. https://doi.org/10.24199/j.mmv.1974.35.06 18 February 1974 DESCRIPTION OF RETUSA CHRYSOMA BURN SP. NOV. (OPISTHOBRANCHIA) AND ITS FOOD RESOURCES FROM CORNER INLET, VICTORIA By Robert Burn and K. N. Bell Honorary Associates, National Museum of Victoria, Melbourne Abstract Retusa chrysoma Burn sp. nov. is described from Corner Inlet, Victoria, and compared with other species reported from the Victorian coastline. Gizzard contents show selective food preferences for foraminifera and juveniles of the air breathing gastropod Salinator fragilis (Lamarck, 1822). Introduction rounded anteriorly, obliquely truncate pos- teriorly. Colour pale yellow, thin periostracum Little is known anatomically of the shell- golden yellow. Sculpture, faint growth lines at bearing opisthobranch molluscs of Victoria. anterior end develop into raised riblets on Similarly, little is known of their food resources posterior third, riblets passing obliquely over and selective preferences. Foraminifera are shoulder into vertex; encircled by fine, vari- believed to form wholly or part of the food of ably spaced, wavy lines, less noticeable pos- several species of retusid opisthobranchs teriorly where the riblets are strongest. Aper- (Bacescu and Caraion 1956, Marcus and ture anteriorly pyriform, medially narrow and Marcus 1969, Moore 1961, Morton 1958, slightly constricted, posteriorly rising above the Rudman 1971), but the overall part they play last whorl and inclined towards the axis. in the marine food-energy cycle is poorly Columella thickened, with a nearly vertical known (Lipps and Valentine 1970). plait rising at mid-length, with a broad reflex- In order to study Australian species/food ion behind the plait. Spire deeply sunk, resources, we have examined a new species of shoulder of the preceding whorl visible, sculp- Retusa collected by one of us (K.N.B.) at tured by oblique riblets descending to a large, Corner Inlet, Victoria. The description of smooth, papillary protoconch. Dimensions Retusa chrysoma has been prepared by the (length x breadth): Holotype 3 06 x 1425 first author (R.B.), the analysis of the food mm, largest paratype 3 x L5 mm, smallest resources by the second author (K.N.B.) paratype 1-425 x 0-78 mm, figured specimen The type series of Retusa chrysoma and a (dry shell) 27 x 1-3 mm. series of foraminiferans from the gizzard con- Animal cream; head quadrate, broader than tents, mounted on slides, have been presented long, with a pair of broad, thin lobes poster- to the National Museum of Victoria, Mel- iorly; yellowish Hancock's organs in furrow bourne. The first author (R.B.) expresses his between head and foot and close to mouth, gratitude to the Science and Industry Endow- strongly developed, thickened, harder than the ment Fund, C.S.I.R.O., for continued support surrounding skin, each with 3 or 4 shallow of this and other research on Australian opis- transverse folds; foot short, rounded anteriorly, thobranch molluscs. truncate posteriorly. Gastral plates (Fig. 2) Systematic Description with many dark tubercles of various sizes, Order Cephalaspidea tubercles largest and highest posteriorly; smaller Superfamily Bullacea largest plate convex on inner face, Family Retusidae plates concave. Male copulatory organ (Fig. oesophagus; atrium long, Retusa chrysoma Burn sp. nov. 3) on right side of Figures 1-3 dilated entally with folded walls, ciliated seminal groove to opening of elongate seminal Description. Shell (Fig. 1) small, cylindrical, 115 — 116 ROBERT BURN AND K. N. BELL 1 prostate gland seminal vesicle atrium seminal groove Figs. 1-3 Retusa ckiysoma Burn sp. nov Shell. 1, 2, Gastral plates. 3, Male copulatory organ. (Figs. 2-3 drawn to same scale) aUaChe t0 f VeSSd Plate dress in reference to ,° ' ' ^ the colour vesicvesicle'lc prostrate h , ^ , SSSS Z?gland shorter lthan vesicle, of the shell h ^'^ Dis !*' <™si™ The authors wholeheartedly agree and w7thwith short papilla»5J?i? mT^TV*?penial sheath. with Valentine's comment (1965 Matenal exanunecL p 42) that From Zostera and mud "The forms of Cylichnina ieLLa) living y int fCef at E Cnd in SE - Australia ' - merit of Rhm- P ^ v ? ^° rev e'w" Examinadon f ^S °f d sMs from colle ^ dSnt concettotfd by K'K. l*tN. Bell,!% ? I?# ? ^ ^ 11 T\April 1971, seven localities lead us to believe that little ran h P specimens (NMV F27490); 1 April 1972, achieved ^ by this metho ye h herto ^11 F2 488 ^ AUStraHan rCC°rdS f retUSids efe ° -d rlThe speci- 2M TmTX op.sthobranchs have - been mens S — " basedt^M.uw»J. uponUUUI1 VlC-dVldead were obtained by sieving the top 1 cm shells. The small of amount of material collected the substrate at mid-tide level. Other opis- alive that we have so thobranchs far examined suggests inhabiting the same biotope were that the animal has much importance Tornatina cf. apicina for (Gould,v '"' ' 1859)m^j, mmand separating r , one species from the r sp next, and that s edcs - s;™"z;, (0ry ^aimard, ? S'Sssr'aS?1833) ^rr^hIn dealing with retusids of SE. Australia, we (Atyid-ie) Rudman etymology.Etymolovv UxrysomaCkrvsomn CV u w ? (1971, p. 192) in allocating Gk. = a gold object, those species with tubercles on the gastral ) DESCRIPTION OF RETUSA CHRYSOMA 117 plates to Retusa Brown, 1827, and those with shell, the gizzard was dissected out, and the smooth gastral plates to Relichna Rudman, contents removed. 1971. The type species of Cylichnina Monte- To see if any selection for food had occurred rosato, 1884, umbilicata (Montagu, 1804), a sample of the sediment of the biotope was has tuberculate gastral plates (Pilsbry, 1893, collected and placed in 70% alcohol. This pre- p. 204, pi. 60, fig. 8) and is no longer held sample was later washed to remove any separate from Retusa (Lemche, 1948, p. 50). servative, placed in rose Bengal stain (1 g/1 Cylichnina must therefore be expunged from solution) for one hour, washed and dried. Australian faunal lists and replaced by Foraminifera were concentrated by flotation in Retusa. carbon tetrachloride. The rose Bengal stains There are only four species of Retusa re- the protoplasm of living specimens a deep red ported from the Victorian coastline (Mac- (Walton 1952). pherson and Gabriel 1962, p. 243). R. amphi- Results zosta (Watson, 1886) was recorded from Portsea by Gatliff and Gabriel (1908, p. 384). The gizzard contents of 11 specimens of Hedley (1914, p. 753) suggested their speci- R. chrysoma consisted of 43 specimens of mens might be his R. iredaleana (1914, p. foraminifera belonging to six species (Table 1 752). After study of a British Museum (Nat- and nine specimens of juveniles of Salinator ural History) photograph of one of the three fragilis (Lamarck, 1822). Also present were syntypes of Bulla {Cylichna) pygmaea A. 17 chitinous opercula which appear to be Adams, 1854, from Port Lincoln, S. Aust., we identical with the operculum of S. fragilis. are inclined to think that R. iredaleana from Table 2 shows the contents of each specimen Middle Harbour, Sydney Harbour, N.S.W., of R. chrysoma. From the sediment sample 15 and Gatliff and Gabriel's specimens are refer- species of living foraminifera were recovered able to R. pygmaea. Cylichnina atkinsoni (Table 3). (Tenison Woods, 1875) has tuberculate Although the number of specimens studied gastral plates (personal observations) and must is small, there is evidence for selection in their be transferred to Retusa The C. pygmaea of food intake. This is most clearly seen with Macpherson and Gabriel (1962, p. 243) may Quinquiloculina seminula which constitutes refer to another, apparently new, species of only 7 5% of the foraminiferal fauna but 28% Retusa that we have from Port Phillip Bay and of the foraminiferal food intake. The higher Shallow Inlet, Vict. It differs from true R. percentages of the food intake of Elphidium pygmaea in the narrower shape of the shell simplex, E. advenum depressulum and Am- and greater inclination of the posterior lip of monia aoteanus may not be significant con- the aperture. R. sculpta (Gatliff and Gabriel, sidering the small numbers involved. The lack jugosa as 1913) has both spiral and axial sculpture, and of any specimens of Q. seminula against this may be a juvenile form. food shows a definite selection foraminiferal The new species, R. chrysoma, is distin- species. The lack of other guished from each of the above species by the TABLE 1 riblets of the posterior third of the shell and Foraminifera in the gizzard of R. chrysoma the fine wavy spiral lines on the remainder of % in the surface. From species for which the animal No. of sediment the density is known, R. chrysoma differs in Foraminiferan Specimens % sample of the tubercles on the gastral plates. A mmotium salsum 18 42 62 Quinquiloculina seminula 12 28 7.5 Gizzard Contents Elphidium simplex 5 12 4 E. advenum depressulum 4 9 6 of Retusa chrysoma Burn Live specimens Ammonia aoteanus 3 7.5 2.5 were collected and preserved in 70% alcohol Brizalina cacozela 1 2.5 7.5 for later study. After carefully fracturing each 18 ROBERT BURN AND K. N. BELL TABLE 2 Number of Foraminifera and Mollusca in R. chrysoma Specimens Gizzard contents abcdefghjkl Total A. salsurn 14 116 12 11 18 Q. seminula 12 5 13 12 E. simplex 12 11 5 E. advenum depressulum 2 1 14 A . aoteanus ' B. cacozela I J Salinator fragilis 11 2 1 2 119 Opercula 2 2 2 16 4 17 Total 4 14 7 species is most likely due to their normal in- expected from the crushing of arenaceous frcquency in the sediment. foraminifera. This indicates that the food is More evidence of food selection is shown obtained by dissolving of the foraminiferal by the presence of Salinator jragilis.