum comprises ten joints Size: Largest males are 6 mm in length, from (Shoemaker 1949) and the first article is not rostrum to end of uropods and the average expanded. size range is 4–6 mm (Coos Bay) and 7.5 mm Antenna 2: Much longer than body in (Siuslaw Estuary). Females are mature male specimens. The fourth article approximately 7 mm in length (Shoemaker has large distal tooth, forming a half-moon, 1949). The illustrated specimen (from Coos and small tooth within (Fig. 3). The fifth article Bay) is 6 mm. has two teeth below: one at distal end and Color: Males are transparent, with brown one near proximal end (Fig. 3). The proximal mottling, especially on large second antenna tooth lies below the flexed half-moon tooth. (Fig. 3). Females, like other Americorophium The gland cone on second article below, is bi- species, are clear, with brown mottling, lobed and elaborate (Fig. 2) (Shoemaker especially on the second antennae. 1949). The second antenna in females is not General Morphology: The body of as massive as in males. The fourth article is amphipod crustaceans can be divided into without a large half-moon tooth and three major regions. The cephalon (head) accessory, but with two single spines on the includes antennules, antennae, mandibles, lower edge and two on the third article (Fig. maxillae and maxillipeds (collectively the 4). The gland cone of females is simpler than mouthparts). Posterior to the cephalon is the that of the male and is without lobes (Fig. 8). pereon (thorax) with seven pairs of Mouthparts: pereopods attached to pereonites followed by Pereon: the pleon (abdomen) with six segments Coxae: Setose lamellae (pairs of comprising three pleonites (together the brood plates attached to bases of coxae) are pleosome), three urosomites (together the present in females only and are used for urosome), and finally a telson at the animal holding eggs and young. Do not confuse with posterior (see Plate 254, Chapman 2007). In fleshy gills, which are also attached to coxae. members of the genus Americorophium, the Gnathopod 1: body is flattened dorso-ventrally and rarely Gnathopod 2: Filtering type, with exceeds 1 cm in total length (including fine long setae, present in both sexes, antennae) in local specimens (see Fig 46, morphology as in other Americorophium Kozloff 1993). species (see Fig. 3, A. brevis in this guide). Hiebert, T.C. 2015. Americorophium salmonsis. 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. A publication of the University of Oregon Libraries and the Oregon Institute of Marine Biology Individual species: http://hdl.handle.net/1794/12687 and full 3rd edition: http://hdl.handle.net/1794/18839 Email corrections to: [email protected] Perepods 3 through 7: however, for the fourth Americorophium Pleon: species, A. spinicorne, where male and Pleonites: female morphologies are similar. Additional Urosomites: Urosome with posterior characteristics that differ between species margin straight, slightly concave and with a (particularly A. brevis and A. salmonis) spine in each corner as well as two spines on include first antenna, telson, first uropods each lateral edge and two on the inside edge and third uropods. (Fig. 6). First uropods with three to six Americorophium stimpsoni, slender spines along outside edge of principally a northern California species, peduncle. Two to three small, blunt spines does not seem to occur in Oregon. Its chief present at distal corner (Fig. 6). Third key characteristic is a prominent male uropods have many slender setae on all rostrum, almost as long as the ocular lobes. edges (Fig. 6). The females are much like those of A. Epimera: salmonis. Telson: Americorophium spinicorne, another Sexual Dimorphism: Males and females prominent northwest species, has less exhibit differing morphology in characters of sexual dimorphism than other the rostrum, Antenna 1 and 2, as well as Americorophium species. Both males and overall body size and color. females have a half-moon tooth on the fourth article of the second antenna, but without the Possible Misidentifications small accessory tooth. Americorophium The gammarid family Corophiidae is spinicorne is also strongly euryhaline and characterized by individuals that build U- often found in fresh-water habitats. shaped tubes in both soft sediments and on Segments of urosome are separate and not hard surfaces, sometimes forming dense fused in A. spinicorne and males and aggregations. Species can be dramatically females can be distinguished by the second sexually dimorphic. Although males may be antennal features and by the presence of easier to identify with taxonomically relevant lamellae and/or eggs in females. characters including the rostrum and Males: Of the Americorophium peduncle of second antennae, most females species in which males have urosome can be reliably identified to species as well segments dissimilar to females, A. stimpsoni, (Chapman 2007). Five corophiid genera A. brevis, and A. salmonis all have a half- occur locally: Americorophium, Corophium, moon and accessory tooth on the fourth Crassicorophium, Laticorophium and article of the second antenna. Monocorophium. The three common Americorophium brevis and A. salmonis estuarine species in this guide (A. brevis, A. often have similar rostrums, but that of A. salmonis, and A. spinicorne) were stimpsoni has a prominent central lobe previously members of the genus nearly as long as the ocular lobes. In A. Corophium (see Shoemaker 1949), but salmonis the first antenna reaches only to were transferred to the genus the middle of the fourth article. Americorophium in 1997 (Bousfield and Americorophium brevis does not have flat Hoover 1997). expanded first articles of the first antenna All Americorophium species have and A. salmonis usually has 14–16 articles in filtering-type second gnathopods and long the flagellum, (though occasional specimens setae on the third uropods. Of the four local will have 11–12). In A. brevis, the males Americorophium species, sexual have about 11 articles in the flagellum of the dimorphism is strong in the three species A. first antenna. The uropods of A. salmonis brevis, A. salmonis, and A. stimpsoni. In and A. brevis are quite dissimilar. In A. particular, the second antenna and fourth salmonis, the peduncle of the first uropod is segment differ between males and females armed on the outside edge with three to six (Shoemaker 1949). This is not the case, long, slender spines and at the distal edge Hiebert, T.C. 2015. Americorophium salmonsis. 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. with two to three short, blunt spines. Temperature: Americorophium brevis has instead only Tidal Level: eight short, blunt spines. The third uropods Associates: of A. salmonis have many more and longer Abundance: Populations often very dense setae than those of A. brevis. The telson and easily observed or collected in the field. shape and spination of the two species are The abundance of Americorophium species also quite different (compare Figs. 4, A. was measured in the Campbell River Estuary brevis, and Fig. 5, A. salmonis in this guide). and ranged from zero to ~15,000–31,000 per Females: A. salmonis and A. square meter in July (Raymond et al. 1985). stimpsoni females are very much alike, with Densities of A. salmonis in the Copper River no strong distinguishing characteristics, so Delta, Alaska were as high as 7,000 per the species should not be differentiated square meter in August (Powers et al. 2002). solely by female specimens. The only Americorophium female of this group to Life-History Information have the half-moon hook is A. spinicorne, Reproduction: Development in most so this species is easily distinguished from amphipods is direct, lacking a larval stage, others. Americorophium brevis has three and little is known about the reproduction and pairs of spines, as well as a spine on the development in A. salmonis. Ovigerous A. gland cone, instead of having two single salmonis females and young have been spines on the underside of the fourth article observed in October (Ten Mile Creek). of the second antenna. The first antenna Ovigerous A. spinicorne females have been has eight joints in the flagellum, while that of observed in February, March, May and A. salmonis has ten. December (Eriksen 1968). In the European species, Corophium volulator, breeding Ecological Information occurs in February (over-wintering population) Range: Type locality is Puget Sound, and again in July–August. Young remain in Washington (Bousfield and Hoover 1997). brood pouch four weeks and females produce Known range along the west coast of North up to four broods per year (Green 1968).