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Protodrilidae
Description
Protodrilids are slender and filiform, range from 2-15 mm in
length and have 21 to 77 segments. The
prostomium has two palps (previously referred to as
‘tentacles’) with internal canals which connect behind the
brain, two nuchal organs, so-called statocysts [actually
photoreceptors, and, in some
species, simple pigmented eyes. Protodrilus species have a
ventral pharynx with a tongue-like organ, whereas a digestive
system is completely lacking in Parenterodrilus. External
ciliation includes single and adjoined stiff sensory cilia, which
are arranged in various patterns. A continuous ventral band of
cilia is always present along the length of the body, and tufts
and rings of cilia may be present on the prostomium and
trunk. The trunk is segmented, but lacks parapodia and
chaetae; usually two pygidial adhesive lobes are present.
The above description is taken from Paxton (2000).
Identification tips
Recognising the family
Protodrilids are perhaps most like the Protodriloididae, but have a pair of flexible palps distinct from the prostomium (in
protodriloids the palps are extensions of the
prostomium).
Distinguishing species
Characters used to distinguish species include the number of segments, presence or absence of simple pigmented eye spots, distribution of cilia on the prostomium and trunk and the presence or absence of pygidial adhesive lobes.
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References |
Identification guide
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