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PRIAPULOIDEA
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PRIAPULOIDEA , a small See also:group of vermiform marine creatures; they have been usually placed in the neighbourhood of the See also:Gephyrea, but their position is uncertain and it is doubtful if they are to be regarded as coelomate animals. They are cylindrical See also:worm-like animals, with a median anterior mouth quite devoid of any See also:armature or tentacles. The See also:body is ringed, and often has circles of spines, which are continued into the slightly protrusible pharynx. The alimentary See also:canal is straight, the anus terminal, though in Priapulus one or two hollow ventral diverticula of the body-See also:wall stretch out behind it. The See also:nervous See also:system, composed of a See also:ring and a ventral See also:cord, retains its Q See also:primitive connexion with the ectoderm. \ There are no specialized sense-See also:organs or vascular or See also: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 See also:blood-space or haemocoel. The Priapuloidea are dioecious, and their male and See also: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 See also:side of the anus. The tips of these tufts enclose a See also:flame-See also:cell similar to those found in Platyhelminths, &c., and these probably See also: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 See also:species P. caudatus, Lam., of the See also:Arctic and See also:Antarctic and neighbouring See also:cold seas, and P. bicaudatus, See also:Dan., of the See also:north See also:Atlantic and Arctic seas; (ii.) Priapuloides australis, de Guerne, of the See also:southern circumpolar See also:waters; and (iii.) Halicryptus, with the species H. spinulosus, v. Sieb., of See also:northern seas. They live in the mud, which they eat, in comparatively shallow waters up to 50 fathoms. Additional information and CommentsThere are no comments yet for this article.
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