Gastropteron pacificum Bergh, 1894 Common name(s): Pacific batwing slug, Pacific wingfoot snail, winged bubble shell, sea devil, sea butterfly
Synonyms: Gastropteron cinereum
Phylum Mollusca Class Gastropoda  Subclass Opisthobranchia Order Cephalaspidea Family Gastropteridae
	Gastropteron pacificum, 4-5 mm long, found and captured from Sharpe Cove dock at night by Jamie Anderson Fields. This is presumably a ventral view with the 'wings' (parapodia) temporarily folded around its body and its head to the bottom right, making it appear similar to an ostracod (to which it is not related). The wings attach ventrally and their free margin wraps around to the dorsal side.
	(Photo by: Dave Cowles, August 2025 )

Description:  Starting in Order Cephalaspidea, this small animal has no externally visible shell. Its body is pale yellow with small red dots. The rear margin of its foot is rounded, without prominent projections. This individual, likely not fully grown, has a full length of  4-5 mm. Its foot is formed like two large "wings" (called parapodia) and it flaps them to fly or glide through the water, with a flight pattern reminiscent of a bat (movie). This species has a single pinnate gill on its right side (hidden under the right parapodium) and a nearly transparent, smooth coiled internal shell. It has no rhinophores. The anus is also on the right side, behind the gill, and the reproductive duct opens on the right side behind the head. A cephalic shield, often rolled into a tube, projects over the head and can occasionally be seen in this movie. The dorsal surface has no projections, although the parapodia fold toward the dorsal side so their margins are dorsal. Total length to about 40 mm. 

How to Distinguish from Similar Species:  Several species which key out similarly have yellow spots, or yellow lines on the cephalic shield, foot, and mantle flaps.

Geographical Range:  Aleutian Islands to the Galapagos Islands.

Depth Range:  Intertidal (not commonly, mainly on mud flats) to 425 m.

Habitat: Benthic on rocks and soft bottoms, but can temporarily become pelagic. An active shape-shifter and swimmer (movie), but still small enough to be planktonic while swimming.

Biology/Natural History:  This species has a single gill on its right side. As with most Opisthobranchs, is a hermaphrodite. The round, pink eggs are laid in a clear, gelatinous mass.

References:

General References:
  Morris et al., 1980
  Lamb and Hanby, 2005

Scientific Articles:
MacFarland, F. M., 1966. Studies of Opisthobranchiate mollusks of the Pacific coast of North America. Memoirs of the California Academy of Sciences 6: pp.1-546

Web sites:

General Notes and Observations: Locations, abundances, unusual behaviors:

In this photo the rolled cephalic shield can clearly be seen to the right, while the wing-like parapodia are wrapped unevenly around its body with their margins aligned along the animal's dorsal side at the top of the photo. The gonoduct, single gill, and anus are all hidden under the right parapodium. The two short projections near the top left of the photo are near the back of the animal. Photo by Dave Cowles, August 2025

In this view under normal daylight, the extended wings can be seen from the reflection from the bottom of the chamber below the animal plus the shadows cast upon the chamber floor. Photo by Dave Cowles, August 2025

Authors and Editors of Page:
Dave Cowles (2025):  Created original page
CSS coding for page developed by Jonathan Cowles

Salish Sea Invertebrates web site provided courtesy of Walla Walla University