Edentellina typica, Gatliff & Gabriel, 1911

EdenTellina typica Gatliff & Gabriel, 1911

( Figs 4A, B, 5A, B, 6, 7)

Edentellina typica Gatliff and Gabriel 1911: 190 , pl. 46, figs 5, 6. Type locality: Portsea , Port Phillip, Victoria, Australia.

Type material

Edentellina typica , syntypes, right and lef valve (not from same specimen), ~ 2.5 mm long ( MV F515).

Additional material examined

Griffith Point , Central Bass Strait, Victoria, Australia, 26 January 2002, one specimen 2.2 mm long (shell) ( MV F91829 View Materials ) . Torquay , Victoria, Australia 21 February 1960, one specimen 4.5 mm long (shell) ( MV F21195 ) . Point Lonsdale , Victoria, Australia, date unknown, two specimens 2–2.5 mm long (shell) ( MV F21539 ) . Portsea , Victoria, Australia, date unknown, one valve 3.1 mm long ( MV F215276 ) .

Description

Body elongate, ≤ 6.1 mm in length, completely retractable inside of shell. Body colour pale green, with minute white speckles on dorsal side of head ( Fig. 5A, B). Head elongate, with eye spots located on dorsal swelling near centre, surrounded by white pigment. Rhinophores enrolled, green, with or without a few white speckles. Oral tentacles short, green. Foot lighter than rest of animal. Mantle visible through shell, pale green, with a few longitudinal light brown irregular lines, variable in size; edge surrounded by conspicuous, alternating cream patches composed of densely arranged speckles. Foot not extending beyond posterior end of shell.

Shell up to 4.5 mm × 3.4 mm in size, tallest point slightly anterior to centre, widest point near centre; shell shape ovoid, dorsal and ventral margins regularly curved; anterior margin convex, regularly curved, posterior margin narrowing gradually, also regularly curved ( Fig. 6C, D). Protoconch on lef valve of teleoconch, ~110 µm long, with 1.5 whorls ( Fig. 6D). Hinge on dorsal margin of shell, formed by flatened, corrugated, nearly straight area, margin on both valves; small, oval condyloid tooth on right valve at posterior end of hinge, and triangular, fossete-like hinge socket on lef valve, at posterior end of hinge ( Fig. 6E, F). Shell translucent, with no visible markings or spots on shell surface, sof parts of body visible through it ( Fig. 6A, B).

Adductor muscle located closer to anterior end of shell, slightly below widest point of shell ( Fig. 7), connected to narrow and elongate head retractor muscle. Adductor scar visible on shell ( Fig. 6D). Gill large, occupying almost height of body, posterior to adductor muscle, covering anterior portion of digestive gland. Penis not observed.

Radula with 19 teeth in descending limb and 5 fully formed teeth + 1 ghost tooth in ascending limb, in 2.5-mm-long specimen from Victoria, Australia ( MV F21539 ) ( Fig. 8A). Active tooth ~70 μm long, with bifid tip; blade elongate, lacking denticles; base short, slightly curved ( Fig. 8B). Ascus containing several disorganized elongate pre-radular teeth .

Biology

Jensen (1980) and Burn (1989) confirmed that E. typica feeds exclusively on the alga Caulerpa broonii (C. Agardh) Endlicher, 1843 .

Range

Temperate Australia: Victoria ( Gatliff and Gabriel 1911, Burn 2006; present paper), Tasmania ( Burn 2006), South Australia ( Burn 2006).

Remarks

Gatliff and Gabriel (1911) described Edentellina typica Gatliff & Gabriel, 1911 based on a right and lef valve of similar size, but not from the same specimen, collected in Victoria, Australia. Gatliff and Gabriel (1911) described the shells as translucent yellow, small, thin and fragile, fatened, broadly ovate, with the posterior side [anterior end] longer and broader, and hinge short, without teeth. Gatliff and Gabriel (1911) also reproduced photographs of the two valves from inner views, with the right valve having a protoconch atached. Tey also mentioned additional larger valves that were not included in the original description because of their poorer preservation, in addition to specimens of a second species from North Queensland, to be described by C. Hedley ( Gatliff and Gabriel 1911).

In 1911, Verco (1911) reported E. typica from South Australia that he described in more detail in 1916 ( Verco 1916). In the interim, Hedley (1912) commented on the original description of E. typica , suggesting that it might represent the internal shell of a sea slug, but if this animal were to be a bivalve, as suggested by Gatliff and Gabriel (1911), Edentellina could be a synonym of Ludovicia . Verco (1916) described several right and lef valves and one complete shell collected in Guichen Bay, South Australia and provided details on its protoconch and teleoconch morphology. Hedley (1920) described the specimens mentioned by Gatliff and Gabriel (1911) from North Queensland as the new species Edentellina corallensis Hedley, 1920 based on shells collected in Hope Island, and for comparison, illustrated the specimens of E. typica reported by Verco (1911, 1916). Hedley (1920) also provided an additional record for E. typica from King George Sound, Western Australia. Coton and Godfrey (1938) described the presence of an anterior tooth in the hinge of E. typica and suggested that the name Edentellina was inappropriate.

Subsequently, Burn (1960a) reported collecting specimens of E. typica alive in Torquay, Victoria, Australia, which he confirmed to be sacoglossans, probably congeneric with the recently described species from Japan, Tamanovalva limax Kawaguti & Baba, 1959 . Additionally, Burn (1960a) reported a second species of bivalved sacoglossan belonging to a different genus from the same area. In a second paper the same year, Burn (1960b) proposed the synonymy between the genera Tamanovalva and Edentellina and with the fossil genus Berthelinia . Burn (1960b) also suggested that T.limax and E.typica are synonyms of? Scintilla chloris Dall, 1918 , originally described from Baja California, Mexico, but not with the specimens identified as E. typica by Verco (1911, 1916) and illustrated by Hedley (1920). However, Burn (1960b) treated Berthelinia typica as a valid name (despite the fact that older names should have priority) and did not use the generic names consistently with his proposed synonymy. Moreover, Burn (1960b) listed several differences between B. typica and T. limax , although he re-emphasized that T. limax and B. typica are synonyms, and also synonyms of E. corallensis and? Scintilla chloris , arguing that this later species was larger but remarkably similar. Burn (1960b) provided a redescription of the shell and radula of B. typica based on the specimens collected in Torquay, and described the second species reported by Burn (1960a) as Midorigai australis Burn, 1960 . Baba (1961a) examined additional specimens from Japan and a paratype of M. australis sent by Burn. Baba (1961a) noted that this paratype belonged to a species different from M. australis because it had smooth radular teeth. Baba (1961a) listed some morphological differences between the shell and radula of Edentellina and Tamanovalva but indicated that these two genera could be synonyms of Berthelinia along with Ludovicia and Midorigai ; a synonymy that was later confirmed by Baba (1961b). Burn (1965) recognized that the paratype of M. australis sent to Baba for examination was a juvenile mistakenly placed in the paratype series of M. australis , and he now identified this specimen as belonging to the true E. typica . Burn (1965) also recognized that the specimens he previously identified as E. typica belonged to an undescribed species that he named Tamanovalva babai Burn, 1965 . Revising his previous assessment, Burn (1965) recognized E. corallensis and? Scintilla chloris as distinct species belonging to the genus Tamanovalva . According to Burn (1965), all three species of bivalved sacoglossans found in Victoria, Australia were easily distinguishable as follows: (i) E. typica has a uniformly green shell, with horizontal parallel black lines on the mantle and smooth and bifid radular teeth (lacking denticles); (ii) T. babai has a completely green shell and denticulate radular teeth; and (iii) M. australis has a green shell with numerous yellow patches, a mantle with yellow to cream-coloured large rounded spots, and denticulate radular teeth. Burn (1989, 2015) depicted all three species alive. Burn (1965) did not provide further clarification on the specimens reported by Verco (1911, 1916) or illustrated by Hedley (1920), but in 1966 ( Burn 1966) reported locating and re-examining those specimens. Based on their shell morphology, Burn (1966) suggested that they could constitute a third species, with characteristics intermediate between T. babai and E. typica .

In this study, we sequenced one specimen with the characteristic horizontal parallel black lines on the mantle described for this species, which was genetically distinct from all other species of Juliidae here examined. We also examined the syntypes of E. typica ( Fig. 4A, B) and several additional specimens from temperate Australia, which were morphologically similar. Terefore, we propose that E. typica is a distinct and valid species. Additionally, phylogenetic analyses place E. typica in the same clade as all other species previously assigned to Berthelinia . Based on geometric morphometrics analyses (see above), Berthelinia , which was described based on fossil shells, is distinct from Recent species. Terefore, Recent species, including E. typica , are here transferred to Edentellina , which is the oldest available name for this clade.