Gymnobela Verrill, 1884

Criscione, Francesco & Hallan, Anders, 2024, Integrative taxonomy of Gymnobela and Pontiothauma (Conoidea: Raphitomidae) from Australian waters provides more evidence of transoceanic distribution in deep-sea gastropods, Journal of Natural History 58 (37 - 40), pp. 1429-1459 : 1444-1445

Genus Gymnobela Verrill, 1884

Type species: Gymnobela engonia , 1884 by subsequent designation, Cossmann (1896, p. 63).

Diagnosis

Shell biconical to biconical-fusiform, moderately thick. Protoconch multispiral, with diagonally cancellate sculpture. Teleoconch white or cream (with or without pale orange bands), suture impressed. Whorl profile moderately to very broad, with wide, oblique subsutural ramp, clearly demarcated from whorl periphery. Lower portion of whorl convex or subcylindrical. Subsutural ramp sculpture of dense arcuate growth lines, reflecting shape of anal sinus. Teleoconch axial sculpture of strongly prosocline ribs below subsutural ramp; spiral sculpture of fine, sometimes flattened cords or shallow grooves; microsculpture of growth lines. Last adult whorl markedly shouldered to rather convex, clearly to very clearly demarcated from rather straight, subcylindrical siphonal canal. Aperture elongated, from about 2/5 to half of total shell length; outer lip thin, unsculptured. Inner lip with distinct whitish callus, with or without orange vertical band. Anal sinus wide, moderately deep to deep, L-shaped.

Animal white or pale blue. Cephalic tentacles cylindrical, blunt, eyes very small; penis large, rather long, coiling clockwise. Venom apparatus: proboscis long, coiled; venom gland long to very long, convoluted; muscular bulb moderate to large, elongated to elongate-ovate, pearlescent.

Radular teeth hypodermic, relatively straight, tightly rolled; approximately 150 µm in length; ventral barb absent, adapical opening long; ventral blade approximately 1/5 of length of tooth; base wide, angular, with lateral process; basal opening large, subcircular, unrestricted. Ligament rather long, broad.

Remarks

This study adopts the concept of Gymnobela , delimited by Criscione et al. (2021b) as a genus-level clade strongly supported by molecular data, whose members share the following combination of morpho-anatomical characters: (a) a broadly biconical to biconical-fusiform shell with angulate whorl profile; (b) shell sculpture of axial ribs more prominent than spirals; (c) subsutural ramp sculpture of dense arcuate riblets; and (d) straight, unbarbed hypodermic teeth with a ventral blade. Our results indicate that, along with the type species G. engonia , these features are shared by G. angulosa , G. frielei and G. agassizi , thus supporting their inclusion in Gymnobela . Unlike these four, none of the remaining 65 currently accepted Gymnobela species can be studied via an integrative taxonomy approach, due to the absence of molecular data and generally insufficient morpho-anatomical evidence. However, for some of these species, the information, extracted from the literature and photographs, allowed us to (at least) test for presence/absence of the aforementioned typical Gymnobela shell and radular features and to revise their generic placement. Along with the three species mentioned above, nine further species exhibited typical Gymnobela shells and (when studied) radulae: namely, G. abyssorum (Locard, 1897) (shell – Figure 8C ; radula – Bouchet 1990, fig. 19), G. bairdii Verrill and Smith, 1884 ( Figure 8A ), G. chyta ( Watson, 1881) ( Figure 8D ), G. glaucocreas ( Barnard, 1963) ( Figure 4G ), G. granulisculpturata Sysoev, 1990 ( Figure 8E ), G. laticaudata Sysoev, 1990 ( Figure 8H ), G. mitrodeta Sysoev, 1997 (shell – Figure 8G ; radula – Sysoev 1997, fig. 19), G. rotundata Sysoev, 1990 ( Figure 8B ) and G. verecunda ( Barnard, 1963) (shell – Figure 8F ; radula – Barnard 1963, Figure 2e ). Sixteen species, currently assigned to Gymnobela , did not possess one or more of its typical features but instead showed typical combined characters of other raphitomid genera, to which they are therefore formally re-assigned. A large elongate-fusiform shell with axial opisthocline ribs (usually weak and/or confined to early whorls), typical of Spergo (Criscione, Hallan, Fedosov, et al. 2021) is possessed by: S. africana ( Sysoev, 1996) comb. n. ( Figure 9A ), and S. bululi (Stahlschmidt, Poppe and Tagaro, 2018) comb. n. ( Figure 9B ). In addition to a similar shell, S. oculifera ( Kantor and Sysoev, 1986) comb. n. ( Figure 9C ) also has typical Spergo hypodermic teeth with no barbs or blades ( Kantor and Sysoev 1986, fig. 2a). This latter species is also an earlier synonym of S. tenuiconcha Criscione, Hallan, Puillandre and Fedosov, 2020 (Criscione et al. 2021, Figure 11B). A fusiform ribbed shell, typical of Austrobela (Criscione et al. 2021) , is shown by A. gypsata ( Watson, 1881) comb. n. ( Figure 9G ) and A. fulvotincta (Dautzenberg and Fischer, 1896) comb. n. ( Figure 9D ), which also exhibit the double-barbed hypodermic teeth characteristic of the genus ( Bouchet and Warén 1980, fig. 24). A broadly fusiform shell with axial sculpture (often limited to the whorl upper portion) and double-barbed hypodermic teeth, that are typical of Theta Clarke, 1959 , are shared by T. chrysopelex ( Barnard, 1963) comb. n. (shell – Figure 9E , radula – Barnard 1963, fig. 3g), T. homeotata ( Watson, 1886) comb. n. (shell – Figure 9F , radula – Bouchet and Warén 1980, fig. 18) and T. latistriata ( Kantor and Sysoev, 1986) comb. n. (shell – Figure 9H , radula – Kantor and Sysoev 1986, fig. 2b). While its radula is unknown, T. camerunensis ( Thiele, 1925) comb. n. also exhibits a typical shell for the genus Theta ( Thiele 1925, pl. 28, fig. 20). Five species exhibit a small shell with a tuberculate girdle and a moniliform subsutural fold, which is typical of the fossil type species of Mioawateria Vella, 1953 , M. personata ( Powell, 1942) ( Figure 10A ). Therefore, M. blakeana ( Dall, 1881) comb. n. ( Figure 10B ), M. brachis ( Dall, 1919) comb. n. ( Figure 10C ), M. clara Thiele, 1925 comb. n. ( Thiele 1925, pl. 29, fig. 11), M. erronea Thiele, 1925 comb. n. ( Thiele 1925, pl. 29, fig. 11) and M. isogonia ( Dall, 1908) comb. n. ( Figure 10C ) are assigned to this genus. Most of the remaining 41 species do not possess morpho-anatomica l features characteristic of Gymnobela , and their current placement in this genus appears untenable. However, a revision of their generic placement is presently not feasible, due to the scarcity of freshly collected topotypical material and the tentative status of raphitomid genus-level taxonomy.

Figures

Figure 2. Maximum likelihood (ML, left) tree and Bayesian consensus phylogram (BI, right) based on analyses of the concatenated sequence dataset. Numbers above branches indicate nodal support by Bayesian posterior probabilities (BPP) and ML bootstrap (BS). BPP values of 1 and BS values of 100% are represented by asterisks. Sequences of samples collected outside Australian waters are underlined. Samples whose shells are figured (scale bar = 10 mm) are in bold. The shell image of P1 has been digitally edited (grey area) to simulate an intact spire. Vertical bars mark distinct primary species hypotheses (PSHs) as delimited by the Automatic Barcode Gap Discovery (ABGD) method.

Figure 4. Shells of Gymnobela primary species hypotheses (PSHs)/species studied herein. (A) G. frielei (Verril, 1885), holotype Smithsonian National Museum of Natural History (USNM) 44653; (B) G4/ G. frielei Australian Museum (AMS) C.571666; (C) G4/G. frielei AMS C.571702; (D) G4/G. frielei AMS C.482314; (E) G4/G. frielei AMS C.571812; (F) G4/G. frielei AMS C.571677;(G) G4/G. glaucocreas (Barnard, 1963), holotype Iziko South African Museum (ISAM) A9821; (H) G3/G. angulosa Sysoev, 1988, holotype Zoological Museum of Moscow University (ZMMU) Lc-22363 (I) G3/G. angulosa AMS C.571649; (J) G3/ G. angulosa AMS C.571648; (K) G3/G. angulosa, Bavarian State Collection of Zoology (ZSM) mol 20070770. Scale bar = 10 mm.

Figure 8. Shells of Gymnobela species vouchers. (A) G. bairdii (Verrill and Smith, 1884), syntype Smithsonian National Museum of Natural History (UNSM) 37824; (B) G. rotundata Sysoev, 1990, holotype Zoological Museum of Moscow University (ZMMU) Lc 5718; (C) G. abyssorum (Locard, 1897), lectotype Muséum National d’Histoire Naturelle (MNHN) IM-2000-2750; (D) G. chyta (Watson, 1881), holotype Natural History Museum of the United Kingdom (NHMUK) 1887.2.9.1108; (E) G. granulisculpturata Sysoev, 1990, holotype ZMMU Lc 5725; (F) G. verecunda (Barnard, 1963), lectotype ISAM A9697; (G) G. mitrodeta Sysoev, 1997, holotype MNHN IM-2000-3121; (H) G. laticaudata Sysoev, 1990, holotype ZMMU Lc 5735; (I) G. engonia figured in Bouchet and Warén 1980 (fig. 123). Scale bar: A, C, F–G, I = 10 mm; B, H = 3.3 mm; D–E = 5 mm.

Figure 9. Shells of deep-sea raphitomid species previously assigned to Gymnobela. (A) Spergo africana (Sysoev, 1996) comb. n., holotype Natural History Museum of the United Kingdom (NHMUK) 1993114; (B) Spergo bululi (Stahlschmidt, Poppe and Tagaro, 2018) comb. n., holotype Muséum National d’Histoire Naturelle (MNHN) IM-2000-30,406; (C) Spergo oculifera (Kantor and Sysoev, 1986) comb. n., holotype Zoological Museum of Moscow University (ZMMU) Lc 22338; (D) Austrobela fulvotincta (Dautzenberg and Fischer, 1896) comb. n., syntype Musée océanographique de Monaco (MOM) INV- 18461; (E) Theta chrysopelex (Barnard, 1963) comb. n., holotype Iziko South African Museum ISAM A9857; (F) Theta homeotata (Watson, 1886) comb. n., holotype NHMUK 1887.2.9.1115; (G) Austrobela gypsata (Watson, 1881) comb. n., syntype NHMUK 1887.2.9.979–80; (H) Theta latistriata (Kantor and Sysoev, 1986) comb. n., holotype ZMMU Lc 22341. Scale bar = 10 mm.

Figure 10. Shells of Mioawateria species. (A) Mioawateria personata (Powell, 1942) holotype Institute of Geological and Nuclear Sciences Limited (GNS) TM3761; (B) Mioawateria blakeana (Dall, 1881) comb. n., Smithsonian National Museum of Natural History (USNM) 87427; (C) Mioawateria brachis (Dall, 1919) comb. n., holotype USNM 96486; (D) Mioawateria isogonia (Dall, 1908) comb. n., holotype USNM 123112. Scale bar = 3 mm.