Priapulid, from Kingsley, 1884.
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Phylum Priapulida Priapulid, from Kingsley, 1884. |
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The phylum Priapulida
includes only about 15 living species of wormlike organisms which range
from very small meiofaunal
species (about 0.55 mm long) to rather large species (about 20 cm.
long). The larger forms typically burrow in fine sediments, mostly in colder waters.
Their body has a trunk, a collar
,
a caudal
appendage, and an eversible proboscis
called an "introvert
". The larger species evert
their toothed pharynx
through the introvert
, which they then use to grasp prey (such as
annelids
and other infaunal
organisms).
When the introvert
retracts, the prey is drawn back into the gut. At least one species feeds on organic detritus
(a deposit feeder), and another lives in a tube and captures prey in a trap made up of
specialized spines.
The relationships between Priapulids and the other phyla are unknown. They have a complete gut (mouth and anus ), and are triploblastic . Whether the body cavity is a true coelom or a pseudocoelom is still being debated. They have no special circulatory system, and have a protonephridial excretory system. Priapulids are dioecious (or gonochoristic , - having separate sexes). References: Barnes, 1980 Barnes, Calow, and Olive, 1993 Brusca & Brusca, 1990 Halstead, 1965 Meglitsch & Schram, 1991 |
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