Goniobranchus albonares (Rudman, 1990)

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 albonares (Rudman, 1990)

Figures 2a, b , 5a, b , 7a-f

Chromodoris albonares Rudman, 1990: 100, 307-309, figs 26E, 35, 36; Gosliner et al. 2008: 220, second photograph from the top.

Goniobranchus albonares : Gosliner et al. 2015: 223, lower left photograph; Gosliner et al. 2018: 153, lower left photograph.

Type locality.

New South Wales, Australia.

Type material.

AM C156989, one specimen, west side of Northwest Solitary Island, 30.017°S, 156.267°E, Coffs Harbour, New South Wales, Australia, 6 m depth, 4 December 1988, J. & J. England, P. Edwards. Not examined in this study due to the original descriptions in Rudman (1990) being comprehensive.

Geographical distribution.

Widely distributed around the tropical and subtropical Indo-Pacific Ocean ( Debelius and Kuiter 2007; Gosliner 2008, 2015, 2018), Mozambique ( Tibiriçá et al. 2017; Strömvoll and Jones 2019), Indonesia ( Debelius and Kuiter 2007), Japan ( Nakano 2018; Ono and Katou 2020), Taiwan ( Jie et al. 2009), Australia ( Rudman 1990), Madagascar, Philippines, Papua New Guinea (present study), New Caledonia ( Hervé 2010), and Gulf of Oman (Fatemi and Attaran-Fariman 2015).

Material examined.

CASIZ 228939, one specimen (2 mm preserved), subsampled for molecular data and dissected, Murals dive site, 13.688°N, 120.866°E, Maricaban Strait , Mabini (Calumpan Peninsula), Batangas Province, Luzon , Philippines, 9-22 m depth, 29 November 2018, T.M. Gosliner, 2018 Verde Island Passage Expedition. CASIZ 191440, one specimen (3 mm preserved), subsampled for molecular data, Madang Province, GPS not available, Papua New Guinea, depth not available, 26 November 2012, V. Knutson, Papua New Guinea Biodiversity Expedition 2012. CASIZ 194037, one specimen (2 mm preserved), subsampled for molecular data, Pointe Evatra , rocky bottom with areas of sand, 24.983°S, 47.083°E, South Madagascar, Madagascar, 22 m depth, 30 April 2010, Atimo Vatae South Madagascar Expedition .

Description.

External morphology. Living animals 5-7 mm in length. Body opaque white, oval and elongated, with the outermost portion of the mantle edge having an orange band that gradually blends into a yellow submarginal band. Gill and rhinophores are translucent white with opaque white edges on the lamellae. Six or seven unipinnate gill branches are moderately spreading when fully extended. Rhinophores are relatively large, ~ 2 × as long as the gill branches. Ten or eleven lamellae per rhinophore.

Buccal mass and radula. The muscular portion of the buccal mass ~ 2/3 the size of the oral tube length (Fig. 5a ). The chitinous labial cuticle found at the anterior end of the muscular portion of the buccal mass bears bifurcated and short jaw rodlets (Fig. 7a, b ). The radular formula of CASIZ 228939 is 37 × 19.1.19 (Fig. 7c ). The rachidian tooth is triangular and short. The inner and outer surfaces of the inner lateral teeth have three denticles on each side of the central cusp (Fig. 7d ). The central cusp on the inner lateral tooth is ~ 2 × the length of the adjacent denticles. The middle lateral teeth have a short central cusp with three or four denticles (Fig. 7e ). The outer lateral teeth have a rounded main cusp with three or four denticles (Fig. 7f ).

Reproductive system (Fig. 5b ). The long, thick, tubular ampulla narrows into a diverging short oviduct and short vas deferens. The proximal prostatic portion of the vas deferens transitions into the muscular ejaculatory portion. The ejaculatory portion narrows and elongates into a wider, long, curved penial bulb that joins with the narrow 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 short uterine duct emerges from the receptaculum seminis, which is adjacent to the vagina, and enters into the female gland mass. The female gland mass has small albumen and membrane glands and a large mucous gland.

Remarks.

Goniobranchus albonares was described by Rudman (1990) from New South Wales, Australia; he described the animal as having an elongate, ovate, opaque white mantle with a bright orange band on the edge of the mantle with the inside edge of the orange band being irregular. The rhinophores and gill branches were translucent white with opaque white edges, which is a distinctive feature of this species. Also, the notum was described as smooth, ringed by an orange marginal band and a yellow submarginal band. This morphological description matches well with the G. albonares specimens in this study, which are quite uniform in color pattern. The vas deferens in G. albonares is also shorter in comparison to that of all the other white Goniobranchus with marginal bands species included in this study. The phylogenetic tree also showed a fully supported (1/100%) monophyly for specimens (n = 4) of this species (intraspecific distance within G. albonares = 1.1-5.2%; Table 2 ).

Goniobranchus albonares was included in this study together with all other white Goniobranchus with marginal bands based on Gosliner et al. (2018). However, in our concatenated phylogenetic tree, G. albonares is a sister clade to G. collingwoodi , G. decorus , G. fidelis , and G. geminus , and is genetically comparatively distant from the remainder of the white Goniobranchus species with marginal bands examined in this study (interspecific p -COI distances between G. albonares and G. verrieri = 16.0-18.2%; see Table 2 ). This suggests a case of convergent evolution of having a white body with marginal bands. Little is known about how predators perceive the color of the nudibranchs (as prey), which may provide clues to factors driving this remarkable similarity.

Figures

Figure 2. a, b Goniobranchus albonares a CASIZ 191440, Papua New Guinea b CASIZ 228939, Philippines c-f Goniobranchus preciosus c CASIZ 208415, Morphotype A, Philippines d CASIZ 208574, Morphotype B, Philippines e CASIZ 176752, Morphotype C, Peninsular Malaysia f CASIZ 176761, Morphotype D, Peninsular Malaysia g, h Goniobranchus rubrocornutus g CASIZ 203047, Morphotype A, Philippines h CASIZ 208563, Morphotype B, Philippines. Photographs TMG. Scale bars: 1 cm.

Figure 5. a buccal mass of Goniobranchus albonares, CASIZ 228939 b reproductive system of Goniobranchus albonares, CASIZ 228939 c buccal mass of Goniobranchus preciosus, CASIZ 208574 d reproductive system of Goniobranchus preciosus, CASIZ 208574 e buccal mass of Goniobranchus rubrocornutus, CASIZ 203047 f reproductive system of Goniobranchus rubrocornutus, CASIZ 203047. 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; mu, mucous gland. Scale bars: 0.1 mm (a, b, e, f); 1 mm (c, d).

Figure 7. Scanning electron micrographs. Goniobranchus albonares, CASIZ 228939, Philippines a jaw b jaw rodlets c radula d central teeth e mid-lateral teeth f outer lateral teeth.