Diversity of form and behaviour among nemertean pilidium larvae

A selection of pilidium larvae are described from plankton collected from Bamfield Inlet in British Columbia, Canada, the Florida Gulf Coast and the Great Barrier Reef of Australia. Among the Bamfield larvae are examples attributable to Cerebratulus and Lineus, the former being among the largest pilidia known, up to 1.45 mm in height, and two previously undescribed types. Pilidium brachiatum from Florida is re-described to highlight differences from Hubrechtella larvae, which are superficially similar, and an assortment of tropical forms is included to illustrate the predominance of the compressed gyrans-type larva in this location. Pilidium larvae have typically been categorized by their shape as seen in lateral view. This account emphasizes the importance of three-dimensional shape, pigmentation, overall architecture and behaviour in distinguishing between the larvae of different species.