Gastropteron pacificum Bergh, 1894

Description

A small gastropterid up to about 12 mm wide (with the parapodia spread). According to Dall's field note the living animal is yellowish with red spotting. In Bergh's alcohol-preserved type material the cephalic shield and the foot with its parapodia were light yellowish with numerous, more or less grouped, closely set red points, denser on the underside and at the free tip of the cephalic shield; the rear body was grey, sometimes with scattered red points anteriorly, and the gill was whitish. Bergh's 13 type specimens were 7.5 mm long along the parapodia, 12 mm wide with the parapodial wings spread, and 5.5 mm high — distinctly smaller than the type species Gastropteron meckelii. The foot is clearly demarcated from the parapodia; the tail almost always ends in a small median triangular point bordered by an indentation on each side. The parapodia are smaller and slightly shorter than in the type species. The mantle margin is narrow, only slightly broader posteriorly, rounded and lacks the flagellum seen in G. meckelii; as a result the gill is left almost exposed, is relatively larger than in the type species, and is directed more downward. The gill leaves resemble those of the type species but are fewer in number (16–20) and have longer free tips. The anal papilla is in the usual position; the black renal pore lies closer to the anus. The shell is spirally coiled posteriorly, chalk-white and radially striate, breaking easily into small angular plates.

Distribution

North Pacific. Type locality: vicinity of Unalaska Island, Aleutian Islands, Alaska, based on 13 specimens dredged by W. H. Dall in August 1874 from rocky bottom at 9–15 fathoms (≈ 16–27 m). The species occurs in cold-water habitats of the North Pacific.

Etymology

The specific epithet pacificum is the neuter of Latin pacificus ("Pacific"), in reference to the type locality in the North Pacific.

Remarks

Originally described by Bergh in Gastropteron and compared in detail with the Mediterranean type species Gastropteron meckelii (Blainville). The name was first used by Bergh in his Malacologische Untersuchungen Heft XVIII 1893 and formally established with the present description 1894 based on the Aleutian type material. Gastropteron is the type genus of the Gastropteridae and these animals swim by undulating their paired parapodia.

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References

• Gastropteron pacificum Bgh. n. sp., Bergh R. (1894). Reports on the dredging operations off the West Coast of Central America to the Galapagos, to the West Coast of Mexico, and in the Gulf of California, in charge of Alexander Agassiz, carried on by the U. S. Fish Commission Steamer "Albatross", during 1891. XIII. Die Opisthobranchien. Bulletin of the Museum of Comparative Zoology at Harvard College. 25(10): 125-235, pls. I-XII.