Leucosyrinx Dall, 1889

Kantor, Yuri I., Fedosov, Alexander & Puillandre, Nicolas, 2025, Revision of the Indo-Pacific species of the genus Leucosyrinx Dall, 1889 (Neogastropoda: Conoidea: Pseudomelatomidae), European Journal of Taxonomy 999, pp. 1-126 : 7-11

Genus Leucosyrinx Dall, 1889

Pleurotoma (Leucosyrinx) Dall, 1889: 75 .

Type species

Pleurotoma (Pleurotomella) verrillii Dall, 1881 (OD).

Diagnosis

Shell small to large, reaching 90 mm in length ( L. bolognai ), narrow to broad fusiform, spire high, siphonal canal distinct, medium-long to long. Shell uniformly colored, from off-white to beige and light brown. Protoconch paucispiral, small, diameter about 1 mm, of 1.5–1.75 rounded whorls. Teleoconch whorls roundly angled at shoulder, at least on upper whorls, with well-defined concave subsutural ramp.

Axial sculpture of usually strong, oblique, axial ribs, present on shoulder and below, not extending to subsutural ramp. Ribs can be reduced just to knobs on shoulder, but can extend to periphery and even shell base. Spiral sculpture from weak to rather strong, of uniform spiral cords, that can be present or absent on subsutural ramp.

Anal sinus moderately deep, subsutural, broadly arcuate, extends across entire subsutural ramp, and confluent with large forward extension of outer lip.

Operculum narrow to medium-broad leaf-shaped, nucleus terminal.

Radular marginal teeth duplex ( Fig. 2 ), narrow to broad lanceolate, rather flat in dorsal view, particularly in anterior part (tooth tip). Major limb pointed, with sharp cutting edges ( Fig. 2C – bl), broadest at midlength and narrowing towards both ends, with rather distinct socket on dorsal surface where accessory limb embeds. Central formation very weak to completely absent, of indistinct symmetrical folds of the membrane and rarely with very weak central cusp.

Remarks

As confirmed by molecular data, Leucosyrinx exhibits significant variability in shell shape, size, and, to a lesser extent, in spiral and axial sculpture. Nonetheless, certain key diagnostic features can be identified. The axial folds, which may be limited to nodules on the shoulder or extend to the shell periphery, are consistently absent on the subsutural ramp. The ramp, including the zone immediately adjacent to the upper suture, is either smooth or exclusively features spiral cords and lacks any other elements. The anal sinus located subsuturally, commences at the upper suture and extends across the entire ramp. Correspondingly, the sinus line in its upper part is prosocline and concave. Below, the sinus is confluent with a notable forward arcuate projection of the outer lip, enhancing the impression of depth in the generally medium-deep sinus.

There are several genera, superficially similar to Leucosyrinx . The species treated here as members of Leucosyrinx were often confused with genera discussed below, and vice versa some species belonging to those genera were erroneously attributed to Leucosyrinx .

Genus Antarctospira Kantor, Harasewych & Puillandre, 2016 (family Borsoniidae )

Antarctospira Kantor, Harasewych & Puillandre, 2016: 4–5 .

Type species

Leucosyrinx badenpowelli Dell, 1990 (OD).

Remarks

The Antarctic-subAntarctic genus Antarctospira shares the axial sculpture pattern as well as the shape and position of the anal sinus with Leucosyrinx ( Kantor et al. 2016) . Notably, four out of the five species attributed to Antarctospira were initially classified as Leucosyrinx : Antarctospira badenpowelli (Dell, 1990) (type species), A. mawsoni (Powell, 1958) , A. paragenota (Powell, 1951) , A. falklandica (Powell, 1951) . However, the examination of the radula revealed that Antarctospira possesses a radula with hypodermic marginal teeth thus suggesting its placement within the family Borsoniidae Bellardi, 1875 . Furthermore, all species of Antarctospira have a much shorter and broader siphonal canal, which is barely separable from high and broad aperture. Its paucispiral protoconch is larger, attaining 2.5 mm in diameter (vs ca 1 mm in Leucosyrinx ).

Genus Comitas Finlay, 1926 (family Pseudomelatomidae )

Comitas Finlay, 1926: 251 .

Type species

Surcula oamarutica Suter, 1917 (= Drillia fusiformis Hutton, 1877 ) (Lower Miocene, New Zealand) (OD).

Remarks

Species of Comitas have a very distinctive radula ( Fig. 3F ), reliably distinguishing them from all other conoideans, including Leucosyrinx . Nonetheless, the radula was examined in very few species, namely: Comitas galatheae Powell, 1969 ( Kosuge 1986: pl. 33 figs 7–11); C. murrawolga (Garrard, 1961) and C. onokeana vivens Dell, 1956 ( Kantor & Taylor 2000: fig. 2a–e); C. pachycercus Sysoev & Bouchet, 2001 ( Sysoev & Bouchet 2001: figs 14, 16); Comitas sp. ( Bouchet et al. 2011: fig. 15c–d). The mentioned species together with the type species of the genus can be separated from Leucosyrinx on the following conchological characters: the shell is generally large, usually over 50 mm in length, with broad and long axial ribs, always extending to the periphery and sometimes to the shell base. The anal sinus is moderately deep, medium broad U-shaped, on the subsutural ramp and occupying the lower part of the subsutural ramp, not on all its width, so that the deepest point is closer to shoulder than to suture ( Fig. 3E ). Correspondingly the sinus line in its upper part is prosocline, but convex.

There is significant overlap in shell characters between Comitas and Leucosyrinx , so that attributing the species known only from empty shells is sometimes problematic. Thus, although Powell (1966) recognized the differences in position of the anal sinus between these genera, he attributed without discussion numerous species with subsutural sinus to Comitas ( Powell 1969) that are conchologically closer to Leucosyrinx as defined here.

Genus Sibogasyrinx Powell, 1969 (family Cochlespiridae )

Leucosyrinx (Sibogasyrinx) Powell, 1969: 343 (23-411).

Type species

Surcula pyramidalis Schepman, 1913 (OD).

Remarks

The molecular phylogenetic analysis of nine species of Sibogasyrinx ( Kantor & Puillandre 2021) demonstrated that all species attributed to the genus have a row of nodules situated directly below the suture ( Fig. 3G–H ). On the contrary, none of Leucosyrinx as defined here by molecular analysis has these nodules. The significance of this diagnostic character was not recognized prior to the current publication and many species with subsutural nodules were erroneously attributed to Leucosyrinx or Comitas mostly by Powell (1969). Radula in Sibogasyrinx is characterized by duplex marginal teeth of varying morphology and the presence of a well-defined central formation with a long cusp ( Kantor & Puillandre 2021).

Genus Comispira Kantor, Fedosov & Puillandre, 2018 (family Cochlespiridae )

Comispira Kantor, Fedosov & Puillandre, 2018: 48 .

Type species

Leucosyrinx mai Li & Li, 2008 (OD).

Remarks

Species of this genus resemble Sibogasyrinx in the presence of the subsutural row of nodules, but differ in usually more pronounced spiral sculpture on the shell base, of broadly-spaced and rather strong spiral cords. It should be mentioned that some species of Comispira , whose generic position is confirmed by molecular analysis, can have very weak, nearly obsolete subsutural nodules and rather uniform weak spiral sculpture on the shell base ( Kantor et al. 2022). The radula is similar to that of Sibogasyrinx .

The mentioned diagnostic characters of Leucosyrinx and of similar genera allowed critical re-assessment of numerous species described on the basis of the shells alone and attributed to the above mentioned genera at one point or another.

Figures

Fig. 2. Details of the radula of Leucosyrinx sp. 7. A. Dorsal view of the radular membrane. B. Bending plane of the radula, with some teeth in lateral view. C. Enlarged lateral view of the tip of marginal tooth showing the cutting edge, blade. Abbreviations: al = accessory limb of the marginal tooth; bl = cutting edge, blade; ml = major limb of the marginal tooth. Scale bars: A–B = 100 µm; C = 50 µm.

Fig. 3. Genera of Conoidea Fleming, 1822, similar to Leucosyrinx Dall, 1889 and confused with it. A–C. Antarctospira badenpowelli (Dell, 1990) (family Borsoniidae). A–B. Holotype, USNM 613118, Victoria Land, McMurdo Sound, east of Cape Hallett,72°08′ S,172°10′ E, 433 m, SL 19.9 mm, apertural view of the shell and enlarged anal sinus. C. Paratype, USNM 860180, South Shetland Is., 72°06′ S, 172°12′ E, 433 m, SL 21.5 mm; radula. D–F. Comitas sp. (family Pseudomelatomidae), MNHN-IM- 2007-17918, Philippines, Bohol Sea, 762–786 m, SL 114.3 mm; apertural view of the shell, enlarged anal sinus, radula. G–I. Sibogasyrinx cf. pyramidalis 1 (Schepman, 1913) (family Cochlespiridae), MNHN-IM-2009-13451, Philippines, off Luzon I., 593–600 m, SL 46.5 mm; apertural view of the shell, enlarged anal sinus (arrow indicates the subsutural row of nodules, present only in Cochlespiridae), radula. J. Comispira mai (B.-Q. Li & X.-Z. Li, 2008), MNHN-IM-2013-61657, South China Sea, 1128– 1278 m, SL 35.5 mm.