Edentellina australis, (Burn, 1960)

EdenTellina australis (Burn, 1960)

( Figs 4J, K, 5E, F, 15–17)

Midorigai australis Burn 1960b: 46 View in CoL , figs 8–14. Type locality: Torquay , Victoria, Australia.

Type material

Midorigai australis , holotype, complete specimen, valves separated, damaged, 4 mm long ( MV F21193).

Additional material examined

Portsea , Victoria, Australia, date unknown, one valve 2.5 mm long ( MV F215277 ) . Pickering Point area , Warrnambool, Victoria, Australia, 23 February 2011, one specimen 2 mm long (shell) ( MV F188699 ) . Duton Way , Portland Bay, Victoria, Australia, 17 February 2012, one specimen 4.1 mm long (shell), isolate JC18 ( MV F194029 ) . Kity Miller Bay , Phillip Island, Victoria, Australia, 13 February 2008, two specimens 1.9–3 mm long (shell) ( MV F158625 ) .

Description

Body elongate, ≤ 5.6 mm in length, completely retractable inside of shell. Body colour pale to dark green, with numerous minute white speckles throughout ( Fig. 5E, F). Head elongate, with eye spots located on dorsal swelling near centre, surrounded by white pigment. Rhinophores enrolled, green, with small white speckles forming two rings. Oral tentacles short, green, with white speckles at base. Foot lighter than rest of animal, with small spots along edge. Mantle visible through shell, dark green, covered with large, whitish-beige patches, variable in size; edge surrounded by alternating opaque white patches composed of densely arranged speckles. Foot not extending to posterior end of shell, forming small triangular projection.

Shell up to 4 mm × 2.6 mm in size, tallest point near anterior margin, widest point near ventral margin; shell shape ovoid to quadrangular, dorsal margin regularly curved with distinct apex, ventral margin more flatened; anterior margin convex, irregularly curved, slightly more flatened dorsally, posterior margin shorter, narrowing gradually ( Fig. 15E, F). Protoconch on lef valve of teleoconch, not observed. Hinge on dorsal margin of shell, formed by flatened, corrugated, nearly straight area, margin on both valves; no distinct condyloid tooth on right valve, but elongate protuberance at posterior end of hinge; triangular, fossete-like hinge socket on lef valve, at posterior end of hinge ( Fig. 15G, H). Shell translucent, with no visible markings or spots on shell surface, and sof parts of body visible through it ( Fig. 15A–D).

Adductor muscle located in line with highest point of shell, slightly below widest point ( Fig. 16A), connected to narrow and elongate head retractor muscle. Adductor scar visible on shell ( Fig. 15F). Gill large, occupying almost height of body, posterior to adductor muscle, covering anterior portion of digestive gland. Anterior half of body in preserved specimens with penis visible above adductor muscle ( Fig. 16B). Penis elongate; distal end pointed, with very elongated, hollow stylet ( Fig. 16D); proximal end of penis wider, with two strong retractor muscles atached and long, tubular deferent duct ( Fig. 16C). A single, reduced pharyngeal appendage observed, connected to the dorsal side of the pharyngeal bulb ( Fig. 16E).

Radula with 35 teeth in descending limb and 6 fully formed teeth + 1 ghost tooth in ascending limb, in 4.1-mm-long specimen from Victoria, Australia ( MV F194029 ) ( Fig. 17A). Active tooth ~260 μm long, with sharp, pointed tip; blade elongate, with central row of numerous long, delicate denticles; base short, slightly curved; juvenile teeth bicuspid ( Fig. 17B). Ascus containing one long, rod-shaped pre-radular tooth and three (possibly four) intermediate teeth ( Fig. 17C) .

Biology

Tis species feeds on Caulerpa simpliciuscula (R. Brown ex Turner) C. Agardh, 1823 (Burn 1989). According to Wisely (1962), E. australis produces egg masses with 50– 52 eggs and operculate veligers with shells 116–118 µm in diameter that hatch afer 11–13 days.

Range

Victoria, Australia ( Burn 1960a, b; present paper), Tasmania and South Australia ( Burn 2006).

Remarks

Burn (1960a) reported finding the first living specimens of Edentellina typica Gatliff & Gabriel, 1911 , in Torquay, Victoria, Australia. Burn (1960a) also reported collecting a second species of bivalved gastropod that ‘undoubtedly’ belonged to a different genus in the same group. In a second paper the same year, Burn (1960b) redescribed E. typica and transferred it to Berthelinia . In addition, Burn (1960b) introduced the new name Midorigai australis Burn, 1960 for the second species mentioned in the previous paper. Burn (1960b) described the live animals of M. australis as dark green, with large yellowish patches on the rhinophores and the rest of the body, including the mantle, which is densely spoted with large, rounded, yellowish-cream patches and has square-shaped yellow patches along the edges. Burn (1960b) described the shell as translucent olive-green with darker rays of green, squarer than in Berthelinia , with the lef valve more convex and higher than the right valve, hinge with no teeth.

For this paper, we have studied several specimens collected in Philip Island, Victoria, Australia (~ 75 km east of Torquay), characterized by having a green body colour with numerous, large, rounded yellowish-green to opaque white spots, larger on the mantle. We obtained nuclear DNA sequence data for two of them. We also examined the holotype of M. australis ( Fig. 4J, K), but it is too damaged to draw any conclusions. Tese animals match the original description of M. australis and are here regarded as members of this species. Both the five-gene sequence data and the geometric morphometrics analyses confirm that these animals belong in the genus Edentellina , but are genetically distinct from all other species. Tus, we regard M. australis as a distinct and valid species of Edentellina .