PRIAPULOIDEA

This article appears in Volume V22, Page 313 of the Encyclopedia Britannica.

Encyclopedia Britannica - Main :: PRE-PYR

PRIAPULOIDEA , a small group of vermiform marine creatures; they have been usually placed in the neighbourhood of the Gephyrea, but their position is uncertain and it is doubtful if they are to be regarded as coelomate animals. They are cylindrical worm-like animals, with a median anterior mouth quite devoid of any

armature

ARMATURE (from Lat. armatura, armour)

or tentacles. The

body

BODY

is ringed, and often has circles of spines, which are continued into the slightly protrusible pharynx. The alimentary canal is straight, the anus terminal, though in Priapulus one or two hollow ventral diverticula of the

body

BODY

wall

WALL (O. Eng. weal, weall, Mid. Eng. wal, wane, adapted from Lat. vallum, rampart; the
original
- ORIGINAL
O. Eng. word for a wall was wag or tenth)
WALL,
RICHARD
(1694-1778)

stretch out behind it. The

nervous

NERVOUS

system

SYSTEM

, composed of a ring and a ventral cord, retains its
Q primitive connexion with the ectoderm.
\ There are no specialized sense-organs or vascular or

respiratory

RESPIRATORY

systems. There is a wide body-cavity, but as this has no connexion with the renal or reproductive organs it cannot be regarded as a coelom, but probably is a blood-space or haemocoel.
The Priapuloidea are dioecious, and their 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 Platyhelminths, &c., and these probably

function

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. There are three genera: (i.) Priapulus, with the species P. caudatus, Lam., of the Arctic and Antarctic and neighbouring cold seas, and P. bicaudatus, Dan., of the north

Atlantic

ATLANTIC

and Arctic seas; (ii.) Priapuloides australis, de Guerne, of the southern circumpolar waters; and (iii.) Halicryptus, with the species H. spinulosus, v. Sieb., of northern seas. They live in the mud, which they eat, in comparatively shallow waters up to 50 fathoms.

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