1911 Encyclopædia Britannica/Priapuloidea
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 or tentacles. The 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-wall stretch out behind it. The nervous
system, composed of a ring and a ventral cord, retains its
Priapulus caudatus
Lam. (Nat. size.) a,
Mouth, surrounded by
spines.
primitive connexion with the ectoderm.
There are no specialized sense-organs or
vascular or 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 flamecell similar to those found in Platyhelminths, &c., 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. There are three genera: (i.) Priapulus, with the species P. caudatus, Lam., of the Arctic and Antarctic and neighbouring cold seas, and P. bicaudalus, Dan., of the north 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.
Authorities.—Apel, Zeitschr. wiss. Zool. (1885), vol xlii.; Scharff, Quart. Journ. Mic. Sci. (1885), vol. xxv.; Ehlers, Zeitschr. wiss. Zool. (1861), vol. xi.; Schauinsland, Zool. Anz. (1886), vol. ix.; De Guerne, Mission scientifique du Cap Horn (1891), vol vi.; Michaelsen, Jahrb. Hamburg-Aust. (1888), vol. vi. (A. E. S.)
