Cheirodonta dupliniana (Olsson, 1916) Fernandes & Pimenta, 2019

Fernandes, Maurício Romulo & Pimenta, Alexandre Dias, 2019, Basic anatomy of species of Triphoridae (Gastropoda, Triphoroidea) from Brazil, European Journal of Taxonomy 517, pp. 1-60 : 12-15

Cheirodonta dupliniana (Olsson, 1916) comb. nov.

Figs 5–6

Cheirodonta mizifio Fernandes & Pimenta, 2015 ; see Fernandes & Pimenta in prep. for synonymy.

Material examined

USA • [1, d] spec.; Georgia; 30°54´18″ N, 80°36´12″ W; 35 m depth; 4 Sep. 1980; RV Bagby leg.; USNM 1438722 .

Description of basic anatomy

OPERCULUM. Ovate-elliptical, thin, semi-transparent, membranous, poorly distinct whorls, nucleus subcentral, dislocated 22% from center toward margin.

JAW. Wing-shaped; outer side with scales rectangular/squared, rectangular-bilobed, acute-lanceolate or puzzle-like; rectangular scales 9.0– 10.3 µm long, 5.2–6.1 µm wide, ratio length/width 1.6–1.9, rectangular-bilobed scales 9.9–10.3 µm long, 4.6–5.2 µm wide, ratio length/width 2.0–2.2, acutelanceolate scales 16.7–18.1 µm long, 5.6–6.7 µm wide, ratio length/width 2.6–3.2, puzzle-like scales 12.9–15.6 µm long (largest lobe to largest lobe), 5.6–9.9 µm wide (perpendicular to the length at the center of scale), ratio length/width 1.4–2.8.

RADULA. Formula 8-1-1-1-8; central tooth usually with seven cusps, median one (cusp 4) is the smallest or even absent, cusps 1, 3, 5 and 7 medium-sized, cusps 2 and 6 considerably broader and robust (1.9– 3.0× longer than cusp 4); lateral teeth with seven main cusps, all with similar length, and an additional small one (cusp 1); M1 with eight to nine cusps, with an increasing length from cusp 1 to cusp 7 (or cusp 8, when nine cusps are present), the latter usually being very elongated, up to 1.7× longer than median cusps, and with a filiform distal half (cusp 6 or 7 may also have a filiform elongation); remaining marginal teeth hand-like, with a long basal plate, usually with nine or ten cusps, also increasing in size from cusp 1 to cusps 7 (or 8) and 8 (or 9), the latter cusps usually having a filiform elongation in the distal half, up to 2.3× longer than median cusps; central tooth 4.9–5.0 µm wide, lateral teeth 4.1–4.6 µm wide, M1 4.1–4.9 µm wide, M2 usually 5.4 µm wide, M3 4.8–5.3 µm wide, outer marginal teeth 5.2–5.4 µm wide.

Remarks

The operculum of C. dupliniana comb. nov. agrees with that of the type species C. pallescens (described in Bouchet 1985). Its radula has a superficial resemblance with the description of C. pallescens by Bouchet & Guillemot (1978) and Bouchet (1985), despite significant differences: C. dupliniana comb. nov. has more marginal teeth (eight, instead of five or six), a completely different central tooth (seven cusps with varied sizes, instead of six to eight homogeneous cusps separated in two groups of three or four cusps by an internal diastema), lateral teeth with seven main cusps plus a smaller one (instead of six cusps in Bouchet 1985 – but seven or eight cusps were similarly indicated in Bouchet & Guillemot 1978), and marginal teeth hand-like with a maximum of 10 long cusps distributed along their length (instead of ‘broad spoon-like’ teeth with 12 to 20 cusps concentrated in the rounded end of teeth in C. pallescens ).

There are significant differences in the illustrated radulae of C. pallescens from French material (based on specimens from the eastern Atlantic and Mediterranean) described by Bouchet & Guillemot (1978: fig. 19) and Bouchet (1985: figs 10–11), especially regarding the central and lateral teeth. More differences emerge when considering the drawn radula of specimens from southern England by Fretter (1951), bearing lateral teeth with nine cusps and marginal teeth with much longer cusps than those illustrated by Bouchet, in addition to a presumably different axis orientation of marginal teeth (downward instead of sideward). With the current limited amount of information, it is uncertain whether C. pallescens represents a single species with a variable radular morphology, or whether the Mediterranean population and perhaps also the population from England constitute one or two new species. The morphology of the central and marginal teeth of specimens from France (especially from Mediterranean) is slightly similar to that of Sagenotriphora osclausum ( Rolán & Fernández-Garcés, 1995) (see below), in spite of consistent differences mainly related to the lateral teeth. Considering only species from the Atlantic, both genera show similarities in shell (e.g., supranumerical cords, smooth subperipheral and basal cords, similar protoconch sculpture) and radula, as herein indicated. They may be proved to be phylogenetically close after a comprehensive phylogeny.

The radula of the southwestern Pacific species Cheirodonta labiata (A. Adams, 1854) , described and illustrated by Marshall (1983), is much similar to that of C. dupliniana comb. nov. They have the same number of marginal teeth (eight), a similar number of cusps and dimensions of the central tooth ( C. dupliniana comb. nov. usually with seven heterogeneous cusps, 5.0 µm wide; C. labiata with seven to nine heterogeneous cusps, 6.8 µm wide), idem for lateral teeth (both usually with eight cusps; 4.1–4.6 µm wide in C. dupliniana comb. nov., 6.8 µm wide in C. labiata ) and marginal teeth (M1–M3 with eight to ten cusps in C. dupliniana comb. nov., 4.1–5.4 µm wide; M1–M3 with eight to nine cusps in C. labiata , about 5.0 µm wide). In this sense, the radula of C. dupliniana comb. nov. is much more similar to C. labiata than to C. pallescens , despite the opposite can be affirmed to shell features.

Radulae of Caribbean species of Nanaphora Laseron, 1958 illustrated in Rolán & Fernández-Garcés (1994), at that time under the name Cheirodonta , are also superficially similar to those of C. dupliniana comb. nov., particularly regarding the elongation of the basal plate of marginal teeth. Another species of Nanaphora from the Pacific was already indicated as similar to Cheirodonta in terms of marginal tooth morphology ( Marshall 1983). However, shell and operculum are consistently different between both genera ( Marshall 1983; Fernandes & Pimenta 2015). Phylogenetic hypotheses will reveal whether these genera are analogous in radular morphology owing to feeding on similar sponge hosts, or whether they share a common and recent ancestral lineage.

Figures

Fig. 5. Cheirodonta dupliniana (Olsson, 1916) comb. nov. A–E. USNM 1438722. A–D. Jaw, outer side. E. Operculum. Scale bars: A = 50 µm; B, D = 10 µm; C = 5 µm; E = 100 µm.

Fig. 6. Cheirodonta dupliniana (Olsson, 1916) comb. nov. A–D. Radula (USNM 1438722). Scale bars: A–B, D = 5 µm; C = 10 µm.