Strobiligera ibex
Creators: name: Fernandes, Maurício Romulo
Publisher: name: Zenodo
Year: 2024
Subjects: Biodiversity
Taxonomy
Animalia
Mollusca
Gastropoda
Triphoridae
Strobiligera
Strobiligera ibex

description: Strobiligera cf. ibex (Dall, 1881)
Figs 18–20
Triforis ibex Dall, 1881: 86.
Triforis (Sychar) inflata var. ibex – Dall 1889a: 249, pl. 20 fig. 12b; 1889b: 138, pl. 20 fig. 12b.
Triphora (Strobiligera) inflata var. ibex – Dall 1924: 89. — Abbott 1974: 112, fig. 1148a (a reproduction of Dall’s illustration).
Inella ibex – Rolán & Fernández-Garcés 2008: 110, figs 14k–m, 36g (the latter a reproduction of Dall’s illustration).
Strobiligera ibex – Fernandes & Pimenta 2014: 169; 2019a: fig. 2o–p.
non Inella colon Dall, 1881 – Rolán & Fernández-Garcés 2008: fig. 16e–f.
Type material
Lectotype CUBA • sh; Yucatán Strait, off Cape San Antonio; depth 1170 m; MCZ 7391.
Rolán & Fernández-Garcés (2008) argued that “three localities [off Cuba, Yucatan Strait and Cape San Antonio] mentioned in the original description are written on the label of the lectotype, and hence there is no exact information about which locality applies to this type”. These localities mainly refer to the same part of the ocean, i.e., the narrowest distance between Cuba and Mexico, and Dall (1881) provided the same depth (640 fms = 1170 m) for Yucatán Strait and off Cape San Antonio. Following the MCZ catalogue book for the lectotype, the type locality is as listed above.
Paralectotypes CUBA • 1 sh; same data as for lectotype; USNM 87313 • 1 sh; off Havana; depth 823 m; MCZ 7392.
Material examined
GUADELOUPE (Karubenthos 2 expedition) • 1 spec. stored in ethanol; stn CP4618; MNHN-IM-2013-61225.
Emended description
Shell sinistral, conical-fusiform, much elongated, up to 33.3 mm long, 5.0 mm wide, length/width ratio 6.7, apical angle of early whorls 14°. Protoconch broken. Teleoconch with at least 28 whorls; two main spiral cords (median and abapical), with a very narrow adapical spiral cordlet becoming more evident in late whorls, remaining weak on body whorl but slightly nodulous; distinct suture, with a narrow, smooth sutural cord; 15 slightly opisthocline axial ribs on 24 th whorl (regarding broken apex); medium-sized, slightly elliptical nodules; wide, smooth subperipheral cord, two smooth basal cords right below it; three supranumerical cords, below each spiral cord (supranumerical cord below abapical spiral cord weakest); elliptical aperture, 3.4 mm long, 2.2 mm wide, length/width ratio 1.5; open, very short anterior canal, 0.45 mm long, 0.80 mm wide, length/width ratio 0.6. Shell mainly beige, with suture, adapical spiral cordlet and base light brown, and eight initial teleoconch whorls whitish.
Head-foot white, with part of intestine greyish; very reduced eyes; extended proboscis reaches 3.3 mm in length, 4.8× as long as extended cephalic tentacles (0.69 mm long); pedal slit covering 71% of foot length. Operculum elliptical, flat, semi-transparent, with poorly distinct whorls, nucleus slightly eccentric, dislocated 31% from center toward margin; diameter of opercular pouch 83% of diameter of operculum. Inner side of jaw with scales gem-shaped (typically 20.6–24.0 µm long, 7.6–8.4 µm wide, ratio length/width 2.7–2.8) at margins, or leaf-shaped (typically 31.8–34.9 µm long, 14.0–15.8 µm wide, ratio length/width 2.0–2.5) at middle portion; outer side of jaw with scales mainly rectangular (16.9– 51.1 mm long, 5.1–21.9 mm wide, ratio length/width 2.3–3.7), rectangular-bilobed (23.8–26.9 µm long, 10.0–11.2 µm wide, ratio length/width 2.1–2.5), squared (13.4–22.6 µm long), hexagonal (14.5–17.4 µm long, 13.0–14.1 µm wide, ratio length/width 1.1–1.2) or curved with extremities slightly to considerably unequal in width (21.0–25.4 µm long, 9.8–14.2 µm wide, ratio length/width 1.6–2.6). Radula with little differentiation in teeth morphology, formula not discernible (but at least 27 overcrowded teeth per row); all teeth with elongated cusps and a small basal area; central tooth scissor-like, with two equal cusps, 2.4–2.8 µm wide; remaining teeth 2.5–3.6 µm wide, with three cusps, innermost (cusp 1) often thinner and shorter (~50–75% of length) than cusps 2 and 3, but occasionally reaching same length.
Remarks
The single specimen from Guadeloupe is an extremely large adult (33.3 mm long for at least 28 teleoconch whorls – apex broken), 3 × as long as the maximum length of the type material of up to only 11.0 mm (Dall 1881). Based on Dall (1881) and the subsequent drawing by Dall (1889a), S. ibex has 19 teleoconch whorls (apex broken), contrasting with the shell designated as lectotype by Rolán & Fernández-Garcés (2008), which is 10.4 mm long for ~14 teleoconch whorls (apex broken) and apparently has a more distinct last whorl than the shell illustrated by Dall (1889a). It is possible that there is more type material of S. ibex hidden in some collections that has not been imaged yet; e.g., Dall (1881) described a complete protoconch, which has not been reported again in the recent literature. Apart from the difference in shell size, the original description, the drawing and available photographs of the types are in considerable agreement with the specimen from Guadeloupe, including the excavated suture and very late development of the adapical spiral cord on the teleoconch [whereas the similar Strobiligera colon (Dall, 1881) comb. nov. has an indistinct suture and adapical cord], the presence of two basal cords in addition to the subperipheral cord (Dall 1881) and the reduced anterior canal (disproportional in relation to the shell length).
The specimen from Guadeloupe is nearly identical to two shells from Mexico and the Straits of Florida identified as I. colon by Rolán & Fernández-Garcés (2008: fig. 16e–f), but these authors recognized the possibility of an erroneous identification. These two shells reach 20.3 mm and 29.4 mm in length, with broken apex. Fernandes & Pimenta (2019a) recognized the similarity between these two shells and the holotype (but not all shells) of S. unicornium, described from NE Brazil (Simone 2006). In fact, the description of the protoconch of S. ibex by Dall (1881) is very similar to the protoconchs tentatively assigned to S. unicornium by Fernandes & Pimenta (2019a). The holotype of S. unicornium has a broken apex, and the broad interpretation of S. unicornium by Fernandes & Pimenta (2019a) encompasses shells with a highly varied development of the adapical spiral cord on the teleoconch, although more or less in a continuum. More material (with protoconch) from these deep-sea triphorids is necessary prior to suggesting any synonymy.
The eyes of S. cf. ibex (Fig. 18B) are more reduced than those of “ I.” longissima (Fig. 2C), suggesting that S. cf. ibex is restricted to the continental slope.
Geographic distribution
USA: Straits of Florida (Dall 1889b; Rolán & Fernández-Garcés 2008 – determined as I. colon); Mexico (Rolán & Fernández-Garcés 2008 – determined as I. colon); off Cuba (Dall 1881); Guadeloupe (this study).
Bathymetric distribution
Empty shells previously known from 236–1170 m (Dall 1881; Rolán & Fernández-Garcés 2008 – determined as I. colon). This study: 780–828 m (live specimen).
description: Published as part of Fernandes, Maurício Romulo, 2024, The deep-sea species of Triphoridae (Gastropoda, Triphoroidea) from Guadeloupe, sampled by the Karubenthos 2 expedition, pp. 1-52 in European Journal of Taxonomy 972 on pages 36-41, DOI: 10.5852/ejt.2024.972.2763, http://zenodo.org/record/14506799