Turrancilla monachalis ( Ninomiya, 1988 )

Kantor, Yuri, Strano, Giorgio, Vervaet, Fred, Weddingen, Mélanie & Puillandre, Nicolas, 2025, Revision of the genus Turrancilla (Neogastropoda: Olivoidea: Ancillariidae) in an integrative taxonomy framework, Zootaxa 5647 (5), pp. 401-434 : 424-428

Turrancilla monachalis ( Ninomiya, 1988)

( Figs 16 , 17 , 18 , 19A , 20A–B )

Ancillus monachalis Ninomiya 1988: 147–148 , pl. 1, figs 12,13

Type material. Holotype NSMT 644460 , paratype 2, NSMT 644461 .

Type locality. Off Southwest Taiwan, 40 fms deep .

Studied material (sequenced). TAIWAN • 2 lv; off Liuqiu I.; 22°13'N, 120°25'E; depth 286–347 m; TAIWAN 2013, stn CP4085; MNHN-IM-2013-41618, MNHN-IM-2013-41629 • 5 lv; off Liuqiu I.; 22°12'N, 120°24'E; depth 343–393 m; TAIWAN 2013, stn CP4086; MNHN-IM-2013-41613, MNHN-IM-2013-41614, MNHN-IM-2013- 41615, MNHN-IM-2013-41616, MNHN-IM-2013-41617 • 2 lv; off Liuqiu I.; 22°11'N, 120°22'E; depth 387–510 m; TAIWAN 2013, stn CP4087; MNHN-IM-2013-41630, MNHN-IM-2013-41631 • 5 lv; off Liuqiu I.; 22°11'N, 120°23'E; depth 372–436 m; TAIWAN 2013, stn CP4088; MNHN-IM-2013-41608, MNHN-IM-2013-41609, MNHN-IM-2013-41610, MNHN-IM-2013-41611, MNHN-IM-2013-41612 • 4 lv; off Liuqiu I.; 22°13'N, 120°25'E; depth 310–330 m; TAIWAN 2013, stn CP4089; MNHN-IM-2013-41619, MNHN-IM-2013-41620, MNHN-IM-2013-41621, MNHN-IM-2013-41622 • 4 lv; off Liuqiu I.; 22°13'N, 120°23'E; depth 329–371 m; TAIWAN 2013, stn CP4090; MNHN-IM-2013-41623, MNHN-IM-2013-41624, MNHN-IM-2013-41625, MNHN-IM-2013-41626,MNHN-IM-2013-41627 • 5 lv; off Liuqiu I.; 22°13'N, 120°24'E; depth 310–346 m; NanHai 2014, stn CP4099; MNHN-IM-2013-44003, MNHN-IM-2013-44005, MNHN-IM-2013-44006, MNHN-IM-2013-44007, MNHN-IM-2013-44008 • 4 lv; off Liuqiu I.; 22°13'N, 120°32'E; depth 327–372 m; DongSha 2014, stn CP4120; MNHN-IM-2013-50002, MNHN-IM-2013-50003, MNHN-IM-2013-50004, MNHN-IM-2013-50007.

Description. Shell of medium size for the genus (up to 37 mm), elongate oval. Protoconch low dome shaped, smooth, light yellow-brownish, of about one whorl with distinct impressed suture, further whorls’ sutures overlaid by callus. Protoconch borders indistinct, rendering whorl count impossible. Spire low, conical; primary callus moderately thick. Primary callus thick and covering all whorls except initial part of protoconch; surface of callus weakly glossy, strongly microshagreened. Secondary callus very thick, forming tongue-shaped pad extending to right-ventral side of last whorl and continuing up as thick pad, covering most of spire whorls. Surface of secondary callus strongly microshagreened and similar to that of primary callus. Body whorl cloak glossy, covered by fairly distinct spiral striation, often cloak with distinct lighter band in lower part adjoining anterior band. Olivoid groove not pronounced, in some specimens shallow depression in anterior part of last whorl close to aperture, corresponding to position of groove (e.g. MNHN-IM-2013-41616 – Fig. 17P ) and terminating in obtuse and very short, rounded extension on outer lip. Rear edge of anterior band distinct in a shape of sharp step. Anterior band different from shell cloak in colour, darker, of different shades of brown-orange. Upper anterior band weakly convex, sometimes nearly flat, separated from lower anterior band by additional distinct ridge. Upper anterior band with submedian darker spiral band. Lower anterior band narrower, nearly flat to weakly convex and separated from plication plate by deep and broad groove. Plication plate with 5–6 (5 in holotype) distinct narrow spiral ridges. Columella smooth. Aperture narrow oval, acute posteriorly, widest medially; outer lip sharp, slightly opisthocline, occasionally with weak extension corresponding to labral denticle; siphonal notch medium deep, asymmetrical. Columella crossed by blurred brown spiral band corresponding to lower part of anterior band, rarely with another spiral band corresponding to upper anterior band. Shell colour variable from very pale creamy to different shades of orange and brown, sometimes part of shell with bluish tint. Primary callus of the same shade as cloak, sometimes slightly darker. Secondary callus creamy on ventral part near aperture and of same shade as primary callus on dorsal side. Anterior band distinctly darker than cloak, brownish with darker median spiral band in upper part. Plication plate white to creamy.

Operculum vestigial, spanning only about 1/5 of aperture ( Fig. 17K ), broadly triangular, very thin ( Fig. 17L ), situated on dorsal part of the foot in live animal and difficult to find in preserved specimen (partially or completely concealed with contracted parapodia: Fig. 18 ).

Radula ( Fig. 20A–B ) studied in one specimen (MNHN-IM-2013-44003, SL 30.7 mm), typical for the genus, of about 70 transverse rows of teeth, 10–15 nascent. Radula about 1.6 mm in length (7.5% of AL), membrane about 135 µm in width (0.6% of AL).

Diagnostic cox-1 sites. 'C' in the site 35, 'A' in the site 55.

Remarks. The species exhibits moderate variability in shell outline and colouration. It was originally described without a precise locality, from a depth of approximately 75 m off southwestern Taiwan. However, all our specimens were collected much deeper, from 286 to 387 m.

The species closely resembles T. glans but differs in its smaller size (the largest specimen of T. monachalis in our collection measures 37 mm in SL, while T. glans reaches 47.8 mm). Another distinguishing feature is the relative width of the anterior and posterior parts of the anterior band. In T. monachalis , the average width of the lower part constitutes 43% of the width of the anterior part (range: 37–47%), whereas in T. glans , it is 29% of the width of the anterior part (range: 26–30%) ( Fig. 19 ). While these conchological differences are subtle, the species have entirely different operculum morphology. Furthermore, molecular data clearly confirm the existence of two distinct species.

Particular attention should be given to the opercula of the type specimens. In the original description, Ninomiya (1988) illustrated the holotype in a partially lateral position, hindering detailed examination of the operculum. Examination of the holotype and paratype 2 clearly demonstrated that they possess the operculum of Amalda , which is oval, thin, and has a subcentral nucleus shifted towards the lower edge ( Fig. 17D ). This is entirely different from the opercula of our specimens. Ninomiya did not specify the source of the material, which most likely came from dealers. It is possible that the opercula were intentionally or unintentionally switched with those of an Amalda species, especially since the vestigial opercula of T. monachalis are challenging to observe and retrieve.

Distribution. Taiwan ( Fig. 16 ).

Figures

FIGURE 16. Distribution of Turrancilla alcocki, T. monachalis, and T. apicalis in the central Indo-Pacific.

FIGURE 17. Turrancilla monachalis (Ninomiya, 1988), Taiwan. A–D. Holotype, NSMT 644460, SL 34.5 mm; D. Operculum, accompanying the holotype, enlarged (see discussion in the text). E. Paratype 2, NSMT 644461, SL 32.8 mm.F–H. MNHN- IM-2013-41618, SL 37.4 mm. I–J. MNHN-IM-2013-41619, SL 28.3 mm. K–L. MNHN-IM-2013-41613, SL 26.2 mm; K. Operculum at the same scale as the shell; L. SEM of the operculum, enlarged. M. MNHN-IM-2013-41624, SL 26.5 mm. N. MNHN-IM-2013-41630, SL 28.6 mm. O–P. MNHN-IM-2013-41616, SL 26.3 mm. All shells at the same scale.

FIGURE 18. Turrancilla monachalis (Ninomiya, 1988), Taiwan. Left – Dorsal view of the body with parapodia of the foot extended to show the operculum; Right – shell of the same specimen, SL 20.9 mm.

FIGURE 19. Comparison of the anterior bands in Turrancilla monachalis (Ninomiya, 1988), MNHN-IM-2013-41626, SL 29.6 mm (A) and T. glans (E. A. Smith, 1899), MNHN-IM-2007-33320, SL 33.2 mm (B). Abbreviations: LAB – lower part of the anterior band; UAB – upper part of the anterior band.

FIGURE 20. Radulae of Turrancilla. A–B. Turrancilla monachalis (Ninomiya, 1988), MNHN-IM-2013-44003, SL 30.7 mm; B – latero–ventral view of the bending plane. C–D. Turrancilla sibuetae (Kantor & Bouchet, 1999), holotype, MNHN-IM-2000- 1459.