Allorchestes Angusta Class: Multicrustacea, Malacostraca, Eumalacostraca
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Phylum: Arthropoda, Crustacea Allorchestes angusta Class: Multicrustacea, Malacostraca, Eumalacostraca Order: Peracarida, Amphipoda, Senticaudata, Talitrida, Talitridira Family: Talitrroidea, Dogielinotidae Taxonomy: Although current intertidal (Barnard 1952) guides (e.g. Chapman 2007) place A. an- Eyes: Eyes large, red and positioned gusta within the family Hyalellidae, Serejo antero-laterally (Fig. 1). (2004) proposes that this family be com- Antenna 1: Shorter than the second bined with the closely related family Hya- antenna in males (Fig. 1). The female's first lidae (Bousfield and Hendrycks 2002) based antenna is subequal. on a 43-character matrix (and including A. Antenna 2: Longer than first five body angusta) to form the resulting Dogielino- segments (Fig. 1) (Barnard 1952). tidae. Authors continue to synonymize A. Mouthparts: Mandible with well devel- oculatus and A. angusta, based on the am- oped rasping surface on molar, 2–3 biguous description of the former species, spines, five teeth and no palps (Fig. 2). The until further material can be examined (see tip of the inner plate of maxilliped with three Hendrycks and Bousfield 2001). stout spines, setae and article four developed Description (Fig. 4). First maxilla is with minute palp (Fig. Size: The illustrated male specimen is 6–8 3) (Shoemaker 1941). mm in length (from South Slough of Coos Pereon: Bay), but females tend to be smaller. Coxae: Coxae 1–3 with posterior cusp, Color: Bright green with dark red eyes and coxa four with lower convex margin, coxa five spots, yellow-green antenna. Females are shallow. Gills are medium to large in size, splotchy brown. sac-like, with the smallest at pereopod two. General Morphology: The body of amphi- Coxal plates 2–4 are deep and broad in fe- pod crustaceans can be divided into three males (Hendrycks and Bousfield 2001). major regions. The cephalon (head) or Gnathopod 1: Stout. Article five is cephalothorax includes antennules, anten- elongated (Fig. 1). nae, mandibles, maxillae and maxillipeds Gnathopod 2: Very large, article five (collectively the mouthparts). Posterior to elongated and article six is oval, tapering and the cephalon is the pereon (thorax) with with palm oblique. The dactyl is large, curved seven pairs of pereopods attached to pere- and fits the palm in males (Fig. 5). Article four onites followed by the pleon (abdomen) with larger than article three. six pairs of pleopods. The first three sets of Pereopods 3 through 7: Pereopods pleopods are generally used for swimming, three and four with short setae and pereopod while the last three are simpler and surround five is longer than pereopod four. the telson at the animal posterior. The ge- Pleon: nus Allorchestes is recognizable with a Pleonites: broad rectangular telson (Barnard 1974). Urosomites: Uropod one and two Cephalon: without marginal spines on outer ramus Rostrum: Small and with lateral (Hendrycks and Bousfield 2001). Third uro- lobes that are broadly subtruncated pod with one small, flexible ramus and one 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. Allorchestes angusta. 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. spine (Fig. 6) (Barnard 1975). similar species in the closely related family Epimera: Plates two and three with Hyalidae, does not have the produced ar- posterior corners acute (Hendrycks and ticle five on the second gnathopod, and has Bousfield 2001). a small inner ramus on the third uropod. Telson: Rectangular and with cleft halfway. Furthermore, its telson has two triangular Telson compressed laterally in cross section lobes. (Fig. 7a, b) (Barnard 1975). Ecological Information Sexual Dimorphism: Among amphipods, Range: Type locality is in California (Barnard males generally have larger eyes, antennae 1974; Hendrycks and Bousfield 2001). and gnathopods (Straude 1987). Female A. Known Pacific range includes Japan to La- angusta are smaller, have subequal anten- guna Beach, California, however A. angusta na, first gnathopod palm that is transverse is rare south of Monterey (Barnard 1969). (not oblique) and second gnathopod slightly Local Distribution: Coos Bay sites at North larger than the first (see Hendrycks and Bay of Cape Arago, Bay channel, South Bousfield 2001). Slough and the Metcalf Preserve (Barnard Possible Misidentifications 1969). The Hyalellidae are a family of Habitat: Algae and eelgrass. Known gammarid amphipods characterized by substrates include mud, wood chips, course highly modified first gnathopods in males sand and cobble although individuals also and correspondingly modified ventral pere- occur in plankton samples (Barnard 1954). onites (pereonite two) and dorsal coxae Allorchestes angusta was also found as a (coxa two) in females. Four species occur member of a phytal (drifting seaweeds) locally, three of which are in the genus Al- community collected from northern Japan lorchestes, which is characterized by a (Sano et al. 2003). smooth posterior edge of pereopod seven, Salinity: article two and a habitat that is primarily Temperature: marine or estuarine. On the other hand, Tidal Level: High intermediate (Metcalf Pre- the local species Hyalella azteca is mostly serve): + 0.6–1.2 meters (Yu et al. 2002). found in freshwater and has a serrated Associates: Associate species include other posterior edge of pereopod seven on arti- tanaid amphipods (e.g. Leptochelia) and cle two. polychaetes. Allorchestes bellabella has an inflat- Abundance: One of the common amphipods ed dactyl on the first gnathopod (males). along the outer coast. Allorchestes rickeri and A. angusta are the Life-History Information most similar species in this genus but can Reproduction: Most amphipods have sepa- be differentiated by the fourth article of the rate sexes with some sex determination corre- fifth pereopod. In A. angusta the width of lated with environmental conditions (Straude the fourth article is 1/2 the length, while in 1987). Females brood embryos in an external A rickeri it is 2/3 the length. Furthermore, thoracic brood chamber and irrigate embryos the female coxa two has a pre-amplexing with a flow of water produced by pleopod notch that is obtuse in A. angusta and at a movement. Development within this brood right angle in A. rickeri (see plate 272H chamber is direct and individuals hatch as ju- and 272J in Chapman 2007). veniles that resemble small adults, with no Parallorchestes ochotensis, a larval stage. Little is known about the devel- 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] opment of A. angusta, however, an oviger- 5. BARNARD, J. L. 1975. Phylum Anthropo- ous female was found in July (Barnard da: Crustacea, Amphipoda: Gammaridea, 1954). The development of Apohyale pu- p. 313-366. In: Light's manual: intertidal gettensis (= Hyale pugettensis), a member invertebrates of the central California of the Talitroidea superfamily and closely coast. S. F. Light, R. I. Smith, and J. T. related family Hyalidae, is described and Carlton (eds.). University of California proceeds as follows: breeding in summer; Press, Berkeley. individuals physically coupled for several 6. BOUSFIELD, E. L., and E. A. HEN- days prior to copulation; brood sizes of 30 DRYCKS. 2002. The Talitroidean amphi- embryos; embryos 5–600 µm in diameter, pod family Hyalidae revised, with empha- hatching after 12 days at room temperature sis on the North Pacific fauna: Systematics but remain within the female brood pouch for and distributional ecology. Amphipacifica. another 3–4 days (Straude 1987). 3:17-134. Larva: Since most amphipods are direct de- 7. CHAPMAN, J. W. 2007. Arthropoda: Am- veloping, they lack a definite larval stage. phipoda: Gammaridea, p. 545-618. In: The Instead, this young developmental stage re- Light and Smith manual: intertidal inverte- sembles small adults (e.g. Fig. 39.1, Wolff brates from central California to Oregon. J. 2014). T. Carlton (ed.). Juvenile: 8. HENDRYCKS, E. A., and E. L. BOUS- Longevity: FIELD. 2001. The amphipod genus Allor- Growth Rate: Amphipod growth occurs in chestes in the north Pacific region: Sys- conjunction with molting where the exoskele- tematics and distributional ecology. Am- ton is shed and replaced. Post-molt individ- phipacifica. 3:3-37. uals will have soft shells as the cuticle grad- 9. RUPPERT, E.E., R.S. FOX and R.D. ually hardens (Ruppert et al. 2004). BARNES. 2004. Invertebrate zoology: a Food: Herbivore and detritivore (Yu et al. functional evolutionary approach, 7TH Edi- 2002; Chapman 2007). tion. Thomson Brooks/Cole, Belmont, Predators: CA. Behavior: 10. SANO, M., M. OMORI, AND K. TANIGU- CHI. 2003. Predator-prey systems of drift- Bibliography ing seaweed communities off the Tohoku 1. BARNARD, J. L. 1952. Some amphipoda coast, northern Japan, as determined by from central California. Wasmann Jour- feeding habit analysis of phytal animals. nal of Biology. 10:20-23. Fisheries Science. 69:260-268. 2. BARNARD, J. L. 1954. Marine amphipo- 11. SEREJO, C. S. 2004. Cladistic revision of da of Oregon. Oregon State Mono- talitroidean amphipods (Crustacea, Gam- graphs, Studies in Zoology. No. 8:1-103. maridea), with a proposal of a new classifi- 3. BARNARD, J. L. 1969. Gammaridean cation. Zoologica Scripta. 33:551-586. amphipoda of the rocky intertidal of Cali- 12. SHOEMAKER, C. R. 1941. On the names fornia: Monterey Bay to La Jolla. Smith- of certain California amphipods. Proceed- sonian Institution Press, Washington. ings of the Biological Society of Washing- 4. BARNARD, J. L. 1974. Gammaridean ton. 54:187-188. amphipoda of Australia, Part. 2.