Danilia boucheti, Herbert, 2012

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 : 412-414

Danilia boucheti sp. n.

Figs 13 , 14

Etymology: Named for Prof. Philippe Bouchet (MNHN), well-known malacologist and co-ordinator of numerous important dredging expeditions.

Description: Shell: Turbiniform with moderately elevated spire (L/D=1.09–1.14); teleoconch of 4.25–4.5 whorls; apical angle approx. 75°; whorls convex and suture indented, level with periphery on spire, but descending below this just prior to outer lip; protoconch sunken and apex thus appearing truncated; outer lip with well-developed subterminal varix. First teleoconch whorl sculptured with approx. 17 orthocline axial pliculae; 4 spiral cords develop during second whorl (P1–P4); additional secondary and tertiary cords arising during subsequent whorls; abapical cord (P4) strongest; axial pliculae narrow, becoming strongly prosocline on later whorls, the crest crisp and leaning forward; spiral cords beaded where crossed by axial pliculae, beads on primary cords scale-like; last adult whorl with P2–P4 (particularly P3 and P4) stronger than other cords; P3 and P4 delimiting an almost cylindrical peripheral band; subsutural cord (P1) also slightly larger and with angular beads that intermesh in a zip-like manner with beads of peripheral cord (P4) of preceding whorl, delimiting a narrow sutural channel; number of intermediary cords variable, generally only 1–2 between P3 and P4; 5–6 between P1 and P3 (including P2); beading of intermediary cords weaker; cords generally somewhat narrower than their intervals and slightly stronger than axial pliculae; interaction of cords and pliculae producing a fine, regular, oblique cancellation with rhomboidal interstices. Base with approx. 10 spiral cords of alternating size; the second one below peripheral cord generally the strongest; axial pliculae continue onto base rendering basal cords finely beaded. Peristome markedly oblique, more or less in one near-tangential plane; aperture roundly D-shaped and flattened in parietal region; columella lip a thickened pillar set with 2 teeth, lower one a well-developed, rounded peg, the upper one smaller; interval between teeth shallowly concave; umbilical region medial to thickened columella pillar sunken, forming an elongate curved pit, broadening basally; umbilical/parietal region covered by a thin, extensive inductural callus; callus translucent, smooth and glossy, raised somewhat basally and confluent with flaring margin of outer lip; interior of outer lip with an in-set varix lying beneath external outer lip varix; internal varix swollen to form prominent bulge near junction of basal and columella lips, creating deep, U-shaped notch below lower columella tooth; apertural varix set with numerous small, ridge-like denticles, these restricted to varix, not running into deeper portions of aperture; interior of aperture with traces of nacre (specimens not fresh), not spirally lirate, though spiral cords of shell exterior visible by translucence; margin of outer lip flaring; external varix ca 0.25 mm wide and set back a similar distance behind lip edge.

Microsculpture: Irregular, vermiform spiral threads present on early whorls; later whorls with evidence of scratch-like sculpture, but sculptural details largely obscured by dirty intritacalx deposit, particularly in interstices.

Protoconch: Present only in holotype; translucent white; diameter 320 µm; sunken into first teleoconch whorl and somewhat tilted; terminal lip evidently more or less straight.

Colour: First teleoconch whorl uniform white, later whorls pale buff with faint brown spots on primary spiral cords; flared outer lip and external varix with brown marks in intervals between paler primary spiral cords. One paratype with darker brown subsutural blotches, stronger spots on the primary peripheral cords and irregular brownish mottling on the base.

Dimensions: Holotype (largest specimen), length 5.32 mm, diameter 4.66 mm.

Operculum, radula and external anatomy: Unknown.

Holotype ( Fig. 14A–C ): MADAGASCAR: Antsiranana, south-west of Cap d’Ambre (12.133°S 48.933°E), - 238–249 m, Campagne Miriky , st’n DW3196, dredged, 28.vi.2009 ( MNHN 24648 ).

Paratypes: Same data as holotype ( MNHN 24649 , 2 specimens) .

Note: The holotype is the most complete specimen, but its apertural dentition is subadult; one of the paratypes has more mature apertural features ( Fig. 14D ), but is missing the apical whorls.

Distribution ( Fig. 13 ): Known only from off the coast of the far north of Madagascar, - 238– 249 m.

Remarks: Danilia boucheti is smaller than any of the other described species of Danilia , most of which attain or exceed 10 mm in length (Vilvens & Héros 2005). Perhaps the most similar species is D. angulosa Vilvens & Héros, 2005 from Melanesia and the Philippines, which is also small (length up to 7.9 mm) and has stronger spiral cords associated with the periphery, creating a cylindrical peripheral band. In that species, however, the cords are stronger than in D. boucheti , the whorls more distinctly shoulder- ed, and there is only one intermediary cord between the shoulder cord (upper peripheral cord) and the subsutural cord. In D. boucheti there are 5 or 6 intermediary cords in this region.

Figures

Fig. 13. Distribution of Danilia species in the south-western Indian Ocean: D. boucheti (square), D. textilis (triangles). Each symbol represents one or more records.

Fig. 14. Danilia boucheti sp. n., south-west of Cap d’Ambre, Antsiranana, Madagascar: (A–C) holotype (apertural features subadult), length 5.3 mm (MNHN 24648); (D) paratype (apertural features adult, apex missing), diameter 4.46 mm (MNHN 24649).