Vaceuchelus semilugubris (Deshayes, 1863) Figs 4L, 50, 51
Turbo semilugubris: Deshayes 1863: 72, pl. 9 [36], figs 9, 10; Martens 1880: 294; Herbert 1996: figs 70, 71 (syntype). Type loc.: Reunion.
Leptothyra semilugubris: Pilsbry 1888: 252, pl. 58, fig. 52a; Viader 1937: 55.
Vaceuchelus semilugubris: Poppe et al. 2006: 47.
Description:
Shell: Small, turbiniform, robust; length more or less equal to diameter (L/D=0.92-1.04); teleoconch of approx. 3.5 whorls, but apex usually badly eroded; sculpture cancellate; first whorl strongly shouldered at mid-whorl, almost horizontal above shoulder and vertical below it; shoulder develops into a strong spiral cord at end of whorl, another cord evident at level of abapical suture; axial pliculae do not develop until near end of whorl; this sculpture strengthening during second whorl with an additional cord arising between first cord and adapical suture; these two cords becoming the large peripheral and supra-peripheral cords of last adult whorl; 1-2 additional secondary cords arising above supra-peripheral cord during third whorl; axial pliculae stronger on second and subsequent whorls, prosocline and raised into granules where they cross spiral cords, granules somewhat angular on second whorl, but becoming progressively more rounded and bead-like on subsequent whorls; interstices quadrate; last adult whorl with 25-30 pliculae. Base with 5 spiral cords, the first level with suture, the fifth small and spiralling into umbilicus; umbilicus narrowly patent even in adults. Peristome oblique and nearly tangential, aperture subcircular; columella shallowly concave with a rounded tooth at its base; interior of outer lip of mature individuals subterminally thickened and set with approx. 10 ridge-like denticles, with an additional row of smaller granules just inside lip edge; apertural dentition absent in immature specimens, in these the outer lip is strongly notched at ends of spiral cords; interior nacreous, weakly angled beneath external cords, but labral denticles not extending into aperture as in-running ridges.
Microsculpture (Fig. 51A, B): Juvenile microsculpture comprising irregular vermiform spiral threads; subsequent microsculpture mostly granular, but with traces of scratchlike markings.
Protoconch (Fig. 51C): White, slightly exsert, eroded in most material; diameter ca 285 [micro]m; strongly sculptured with an irregular superficial reticulation showing traces of axial alignment, but no spiral element. Terminal lip more or less straight, but perhaps evincing signs of a broken beak-like projection; becoming concave toward abapical suture.
Colour: Shell white, variously patterned with black spots, blotches or axial bands, orientation of pattern prosocline in some specimens, opisthocline in others; markings generally finer on base; pattern fading to brown in old material. Occasional specimens with almost no black markings (Fig. 50F). Coloration of fresh specimens somewhat obscured by dirty buff intritacalx deposit, superficial calcareous encrustations and debris.
Dimensions: Largest specimen, length 3.55 mm, diameter 3.40 mm; smallest specimen with mature apertural dentition, length 2.6 mm, diameter 2.7 mm.
Operculum (Fig. 4L): Relatively tightly multispiral throughout.
Radula (Fig. 51D, E): Formula [infinity]+3+1+3+[infinity]; ca 50 transverse rows of teeth; transition from lateral to marginal series clear. Rachidian with broad, trigonal cusp, well-developed hood, and a distinct transverse basal ridge; cutting edge with a slender,...