One of the more abundant gelatinous animals in Monterey Bay is this pelagic snail.  The body is almost totally transparent, with the most obvious part of the body being the dark gut nucleus.  Corolla lacks an external shell -  an internal gelatinous pseudoconch provides skeletal support.   Occasionally the slipper-like pseudoconchs, which are covered with tubercles, are found washed up on beaches.  The large lateral oval wing-plates may have a span of up to 8 cm and flap to maintain position or move in the water column (hence the name "sea butterfly").   Each side possesses a row of 12 mucus glands.  Small planktonic particles are captured by a large, delicate mucous sheet (up to 2 meters diameter) that is formed by the proboscis.  When disturbed, Corolla swims away rapidly and usually sheds the mucous sheet.   Sea butterflies may form large surface aggregations in Monterey Bay and other temperate waters of the Pacific Ocean.  This species is the only Corolla found off the West Coast of North America.  

All photographs © David Wrobel and may not be used or copied without permission!