Bill Frank |
Helicodiscus parallelus (Say, 1817)
compound coil
Family
Helicodiscidae
Order Stylommatophora
The shell
of this small snail can be recognized in the field as a
little greenish tire. It is flattened and has spiral lirae
that look like tire treads at first glance, though upon
close inspection they are seen to be raised rather than
indented.
The compound
coil’s shell is approximately 3.5mm wide and 1.3mm
tall, and has a wide umbilicus (Pilsbry,
1948). The four whorls are tubular, expanding
slowly, the aperture is relatively small. Inside the final
whorl of the shell are two or three series of denticles
that may be seen from the outside as opaque spots. The
shell is often tinted green and not at all reflective,
possibly helping to camouflage this animal.
The
compound coil is sometimes not easily distinguished from
close relatives, as the diagnostic characters are relatively
subtle variations in shell shape, lirae and denticles.
In Pennsylvania, it can be separated from the temperate
coil (Helicodiscus shimeki) by its smaller,
steeper-sided umbilicus (Hubricht,
1962).
Like
many others of its family, the compound coil is similar
to cave dwelling animals, being blind and having a mostly
white body. It lives in damp leaf litter or decaying wood.
This coil is widespread in Pennsylvania and the Eastern
United States and Canada.
Ken Hotopp,
4/29/06
|
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