Suborder VALVIFERA G.O. Sars, 1883

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Suborder VALVIFERA G.O. Sars, 1883

Compiler and date details

Gary C.B. Poore, Helen M. Lew Ton & Tania M. Bardsley

Valvifera Sars, G.O. 1883. Oversigt af Norges Crustaceer medforelobige bemaerkninger over de nye eller mindre bekjende Arter. 1. (Podophthalmata-Cumacea-Isopoda-Amphipoda). Bulletin of the Mauritius Institute 18: 1-124 [publication dated 1882] [33].

Introduction

Isopods of the suborder Valvifera are distinguished from all other suborders by the manner in which the uropods attach laterally on the pleotelson and are modified to form opercular plates covering the pleopods ventrally. With the exception of one species, all valviferans lack a mandibular palp. Valviferans range is size from a few millimetres long to some of the largest isopods known, Bathynomus excepted. In Antarctica Glyptonotus antarcticus Eights, 1852 grows up to 90 mm long.

Valviferans fall naturally into two groups, differentiated on the basis of general body shape, fusion of the head and pereonite 1, arrangement of pereopods, and sexual modification of the male pleopod 1. Although not previously formally recognised they are treated as superfamilies here, Arcturoidea and Idoteoidea.

Arcturoids generally have cylindrical bodies with fused head and pereonite 1 and long modified pleopods 1. Some arcturoids use their long setose pereopods 2–4 as filter-feeding baskets while others have these pereopods modified in other ways. Some arcturoids reach the deepest parts of the ocean. Idoteoids are usually flat with free heads and unmodified first pleopods. They include some of the few herbivorous isopods.

A comprehensive review of the systematics and phylogeny of the group (Brusca 1984) recognised six families but recent revisions suggest that 12 families exist (Poore 1985, 2001, 2015; Poore & Bardsley 1992). Not all are represented in Australian waters.

Diagnosis

Head-pereonite 1 free, or fused. Dorsal pereopodal coxal plates present (secondarily reduced in some species); coxal plate of pereopod 1 fused to tergite; coxal plate 7 present; ventral coxal plates 1–7 (medial extension of coxa replacing sternite) extending to midpoint (well defined and separated by suture). Pleonites 4–6 fused into pleotelson, pleonites 1–3 free or variously fused. Pleotelson underside vaulted, branchial chamber defined by ridges along mesial margin of lateral edge; ventrolateral margins of pleon and pleotelson narrow. Penial processes medial, on anterior margin or directly on pleonite 1. Mandibular lacinia mobilis present on both sides; molar usually a cylindrical process with triturative flat end; palp absent (present in Holognathus). Maxilla trilobed. Maxillipedal endite reaching at least distal margin of palp article 2, usually distally truncate and setose. Pereopods 1–3 more or less prehensile, directed anteriorly; pereopods 4–7 directed posteriorly. Pleopodal exopods uniarticulate. Pleopod 1 biramous. Pleopod 2 biramous. Pleopod 3 biramous; endopod roughly triangular (or at least with inner angle sharper than outer). Telsonic region of pleotelson elongate, anus situated anteriorly on pleotelson. Uropod situated anterolaterally on pleotelson; peduncle and short rami enclosing pleopods in branchial chamber; rami lateral to margin of pleotelson, articulating in longitudinal axis and folding down alongside branchial chamber.