|Desmopterus papilio Chun, 1889
Phylum Mollusca / Class Gastropoda / Subclass Opisthobranchia / Order Thecosomata / Family Desmopteridae
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.
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