Here's one you don't see everyday - in fact you'll need to look pretty hard to find this pteropod since it's elongate body is only 2 to 3 mm long.  The pair of wings unite to form a plate with a span up to 6 mm.  The rear of the plate has 5 lobes, and each side possesses a distinctive ciliated tentacle.  Flapping of the wing plate is used for swimming, typically in a loop pattern when disturbed.  Most of the time Desmopterus hangs motionless.  The head hangs ventrally, and has a terminal mouth with small jaws and a radula.  Reddish-brown spots may be scattered throughout the body, particularly at the margins of the wings.  This species lacks a shell, pseudoconch, mantle cavity and mucus producing glands.  It ranges throughout tropical and subtropical oceanic waters and may rarely be found as far north as central California.  With its diminutive stature, only a careful search of the contents of a plankton tow will reveal its presence.  A closely related species, Desmopterus pacificus, is a more common visitor to California waters and more likely to be encountered.  Its main distinguishing characteristic is the shorter wing plate tentacles compared to those in D. papilio.  

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