Identified pilidiophoran larvae

The larvae of the genus Hubrechtella (Palaeonemertea) are characterized by the pilidium auriculatum morphotype. We've identified the larva of H. juliae (left), which is the first record of a hubrechtid nemertean species in the NE Pacific.

The larva of Cerebratulus albifrons (above) have a large pyramid-shaped episphere, however they lack any larval pigment as is sen in other larvae of similar morphology (e.g. Cerebratulus californiensis)

The Cerebratulus californiensis species complex consists of three closely related species, all of which have larval pigment spots on their lobes and lappets. Shown at left, is the larva of Cerebratulus californiensis.

Cerebratulus cf. marginatus (below) and a closely related and undescribed species, Cerebratulus sp. "spade head" (larva shown above right) are characterized by large epispheres.

The larva of Lineus flavescens (left) was the first wild-caught larva we identified in this project. We now understand that this larval morphotype is seen in several other closely related (and currently undescribed lineid species).

The larva of the undescribed species Lineus sp. "crescent" (above right) are recognizable by their large episphere, that is almost as wide as it is tall, and floppy anterior and posterior lobes.

The larvae of Micrura wilsoni (above) have pigment spots on either side of their anterior lobe only. This is similar to the larvae of members of the Cerebratulus californiensis species complex, however, the latter larvae have spots on their lateral lappets, which has not been observed in the larvae of Micrura wilsoni.

Maculaura alaskensis (above) and Maculaura magna (right). — *Maculaura alaskensis* (above) and *Maculaura magna* (right).

Larvae that characterize the Maculaura genus are recognizable with polka dot pigment spots on the amnion inside which the juvenile nemertean develops (pilidium maculosum morphotype). Maculaura alaskensis and M. magna larva are shown (above) but variations of this larval form has been observed in four of the five species in this genus.

This larva (left) belongs to a currently unknown nemertean species, Heteronemertea gen. sp. 4. We call the larva pilidium robustum because of its strong episphere. The juvenile posterior also has conspicuous lipid granules.

The larvae of the genus Riserius exhibit the pilidium recurvatum morphotype, which resembles more a sock that the hat shape of the typical pilidium larva. We've observed this larva for two Riserius species, which we have yet to find as adults, but are likely mesopsammic species.

Some pilidiophoran species produce lecithotrophic larvae. While some lecithotrophic pilidiophoran larvae resemble palaeo- or hoplonemertean larvae (see modified pilidia below), the larvae of the pilidium nielseni morphotype superficially resemble trochophore larvae of annelids and mollsuks. They have two transverse ciliated bands, an apical tuft and a posterior cirrus. Currently, there are five pilidiophoran species known to produce larvae of this morphotype.

Another type of lecithotrophic development which has been observed for some pilidiophoran species are a sort of modified pilidia, where the juvenile develops inside the larval body, but the larval body superficially resembles the vermiform shape of palaeo- or hoplonemertean larvae. There are at least three local species which we have observed produce modified pilidia where the larva is uniformly ciliated, with apical tuft and the juvenile inside develops opposite of the larval axis.

Identified pilidiophoran larvae

Back to Hoplonemertea or Palaeonemertea