Enigmaticolus Fraussen, 2008: 75–77

Chen, Chong, Xu, Ting, Fraussen, Koen & Qiu, Jian-Wen, 2021, Integrative taxonomy of enigmatic deep-sea true whelks in the sister-genera Enigmaticolus and Thermosipho (Gastropoda: Buccinidae), Zoological Journal of the Linnean Society 193 (1), pp. 230-230 : 230-

publication ID	https://doi.org/ 10.1093/zoolinnean/zlaa134
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scientific name	Enigmaticolus Fraussen, 2008: 75–77
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Enigmaticolus Fraussen, 2008: 75–77 .

Type species: Enigmaticolus monnieri Fraussen, 2008 [by original designation, = Enigmaticolus nipponensis ( Okutani & Fujiwara, 2000) comb. nov.]

Diagnosis (emended from Fraussen & Stahlschmidt, 2016): Shell large, up to 99.4 mm. Brownish or purplish in coloration, typically thick and solid. Broadly fusiform in shape with moderately high spire that is usually corroded to different degrees. Sculpture of strong axial folds on the spire, stronger in earlier teleoconch whorls. Spiral sculpture consists only of fine lines. Base with weak to strong spiral cords. Periostracum thick, brown, shiny or metallic in appearance, adherent. Radula with two cusps on lateral teeth, the outer cusp being usually larger. Central tooth with triangular base, normally tricuspid but occasionally with a further smaller denticle. Operculum thick, corneous, brown, with a terminal nucleus, semi-oval in shape and smaller than the aperture.

Distribution: Deep waters (641–2750 m) in the Pacific and Indian Oceans, known definitively from vents and seeps and some records with unknown habitat type. Izu-Bonin Arcs; Okinawa Trough, East China Sea; South China Sea; Manus, North Fiji, Lau Basins; Kermadec Ridge; New Caledonia; Mozambique Channel off Madagascar.

R e m a rk s: S y n t h e s i z i n g t h e r e s u l t s f r o m t h e present study, we can evaluate taxonomically informative morphological characteristics that distinguish Enigmaticolus and Thermosipho . The most important diagnostic shell characters that distinguish Enigmaticolus from Thermosipho are: (1) the presence of spiral cords of variable strength on the base (completely smooth in Thermosipho ), (2) the presence of axial folds of various strength on the spire that are stronger in earlier teleoconch whorls (absent in Thermosipho ) and (3) a clearly accentuated, longer anterior siphonal canal (not well defined in Thermosipho ). Some previously identified characters of Enigmaticolus , such as smaller aperture and narrower shell ( Fraussen & Stahlschmidt, 2016), are still generally true but are of limited usefulness due to morphological variability in the genus and also the fact that the spire is usually corroded to different degrees in every specimen. However, the subsutural ramp is a species-level diagnostic character lacking in E. desbruyeresi , mostly useful in distinguishing E. desbruyeresi from other Enigmaticolus species. We also show that within Enigmaticolus each species may be variable in the inflatedness and breadth of the shell, length and shape of the siphonal canal, strength of the subsutural ramp and the strength of axial sculptures. Enigmaticolus is distributed in vents, seeps and perhaps other habitats in the Indo-West Pacific, while Thermosipho is only found in vents in the East Pacific. Table 2 summarizes key informative characters for Enigmaticolus and Thermosipho .

Included species: Enigmaticolus nipponensis ( Okutani & Fujiwara, 2000) (originally as: Eosipho desbruyeresi nipponensis ). Synonyms: Enigmaticolus monnieri Fraussen, 2008 , Enigmaticolus inflatus Zhang et al., 2020 .

Enigmaticolus desbruyeresi ( Okutani & Ohta, 1993) (originally as: Eosipho desbruyeresi ).

Enigmaticolus marshalli Fraussen & Stahlschmidt, 2016 .

Enigmaticolus voluptarius Fraussen & Stahlschmidt, 2016 .

ENIGMATICOLUS NIPPONENSIS ( OKUTANI & FUJIWARA, 2000) COMB. NOV.

( FIGS 3 View Figure 3 , 4 View Figure 4 , 5A–C View Figure 5 , 7 View Figure 7 , 9A, B View Figure 9 )

Eosipho desbruyeresi nipponensis Okutani & Fujiwara, 2000: 125 , figs 6–10; Sasaki et al., 2005: 122, fig. 17.

Enigmaticolus monnieri Fraussen, 2008: 77–78 , pl. 1, figs 1–3, pl. 2, figs 4–6; – Kantor et al., 2013: 2179, figs 1–4; – Fraussen & Stahlschmidt, 2016: 444, figs 139–141.

Enigmaticolus inflatus Zhang et al., 2020: 385 View Cited Treatment , figs 1, 2.

Enigmaticolus sp. 1 – Fraussen & Stahlschmidt, 2016: 447, fig. 149.

Enigmaticolus sp. 2 – Fraussen & Stahlschmidt, 2016: 448, fig. 150.

Diagnosis: An Enigmaticolus possessing a shell with a subsutural ramp (may be weak), brownish to dark purplish in colour and strong spiral cords on the base.

Type material: Eosipho desbruyeresi nipponensis – holotype (NSMT-Mo 71689; Fig. 3A View Figure 3 ), paratype #1 (male, dissected, NSMT-Mo 71690), paratype #2 (NSMT-Mo 71691), paratype #3 (JAMSTEC 009599), paratype #4 (JAMSTEC 009556; Fig. 3B View Figure 3 ). Enigmaticolus monnieri – holotype MNHN IM-2000–20464 ( Fig. 9A View Figure 9 ) and one paratype in Koen Fraussen collection #4178. Enigmaticolus inflatus – holotype MBMCAS 286512, one paratype MBMCAS 286513.

Type locality: Eosipho desbruyeresi nipponensis – North Knoll of Iheya Ridge (27°47.180’N 126°54.149’E, 1049 m), Okinawa Trough, vent. Enigmaticolus monnieri – Mozambique Channel (800 m), Tulear, Madagascar, trawled by commercial shrimpers, seep (not definitively but trawled with typical seep taxa such as Bathymodiolus and Solemya ; Kantor et al., 2013). Enigmaticolus inflatus – South China Sea (22°07′N 119°17’E, 1119 m), seep.

Material examined: Type material listed above. One specimen, collected live, 99% ethanol, Iheya North Original site, Iheya North hydrothermal field (27°47.4495’N, 126°53.8149’E), 1002 m deep, shell length 80.2 mm (NSMT-Mo 79171, GenBank accession for COI sequence MT 894131 View Materials ; Fig. 3C View Figure 3 ). One specimen, collected live, 99% ethanol, Natsu site, Iheya North hydrothermal field (27°46.8522’N, 126°54.0584’E; Fig. 3D View Figure 3 ), 1078 m deep, shell length 81.2 mm (NSMT-Mo 79172, GenBank accession for COI sequence MT 894132 View Materials ). One specimen from the same locality, collected live, 99% ethanol, shell length 90.4 mm (NSMT-Mo 79173; Fig. 4A View Figure 4 ). One specimen, collected live, 99% ethanol, Aki site, Iheya North hydrothermal field (27°46.103’N, 126°54.090’E), 1086 m deep, shell length 84.6 mm (NSMT-Mo 79174; Fig. 4B View Figure 4 ). One specimen from the same locality, 10% formalin, shell length 79.0 mm (NSMT-Mo 79175; Fig. 4C View Figure 4 ). One specimen, 10% formalin fixed and preserved in 70% ethanol, Kuroshima Knoll hydrocarbon seep site (24°07.830’N, 124°11.562’E), 641 m deep, shell length 88.7 mm (NSMT-Mo 79176; Fig. 4D View Figure 4 ). One specimen, –80 °C frozen and transferred to 99% ethanol, South China Sea (22°06.945’N, 119°17.128’E), 1128 m deep, shell length 94.9 mm ( HKBU Mol-2020010001, GenBank accession for COI sequence MT 894133 View Materials ; Fig. 5A View Figure 5 ). One specimen from the same locality, shell length 87.5 mm ( HKBU Mol-2020010002; Fig. 5B View Figure 5 ). One specimen, 99% ethanol, ‘F site’ methane seep, South China Sea (22°6.912’N, 119°17.104’E), 1127 m deep, shell length 91.4 mm ( HKBU Mol-2020010003; Fig. 5C View Figure 5 ) GoogleMaps .

Distribution: Hydrothermal vents in the Iheya North field (Iheya North Original, Natsu, and Aki sites), Okinawa Trough. Vents on the Izu-Bonin Arcs (Myojin Knoll, Sumisu Caldera). ‘F site’ methane seep in the South China Sea. Mozambique Channel, off Madagascar. Depth range of live individuals 641–1187 m. In both Iheya North field and the ‘F site’ seep, individuals were mostly seen among aggregations of the mussels Bathymodiolus spp. , which it probably feeds on ( Fig. 2A, B, D, E View Figure 2 ), but on rare occasions it was also seen on basalt rock in the vent periphery ( Fig. 2C, F View Figure 2 ).

Remarks: Distinguished from Enigmaticolus desbruyeresi by the presence of subsutural ramp and stronger spiral cords on the base. Also see ‘Remarks’ of Enigmaticolus . Two empty shells trawled by fishermen from the East China Sea shown in Fraussen & Stahlschmidt (2016) and referred to as ‘ Enigmaticolus sp. 1 ’ and ‘ Enigmaticolus sp. 2 ’ are similar to the newly available specimens examined herein. Given their locality and the variation seen among E. nipponensis specimens, these two specimens are also referred to E. nipponensis . The collection depth of ‘ Enigmaticolus sp. 1 ’ was shallow (118–122 m), but it was dead collected and purchased from fishermen so the data may be inaccurate.