English: Priapulid worms; Penis worms; from the Greek Priapus, god of fertility.
Genera: 16 species.
Habitat: marine; shallow waters up to 90 metres; tolerant of hydrogen sulfide and anoxia.
ZoologyPriapulida are marine worms; they live in and eat the mud; they have an extensible spiny proboscis. They are relatively large in size. They were likely major predators of the Cambrian period. There are 16 known species of Priapulid worms.
They are cylindrical worm-like animals, with a median anterior mouth quite devoid of any armature or tentacles. The body is ringed, has circles of spines, which are continued into the slightly protrusible pharynx. The alimentary canal is straight, the anus terminal. The nervous system, composed of a ring and a ventral cord, retains its primitive connection with the ectoderm.
There are no specialized sense organs or vascular or respiratory systems. Hemerythrin is the protein responsible for oxygen transportation. There is a wide body-cavity, which has no connection with the renal or reproductive organs. It cannot be regarded as a coelom, but probably is a blood-space or hemocoel.
Priapuloidea are hermaphroditic. Male and female organs, which are one with the excretory organs, consist of a pair of branching tufts, each of which opens to the exterior on one side of the anus.
The tips of these tufts enclose a flame-cell similar to those found in flatworms and other animals, and these probably function as excretory organs. As the animals become adult, diverticula arise on the tubes of these organs, which develop either spermatozoa or ova. These pass out through the ducts. Nothing is known of the development.
TaxonomyTheir nearest relatives are probably
Kinorhyncha and
Loricifera with which they constitute the taxon
Scalidophora.
GeneraClass Priapulimorpha
Order Priapulimorphida
Family Priapulidae: Acanthopriapulus, Priapulopsis, Priapulus
Family Tubiluchidae: Meiopriapulus, Tubiluchus
Class Halicryptomorpha
Order Halicryptomorphida
Family Halicryptidae: Halicryptus
Class Seticoronaria
Order Seticoronarida
Family Maccabeidae: Maccabeus