Turridrupa cincta (Lamarck, 1822)

(Figs. 12 A–J, 23 E–H)

Pleurotoma cincta Lamarck, 1822: 92; Kiener, 1840: 60, pl. 19, fig. 3; Reeve, 1843: sp. 99. Type loc.: Ile de France [Mauritius].

Turridrupa cincta; Oyama & Takemura, 1960: Turridrupa, figs 1–2; Powell, 1967: 421, pl. 301, fig. 5; Cernohorsky, 1978:151, pl. 54, fig. 1; Kilburn, 1988: 235, figs 4 (operculum), 30 (protoconch), 39 (radula); Wilson, 1994: 195; Boutet et al., 2020: 457, unnumbered fig.

Pleurotoma modesta G. B. Sowerby I, 1834: 136 . Type loc.: Real Llajos, Nicaragua, 15 m and [here restricted] Annaa Island, Tuamotu Archipelago.

Pleurotoma modesta; Pease, 1868; Weinkauff, 1875: 44, pl. 9, fig. 9.

Type material

SYNTYPES: 16.5 mm,18.0 mm (MHNG 1097/54/1; Figs. 12 A–D) .

Sequenced material

MADAGASCAR: ATIMO VATAE: Stn BM12 (MNHN-IM-2009-14777)—Stn BS02 (MNHN-IM-2009-14904; MNHN-IM-2009-14657)—Stn BS03 (MNHN-IM-2009-14871)—Stn BS04 (MNHN-IM-2009-14766)—Stn TB06 (MNHN-IM-2009-14773; MNHN-IM-2009-14875)—Stn TS02 (MNHN-IM-2009-14769)—Stn TS13 (MNHN- IM-2009-14654; MNHN-IM-2009-14775; MNHN-IM-2009-14853; MNHN- IM-2009-14911).— PAPUA NEW GUINEA: PAPUA NIUGINI: Stn PB16 (MNHN-IM-2013-12843)—Stn PB47 (MNHN-IM-2013-18087)—Stn PM25 (MNHN-IM-2013-2994; MNHN-IM-2013-13349)—KAVIENG 2014: Stn KB30 (MNHN-IM-2013- 51291).— NEW CALEDONIA: KOUMAC 2.3: Stn KB636 (MNHN-IM-2019-8435).

Material examined

MOZAMBIQUE: Nacala Bay, 3–4 m, buried in sandy mud (PS- 203).— MADAGASCAR: ATIMO VATAE: Stn BS16, 17 spms (MNHN-IM-2014-541)—Stn BV04, 1 spm (MNHN-IM-2014-550)—Stn BV20, 1 spm (MNHN- IM-2014-543)—Stn TA01,2 spms (MNHN-IM-2014-545; MNHN-IM-2014-740, radula voucher)—Stn TA20, 1 spm (MNHN-IM-2014-539)—Stn TA36, 1 spm (MNHN-IM-2014-549)—Stn TA45, 1 spm (MNHN-IM-2014- 554)—Stn TA50, 1 spm (MNHN-IM-2014-540)—Stn TB01, 2 spms (MNHN-IM-2014-542; PS- 453)—Stn TB10, 1 spm (MNHN-IM-2014-553)—Stn TB11, 2 spms (MNHN-IM-2014-555)—Stn TB12, 4 spms (MNHN-IM-2014-546)—Stn TM03, 2 spms (MNHN-IM-2014-558)—Stn TP07, 2 spms (MNHN-IM-2014-557)—Stn TP12, 1 spm (MNHN-IM-2014-551)—Stn TP13, 6 spms (MNHN-IM-2014-552)—Stn TS02, 5 spms (MNHN-IM-2014- 561)—Stn TS03, 1 spm (MNHN-IM-2014-547)—Stn TS04, 2 spms (MNHN-IM-2014-559)—Stn TS11, 1 spm (MNHN-IM-2014-538)—Stn TS12, 1 spm (MNHN-IM-2014-560)—Stn TS15, 4 spms (MNHN-IM-2014-544)— Stn TS20, 1 spm (MNHN-IM-2014-556)—Stn TV19, 1 spm (MNHN-IM-2014-548)—Stn TV22, 1 spm, (MNHN- IM-2014-562).— REUNION: Boucan Canot, 76 spms (MNHN-IM-2014-537).— PHILIPPINES: PANGLAO 2004: Stn M58, 1 spm (MNHN-IM-2014-77)—Stn. S24, 1 spm (MNHN-IM-2014-78).— PAPUA NEW GUINEA: PAPUA NIUGINI: Stn PR223, 1 spm (MNHN-IM-2014-106)—Stn PS 45, 1 spm (MNHN-IM-2014-99).— NEW CALEDONIA: MONTROUZIER: Stn 1240, 1 spm (MNHN-IM-2014-536)—Stn 1287, 1 spm (MNHN-IM-2014- 105)—Stn 1352, 1 spm (MNHN-IM-2014-102)—LIFOU 2000: Stn 1410, 1 spm (MNHN-IM-2014-103)—Stn 1432, 2 spms (MNHN-IM-2014-98)—Stn 1435, 2 spms (MNHN-IM-2014-100)—Stn 1451, 1 spm (MNHN-IM-2014-104).—CORAIL 2: Stn DW92, 1 spm (MNHN-IM-2014-101).

Distribution

From northern Mozambique to southern Japan in the northeast and French Polynesia (Boutet et al. 2020) in the southeast, from intertidal to 56 m.

Description

Shell medium-sized for genus, up to 18.0 mm in height, somewhat biconic to claviform, very solid; spire more than 1.5 times height of aperture including siphonal canal; suture narrow and incised, siphonal canal, very short, truncated, with an oblique, shallowly-notched termination; anal sinus shallow, U-shaped, expanding on the opening, its apex on the weak second spiral cord; inner lip with thick callus, forming a pad adjacent to end of aperture, stromboid notch very short and shallow.

Sculpture of smooth, strong spiral cords, each whorl with 3–4 evenly-spaced spiral cords (the 4 th usually hidden by succeeding whorls); subsutural cord strong, followed by a weak, low, and narrow second sinus spiral cord, rarely broken into feeble, oblong nodules, and then a strong spiral cord below it. Base of last whorl with 3–4 stronger cords rostrum with additional 4–6 closely-spaced spiral cords, weakening anteriorly; interstices between spiral cords with weak, microscopic spiral threads and microscopic axial plica.

Protoconch domed, eroded in all examined specimens, of approximately 3 whorls, about last two whorls with strong arcuate axial riblets.

Colour uniform beige-yellowish to light to dark brown.

Radulae of two specimens examined: one from south Madagascar (Figs. 23 E–F) and one from New Caledonia (Figs. 23 G–H). In south Madagascar specimen radula very long, 71 rows of teeth, including 30 nascent rows; length ~2.1 mm. Central formation with three elements: arrowhead-shaped central cusp (length/width ~4) and broad, narrow lateral elements resembling transverse membrane folds. Marginal teeth ~80 µm long (1.2% AL), broad major limb with shallow socket for accessory limb. Accessory limb very narrow anteriorly, broadens sharply, nearly matching major limb’s width. Length ~0.75 of major limb, extends to its outer limit. Radula of New Caledonia specimen morphologically similar, main difference is marginal teeth ~80 µm long (1.7% AL).

Remarks

In regard of described species, Turridrupa cincta stands nearest to Turridrupa bijubata in size and general appearance but is easily distinguished from that species by the uniform yellowish or brown colour, the lack of axial undulations, and the different arrangements of the spiral cords on the spire-whorls with the subsutural one being far heavier than the other two, of which the median sinus one is quite weak. For comparison with the closest species, Turridrupa polynesia sp. nov., we refer to the remark section of that species.

The identity of Pleurotoma modesta Sowerby I, 1834 has a history of dispute.Although Powell (1967) concluded that “Upon the available evidence, the status of this species [ P. modesta] cannot be determined”, syntypes (Fig. 12 J) are extant in NHMUK, which demonstrates its similarity to Turridrupa cincta . The type locality for P. modesta is given as “Real Llajos, Nicaragua, 15 m and Annaa Island, Tuamotu Archipelago”. The genus Turridrupa is only known from the Indo-Pacific and we consider the occurrence in Nicaragua as very unlikely and restrict the type locality to Annaa Island, Tuamotu Archipelago (French Polynesia) herein.

Compared with typical Indian Ocean T. cincta, individuals from Tuamotu and sometimes from New Caledonia appear to have slightly broader shells, with stronger cords, and the sinus cord is occasionally also shallowly notched into very feeble nodules. However typical T. cincta also occurs in New Caledonia, and no clear difference in characters can be detected; even the extremes differ only in small degree. Therefore, we consider P. modesta being a synonym of Turridrupa cincta .

Based on cox1 data, Turridrupa cincta specimens from southern Madagascar appear to be divergent from those from the western Pacific (Fig. 1), but these two groups are recognized as separate PSHs only in the less inclusive ASAP-partition, with the second worst asap-score. Furthermore, there is no clear difference in morphological characters, and we thus consider these two groups as a single species.