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Opheliidae
Description
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The head is compact and lacks appendages. Some species are iridescent.
They burrow head downwards in sand or mud. The prostomium is usually conical,
and a distal palpode is present in some taxa. The peristomium is reduced
and fused with the prostomium or forms a distinct ring. Antennae and palps
are absent. The nuchal organs are paired and eversible. The longitudinal
muscles are grouped in bundles, and segmentation is usually not distinct.
The first segment is similar to subsequent segments, and all parapodia are
similar. Both parapodial rami are small, and in most taxa the notopodium
is slightly smaller than the neuropodium, but in Travisia, both rami
are well developed and large. The branchiae are single filaments closely
associated with the notopodium. Dorsal and ventral cirri and epidermal papillae
are lacking. The pygidium is either hoodshaped without internal and marginal
cirri or hoodless with multiple cirri. Lateral organs are present, but dorsal
cirrus organs have not been observed. The buccal organ is axial and simple,
and has a sac-like eversible proboscis.
The above description is based on Hutchings (2000), which in turn is based on Fauchald & Rouse (1997).
Identification tips
Recognising the family
Opheliids have a distinctive fusiform-shaped body with relatively few,
indistinct segments and poorly developed parapodia. The head is compact
and lacks appendages. Live specimens of opheliids often exhibit a characteristic whip-like motion, and may be bright red in colour (the haemoglobin is visible through the thin body wall).
Distinguishing species
The general appearance of the body enables quick recognition of some taxa. For example, members of the genus Armandia have smooth
tapered bodies that may be iridescent (superficially like a very large
nematode, but with segments), while species of Travisia have
wrinkled bodies, although still tapered and with a limited number of segments. Other characters include the number of segments, the presence of lateral eye-spots and the number of segments with branchiae. Several species have been reported to have a wide geographical range, however this seems unlikely and it is suggested that they will eventually be found to represent a suite of species. One such example is Polyophthalmus pictus.
Description | Identification
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