Phanerophthalmus cylindricus (Pease, 1861)

Description

A slender cephalaspidean reaching about 20 mm in body length. The body is elongate, smooth, sub-cylindrical, with sides nearly parallel. The cephalic disk is about one-fourth of the entire length of the animal, depressed, sub-caudate, convexly truncate in front, and furnished posteriorly with two small, appressed, triangular lobes. The eyes lie beneath the cephalic disk and are inconspicuous from above, but can be seen distinctly by turning up the edges of the disk. The lateral lobes closely envelop the body, extending from the head to the excretory tube, the left one overlapping the right. The excretory tube at the posterior end of the body is short and convolute. In life the ground colour is dusky olive, with the margins of the cephalic disk paler than the centrally and the locomotive disk paler than above. Pease's type was collected on sea-weed in the Pacific Islands.

Distribution

Indo-Pacific to the central Pacific. Type locality: Tahiti, Society Islands, based on a specimen collected on sea-weed by Andrew Garrett and described by Pease. Subsequently recorded from French Polynesia, the Hawaiian Islands, southern Japan, the Philippines, Indonesia, Guam and elsewhere.

Etymology

The specific epithet cylindricus is the Latin adjective meaning "cylindrical", in reference to the elongate sub-cylindrical body. Pease did not state an etymology, but the meaning is consistent with his "Animal elongate, smooth, subcylindrical, sides nearly parallel".

Remarks

Originally placed by Pease in Cryptophthalmus. The genus name "Cryptophthalmus" ("hidden-eye") corresponds to Pease's observation that the eyes lie beneath the cephalic disk and are inconspicuous from above. The species was later transferred to Phanerophthalmus; the parentheses in the author citation reflect this generic transfer. Note that Phanerophthalmus means "visible-eye", the opposite sense of the original genus.

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References

• Cryptophthalmus cylindricus Pease n. sp., Pease W.H. (1861). Descriptions of new species of Mollusca from the Pacific Islands. Proceedings of the Zoological Society of London. 1861: 242-247.
• Austin J., Gosliner T. & Malaquias M.A.E. (2018). Systematic revision, diversity patterns and trophic ecology of the tropical Indo-West Pacific sea slug genus Phanerophthalmus A. Adams, 1850 (Cephalaspidea, Haminoeidae). Invertebrate Systematics. 32(6): 1336-1387. https://doi.org/10.1071/is17086
• Phanerophthalmus cylindricus, Terrence Gosliner, Ángel Valdés and David Behrens. (2018). Nudibranch and Sea Slug Identification Indo-Pacific 2nd Edition. New World Pubns Inc.
• Oskars T.R., Too C.C., Rees D., Mikkelsen P.M., Willassen E. & Malaquias M.A.E. (2019). A molecular phylogeny of the gastropod family Haminoeidae sensu lato (Heterobranchia: Cephalaspidea): a generic revision. Invertebrate Systematics 33(3): 426-472.