Priapulus.—The body is continued into one or two caudal appendages, beset with hollow papillae; these are ventral to the anus. The introvert forms ¼ to ⅓ of the total body-length; it is covered with spines in conspicuous longitudinal rows, the rest of the body being ringed. The retractor muscles are numerous, and are attached to the body-wall, some anteriorly and some posteriorly.
The genus includes the following five species:—
P. caudatus Lam. (Fig. 218). Hab. Coasts of Greenland, Norway, Great Britain, the North Sea, and the Baltic.
P. bicaudatus Dan. Hab. North Sea and Arctic Ocean.
P. glandifer Ehlers. Hab. Coast of Greenland, North Sea.
P. brevicaudatus Ehlers. Hab. North Sea and Baltic, from ten fathoms.
P. tuberculato-spinosus Baird. Hab. Falkland Islands.
Halicryptus.—No caudal appendages. Introvert ⅒ to 1⁄12 of the total body length, with numerous spines arranged in close circles. Retractors numerous and all attached to the body-wall anteriorly.
H. spinulosus v. Sieb. (Fig. 219). Hab. North Sea, Arctic Ocean, and Baltic, in from two to fifty fathoms.
It will be noticed that with the exception of P. tuberculato-spinosus, described by Baird from a single specimen, the whole family is confined to northern seas.