Goniobranchus fabulus Soong & Gosliner, 2022

Soong, Giun Yee, Bonomo, Lynn J., Reimer, James D. & Gosliner, Terrence M., 2022, Battle of the bands: systematics and phylogeny of the white Goniobranchus nudibranchs with marginal bands (Nudibranchia, Chromodorididae), ZooKeys 1083, pp. 169-210 : 169

Goniobranchus fabulus Soong & Gosliner sp. nov.

Figures 4a-d , 6e, f , 12a-f

Chromodoris preciosa (Kelaart, 1858): Rudman 1985: figs 12b, 13b, 17; Gosliner et al. 2008: 219, upper right photo (misidentifications).

Goniobranchus preciosus (Kelaart, 1858): Gosliner et al. 2015: 222, lower middle right photo; Gosliner et al. 2018: 152: middle right photo (misidentifications).

Type material.

Holotype: CASIZ 191271 (morphotype B), one specimen (5 mm preserved), subsampled for molecular data and dissected. Siar Island, 5.187°S, 145.807°E, Madang Province, Papua New Guinea, depth not available, 16 November 2012, V. Knutson, Papua New Guinea Biodiversity Expedition 2012.

Paratypes: CASIZ 177517 (morphotype A), one specimen (3 mm preserved), subsampled for molecular data, Arthur’s Rock, 13.417°N, 120.517°E, Maricaban Strait, Mabini (Calumpan Peninsula), Batangas Province, Luzon, Philippines, 3 m depth, 21 March 2008, T.M. Gosliner et al., Philippines Expedition March 2008. CASIZ 177685 (morphotype A), one specimen (6 mm preserved), subsampled for molecular data, Bethlehem Channel, 13.672°N, 120.841°E, Bethlehem, Maricaban Island, Batangas Province, Philippines, 15 m depth, 20 April 2008, T.M. Gosliner. CASIZ 201949 (morphotype A), one specimen (5 mm preserved), subsampled for molecular data, Lago de Oro Hotel, 13.917°N, 120.616°E, Verde Island Passage coast, Calatagan, Batangas Province, Luzon Island, Philippines, 2 m depth, 19 May 2014, VIP Team, 2014 Verde Island Passage Expedition. CASIZ 191118 (morphotype B), one specimen (4 mm preserved), subsampled for molecular data, Mangroves, GPS, Madang Province, Papua New Guinea, 3 m depth, 10 November 2012, Papua New Guinea Biodiversity Expedition 2012.

Geographical distribution.

This species appears to be restricted to the western and southern central Pacific tropics ( Gosliner et al. 2008, 2015, 2018) with reports from the Philippines (present study), Japan ( Nakano 2018), Papua New Guinea, New Caledonia, Tonga, Vanuatu ( Gosliner et al. 2008), Australia, and Fiji ( Rudman 1985).

Description.

External morphology. Living animals 12-18 mm in length. Body oval with three marginal bands on the mantle edge. Notum smooth with no apparent spots. Six to ten unipinnate gill branches. Eleven or twelve lamellae on rhinophores. The color pattern exhibits two distinct morphotypes. Morphotype A (Fig. 4a-c ) has a creamy opaque white body. The outermost portion of the mantle edge is tinged an opaque bluish white, followed by a deep red band, followed by a yellow submarginal band, and then an opaque white band, with all bands having similar widths. Gill branches and rhinophores are reddish purple with white edges. Morphotype B (Fig. 4d ) has an opaque creamy white body. The outermost portion of the mantle edge is surrounded by a speckled opaque white band, followed by a deep red band, a yellow submarginal band, and then an innermost opaque white band. The gill and rhinophores are reddish purple with white edges and opaque white speckles.

Buccal mass and radula (morphotype B). The muscular portion of the buccal mass is approximately the same size as the oral tube length (Fig. 6e ). The chitinous labial cuticle found at the anterior end of the muscular portion of the buccal mass and bears bifurcated and short jaw rodlets (Fig. 12a, b ). The radular formula of CASIZ 191271 is 42 × 35.1.35 (Fig. 12c ). The rachidian tooth is triangular. The innermost lateral teeth have two denticles on the inner side of the cusp and three or four denticles on the outer side (Fig. 12d ). The central cusp on the inner lateral tooth is elongate and ~ 2 × the length of the adjacent denticles. The middle lateral teeth have an elongated central cusp with 5-7 denticles (Fig. 12e ). The outer lateral teeth have a rounded tooth with 2-5 denticles (Fig. 12f ).

Reproductive system (Fig. 6f ). The thin, tubular ampulla narrows into a diverging short oviduct and long vas deferens. The proximal prostatic portion of the vas deferens is thin and convoluted and transitions into the muscular ejaculatory portion. The long, narrow, convoluted ejaculatory portion transitions into a wider, long penial bulb, which joins with the moderately wide distal end of the vagina. The vagina is elongate and narrow, joining the larger, spherical bursa copulatrix and the smaller, curved receptaculum seminis at its distal end. A moderately long uterine duct that emerges from this junction of vagina, bursa copulatrix, and receptaculum seminis. The uterine duct connects the receptaculum seminis with the female gland mass. The female gland mass has smaller albumen and membrane glands and a larger mucous gland.

Etymology.

Goniobranchus fabulus sp. nov. is named after the Latin word which, in one translation, means a small bean, in reference to the body shape of the nudibranch.

Remarks.

Goniobranchus fabulus sp. nov. was recovered as a sister species to G. daphne in our phylogenetic analyses, with an interspecific distance of 2.5-4.5% (Table 2 ). Goniobranchus daphne possess red spots of different sizes on the notum and can only be found in the Australian waters.

Goniobranchus fabulus sp. nov. morphotype A in our study matches well with Rudman’s (1985) description of Goniobranchus preciosus from New Caledonia based on morphological characteristics. However, in our opinion the morphological characteristics of G. preciosus sensu Rudman did not match with the original description of G. preciosus and our specimen sequences are also genetically distinct from G. preciosus in this study (interspecific p -COI distance between G. fabulus and G. preciosus = 6.8-9.2%) (Fig. 1 ; Table 2 ). Hence, we have assigned G. preciosus sensu Rudman (1985) to G. fabulus sp. nov.

Goniobranchus fabulus sp. nov. morphotype B is slightly different from morphotype A in having opaque white speckles all over the gills and around the outermost edge of the mantle. This morphotype is only known from Papua New Guinea ( Wakeling 2001; Gosliner et al. 2018). There is little genetic difference between the two morphotypes (intraspecific p -COI distances within G. fabulus sp. nov. = 0.2-3.4%). Confusion of this species with G. preciosus is discussed in the remarks section of G. preciosus .

Figures

Figure 1. Molecular phylogeny based on the combined dataset (COI + 16 S rDNA) inferred by maximum likelihood (ML) and Bayesian inference (BI). Numbers on nodes represent Bayesian posterior probabilities (> 0.95) / ML bootstrap values (only> 50 % values are shown). Black bars indicate the clade groupings of ABGD analysis on the COI + 16 S dataset.

Figure 4. Goniobranchus fabulus sp. nov. a CASIZ 177517, morphotype A, Philippines b CASIZ 177685, morphotype A, Philippines c CASIZ 201949, morphotype A, Philippines d CASIZ 191118, morphotype B, Papua New Guinea. Photographs TMG. Scale bars: 1 cm.

Figure 6. a buccal mass of Goniobranchus sinensis, MISE- 047 - 19 b reproductive system of Goniobranchus sinensis, MISE- 047 - 19 c buccal mass of Goniobranchus verrieri, CASIZ 203059 d reproductive system of Goniobranchus verrieri, CASIZ 203059 e bBuccal mass of Goniobranchus fabulus sp. nov., CASIZ 191271 f reproductive system of Goniobranchus fabulus sp. nov., CASIZ 191271. Abbreviations: am, ampulla; bb, buccal bulb; bc, bursa copulatrix; ej, ejaculatory duct; es, esophagus; fgm, female gland mass; ot, oral tube; p, penis; pr, prostate; ra, radular sac; rs, receptaculum seminis; va, vagina. Scale bars: 0.1 mm (c, d, e, f); 1 mm (a, b).

Figure 12. Scanning electron micrographs. Goniobranchus fabulus sp. nov., CASIZ 191271, Philippines. a jaw b jaw rodlets c radula d central teeth e mid-lateral teeth f outer lateral teeth.