OXYCEPHALIDAE Bate, 1862

Zeidler, Wolfgang, 2016, A review of the families and genera of the superfamily PLATYSCELOIDEA Bowman & Gruner, 1973 (Crustacea: Amphipoda: Hyperiidea), together with keys to the families, genera and species, Zootaxa 4192 (1), pp. 1-136 : 69

Family OXYCEPHALIDAE Bate, 1862

Diagnosis. Body length up to 150 mm (mostly rostrum and telson in Rhabdosoma ) but usually only 10–30 mm; body form variable, ranging from extremely elongate to relatively compact. Head usually produced into long rostrum, with distinct neck, sometimes globular, with relatively short rostrum. Eyes large, occupying most of head surface, except rostrum and neck. Coxae totally fused, partly fused or not fused, with pereonites. Antennae 1 of females with 0–3 articulate peduncle, and enlarged first flagellar article (callynophore), followed by 0–2 smaller terminal articles. Antennae 1 of males with 1–2 articulate peduncle, and enlarged, curved first flagellar article (callynophore), often with antero-distal corner transformed into distinct “horn”, with 1–2 field brush of aesthetascs medially, and 1–3 smaller, slender articles inserted just below antero-distal corner of callynophore. Antennae 2 absent in females. Antennae 2 of males with four slender articles, usually of similar length, folded back on one another, plus one tiny terminal article, all held underneath head and anterior part of pereon. Mandibles without palp in females; with palp in males, ranging from very elongate in species with long rostrum to one article in Glossocephalus . Maxillae 1 very reduced in size consisting of tiny rounded lobes, sometimes not discernible, or absent. Maxillae 2 absent. Gnathopoda chelate or sub-chelate. Pereopod 5 usually the longest. Pereopods 5 & 6 usually with moderately enlarged basis, often shorter than remaining articles combined, which are inserted terminally. Pereopod 7 reduced in size, with full complement of articles, or distal articles sometimes reduced in number ( Tullbergella ), or absent ( Rhabdosoma ), with enlarged basis which is longer than remaining articles combined. Uropod 1 with articulated endopoda and exopoda. Uropods 2 & 3; endopoda sometimes fused with peduncle. Telson triangular and pointed, sometimes rounded, usually extending beyond limit of U3, usually fused with double urosomite. Gills with or without folds, usually on pereonites 2–6, sometimes rudimentary or absent on one or more of pereonites 2–4. Oostegites usually on pereonites 2–5, sometimes only on pereonites 3–5, sometimes reduced in size.

Genera. Oxycephalus Milne-Edwards, 1830 ; Rhabdosoma White, 1847 ; Leptocotis Streets 1877 ; Calamorhynchus Streets, 1878 ; Glossocephalus Bovallius, 1887 ; Tullbergella Bovallius, 1887 ; Streetsia Stebbing, 1888 and Cranocephalus Bovallius, 1890 .

Remarks. This family appears to be polyphyletic, based on initial morphological analysis (note variability of characters in diagnosis), but a great deal more detailed taxonomic work is required to resolve the systematic status of the eight genera currently recognised. These genera are grouped together in the family Oxycephalidae mainly on the basis of having a well-developed rostrum, which may vary considerably in length and general morphology, but is generally much longer than found in any other family of Hyperiidea.

The family Oxycephalidae was reviewed by Bovallius (1890) and Nair (1995), and to some extent by Fage (1960). However, Fage was only concerned with material from the Dana expeditions (1928-1930) and his taxonomic treatment of the family is limited. Therefore, except for Nair (1995), no thorough taxonomic revision of the family has appeared this century. Since the review of Fage (1960), the systematics of the family has changed little except for the exclusion of Simorhynchotus , which has been transferred to the family Lycaeidae , and Metalycaea , which Nair (1993) argued should be recognised as a valid genus of Oxycephalidae , but which is now regarded a synonym of Lycaea .

The phylogenetic analysis ( Figs 1 –2) supports the view that Rhabdosoma , Glossocephalus , and Tullbergella vary somewhat from other genera of Oxycephalidae (and each other) and may warrant removal from this family. However, Hurt et al. (2013), using more reliable molecular techniques, found “high support for the monophyly of Oxycephalidae ”.

Most genera, for which data are available, are preferentially associated with ctenophores.

Figures

FIGURE 1. Phylogenetic analysis of the genera of the superfamily Platysceloidea. One of three equally most parsimonious trees derived from a PAUP 4.0 analysis of the DELTA data base; length 275 steps, consistency index = 0.5164, rescaled consistency index = 0.3476. Branches are marked with the number of character changes. Vibilia is used as the out-group.