Leptosomatum bacillatum

In 1863, Eberth described a 6 mm long nematode from the harbor of Nice as Phanoglene bacillatum. In 1865 Bastian described a closely related species from the UK which he, because of its 12 mm long body, named Leptosomatum elongatum. De Man collected new material from the same locality as Bastian and redescribed and figured L. elongatum in 1893 (article: Cinquième note). De Man’s material is still present, it is deposited in the Zoological Museum in Amsterdam.

Leptosomatum lives in sponges, also in sponges along the Dutch coast. It is remarkable that the two species, differing in length, live in the same sponge. Are it two different species or is it one species which is variable en length? To get more insight, we sampled sponges monthly along the Dutch island Texel and measured the length of every individual. It appeared that the eggs are deposited in autumn. In spring the first small adults are found. They continue growing till they reach a length of 12 mm. In late summer, the first eggs are formed. We concluded that the small and larger Leptosomatum belong to one and the same species: Leptosomatum bacillatum. It is remarkable that males are very common along the Dutch coast but that females are not fertilized. The males don’t feed, they become inactive and their pharynx and intestine atrophies. Along the island of Curacao, we found many females, all fertilized, but no males: do males immediately die after copulation?

(click on the pictures for an enlargement, © Laboratory of Nematology)