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Onuphidae
Description
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The rounded
prostomium bears a pair of small dorsal frontal lips (rarely
absent), three antennae and two palps. Each
the antennae and palps comprises a basal ringed ceratophore
and a distal smooth style. Ventrally, a pair of large bulbous
upper lips is present. Eyes may be present or absent. The
peristomium is a single apodous ring, with or without a pair
dorsal peristomial cirri.
The first two to eight pairs of parapodia are modified. They are often longer, have different
parapodial lobes and chaetae than those following, and thus
are specialised for digging, locomotion or tube building. The
modified parapodia have digitiform ventral cirri, the remaining unmodified ones have
glandular pads. Dorsal cirri are present
throughout or are reduced to absent on posterior chaetigers.
Filaments of the branchiae, when present, are simple,
pectinately or dichotomously branched, or spirally arranged. Parapodia are sub-biramous; the notopodium
represented only by a dorsal cirrus with or without embedded
aciculae. Modified parapodia have simple or pseudocompound
hooks; pectinate and/or limbate
chaetae are present or absent. Chaetae of unmodified
parapodia are pectinate, simple limbate
and subacicular hooks; compound
limbate chaetae (spinigers) are sometimes present and
falcigers are rare. Pygidial cirri number two or four.
The jaws consist of ventral, unfused mandibles, and dorsal
maxillae of the labidognath type. The
maxillae are mineralised with aragonite, and comprise a pair
of short carriers and 3-5 toothed plates on the right and 4-toothed plates on the left. The maxillary plates are asymmetrical with the right maxilla III missing and the right maxilla IV being larger than the corresponding left one.
The above description is based on Paxton (2000), which in turn is based on Fauchald & Rouse (1997).
Identification tips
Complete mature individuals are needed for species determination, as many characters are not evident in juveniles. Onuphid tubes are regularly collected, although anterior tube fragments are typically empty, the animal having withdrawn further back down into the tube. Some tubes are characteristic consisting of shell fragments and gravel cemented together with a chitinous lining and may protrude several mm above the surface and forming dense colonies. In such situations worms can be enticed a few centimetres from the tube in pursuit of a fragment of algal or animal food. However, capturing these worms is another matter.
Recognising the family
Onuphids are readily distinguished from all other
eunicidans by having five prostomial sensory appendages
with ringed ceratophores.
Distinguishing species
Characters used to distinguish species include the arrangement of branchial filaments, the dental formulae of the jaws, and the structure and distribution of the chaetal types.
Description | Identification
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