Monterey Bay Aquarium 3, Monterey County, California, USA. 1996. Photos: Daniel Geiger. (left photo of preserved specimen labelled by Bill Rudman). Shell length approx 7mm.
Thecosome pteropods such as Creseis acicula are a group of planktonic sea slugs with either an external lightly calcified shell or a leathery pseudoconch. They are plankton feeders, catching their prey by producing mucous speherical webs or flattened nets, some of which can be up to 2 meters in diameter.
Creseis has a needle-shaped, lightly calcified external shell, and a pair of wing-like flaps which are used in swimming. It feeds by trapping other plankton in a transparent muccous wen which it suspends above it in the water. The web is drawn into the mouth at intervals and food particles, including both plant and animal plankton, ingested.
• Lalli, C.M. & Gilmer, R.W. (1989) Pelagic Snails. The biology of holoplanktonic gastropod molluscs. Stanford University Press: Stanford, California.
Rudman, W.B., 2000 (July 4) Creseis acicula (Rang, 1828). [In] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/factsheet/cresacic