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Sternaspidae
Description
The prostomium is distinct and truncate anteriorly, and the
peristomium is reduced to lips around the mouth. Antennae
and palps are absent; nuchal organs are also lacking. Longitudinal muscles are grouped in many
bands, and segmentation is distinct. The first segment is
similar to those behind, and bears similar chaetae. The whole
of the anterior part of the body is retractable. Several
segments of the posterior venter are covered by a sclerotinised
shield. The parapodia are biramous except at the posterior
end. Only notopodia are present in the posterior region
covered by the shield, and consist of very short, truncate
cylinders. Rami are short, barely raised
papillae. Dorsal and ventral cirri are absent. The simple
branchiae are situated posteriorly and dorsally. Epidermal
papillae similar to flabelligerid papillae are present. Pygidial
cirri are absent. There is an eversible axial sac-like pharynx
and the gut is folded. A gular membrane is lacking. The
segmental organs are mixonephridia, of which the
anteriormost pair is excretory, and the posterior pair are
gonoducts. The circulatory system is closed,
and a heart body is lacking. Aciculae are
absent. Chaetae consist of capillaries and heavy spines.
The above description is taken from Hutchings (2000), which in turn is based upon that of Fauchald & Rouse (1997).
Identification tips
Recognising the family
Sternaspids should be readily recognised by their short inflated
bodies and the ventral sclerotinised plate which is reddish and surrounded by chaetae.
Distinguishing species
Characters used to separate species of Sternaspis include the amount of sculpture and colour of the ventral shield as well as its shape, the total number of segments and the number of segments which contribute to the shield. It appears that only one or two species occur in any one region.
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Identification guide
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