Suborder SPHAEROMATIDEA Wägele, 1989

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Regional Maps

• Sphaeromatidea Wägele, J.W. 1989. Evolution und phylogenetisches System der Isopoda. Stand der Forschung und neue Erkenntnisse. Zoologica (Stuttgart) 140: 1-262 [163].

Introduction

Wägele's (1989) concept of the Sphaeromatidea included Limnoriidae, Hadromastacidae and Keuphyliidae, families treated here in their own suborder. The remaining families, once members of the Flabellifera, are all those not included in the scavenging, parasitic and predatory cymothoidan group. Many species are herbivores or detritivores without specialised mouthparts.

Sphaeromatidea have the pleonites fused to some degree and differ from the other large group of the former ‘Flabellifera’ in having the uropodal rami lateral to the margin of the pleotelson and folding down alongside the branchial space, whereas in Cymothoidea the uropodal rami are ventral to the pleotelson and articulating from side to side along a vertical axis inside the branchial space.

Brandt & Poore (2003) separated superfamily Seroloidea (four families) from Sphaeromatoidea (three families) but the morphological criteria on which this was done were weak. The small families Bathynataliidae and Basserolidae are similar to the larger Serolidae. The small families Ancinidae and Tecticipitidae are similar to the much larger Sphaeromatidae. But the relationships of Plakarthriidae and the enigmatic Paravireia are problematic. The superfamilies are not recognised here. The smaller families have diagnostic maxillula and maxilla being somewhat more reduced than in the Sphaeromatidae.

Wetzer et al. (2013) provisionally found using molecular data (16S, 18S genes) that Sphaeromatidea was not monophyletic but was part of a larger clade including Serolidae and Valvifera. Later, Wetzer et al. (2018) concluded that Sphaeromatidea (represented by Serolidae, Ancinidae, Plakarthriidae and many genera of Sphaeromatidae) was monophyletic. The largest family Sphaeromatidae is highly diverse, and the Plakarthriidae was doubtfully embedded within it.

Diagnosis

Head free from, or fused to pereonite 1. Pereopodal coxal dorsal plates present (secondarily reduced in some species); coxal dorsal plate of pereopod 1 fused to tergite, or free from tergite (Plakarthrium); coxal plate 7 present, or absent (coxal dorsal plate 6 and pleonal epimera 1 or 2 in contact); coxal ventral plates 1–7 (medial extension of coxa replacing sternite) obsolete (not distinguished from sternite), or extending to midpoint (well defined and separated by suture). Pleonites 1–5 variously fused, occasionally fused to pleotelson , pleonites 1–3 sometimes indicated by lateral sutures . Pleotelson underside vaulted, branchial chamber defined by ridges along mesial margin of lateral edge (except in Sphaeromatidae ‘Cassidiniinae’; ventrolateral margins of pleon and pleotelson narrow, or broad and flattened. Telsonic region of pleotelson elongate, anus situated anteriorly on pleotelson. Penial processes mesial, closer to midpoint than to pereopods. Mandibular lacinia mobilis present on both sides, or present on left side, reduced and fused with spine row on right, or absent; molar usually a cylindrical process with triturative flat end, or absent; palp present, or absent (-Plakarthrium). Maxilla trilobed. Maxillipedal endite reaching at least distal margin of palp article 2, usually distally truncate and setose. Pereopods 1–3 usually ambulatory (pereopod 1 sometimes subchelate or subprehensible), directed anteriorly; pereopods 4–7 directed posteriorly. Pleopods 1 and 2 biramous. Uropod attached anterolaterally on pleotelson or on posterior margin of pleotelson; peduncle not operculate; rami lateral to margin of pleotelson, articulating in longitudinal axis and folding alongside branchial space .

General References

Brandt, A. & Poore, G.C.B. 2003. Higher classification of the flabelliferan and related Isopoda based on a reappraisal of relationships. Invertebrate Systematics 17: 893-923

Wägele, J.W. 1989. Evolution und phylogenetisches System der Isopoda. Stand der Forschung und neue Erkenntnisse. Zoologica (Stuttgart) 140: 1-262

Wetzer, R., Bruce, N.L. & Pèrez-Losada, M. 2018. Relationships of the Sphaeromatidae genera (Peracarida: Isopoda) inferred from 18S rDNA and 16S rDNA genes. Arthropod Systematics & Phylogeny 76: 1-30

Wetzer, R., Pérez Losada, M. & Bruce, N.L. 2013. Phylogenetic relationships of the family Sphaeromatidae Latreille, 1825 (Crustacea: Peracarida: Isopoda) within Sphaeromatidea based on 18S-rDNA molecular data. Zootaxa 3599: 161-177

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