Fig. 223.—Echiurus pallasii Guér. × ½. a, Mouth at the end of the grooved proboscis; b, ventral hooks; c, anus.
Nothing is known of the development of Hamingia or of Saccosoma.
Species of Echiuroidea.—Echiurus. Proboscis not bifurcated at the end. Two ventral hooks and a single or double peri-anal ring of bristles. The body is to a varying extent marked by rings bearing spines. Two or three (E. chilensis) pairs of nephridia, their external orifice often lengthened and spirally coiled. Both sexes alike.
Greef[[487]] mentions six species of Echiurus, viz. E. pallasii, E. forcipatus, E. sitchaensis, E. chilensis, E. carabaicus, and E. chrysacanthophorus; to these must be added E. unicinctus. It seems probable that E. forcipatus of Reinhardt is identical with E. pallasii, although bigger, whilst E. sitchaensis, E. carabaicus, and E. chrysacanthophorus are inadequately described. The distribution of the remaining three species is as follows:—
E. pallasii Guérin (Fig. 223). North Sea, Atlantic, English Channel.
E. unicinctus Drasche. Japan.
E. chilensis Max Müller. Chili.
Thalassema.—Proboscis rather pointed at the end, not bifurcated. No peri-anal bristles, but two ventral hook-like bristles placed anteriorly. One to three or four pairs of nephridia. The sexes resemble each other.
Greef mentions eight species of Thalassema and Rietsch thirteen; three of these, however, Th. grohmanni, Th. lessonii, and Th. pelzelnii, were not seen by either author, and their description is taken from Diesing. There is some reason for thinking that the two first-named species are identical with Th. neptuni. Conn has established a new species for the specimens whose embryology he worked out at Beaufort, Virginia, and Selenka described a new species from the Challenger material.