Abstract
Ilyphagus Chamberlin, 1919 includes abyssal, fragile benthic species. Most species have large cephalic cages but chaetae are brittle and easily lost which may explain why the original definition included species with a cephalic cage or without it. The type species, Ilyphagus bythincola Chamberlin, 1919, together with another species (Ilyphagus pluto Chamberlin, 1919) were described as lacking a cephalic cage whereas a third species (Ilyphagus ascendens Chamberlin, 1919) was described with one. To clarify this situation, all available type and non-type materials were studied. Ilyphagus is redefined to include species with digitiform bodies, abundant filiform papillae and a thin body wall; their neurochaetae are thick, anchylosed aristate spines, and all species have a cephalic cage (in the type species the presence of a cage is inferred from the remaining chaetal scars). Ilyphagus pluto, which also lacks a a cephalic cage is determined here to be a holothurian. The redefined genus contains Ilyphagus bythincola (incl. Ilyphagus ascendens), Ilyphagus coronatus Monro, 1939, Ilyphagus hirsutus Monro, 1937, and Ilyphagus wyvillei (McIntosh, 1885).
Highlights
Juveniles have thinner bodies and may be confused with some species of Bradabyssa Hartman, 1967; in Ilyphagus, the body wall is thin and covered by delicate, long papillae, which are not embedded by the tunic, resulting in a pilose surface
All cephalic cage chaetae can be broken off, but their presence can be determined by chaetal scars or holes through the body wall, or by making a longitudinal dissection along the anterior end, if there are several specimens available and papillae cover chaetal scars
Holotype of I. bythincola (USNM-19748) damaged, ovoid, body wall broken by compression, depressed (Fig. 1A); 48 mm long, 26 mm wide, cephalic cage chaetae broken, 21 chaetigers
Summary
All cephalic cage chaetae can be broken off, but their presence can be determined by chaetal scars or holes through the body wall, or by making a longitudinal dissection along the anterior end, if there are several specimens available and papillae cover chaetal scars. The type species, I. bythincola Chamberlin, 1919, originally described as lacking cephalic cage, in reality has one but the chaetae are broken and only their embedded bases or some chaetal scars are left. Holotype of I. bythincola (USNM-19748) damaged, ovoid, body wall broken by compression, depressed (Fig. 1A); 48 mm long, 26 mm wide, cephalic cage chaetae broken, 21 chaetigers.
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