Fig. 79.—Mature female of Chaetosoma claparedii Metschni., × 57. (From Metschnikoff.) a, Oesophagus; b, intestine; c, anus; d, ovary; e, generative pore; f, ventral bristles.
The genus Tristicochaeta[[199]] differs from the foregoing in having three rows of locomotor projections instead of two.
Fig. 80.—Tristicochaeta inarimense Panceri, in one of its most usual positions, showing the triple row of ventral bristles, × 100. (From Panceri.)
Rhabdogaster has no head distinct from the body, though the anterior part of the body is swollen. A second swelling occurs, as is also the case with Chaetosoma, in the region of the opening of the genital ducts. The female in Rh. cygnoides attains a length of 0.36 mm. In this genus the hairs are confined to the dorsal middle line. The locomotor projections are hooked, and are much finer than those of Chaetosoma, and they are situated farther forward than in the last-named genus. Rhabdogaster occurs in the same surroundings as Chaetosoma. Ch. ophicephalum is recorded from the English Channel.
(ii.) Desmoscolecidae.—The members of this family are minute, and are characterised by the presence of well-marked ridges which surround the body and give it an appearance of segmentation. The head, which is somewhat swollen, bears four bristles, and single pairs are borne by a certain number of the ridges, some on the dorsal and some on the ventral surface. These hairs can be moved independently of one another. Two red eye-spots are described between the fourth and fifth rings. The sexes are distinct, and the internal organs generally have a marked resemblance to those of the true Nematoda. The Desmoscolecidae move by looping their bodies after the manner of the Geometrid caterpillars, as well as by creeping with their bristles. The genus contains numerous species[[200]]: D. minutus Clap. (English Channel), D. nematoides Greef, D. adelphus Greef, D. chaetogaster Greef, D. elongatus Panceri, and D. lanuginosa Panceri. They are exclusively marine.
Fig. 81.—Female Desmoscolex elongatus Panceri, ventral view, × 260. a, Ovary. (From Panceri.)
Trichoderma oxycaudatum Greef[[201]] is a minute animal, 0.3 mm. long, which has no head or ventral spines, but whose body is ringed and covered with long hair-like bristles. The male has two spicules, and the internal organisation recalls that of other Nematodes; still its ringed body has induced some authorities to place it near to Desmoscolex.
The Life-History of Nematodes.