The juvenile anatomy and post-hatching development of the marine leech Oceanobdella blennii (Knight-Jones, 1940)

Summary

The youngest post-hatching Oceanobdella blennii which are about 2·5 mm long and occur in the branchial chamber of the host fish, have more or less cylindrical bodies and comparatively large oral suckers. As the leeches enlarge and seek the adult location behind the pectoral fins, the abdomen becomes wider and flatter but the oral sucker stays small.

Maturation of ova and activity of the clitellar and preclitellar glands begin when the leeches are half grown (nearly 6 mm long). Spermatogenesis begins somewhat earlier, but the transverse segmental communications do not appear until considerably later (table 2). These join the dorsal and lateral lacunae in most segments of the testicular region and are characteristic of the genera Oceanobdella and Malmiana.

The original description of this species is thus extended to cover developmental and individual variation. The annulation is more distinct in juveniles than in adults. The post-caeca, though usually separate, are not invariably so. Although the number of separate ganglia is less than that typical of leeches, the reduction involves confluence rather than fusion.