Family DEXAMINIDAE Leach, 1814

Syndexamine wunda

© Copyright from Barnard 1972: fig. 81.

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Introduction

Dexaminid amphipods are a relatively large family currently divided into two subfamilies, Dexamininae and Prophliantinae. Worldwide, 18 genera and 185 species have been recorded. In Australian waters, the genus Paradexamine is the most diverse with 24 species mainly described from south-western Australia by J.L. Barnard (1972). Dexaminids from other areas of Australia are not well known.

Dexaminids are mainly algal-dwellers. Edgar (1983, 1990) reported Paradexamine churinga Barnard, 1972 as one of the more common species living among algae in south-eastern Tasmania. The genus Polycheria is known to be associated with ascidians and Tritaea may be associated with sponges (Enequist 1949). Nothing is known of life-histories or of reproductive strategies in the dexaminids, but Bousfield (1979) generally considered dexaminoid amphipods to be non-mate-guarders because at least in some species males develop secondary sexual characters which indicate pelagic mate searching. Dexaminids are of average size with individuals varying from about 2–15 mm in length. A key to all genera is provided by Barnard & Karaman (1991).

Diagnosis

Head as long as deep, longer than deep or deeper than long; anteroventral margin weakly or moderately recessed, straight or concave and deeply or shallowly excavate, anteroventral corner rounded or hooked; rostrum short, moderate, long or absent; eyes well developed (round, ovoid or reniform), obsolescent or absent. Body laterally compressed or subcylindrical; smooth or processiferous and dorsally carinate; with robust setae, with sparse slender setae or without setae. Antenna 1 shorter than, subequal to, or longer than antenna 2; peduncular article 1 shorter than, subequal to, or longer than article 2; article 2 longer than article 3; article 3 shorter than article 1; accessory flagellum present or absent; primary flagellum less than or more than 5-articulate; callynophore absent. Antenna 2 short, medium length, long or longer than body; flagellum shorter or longer than peduncle; less than or more than 5-articulate. Mandible incisor dentate; lacinia mobilis present on both sides; molar fully triturating; palp present or absent. Maxilla 1 inner plate strongly setose along medial margin, weakly setose apically or without setae; palp large or reduced, 1- or 2-articulate. Maxilliped inner plates well developed; outer plates very large, large or small. Coxae 1–4 longer than broad, as long as broad or broader than long, overlapping or discontiguous; coxa 1 anteroventrally acuminate or not; coxae 1–3, coxae 2–4 or coxa 4 ventrally acuminate. Gnathopod 1 not sexually dimorphic; smaller (or weaker) than or subequal to gnathopod 2; subchelate, parachelate or chelate; coxa smaller than, subequal to or larger than coxa 2; carpus shorter than, subequal to, or longer than propodus, slightly or not produced along posterior margin of propodus. Gnathopod 2 not sexually dimorphic; subchelate, parachelate or chelate; coxa smaller than or subequal to but not hidden by coxa 3; ischium short; carpus short or long, shorter than, subequal to, or longer than propodus, slightly or not produced along posterior margin of propodus. Pereopods heteropodous (3–4 directed posteriorly, 5–7 directed anteriorly or 3–6 directed posteriorly, 7 directed anteriorly) or homopodous (3–7 directed posteriorly); some, all or none prehensile. Pereopod 3 coxa longer than broad or broader than long; carpus shorter than, subequal to, or longer than propodus, not produced. Pereopod 4 coxa smaller than, subequal to, or larger than coxa 3, with or without well developed posteroventral lobe; carpus shorter than, subequal to, or longer than propodus, not produced. Pereopod 5 shorter than, subequal to, or longer than pereopod 6; coxa smaller than, subequal to, or larger than coxa 4, with or without posterior lobe; basis expanded or linear, subrectangular, with or without posteroventral lobe; carpus weakly expanded or linear. Pereopod 6 shorter than, subequal to, or longer than pereopod 7; basis expanded or linear. Pereopod 7 shorter than or subequal to pereopod 5; similar or different in structure to pereopod 6; basis expanded or linear. Pleonites 1–3 with or without lateral teeth or ridging, pleonite 3 with or without dorsal carina. Epimeron 2 setose or without setae. Urosomites 1–3 coalesced or 1 free, 2 and 3 coalesced; urosomite 1 carinate or urosomites not carinate or urosomite 3 carinate. Uropods 1–2 apices of rami with robust setae. Uropod 3 biramous; peduncle short or long; rami lanceolate; outer ramus longer than peduncle; inner ramus apically setose. Telson laminar; deeply cleft; longer than broad; dorsal and apical robust setae present or absent.

General References

Barnard, J.L. 1972. Gammaridean Amphipoda of Australia, Part I. Smithsonian Contributions to Zoology 103: i-vi 1-333

Barnard, J.L. & Karaman, G.S. 1991. The families and genera of marine gammaridean Amphipoda (except marine gammaroids). Records of the Australian Museum, Supplement 13: 1-866

Bousfield, E.L. 1979. A revised classification and phylogeny of amphipod crustaceans. Transactions of the Royal Society of Canada 16: 343-390

Edgar, G.J. 1983. The ecology of south-eastern Tasmanian phytal animal communities. I. Spatial organisation on a local scale. Journal of Experimental Marine Biology and Ecology 70: 129-157

Edgar, G.J. 1990. Population regulation, population dynamics and competition amongst mobile epifauna associated with seagrass. Journal of Experimental Marine Biology and Ecology 144: 205-234

Enequist, P. 1949. Studies on the soft-bottom amphipods of the Skagerak. Zoologiska Bidrag Från Uppsala 28: 297-492

Leach, W.E. 1814. Crustaceology. pp. 383-437 in Brewster, D. Sir (ed.). The Edinburgh Encyclopaedia. Edinburgh : John Murray Baldwin & Cradocle Vol. 7 (2).

Poore, A.G.B. 1994. Selective herbivory by amphipods inhabiting the brown alga Zonaria angustata. Marine Ecology Progress Series 107: 113-123

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