Herpetopoma, : Pilsbry, 1890

Herbert, D. G., 2012, A revision of the Chilodontidae (Gastropoda: Vetigastropoda: Seguenzioidea) of southern Africa and the south-western Indian Ocean, African Invertebrates 53 (2), pp. 381-381 : 437-439

Herpetopoma (s.s.) stictum sp. n.

Figs 28 , 30 , 31

Euchelus gemmatus [non Gould, 1845]: Jay 2009.

Etymology: From Greek stiktos (spotted); in reference to the colour pattern.

Description:

Shell: Small, trochoid-turbiniform, relatively solid; length slightly exceeding diameter (L/D=1.07–1.19); teleoconch of approx. 4.5 whorls; spire whorls rather flat-sided, last adult whorl rounded, but slightly flatter below periphery; suture indented, level with subperipheral spiral cord, but descending below this immediately prior to aperture in fully mature individuals; first teleoconch whorl initially sculptured only with axial pliculae (ca 20); 2 spiral cords arising in latter half of whorl, a third arising beneath adapical suture during second whorl, a fourth arising below subsutural cord during third whorl; end of penultimate whorl with 4 spiral cords of more or less equal strength above abapical suture; cords equal to or slightly narrower than their intervals and crossed by prosocline axial pliculae; pliculae slightly narrower than spiral cords, the latter with roundly angular beads where crossed by pliculae, those on subsutural and peripheral cords slightly stronger (ca 30 on peripheral cord of last adult whorl); interstices roundly quadrate. Base with 5 spiral cords, the outer (subperipheral) one strongest and with roundly angular beads, the others progressively with lower, more rounded beads; a weak sixth cord bordering umbilicus; cords slightly wider than their intervals. Umbilicus open in juveniles and subadults, steep-sided, occasionally remaining narrowly patent even at maturity, but generally occluded by reflected columella lip and if evident at all then only as a shallow depression. Peristome markedly oblique, almost tangential; aperture D-shaped, somewhat flattened parietally; columella pillar well developed, a little oblique and protruding slightly into aperture; a distinct, peg-like tooth at its base with a second low bulge sometimes evident above this; interior of outer lip thickened and set with 7 or 8 primary denticles which extend into aperture as in-running ridges; that nearest columella larger, a deep U-shaped notch separating it from basal columella tooth; outer portion of lip flaring and bearing additional secondary granules and wrinkles external to primary denticles; these continue around reflected portion of columella lip, one particularly strong secondary granule near base of basal columella notch; parietal callus not extending beyond limit of peristome, sometimes with traces of superficial wrinkle-like ridges; interior of aperture nacreous.

Microsculpture ( Fig. 31B, C ): Apical whorls with vermiform spiral threads; weak scratch-like sculpture developing subsequently, but retaining traces of vermiform threads on spiral cords; interstices with sparse microscopic granules.

Protoconch ( Fig. 31A, C ): Translucent whitish in fresh specimens, last quarter whorl and initial half of first teleoconch whorl mauve-brown; more or less level with early part of first teleoconch whorl, its apex slightly down-tilted; diameter 250–280 µm; terminal lip weakly convex; superficial sculpture well developed, irregular and wavy, with a predominant axial alignment; no spiral component evident.

Colour: Whitish with sparse, mauve-brown spots on spiral cords; spots sometimes aligned into diffuse axial bands on last adult whorl; base with fewer spots, generally more uniform white; spots fading to pinkish brown in old or worn specimens; fresh examples with a thin, dirty-buff, chalky intritacalx deposit.

Dimensions: Holotype, length 4.9 mm, diameter 4.25 mm; length variation of mature specimens 3.3–5.3 mm.

Operculum, radula and external anatomy: Unknown.

Holotype ( Fig. 30 ): RÉUNION: not further localised (M. Jay coll’n, MNHN 24651 ).

Paratypes: RÉUNION: same as holotype (M. Jay coll’n, MNHN 24652 , 12 specimens). MAURITIUS: off Troux aux Biches (20.0325°S 57.5411°E), reef front, ca - 5 m, fine sand, D. Herbert, ix.1991 ( NMSA

K8309/T2757, 1 specimen); ditto (20.0325°S 57.5408°E), reef front, ca - 10 m, fine sand, D. Herbert, ix.1991 ( NMSA K8593 /T2739, 11 specimens) ; Riambel lagoon (20.5206°S 57.4883°E), beach-drift, R. Kilburn & D. Herbert, ix.1991 ( NMSA K7767 /T2755, 45 specimens, K7771/T2756, 5 specimens); Gris Gris (20.5243°S 57.5239°E), debris on surf beach opposite reef-break, R. Kilburn & D. Herbert, ix.1991 ( NMSA K8294 / TT 2753, 1 specimen, K9324/T2754, 10 specimens) .

Additional material examined (all NMSA): MAURITIUS: Pointe Radeau, south of Roches Noires (20.1287°S 57.7573 E), shell debris near reef gap, R. Kilburn & D. Herbert, ix.1991 (K9587) ; Tamarin Bay (20.3264°S 57.3775°E), beach-drift, R. Kilburn & D. Herbert, ix.1991 (K8497) ; Souillac, lagoon below cliffs west of Gris Gris (20.525854°S 57.527375°E), living, in washings from algae and dead coral blocks, D. Herbert, 14.ii.2011 (L8356, L8402 living juvenile) . RODRIGUES: Between Anse aux Anglais and Pointe Venus (19.6752°S 63.4313°E), beach-drift, D. Herbert, ix.1991 (K7795) ; Anse aux Anglais (19.6716°S 63.4334°E), reef crest and platier nécrose, exposed at LT, D. Herbert, ix.1991 (K8672) ; Grand Baie (19.67175°S 63.45089°E), beach-drift near stream, D. Herbert, ix.1991 (K9162).

Distribution and habitat ( Fig. 28 ): Known only from the Mascarene Islands. Dead shells are moderately common in beach-drift samples, but living material has rarely been found. Jay (2009) reported it (as Euchelus gemmatus ) as ‘living under stones at 10– 15m. Rare’ in Réunion, and I obtained a single live-taken juvenile from algal and coral washings collected at LST on the reef crest at Souillac, Mauritius.

Remarks: With its spotted colour pattern, Herpetopoma stictum resembles H. serratocinctum , however, the present species attains a larger size (max. length 5.3 vs 3.1 mm), and has a less globose, more trochiform profile. In addition, H. serratocinctum has sharper sculpture, with spiral cords of alternating size and a saw-toothed peripheral cord. H. howensis Jansen, 1994 from Lord Howe Is. is also spotted, but has a less elevated spire, a weaker basal columella tooth and has intermediary spiral threads between the primary spiral cords.

The Hawaiian H. corrugatum ( Pease, 1861) has a more roundly beaded sculpture, a weaker basal columella tooth, a less obviously spotted colour pattern and commonly retains an open umbilicus ( Fig. 69A, B ). H. fimbriatum ( Pease, 1861) , also reportedly from Hawaii, has a more angular periphery and only three spiral cords on the penultimate whorl, and lacks a spotted colour pattern ( Fig. 69C, D ). Jay (2009) confused the present species with another Pacific species, H. gemmatum (Gould, 1845) , but that species has more rounded whorls, a more finely beaded sculpture and a clearly patent umbilicus. (NB: The shell figured by Johnson (1964: pl. 15, fig. 10) as the lectotype of Trochus (Monodonta) gemmatus Gould, 1845 , with a diameter of 20 mm cannot in fact be the genuine lectotype.) Diloma verruca Gould, 1861 , a very poorly documented species from Chinese waters, also belongs within this group of Herpetopoma species, but has two widely spaced primary spiral cords at and just above the periphery of the last adult whorl ( Fig. 69E, F ).

Figures

Fig. 28. Distribution of Herpetopoma serratocinctum (squares) and H. stictum (triangles). Each symbol represents one or more records.

Fig. 30. Herpetopoma stictum sp. n.: holotype, length 4.9 mm, diameter 4.25 mm, Réunion (M. Jay coll’n, MNHN).

Fig. 31. Herpetopoma stictum sp. n., paratypes, off Troux aux Biches, Mauritius (NMSA K8593/T2739): (A) apex, bar = 0.5 mm; (B) adult microsculpture, bar = 200 µm; (C) protoconch, bar = 100 µm.

Fig.69.Herpetopoma species examined for comparison:(A, B) Euchelus corrugatus Pease,1861, lectotype (designated Kay 1965: 58), Sandwich Islands [Hawaii], length 3.8 mm, diameter 3.7 mm (NHMUK 1962821); (C, D) Euchelus fimbriatus Pease, 1861, holotype, Sandwich Islands [Hawaii], length 3.7mm, diameter 3.6 mm (NHMUK 1962823); (E, F) Diloma verruca Gould, 1861, lectotype (designated Johnson 1964: 167), Coral Seas, China, length 3.2, diameter 2.7 mm (USNM 420).