Roboastra, TIGRIS FARMER, 1978

Pola, M., Cervera, J. L & Gosliner, T. M., 2005, Review of the systematics of the genus Roboastra Bergh, 1877 (Nudibranchia, Polyceridae, Nembrothinae) with the description of a new species from the Galápagos Islands, Zoological Journal of the Linnean Society 144 (2), pp. 167-189 : 178-179

ROBOASTRA TIGRIS FARMER, 1978

( FIGS 3C , 4C , 6B , 7C, D )

Material examined: Bahía de Los Angeles , Baja California, Gulf of California , Mexico, October 1975, 3 specimens, 12–21 m depth, 20–35 mm preserved length, collected by M. Michel & D. Mulliner. ( LACM: 140747). Bahía de Los Angeles, Baja California, Gulf of California, Mexico, October 1984, 1 specimen, 7– 10 m depth, 30 mm preserved, collected by R . Van Syoc & A.J. Ferreira ( CASIZ: 057321). Bahía de Los Angeles, Baja California, Gulf of California, Mexico, January 1985, 1 specimen, 1–7 m depth, 40 mm preserved, collected by R. Van Syoc et al. ( CASIZ: 057613). Isla San Esteban , Sonora, Gulf of California, Mexico, April 1985, 1 specimen, 12 m depth, 40 mm preserved, collected by L. Dunne ( CASIZ 072629 ). Baja California Sur, Gulf of California, Mexico, September 1965, 1 specimen, 30 m depth, collected by D. Wobber ( CASIZ: 68357) .

Distribution: Roboastra tigris has been reported from offshore islands in the central and southern Gulf of California (Islas San Pedro, Monserrate and San Diego, Guaymas, and islands in the region of Bahía de Los Angeles and La Paz) ( Farmer, 1978).

External morphology ( Fig. 6B ): Body elongate and limaciform with a long and pointed posterior end of the foot. The preserved animals are 20–40 mm in length. The body surface is lightly wrinkled with most of the wrinkles following the longitudinal stripes on the notum and both sides of the body. The predominant body colour is a greenish, yellow-ochre, or brown, with five longitudinal dark navy blue stripes outlined by light green. There is a band surrounding the notal edge. Another midline extends from the anterior part, near the edge of the notum, to the middle gills and continues behind these gills. Two other lines start from the rhinophore sheaths and run parallel until they join in the postbranchial region. The line that results from the two joined lines continues to the posterior end of the foot.

The eyespots are bluish in colour and well defined. They join with the rhinophores to form two shorter lines that continue for a little way behind the eyespots. The sides may have an interrupted stripe. The sole of the foot is blue-black and the foot margin is blue. The head is rounded with a pair of conical, completely retractile perfoliate rhinophores with approximately 35 tightly packed lamellae. The oral tentacles are strongly developed and dorsolaterally grooved along a part of their length and they also are blueblack. There are five nonretractile tripinnate gills; the three anteriormost gills are more highly developed. The gills form a semicircle surrounding the anal papilla, which is elevated and is blue-black. The pinna of the gills is dark blue, while the inner side of the rachis is yellow. The rhinophores and their sheaths are blue-black with light green central axes. The oral area is cobalt blue. The genital pore opens on the right side, midway between the gills and the rhinophores.

Internal morphology: All specimens were dissected. The anterior digestive tract begins with a long, thickwalled, muscular oral tube, which continues into the buccal mass. The buccal mass is elongate and tubular, with a pair of slender elongate pouches opening into the digestive system at the junction of the oral tube and the buccal mass. The salivary glands are small and short, entering on the buccal mass and flanking the oesophagus. The labial cuticle and the labial armature are absent. There is a well-developed blood gland that is granular in texture. The radular formula of one 40-mm-long specimen (preserved) is 28 ¥ 4.1.1.1.4; that of the 30-mm-long specimen (preserved) is 30 ¥ 4–3.1.1.1.3–4. The rachidian tooth ( Fig. 7C ) is broad, thin and very arched at its base with two welldifferentiated lateral cusps and a small one in the middle. The inner lateral tooth ( Fig. 7C ) is very curved, with two very well developed cusps. The inner cusp is simple and larger than the outer one, which is very slender. The remaining lateral radular teeth (3- 4) are quadrangular, lack cusps or denticulation and become smaller near the margin ( Fig. 7D ).

The reproductive system is triaulic. Figure 3C shows that of the 40-mm-long specimen (preserved) (CASIZ: 072629). The whole genital mass is very small, filling a third of the second body cavity. The hermaphroditic duct widens into a small S-shaped ampulla. The ampulla narrows into a large and wide postampullary duct, which bifurcates into the vas deferens and oviduct. The short oviduct enters the female gland mass. The deferent duct, which lacks a morphologically well-differentiated prostate, is long and coiled, ending in a dilated and darkly pigmented penial sac. The deferent duct has a uniform width, but it is slightly wider and thicker in the prostatic part.

The distal part of the vas deferens enters the wide penial bulb. The penis is located within the distal end of this muscular portion, and it is armed with at least three different kinds of hooked and chitinous spines arranged in helicoidal rows ( Fig. 4C ). The bursa copulatrix and seminal receptacle are very small. The former is rounded and the latter is elongate; both are similar in size. The seminal receptacle has a short duct that connects to the vagina after making two loops near the bursa. The vagina is long and straight. Nearly halfway along its length, it branches into the uterine duct, which is long and convoluted and joins with the oviduct. There is a large, thick-walled, inverted L-shaped vaginal gland, which joins the distal part of the vagina; both open into the genital atrium. The reproductive system in this species is very small in the context of the total size of the specimens, and when compared with that of the other species.

Remarks: Roboastra tigris was described by Farmer (1978). It is easily distinguishable by its colour pattern and large size. Farmer suggested that its size might be linked to its feeding mechanism and explained the role of the coelomic cavity. Roboastra tigris feeds on other polycerids, such as Tambja abdere Farmer (1978) and T. eliora ( Marcus & Marcus, 1967) . It was named R. tigris for its stripes and carnivorous appetite.

Carté & Faulkner (1983, 1986) and Faulkner & Ghiselin (1983) studied the defensive metabolites of R. tigris . This species, and its prey T. abdere and T. eliora , contain tambjamines A- D. These have been traced to a food source, the bryozoan Sessibugula translucens and are implicated in the chemical defence mechanism of the Tambja species. The radula of R. tigris is very similar to that of R. leonis sp. nov., but in fully mature specimens the reproductive system is smaller than in R. leonis . The bursa copulatrix and the seminal receptacle are both similar in size while in R. leonis they are unequal in size. These differences were consistent in all specimens of each species examined here.

Figures

Figure 3. Drawings of reproductive systems of Roboastra spp. A, R. gracilis. B, R. luteolineata. C, R. tigris. D, R. europaea (adapted from Pola et al., 2003). E, R. caboverdensis. F, R. leonis sp. nov. Scale bar = 1 mm. Abbreviations: am, ampulla; bc, bursa copulatrix; fglm, female gland mass; ga, genital atrium; p, penis; pr, prostate; rs, receptaculum seminis, ud, uterine duct; va, vagina; vd, vas deferens; vgl, vaginal gland.

Figure 4. Penial morphology of Roboastra spp. A, R. gracilis (CASIZ 087131), scale bar = 30 Mm; B, R. luteolineata (CASIZ 115739), scale bar = 30 Mm. C, R. tigris (NHMLAC 140747), scale bar = 300 Mm. D, R. europaea (MNCN 15.05/46613), scale bar = 50 Mm. E, R. caboverdensis (MNCN 15.05/46614), scale bar = 90 Mm. F, R. leonis sp. nov. (CASIZ 097577), scale bar = 300 Mm. G-I, detail of the three different kinds of spines in R. caboverdensis (MNCN 15.05/46614), scale bar = 10 Mm. J, T. morosa (CASIZ 142786; 35 mm preserved), scale bar = 20 Mm.

Figure 6. Photographs of living animals: A, Roboastra luteolineata, Papua New Guinea (photo T.M. Gosliner). B, R. tigris, Mar de Cortés (photo H. Debelius). C1, R. europaea, Carroñera, Spain (light form) (photo L. Tocino). C2, R. europaea, Tarifa, Spain (black form) (photo T.M. Gosliner. D, R. caboverdensis, Cape Verde (photo P. Wirtz). E, R. leonis sp. nov., the Galápagos Islands (photo T.M. Gosliner).

Figure 7. Scanning electron micrographs of the radula. A, right half of the radula, Roboastra luteolineata (CASIZ 115739), scale bar = 300 Mm. B, innermost lateral teeth, R. luteolineata (CASIZ 086319), scale bar = 30 Mm. C, left half of the radula, R. tigris (CASIZ 057321), scale bar = 300 Mm. D, outermost lateral teeth, R. tigris (CASIZ 068357), scale bar = 90 Mm. E, innermost lateral teeth, R. europaea (CASIZ 166053); white lines indicate the bifid upper cusp of some inner teeth, scale bar = 200 Mm. F, right half of the radula, R. caboverdensis (MNCN 15.05/46614), scale bar = 300 Mm. G, innermost lateral teeth, R. caboverdensis (MNCN 15.05/46614), scale bar = 90 Mm. H, right half of the radula, R. leonis sp. nov. (CASIZ 097577), scale bar = 300 Mm.