Gymnobela engonia 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 : 1446-1448

Gymnobela engonia Verrill, 1884 (PSH G2)

( Figures 3 C-H, 8 I, 6B)

Pleurotomella engonia ( Verrill, 1884) – Verrill 1884, p. 157– 158 Holotype. North-western Atlantic Ocean , United States, SE of Nantucket Shoals, Massachusetts 2041 (39.3806°N, − 68.4167°W), Station no . 2041, 2941 m, Research Vessel ( RV) Albatross, United States Fish Commission , 30 July 1883, Smithsonian National Museum of Natural History ( USNM 34835 ) .

Material examined

Australia, New South Wales, Jervis CMR (35.114°S, 151.469°E), station IN2017_ V03 _053, 3952–4011 m, 1 wet (= ethanol preserved specimen) ( AMS C.482286); off Byron Bay (28.371°S, 154.649°E), IN2017_ V03 _099, 3825– 3754 m, 1 wet ( AMS C.482287); AIOT, Territory of Christmas Island, Christmas Island SE (10.556°S, 105.764°E), IN2021_ V04 _007, 3200–3345 m, 1 wet ( AMS C.593510), 1 wet ( AMS C.571816); Cocos (Keeling) Islands Territory, Muirfield Seamount (13.437°S, 96.305°E), IN2022_ V08 _183, 3948–4047 m, 1 wet ( AMS C.594980) .

Distribution

Atlantic Ocean, E Indian Ocean, off Cocos and Christmas Islands ; SW Pacific Ocean, off the New South Wales ( NSW) coast ( Australia) .

Remarks

The holotype ( Figure 3C ) was described without mention of its radular morphology ( Verrill 1884, p. 157). Bouchet and Warén (1980) studied relatively abundant East Atlantic material of the species, figuring a shell ( Figure 8I ; Bouchet and Warén 1980, fig. 123) and a hypodermic tooth ( Bouchet and Warén 1980, fig. 26), whose details were utilised by Criscione et al. (2021b) as an example of typical radular morphology of the genus.

We provide below some anatomical details of one of the samples studied here (AMS C.482286): animal white. Hypodermic teeth large, straight, tightly rolled; approximately 170 µm in length; unbarbed; adapical opening long; ventral side forming blade approximately 1/5 of length of tooth; base moderately wide, angular, with lateral process, texture rugose; basal opening large, subcircular. Ligament long, rather broad.

The shell of G. engonia is very similar to that of G. agassizi , G. agasizzi and G. verecunda , but differs by possessing fewer spiral ribs. While their essential conchological similarity with the holotype of G. engonia strongly supports the attribution of the samples studied here to this species, no molecular data on Atlantic populations are available. The transoceanic distribution of this taxon is hence treated here as tentative [see for instance Theta lyronuclea ( Clarke, 1959) (in Criscione et al. 2021)].

Figures

Figure 3. Shells of Gymnobela primary species hypotheses (PSHs)/species studied herein. (A) G1/ G. agassizi (Verrill and Smith, 1880), Australian Museum (AMS) C.519355; (B) G. agassizii (Verrill and S. Smith, 1880), holotype UNSM 37828; (C) G. engonia (Verrill, 1884), holotype Smithsonian National Museum of Natural History (USNM) 3483; (D) G2/G. engonia AMS C.594980; (E) G2/G. engonia AMS C.593510; (F) G2/G. engonia AMS C.482287; (G) G2/G. engonia AMS C.482286; (H) G2/G. engonia AMS C.571816. Scale bar: A–D, F–H = 10 mm; E = 5 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.