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Parergodrilidae
Description
Parergodrilids have a rounded prostomium and the
peristomium is a complete annulus. Antennae and palps are
absent. A pair of retractable nuchal organs are present on the
prostomium in Stygocapitella, but absent in
Parergodrilus. Numerous sensory papillae
cover the body surface. A muscular gular membrane is absent,
but the septum behind the head is better developed than
subsequent ones, which are almost lacking. Segments are few (8 to 13), all similar and
lack parapodia. Aciculae are absent, but simple chaetae are
present in paired ventro-lateral bundles; capillaries and
furcate types in Stygocapitella and spines in
Parergodrilus. The pygidium lacks anal cirri. The eversible
ventral buccal organ leads to an oesophagus, stomach,
intestine and hind gut; the intestine is coiled in Stygocapitella.
Nephridia, as metanephridia, are present along the body
(Stygocapitella) or restricted in distribution (Parergodrilus).
The circulatory system of Parergodrilus is closed and a heart
body is absent; it is presumably present in Stygocapitella and
lies at the level of the oesophagus.
The purported autapomorphy of the group is the unique
arrangement of muscle and glandular cells of the ventral
pharynx (Rouse & Fauchald 1997); however, the pharynx of
the two genera differs slightly in the form of the tongue like organs
and the muscle bulb, present in Stygocapitella, is
lacking in Parergodrilus.
The description above is taken from Glasby (2000).
Identification tips
Recognising the family
Parergodrilids are very small grub-shaped worms that lack a head, pygidial appendages and parapodial lobes. Some species occur interstitially in intertidal sediments and some have been found in decomposing terrestrial plant debris.
Distinguishing species
Characters used to distinguish species include the types of chaetae present; these include furcate chaetae and spines. The distribution of metanephridia along the body is another useful specific character. Species tend to be habitat specific.
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Identification tips |
Natural History |
Diversity |
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References |
Identification guide
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