Allorchestes Angusta Class: Malacostraca Order: Amphipoda, Gammaridea Family: Hyalellidae

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Phylum: Arthropoda, Crustacea Allorchestes angusta Class: Malacostraca Order: Amphipoda, Gammaridea Family: Hyalellidae

Taxonomy: Although current intertidal Mouthparts: Mandible with well guides (e.g. Chapman 2007) place A. angusta developed rasping surface on molar, 2–3 within the family Hyalellidae, Serejo (2004) spines, five teeth and no palps (Fig. 2). The proposes that this family be combined with tip of the inner plate of maxilliped with three the closely related family Hyalidae (Bousfield stout spines, setae and article four developed and Hendrycks 2002) based on a 43- (Fig. 4). First maxilla is with minute palp (Fig. character matrix (and including A. angusta) to 3) (Shoemaker 1941). form the resulting Dogielinotidae. Authors Pereon: continue to synonymize A. oculatus and A. Coxae: Coxae 1–3 with posterior angusta, based on the ambiguous description cusp, coxa four with lower convex margin, of the former species, until further material coxa five shallow. Gills are medium to large can be examined (see Hendrycks and in size, sac-like, with the smallest at pereopod Bousfield 2001). two. Coxal plates 2–4 are deep and broad in females (Hendrycks and Bousfield 2001). Description Gnathopod 1: Stout. Article five is Size: The illustrated male specimen is 6–8 elongated (Fig. 1). mm in length (from South Slough of Coos Gnathopod 2: Very large, article five Bay), but females tend to be smaller. elongated and article six is oval, tapering and Color: Bright green with dark red eyes and with palm oblique. The dactyl is large, curved spots, yellow-green antenna. Females are and fits the palm in males (Fig. 5). Article four splotchy brown. larger than article three. General Morphology: The body of Pereopods 3 through 7: Pereopods amphipod crustaceans can be divided into three and four with short setae and pereopod three major regions. The cephalon (head) or five is longer than pereopod four. cephalothorax includes antennules, antennae, Pleon: mandibles, maxillae and maxillipeds Pleonites: (collectively the mouthparts). Posterior to Urosomites: Uropod one and two the cephalon is the pereon (thorax) with without marginal spines on outer ramus seven pairs of pereopods attached to (Hendrycks and Bousfield 2001). Third pereonites followed by the pleon (abdomen) uropod with one small, flexible ramus and one with six pairs of pleopods. The first three sets spine (Fig. 6) (Barnard 1975). of pleopods are generally used for swimming, Epimera: Plates two and three with while the last three are simpler and surround posterior corners acute (Hendrycks and the telson at the animal posterior. The genus Bousfield 2001). Allorchestes is recognizable with a broad Telson: Rectangular and with cleft halfway. rectangular telson (Barnard 1974). Telson compressed laterally in cross section Cephalon: (Fig. 7a, b) (Barnard 1975). Rostrum: Small and with lateral lobes Sexual Dimorphism: Among amphipods, that are broadly subtruncated (Barnard 1952) males generally have larger eyes, antennae Eyes: Eyes large, red and positioned and gnathopods (Straude 1987). Female A. antero-laterally (Fig. 1). angusta are smaller, have subequal antenna, Antenna 1: Shorter than the second first gnathopod palm that is transverse (not antenna in males (Fig. 1). The female's first oblique) and second gnathopod slightly antenna is subequal. larger than the first (see Hendrycks and Antenna 2: Longer than first five Bousfield 2001). body segments (Fig. 1) (Barnard 1952).

A publication of the University of Oregon Libraries and the Oregon Institute of Marine Biology Individual species: http://hdl.handle.net/1794/12685 and full 3rd edition: http://hdl.handle.net/1794/18839 Email corrections to: [email protected] Possible Misidentifications member of a phytal (drifting seaweeds) The Hyalellidae are a family of gammarid community collected from northern Japan amphipods characterized by highly modified (Sano et al. 2003). first gnathopods in males and Salinity: correspondingly modified ventral pereonites Temperature: (pereonite two) and dorsal coxae (coxa two) Tidal Level: High intermediate (Metcalf in females. Four species occur locally, Preserve): + 0.6–1.2 meters (Yu et al. 2002). three of which are in the genus Associates: Associate species include other Allorchestes, which is characterized by a tanaid amphipods (e.g. Leptochelia) and smooth posterior edge of pereopod seven, polychaetes. article two and a habitat that is primarily Abundance: One of the common amphipods marine or estuarine. On the other hand, the along the outer coast. local species Hyalella azteca is mostly found in freshwater and has a serrated Life-History Information posterior edge of pereopod seven on article Reproduction: Most amphipods have two. separate sexes with some sex determination Allorchestes bellabella has an correlated with environmental conditions inflated dactyl on the first gnathopod (Straude 1987). Females brood embryos in (males). Allorchestes rickeri and A. angusta an external thoracic brood chamber and are the most similar species in this genus irrigate embryos with a flow of water produced but can be differentiated by the fourth article by pleopod movement. Development within of the fifth pereopod. In A. angusta the this brood chamber is direct and individuals width of the fourth article is 1/2 the length, hatch as juveniles that resemble small adults, while in A rickeri it is 2/3 the length. with no larval stage. Little is known about the Furthermore, the female coxa two has a development of A. angusta, however, an pre-amplexing notch that is obtuse in A. ovigerous female was found in July (Barnard angusta and at a right angle in A. rickeri 1954). The development of Apohyale (see plate 272H and 272J in Chapman pugettensis (= Hyale pugettensis), a member 2007). of the Talitroidea superfamily and closely Parallorchestes ochotensis, a similar related family Hyalidae, is described and species in the closely related family proceeds as follows: breeding in summer; Hyalidae, does not have the produced individuals physically coupled for several days article five on the second gnathopod, and prior to copulation; brood sizes of 30 has a small inner ramus on the third uropod. embryos; embryos 5–600 µm in diameter, Furthermore, its telson has two triangular hatching after 12 days at room temperature lobes. but remain within the female brood pouch for another 3–4 days (Straude 1987). Ecological Information Larva: Since most amphipods are direct Range: Type locality is in California (Barnard developing, they lack a definite larval stage. 1974; Hendrycks and Bousfield 2001). Instead, this young developmental stage Known Pacific range includes Japan to resembles small adults (e.g. Fig. 39.1, Wolff Laguna Beach, California, however A. 2014). angusta is rare south of Monterey (Barnard Juvenile: 1969). Longevity: Local Distribution: Coos Bay sites at North Growth Rate: Amphipod growth occurs in Bay of Cape Arago, Bay channel, South conjunction with molting where the Slough and the Metcalf Preserve (Barnard exoskeleton is shed and replaced. Post-molt 1969). individuals will have soft shells as the cuticle Habitat: Algae and eelgrass. Known gradually hardens (Ruppert et al. 2004). substrates include mud, wood chips, course Food: Herbivore and detritivore (Yu et al. sand and cobble although individuals also 2002; Chapman 2007). occur in plankton samples (Barnard 1954). Predators: Allorchestes angusta was also found as a Behavior:

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