Strobiligera variabilis, Fernandes, 2024

Fernandes, Maurício Romulo, 2024, The deep-sea species of Triphoridae (Gastropoda, Triphoroidea) from Guadeloupe, sampled by the Karubenthos 2 expedition, European Journal of Taxonomy 972, pp. 1-52 : 21-24

Strobiligera variabilis sp. nov.

urn:lsid:zoobank.org:act:56F72111-A572-400C-80ED-DCDB2748CBE2

Fig. 11

Triphora sp. 2 – Lamy & Pointier 2018: 289, pl. 92 fig. 13.

Diagnosis

Protoconch with a small nucleus; teleoconch with an initially weak adapical spiral cord, often reaching same size as other spiral cords between the fifth and seventh whorls.

Etymology

Latin, ‘ variabilis ’ = ‘variable’. The specific epithet alludes to the morphological variation in the shells of this species.

Type material

Holotype

GUADELOUPE (Karubenthos 2 expedition) • sh; stn DW4634; MNHN-IM-2000-38784.

Paratypes

GUADELOUPE (Karubenthos 2 expedition) • 2 sh; stn DW4536; MNHN-IM-2000-38785 • 1 sh; stn DW4538; MNHN-IM-2000-38786 • 1 sh; stn DW4572; MNHN-IM-2000-38787 • 2 sh; stn DW4600; MNHN-IM-2000-38788 • 17 sh; stn DW4634; MNHN-IM-2000-38792 • 1 spec. stored in ethanol; stn DW4634; MNHN-IM-2019-20013 • 1 sh; stn DW4635; MNHN-IM-2000-38789 • 6 sh; stn DW4638; MNHN-IM-2000-38790 • 2 sh; stn DW4646; MNHN-IM-2000-38791.

Type locality

Guadeloupe, 15°48′ N, 61°26′ W, 304–310 m depth.

Description

Shell sinistral, conical-fusiform, rarely with apex slightly constricted, up to 11.0 mm long (incomplete shell; adult shells reach at least 5.0 mm in length), 2.0 mm wide, length/width ratio 4.1–5.6, apical angle of early whorls 16–18°. Protoconch paucispiral, sub-columnar, 2.0–3.0 whorls, often 0.44–0.52 mm long (one discrepant protoconch up to 0.65 mm long), 0.50–0.61 mm wide; small nucleus rises in an adapical direction and further goes abapical in an oblique descent; two main spiral cords (in addition to a very narrow subsutural cord), situated at 32–36% and 72–75 % of last whorl height and often smooth, but both cords may have some degree of nodules (especially adapical one, which may show pointed, triangular nodules, resembling a thorn crown); gradual transition to teleoconch, from an often smooth spiral sculpture to a nodulous one. Teleoconch with up to 16 whorls; three main spiral cords (continuous with those of protoconch), adapical one initially reduced, gradually strengthening and may reach nearly same size as other cords between fifth and seventh whorls, or occasionally not reaching same size as other cords until body whorl; suture very shallow, nearly indistinct, with a narrow sutural cord; 17–23 nearly orthocline axial ribs on 12 th teleoconch whorl; medium-sized, rounded to slightly elliptical nodules; smooth, broad subperipheral cord, with a smooth, narrow basal cord right below it; a very weak supranumerical cord may form (or not) between median and abapical spiral cords; slightly elliptical aperture, 0.76–1.25 mm long, 0.51–0.85 mm wide, length/width ratio 1.5; anterior canal very short, often open, 0.14–0.22 mm long, 0.22–0.31 mm wide, length/width ratio 0.6–0.7. Shell white to dirty-white.

Remarks

Shells of Strobiligera variabilis sp. nov. are highly variable with respect to length (there are small adults – Fig. 11A , and large immatures – Fig. 11K ), width, sculpture of spiral cords of protoconch (smooth to slightly nodulous), strength of the adapical spiral cord of the teleoconch, and number of axial ribs. However, variation is often continuous, and it is hard to define whether more than one species is involved with only empty shells at hand (only one live specimen was sampled, and the head-foot was used for DNA extraction – unpubl. data). Until compelling evidence indicates otherwise, I conservatively consider this as a single (but variable) species. The holotype is a small adult shell ( Fig. 11A ) with slightly nodulous spiral cords on the protoconch ( Fig. 11L ).

The most similar species to S. variabilis sp. nov. is Strobiligera sp. A ( Fig. 10 ), which seems smaller when comparing shells with the same number of teleoconch whorls, has a narrower protoconch (0.38– 0.47 mm wide vs 0.50–0.61 mm in S. variabilis ), and a shallower suture. A deep-sea species from Georgia ( USA) with a similar teleoconch morphology to S. variabilis is Strobiligera meteora ( Dall, 1927) , which in contrast has an inflated first protoconch whorl ( Rolán & Fernández-Garcés 2008).

A slightly similar species is Strobiligera compsa ( Dall, 1927) from Georgia ( USA). Its type material consists of two shells without protoconch and base ( Rolán & Fernández-Garcés 2008; Fernandes & Pimenta 2019a), precluding further comparisons. Some shells of S. variabilis sp. nov. (e.g., Fig. 11C ) have a similar shape to these types, but the adapical spiral cord of the teleoconch in S. variabilis is often more developed. In addition, shells of S. variabilis are narrower, with the largest one reaching 11.0 mm in length and 2.0 mm in width for 14.5 teleoconch whorls vs 12 mm in length and 3.3 mm in width for 13 teleoconch whorls in S. compsa (based on the counting of whorls in the lectotype, not the 12 whorls described by Dall 1927).

Strobiligera variabilis sp. nov. is similar to S. cf. enopla from Guadeloupe, but the two species are distinguished by the hell shape ( S. variabilis is broader, with the apical angle of early whorls 16–18° vs ~10° in S. cf. enopla ), the strength of the adapical spiral cord of the teleoconch (often reaching nearly the same size as other cords between the fifth and seventh whorls in S. variabilis , vs only in the 21 th –23 th whorl in S. cf. enopla ) and the strength of the median spiral cord on the initial whorls of the teleoconch (with the same size of abapical cord in S. variabilis , vs often more reduced than the abapical cord in S. cf. enopla ). The protoconch of S. variabilis sometimes has nodules on the spiral cords (especially the adapical one), which is not observed in S. cf. enopla ; on the other hand, the first protoconch whorl of S. cf. enopla is often slightly inflated (but never inflated in S. variabilis ). The Bahamian species Inella apexbilirata Rolán & Fernández-Garcés, 2008 has one protoconch whorl more than S. variabilis , in addition to a much weaker adapical spiral cord on the teleoconch.

The complex taxonomic situation of “ Inella ” triserialis ( Dall, 1881) [and to a lesser extent of “ Inella ” intermedia ( Dall, 1881) ] is carefully explained here in order to avoid further confusion. I complement the observations of Fernandes & Pimenta (2019a: 7), who corrected the lectotype designation of “ I.” intermedia because the previous designation by Rolán & Fernández-Garcés (2008): (1) erroneously considered a wide range for the type locality of “ I.” intermedia [although Dall (1881) mentioned only “station 2, 805 fms”]; (2) ignored the MCZ labels and annotations in the catalogue book [which indicated MCZ 7382 and MCZ 7384 as syntypes of “ I.” triserialis , as observed but not followed in Rolán & Fernández-Garcés (2008: caption of fig. 14g –h]; (3) and followed the subsequent drawing of Dall (1889a) for the choice of lectotype [although the shell in MCZ 7384, with 13 teleoconch whorls, does not match the drawing of “ I.” intermedia , with 17 teleoconch whorls]. Dall (1881) stated for “ I.” intermedia that the ‘specimen measured is the most perfect, but not the largest’; it was 11.0 mm long and smaller than the lectotype designated by Fernandes & Pimenta (2019a), which was 12.6 mm long for ~19 teleoconch whorls [i.e., less than the largest shell, with about 23 whorls ( Dall 1881)]. Because the lectotype is worn, it is possible that the shell illustrated in Dall (1889a) would be the ‘most perfect’, and has not been photographed yet. Apart of that, “ I.” intermedia and the paralectotypes MCZ 7382 and MCZ 7384 of “ I.” triserialis are possibly conspecific with “ I.” longissima , thus requiring the examination of more material. The type material of “ I.” triserialis stored in the NMNH collection (lectotype and one paralectotype) seems different, apparently with a much earlier emergence of the median spiral cord of the teleoconch ( Rolán & Fernández-Garcés 2008), and it possibly includes a shell illustrated by Dall (1889a: fig. 5a), despite the broken apex. However, as also recognized by Rolán & Fernández-Garcés (2008), the other shell illustrated by Dall (1889a: fig. 6a) as “ I.” triserialis is another species, much longer and apparently with the adapical spiral cord weaker on the initial whorls of the teleoconch (although this is hardly visible in the drawing). This shell has no precise locality, and it seems very similar to some shells of S. variabilis sp. nov. (e.g., Fig. 11K ), albeit slightly longer (15.5 mm vs 11.0 mm in an incomplete shell of S. variabilis ). More material is required in order to check the geographic range of S. variabilis .

Geographic distribution

Guadeloupe ( Lamy & Pointier 2018; this study).

Bathymetric distribution

Empty shells previously known from 200 m ( Lamy & Pointier 2018, determined as Triphora sp. 2 ). This study: 250–680 m (empty shells), 304–310 m (live specimen).

Figures

Fig. 11. Strobiligera variabilis sp. nov. A, L. Holotype, MNHN-IM-2000-38784, 5.5 mm. B. Paratype, MNHN-IM-2000-38786, 5.0 mm. C. Paratype, MNHN-IM-2000-38787, 5.4 mm. D. Paratype, MNHN-IM-2019-20013, 7.1 mm. E–F. Paratypes, MNHN-IM-2000-38785, 7.4 mm, 8.0 mm. G, I–J, M–O. Paratypes, MNHN-IM-2000-38792 (M–N, same shell as Fig. H), 7.9 mm, 9.5 mm, 10.0 mm. H. Paratype, MNHN-IM-2000-38788, 9.2 mm. K. Paratype, MNHN-IM-2000-38789, 10.5 mm. Scale bars: A–K, N–O = 1 mm; L–M = 500 µm.

Fig. 10. Strobiligera sp. A. A–B. MNHN, stn CP4513, 2.8 mm. C–D. MNHN, stn DW4549, 4.5 mm. E–F. MNHN, stn DW4550, 5.0 mm. G. MNHN, stn DW4599, 3.1 mm. Scale bars: A, C, E, G = 1 mm; B, D, F = 500 µm.