Family LYSIANASSIDAE Dana, 1849

Parawaldeckia yamba

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Family LYSIANASSIDAE Dana, 1849

Introduction

The Lysianassidae are the largest amphipod family with 77 genera and nearly 500 species. The family is currently divided into two subfamilies, the Lysianassinae and the Tryphosinae. The lysianassines are epibenthic amphipods characterised by a simple first gnathopod, a reduced mandibular molar and usually with an entire telson. Not much is known about the life styles of lysianassines. The Tryphosinae are three times as speciose as the lysianassines. They are characterised by subchelate first gnathopods, a well-developed, triturating molar and, usually, a cleft telson. Many tryphosines are demersal scavengers feeding dead animals on the sea bottom.

In Australian waters there are 35 known lysianassid species, but the group is currently under study by Lowry & Stoddart and many new species are being described. The main scavengers are in the genus Tryphosella. Lysianassids are traditionally known as cold-water amphipods and they are diverse in the Australian Antarctic Territories, particularly the tryphosine scavengers in the genera Orchomenella and Tryphosella.

Diagnosis

Head exposed, concealed or partially concealed; as long as deep, longer than deep or deeper than long; anteroventral margin weakly recessed, moderately recessed, rounded or oblique and deeply, shallowly or not excavate; anteroventral corner rounded or subquadrate; rostrum short or absent; eyes well developed (round, ovoid, reniform, lageniform, long and narrow, subsigmoid or subrectangular), obsolescent or absent. Body laterally compressed; smooth or dorsally carinate; with sparse slender setae, densely covered in short setae or without setae. Antenna 1 shorter than or subequal to antenna 2; peduncular article 1 longer than article 2; article 2 subequal to, or longer than article 3; article 3 shorter than article 1; peduncular articles 1–2 geniculate or not; accessory flagellum present or absent; primary flagellum less than or more than 5-articulate; callynophore present or absent. Antenna 2 short, medium length, long or longer than body; flagellum shorter than, as long as or longer than peduncle; less than or more than 5-articulate; calceoli present or absent. Mouthparts well developed or reduced. Mandible incisor smooth; lacinia mobilis present on left side only or absent; molar medium, small, vestigial or absent; triturating, weakly triturating, setose with reduced triturating surface, fully setose or a smooth, nonsetose flap; palp present or absent. Maxilla 1 inner plate weakly setose apically or without setae; palp 1- or 2-articulate or absent. Maxilliped inner plates well developed; outer plates very large, large or small. Coxae 1–4 longer than broad or as long as broad, overlapping. Coxae 1–3 with none vestigial or reduced or with coxa 1 reduced, tapering or vestigial. Gnathopod 1 sexually dimorphic or not; smaller (or weaker) than, subequal to, or larger (or stouter) than gnathopod 2; simple, weakly subchelate, subchelate, parachelate or chelate; coxa vestigial, hidden or partially hidden by coxa 2, or smaller than, subequal to, or larger than coxa 2; carpus shorter than, subequal to, or longer than propodus; dactylus large, small or minute, strongly or weakly covered in setae. Gnathopod 2 sexually dimorphic or not; subchelate or chelate; coxa subequal to but not hidden by coxa 3; ischium long; carpus long, subequal to, or longer than propodus; dactylus minute or absent. Pereopod 3 coxa longer than broad; carpus shorter than, subequal to, or longer than propodus, not produced. Pereopod 4 coxa subequal to, or larger than coxa 3, with well developed posteroventral lobe; carpus shorter than, subequal to, or longer than propodus, not produced. Pereopods 5–7 with many marginal slender setae and few or no robust setae or with few setae. Pereopod 5 shorter than or subequal to pereopod 6; coxa smaller than, subequal to, or larger than coxa 4, with ventrally produced posterior lobe or without posterior lobe; basis expanded or slightly expanded, subrectangular, subquadrate or subovate, with or without posteroventral lobe; carpus linear. Pereopod 6 shorter than, subequal to, or longer than pereopod 7; basis expanded or slightly expanded. Pereopod 7 subequal to, or longer than pereopod 5; basis expanded or slightly expanded, with broad posteroventral lobe, subrectangular or subovate. Pleonites 1–3 with or without dorsal carina. Urosomites 1–3 free or 1 free, 2 and 3 coalesced; urosomite 1 longer or much longer than urosomite 2; urosomite 1 carinate, urosomite 3 carinate or urosomites not carinate. Uropods 1–2 apices of rami without robust setae. Uropod 1 peduncle with or without long plumose setae, without ventromedial spur. Uropod 3 biramous, uniramous or rami absent; peduncle short or long; rami lanceolate; outer ramus shorter than, subequal to, or longer than peduncle; inner ramus not apically setose. Telson laminar or hemiacetabulate; deeply, moderately or weakly cleft, notched, emarginate or entire; longer than broad, as long as broad or broader than long; dorsal and apical robust setae present or absent.