Desmopterus pacificus Essenberg, 1919
This is a completely shell-less pteropod, very small in size as the swimming disc diameter is only 0.5 cm. The wings are disc-shaped and transparent except for a few muscle fibres. The visceral mass forms an opaque appendix curved around the swimming disc. Besides the median lobe the disc has two short tentacles. There is no separate proboscis. It is an elegant swimmer and a mucus feeder feeding on microplankton. It lives in the E-Pacific Ocean (Desmopterus pacificus 1).
The general shape is identical to that of Desmopterus papilio although it is probably more rounded and smaller. The barrel-shaped body bends anterior ventrally, but not as distinctly as in the other species. The anterior margin of the swimming plate extends beyond the posterior extremity of the body. The posterior margin of the disc shows interruptions, which divides the disc into five lobes. The epipodial tentacles are short, only 12 times as long as wide, they are covered by cilia and supplied with a nerve (Desmopterus pacificus). The muscle system in the swimming disc closely resembles that of Desmopterus papilio.
The length of the body is 1.0 to 2.5 mm, the diameter of the swimming disc 4 to 5.5 mm.
A special description is not available.
This species is a protandric hermaphrodite.
This species is phytophagous and epipelagic.
Desmopterus pacificus is endemic to the E-Pacific and is probably a vicarious species of Desmopterus papilio which it replaces in the E-Pacific. This pattern is also found for Cavolinia tridentata forma occidentalis and for some other planktonic groups, see the Desmopterus pacificus map.
Desmopterus pacificus Essenberg, 1919: 86, fig. 2.
Syntypes: the two spec. are not preserved in USNM.
Type locality: 32°53'N 117°15'W. Col. U.S. BUR. FISH.