HYPSELODORIS MELANESICA, 2019

Epstein, Hannah E., Hallas, Joshua M., Johnson, Rebecca Fay, Lopez, Alessandra & Gosliner, Terrence M., 2019, Reading between the lines: revealing cryptic species diversity and colour patterns in Hypselodoris nudibranchs (Mollusca: Heterobranchia: Chromodorididae), Zoological Journal of the Linnean Society 186, pp. 116-189 : 151-153

HYPSELODORIS MELANESICA

GOSLINER & JOHNSON SP. NOV.

( FIGS 13E, 18E, 20)

LSID: urn:lsid:zoobank.org:act:948DE50E-A684-4E57-8126-658578AF3E06

Hypselodoris bullocki misidentification, not C. bullockii Collingwood, 1881 ; Johnson, 2000; Coleman, 2001: 79, lower right photograph; Gaensslen, 2007; Rudman, 2007; Hanchard, 2009.

Hypselodoris sp. 7 Gosliner et al., 2008: 268, second photograph from top.

Hypselodoris sp. 16 Gosliner et al., 2015: 262, bottom left photograph.

Type material

Holotype: CASIZ 191246 , subsampled for molecular study, Southern Sek Island , 5.0985°S, 145.8210°E, 8 m depth, Madang Lagoon, Madang, Papua New Guinea 15 November 2012.

Paratypes: CASIZ 185100 , five specimens, one subsampled for molecular study, various locations, Milne Bay , Milne Bay Province, 5–12 m depth , R. Steene . CASIZ 069754 , one specimen, Anemone Reef , near Ruo , Island, Madang Lagoon, Madang, Papua New Guinea, 20 July 1989 , M. Jebb. CASIZ 069787 , one specimen, dissected, Madang Lagoon , Madang, Papua New Guinea, August 1989 , M. Gosliner. CASIZ 069785 , three specimens, Madang Lagoon , Madang, Papua New Guinea, August 1989 , M. Gosliner. CASIZ 065356 , one specimen, Hole in the Wall, north of Hussein Village , north of Madang, 20 m depth, 3 February 1988 , T. Gosliner . CASIZ 071237 , one specimen, patch reef off N side Kranket Island , 24 m depth, 24 January 1988 , T. Gosliner . CASIZ 071474 , two specimens, Takahate Bay , Big Nggela Island, Florida Group, Solomon Islands, 15–23 m depth, 1 September 1986 , R. Van Syoc . CASIZ 191392 , one specimen, N. Tadwai Island, 4.985°S, 145.7915°E, Madang Lagoon , Madang, Papua New Guinea, 11 m depth, 22 November, 2012 . CASIZ 191160 , one specimen, Sek Island , Madang Lagoon, Madang, Papua New Guinea, 12 November 2012 . CASIZ 191227 , one specimen, Southern Sek Island , 5.0985°S, 145.8210°E, 8 m depth, Madang Lagoon, Madang, Papua New Guinea, 15 November 2012 . CASIZ 190823 , one specimen, Cement Mixer Reef , 5.15176°S, 145.81832°E, 2–23 m depth, Madang Lagoon , Madang, Papua New Guinea 12 December 2012 , T. Gosliner . CASIZ 191326 , one specimen, south Rempi 5.0367°S, 145.8066°E, Madang, Papua New Guinea, 19 November 2012 , Francois Michonneau . CASIZ 191139 , one specimen, Bilbil Island 5.2967°S, 145.7816°E, Madang, Papua New Guinea, 22 m depth, 12 November 2012 , Heok Hui Tan. CASIZ 191066 , one specimen, N. Siar Island, 5.1967°S, 145.8067°E, Madang, Papua New Guinea 9 November 2012 , Heok Hui Tan. CASIZ 190842 , one specimen, from orange sponge, Madang Lagoon , November–December 2012 , Marco Oliverio .

Geographical distribution

Known only from the Papua New Guinea and the Solomon Islands (present study).

Etymology

Hypselodoris melanesica is named for Melanesia, the region to which this species is geographically restricted.

Description

External morphology: Living animals ( Fig. 18E) of moderately size, reaching 30 mm in length. Body translucent purple, with thin white band encircling the margin of notum and foot. Five unipinnate gill branches on notum. One large specimen ( CASIZ 071237) with seven gill branches. Gill branches light orange, with darker orange at their common base. Base of gill pocket deep violet. Bulb of rhinophores bright orange, with redder apex. Bulb with ~25 densely packed lamellae. Base of rhinophore sheath deep violet to purple.

Mantle glands: Subcutaneous mantle glands entirely absent.

Buccal armature: Muscular portion of buccal mass about twice the length of oral tube. Chitinous labial cuticle found at anterior end of muscular portion of the buccal mass bearing numerous jaw rodlets ( Fig. 20A). Rodlets narrow with short base and evenly curved, with single, acutely pointed apex. Radular formula of one paratype ( CASIZ 069787) 57 × 59.0.59. Rachidian row of teeth absent ( Fig. 20B). Innermost lateral teeth having one pointed denticle on inner side of bifid primary cusp, with another one or two outer denticles. Denticles not extending far beyond middle of elongate primary cusp. Next several laterals lacking inner triangular denticle but possessing three or four denticles on outer side of primary bifid cusps. Midlateral teeth ( Fig. 20C) all lacking inner denticles but having four or five rounded to triangular outer denticles and extended primary cusp. Outermost teeth having a narrower base and shorter tooth shape, with three rounded outer denticles ( Fig. 20D), often larger than bifid cusps.

Reproductive system: Reproductive organs of the paratype ( CASIZ 069787) fully mature ( Fig. 13E). Ampulla thick, tubular and slightly curved, narrowing somewhat before bifurcating into oviduct and vas deferens. Short oviduct entering female gland mass near albumen gland. Prostatic proximal portion of vas deferens convoluted, curved and thick, and narrowing slightly as it transitions into muscular ejaculatory portion. Prostatic portion enveloping bursa copulatrix. Ejaculatory portion convoluted, narrow, entering short, wider penial bulb. Penial bulb adjacent to straight, moderately wide vaginal duct at common gonopore. Distal end of vas deferens devoid of penial hooks. Female gland mass consisting of large mucous gland and small membrane and albumen glands. Large, lobate vestibular gland situated near exit of mucous gland. Relatively long vagina leading to small, straight receptaculum seminis and larger spherical, thin-walled receptaculum seminis. Receptaculum seminis appressed against vagina in distal half of vaginal length. Moderately short uterine duct emerging from vagina close to base of bursa and entering female gland mass near the albumen gland.

Remarks

In our phylogenetic analyses, H. melanesica is always sister to H. bullockii but forms a distinct clade. In the ABGD analysis, H. melanesica is included in the same group as H. bullockii , thus suggesting that they should be considered as conspecific. Their uncorrected p-distances for the COI gene range between 2.0 and 2.6% different, right near the boundary for consideration of these two as distinct species. Although H. melanesica resembles H. bullockii in its shape and body colour, there are consistent morphological differences. In H. bullockii , the body colour is generally light pink to a deep purple. There may or may not be darker pigment at the base of the gill and the rhinophores. When present, the purple pigment is a wide band that is very diffuse, without distinctly defined edges. In contrast, H. melanesica is always light purple in colour and always has well-defined narrow bands of darker pigment at the base of the rhinophores and gill. The bands at the base of the rhinophores of H. melanesica always have a break in the band on the posterior side of the rhinophores. Internally, H. melanesica ( CASIZ 069787) has a radular formula of 65 × 68.0.68 vs. 77 × 97.0. 97 in one specimen of H. bullockii ( CASIZ 083685). Also, the primary cusps of the radular teeth of H. melanesica appear shorter than those of H. bullockii ( Figs 20, 21). The reproductive system of H. melanesica has a shorter penial bulb and a longer ejaculatory duct that is more convoluted than that found in H. bullockii ( Fig. 13F). Also, H. melanesica has a longer vaginal duct than that of H. bullockii .

Hypselodoris melanesica is known only from Papua New Guinea and the Solomon Islands, whereas H. bullockii is known from the western Pacific of Australia, New Caledonia, Malaysia, Indonesia, Japan, Taiwan, Philippines, Marshall Islands ( Gosliner et al., 2008) and Palau (present study). Hypselodoris melanesica and H. bullockii are geographically isolated and have minor but consistent differences in their coloration and internal morphology spanning several organ systems. Based on these consistent differences, we consider H. melanesica as a distinct species from H. bullockii despite the fact that the ABGD analysis clusters these species as conspecifics.