Dermatobranchus oculus, Gosliner & Fahey, 2011

Gosliner, Terrence M. & Fahey, Shireen J., 2011, Previously undocumented diversity and abundance of cryptic species: a phylogenetic analysis of Indo-Pacific Arminidae Rafinesque, 1814 (Mollusca: Nudibranchia) with descriptions of 20 new species of Dermatobranchus, Zoological Journal of the Linnean Society 161 (2), pp. 245-356 : 325-327

publication ID	https://doi.org/ 10.1111/j.1096-3642.2010.00649.x
persistent identifier	https://treatment.plazi.org/id/761B2D60-4826-E203-096E-F94AFB953D7D
treatment provided by	Valdenar
scientific name	Dermatobranchus oculus
status	sp. nov.

Treatment

DERMATOBRANCHUS OCULUS View in CoL SP. NOV.

( FIGS 58E View Figure 58 , 67 View Figure 67 , 68 View Figure 68 )

Dermatobranchus sp. Coleman 2001: 103 .

Dermatobranchus sp. Coleman 2008: 120 , as Okinawa Dermatobranchus View in CoL .

Dermatobranchus sp. 8 Gosliner, Behrens & Valdés, 2008:311, above bottom photo.

one 8 mm dissected, Okinawa, Ryukyu Islands , Japan, 13 m depth, collected 9.vii.1991 by R . Bolland ( RFB 2622 -K) .

Geographical distribution: This species is known only from Okinawa (present study).

Etymology: The specific name oculus is from the Latin word meaning ‘eye’ or ‘bud’ referring to the evenly spaced oscillated spots on the dorsum.

Type material: Holotype: CASIZ 174138 , 8 mm, Okinawa, Ryukyu Islands , Japan, 13 m depth, collected 9.vii.1991 by R. Bolland ( RFB 2622 -K) . Paratypes: CASIZ 079270 , three specimens, 7–8 mm, External morphology: The body shape of the living animal ( Fig. 58E View Figure 58 ) is elongate and narrows at the posterior end. The foot does not project beyond the distinct mantle margin. There is a series of longitudinal dorsal ridges. The oral veil extends forward and has blunt extensions at the corners. The widely spaced rhinophores are behind the oral veil. They have a series of longitudinal lamellae on the rounded club. The stalk does not narrow noticeably. There are visible marginal sacs along the mantle edge. There are no branchial or hyponotal lamellae. The genital opening is situated at the anterior quarter of the body side and the anus is situated in the anterior half .

The ground colour of the dorsum and foot is opaque white. The depressions between the dorsal ridges are light grey. There are dark centred ocellated spots on the dorsum surrounded by pink pigment. The rhinophore stalk is white and the club is black. The oral veil is opaque white with a light grey border.

Buccal armature: The jaws are large and thickly cuticularized, with a thick masticatory margin and seven rows of long, pointed denticles ( Fig. 67A View Figure 67 ). The radular formula of a paratype (CASIZ 079270) is 23 ¥ 10–8.1.1.1.8–10. Additional rows of teeth may have been lost during preparation of the radula. The rachidian teeth ( Fig. 67B View Figure 67 ) have a broad base with a large, thick, and long central cusp that is wider than the up to seven flanking denticles on each side. The central cusp may have two attached, smaller denticles; one per side. The inner lateral teeth ( Fig. 67B View Figure 67 ) have a wide base with a slightly longer first denticle with a small secondary denticle on the outside edge and ten shorter and narrower, pointed denticles adjacent. The next eight to ten lateral teeth are long hooks without denticles ( Fig. 67C View Figure 67 ).

Reproductive system: The reproductive organ arrangement is androdiaulic. The hermaphroditic duct leads into the wide, tubular ampulla ( Fig. 68 View Figure 68 ). The ampulla bifurcates into the female gland mass via a short oviduct and into the short, narrow prostate. The prostate curves, then expands into the elongate, tubular penial sheath that is as long as the entire prostate. The round bursa copulatrix is smaller than the ampulla. From the bursa, the short, narrow vaginal duct extends into the equally narrow vagina, which exits into the genital aperture adjacent to the penial sheath.

Remarks: Externally, D. oculus most closely resembles D. otome , D. semistriatus Baba, 1949 , and D. primus Baba, 1976 . All of these species have a white ground colour, raised longitudinal ridges with darker coloration in the depressions between the ridges, and dark ocellated spots on the dorsum. Of these, D. otome has orange rhinophores, whereas the remaining species have black or dark brown pigment on the rhinophores. In D. primus , the dark pigment is on the base of the rhinophore stalk and the apex is orange, whereas the black pigment is on the club in both D. semistriatus and D. oculus . Additionally, the frontal margin of the oral veil of D. semistriatus and D. primus is orange whereas it is grey in D. oculus . Dermatobranchus otome lacks a marginal band, and the entire oral veil is white.

The radular morphology of these species has some similarities. The number of rows of teeth is similar, about 20 in a 10 mm specimen of D. primus , 25 in a 20 mm specimen of D. semistriatus and 23 or more in an 8 mm specimen of D. oculus . The rachidian tooth of all species has a long, thick central cusp with flanking denticles (up to seven in D. oculus , five to six in D. primus , and 11–14 in D. semistriatus ). Both D. oculus and D. semistriatus have a differentiated first lateral tooth, whereas D. primus does not and all of its lateral teeth lack denticulation. The morphology of the remaining lateral teeth differs between that of D. oculus and D. semistriatus . The succeeding four to five lateral teeth of D. semistriatus are denticulate, followed by 50–60 nondenticulate teeth, but only the first lateral tooth of D. oculus is denticulate, and the remaining eight to ten teeth are hook-shaped and smooth. The lateral teeth of D. primus have a rounded knob on the top but the lateral teeth of D. oculus have either straight, or slightly depressed tops. The jaw of these species also differs in the number of rows of rods. Baba (1949) described one to two rows of spiny denticles for D. semistriatus and three to four rows of ‘scale-like’ denticles for D. primus ( Baba, 1976) . Dermatobranchus oculus has seven rows of long, pointed denticles.

The radular configuration of D. oculus , with only the inner lateral tooth denticulate, is similar to D. otome , D. striatus , D. albus , and D. diagonalis . Additionally, all of these species have jaws with multiple rows of denticles situated only at the base of the jaws. All of these species have colour patterns that are very different from that of D. oculus , and their reproductive systems differ markedly, as well. In D. oculus , the prostate is relatively narrow and expands into a much wider elongate penial sheath. In the remaining species the penial sheath is only slightly wider than the prostate and is relatively shorter and conical.

Dermatobranchus oculus also externally resembles some specimens of D. funiculus from Okinawa. Both species have white ground colour and raised longitudinal ridges with darker coloration in the depressions between the ridges. However, there are no ocellated spots on the dorsum of D. funiculus as there are in D. oculus .

The radular formula of these two species is also very different, with D. funiculus having a formula of 31–34 ¥ 8.1.1.8 as opposed to 23 ¥ 10–8.1.1.1.8– 10 in D. oculus . Even more significantly, the majority of the lateral teeth of D. funiculus ( Figs 54–56 View Figure 54 View Figure 55 View Figure 56 ) are denticulate whereas only the inner laterals of D. oculus are denticulate ( Fig. 67 View Figure 67 ).

The reproductive morphology of these two species shares some similarities, such as a wide penial sheath and a narrow vaginal duct and vagina, but the prostate in D. funiculus ( Fig. 57 View Figure 57 ) is coiled and longer than that of D. oculus ( Fig. 68 View Figure 68 ).