Phanerophthalmus albotriangulatus Austin, Gosliner & Malaquias, 2018

Description

Body cylindrical, elongated; dark brown. Anterior half of cephalic shield quadrangular, posterior half triangular, notched, ending in a pair of posterior lobes, slightly separated. Posterior triangular area white. Left parapodial lobe overlapping right lobe. Shell not visible. Eyes visible; periocular area unpigmented. Shell H = 2 mm (fixed spc. TL = 4 mm); external, plate-like, thin, fragile; white to translucent; squarish oval, right and left sides straight; anterior aperture expanding slightly outwards beyond columella; shoulder present, pointed; anterior end angled and rounded. Jaws semi-circular, elongate; rods ending in finger-like denticles. Radula formula 36×10.1.10; lateral teeth hook-shaped with wide base, slim, elongated, pointed cusp with thinner margins; rachidian with triangular-rounded central cusp with developed brim and one smaller triangular cusp on either side. Gizzard plates with single row of rods on top of ridges; inner rods present only along rachis of plate on anterior side of ridges. Penial sheath long, similar in length to prostate; seminal duct slender, shorter; prostate cylindrical, bulbous, elongate.

Distribution

The Philippines (current study), the Ryukyu Is., Japan (Atsushi 1999, 2004: as P. smaragdinus var.), and Madang, Papua New Guinea (Gosliner et al. 2008, 2015: as P. albocollaris) (Fig. 25). Type locality: Lubang Island, Mindoro, the Philippines.

Etymology

Verbatim from the original description (Austin et al. 2018, Invertebrate Systematics 32: 1363):

Named after the colouration of the upper part of the cephalic shield, which depicts a striking white triangle (white, L. alba, triangle, L. triangulum).

Remarks

Described as a new species in a 2018 systematic revision of Phanerophthalmus. The brownish colour pattern of P. albocollaris, P. albotriangulatum and P. cerverai all share a white W-mark posteriorly on the cephalic shield, but P. albocollaris is endemic to the Red Sea while P. albotriangulatum and P. cerverai co-occur in the Coral Triangle. P. albotriangulatum lacks the white pigmentation on the anterior part of the cephalic shield present in P. cerverai, and anatomically has a male reproductive system with a shorter seminal duct of similar size to the penial sheath, whereas P. cerverai bears a seminal duct twice as long as the penial sheath. P. albotriangulatum was recovered as sister to the Red Sea endemic P. olivaceus (COI uncorrected p-distance = 10.9%; PP = 1, BS = 97; p.1363).

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References

• チョウチョウミドリガイ, 小野篤司. (2004). 沖縄のウミウシ. ラトルズ.
• チョウチョウミドリガイ, 中野理枝. (2004). 本州のウミウシ. ラトルズ.
• Phanerophthalmus albocollaris, Terrence Gosliner, Ángel Valdés and David Behrens. (2015). Nudibranch and Sea Slug Identification Indo-Pacific. New World Pubns Inc.
• 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 sp.2, 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.