Lyrischapa brevispira, Merle et al., 2014

Merle, Didier, Pacaud, Jean-Michel, Métais, Grégoire, Bartolini, Annachiara, Lashari, Rafiq A., Brohi, Imdad A., Solangi, Sarfraz H., Marivaux, Laurent & Welcomme, Jean-Loup, 2014, Volutidae (Mollusca: Gastropoda) of the Lakhra Formation (Earliest Eocene, Sindh, Pakistan): systematics, biostratigraphy and paleobiogeography, Zootaxa 3826 (1), pp. 101-138 : 116

Lyrischapa brevispira sp. nov.

( Figs 6 G–I, 7A–D)

Etymology. From the Latin brevis (short) and spira (spire).

Type locality. Stn 4: Lakhra Dome, Lakhra village section, base of the Lakhra Formation.

Type material. Holotype (stn 4: CPAG.RAN. I.18, cast MNHN.F.A50356), paratype 1 (stn 4: CPAG.RAN. I.19, cast MNHN.F. A50357 ), paratype 2 (stn 4: CPAG.RAN. I.20, cast MNHN.F.A50358).

Other material. 18 spm (stn 4: MNHN).

Description. Shell conical, very narrow, H 64, D ca. 35 mm (holotype (subadult) H 38.2, D 20.2 mm). Protoconch smooth, very flat, of two whorls, H 10–12, D 10 mm when complete. Transition protoconch/teleoconch not defined. Teleoconch of 3 whorls. Spire very low, occupying 6% of total shell height. Spiral whorls flat, narrow, separated by shallow suture. Sutural ramp extending partially onto preceding whorl. Last whorl narrow, rather conic. Spiral sculpture of obsolete threads, present only on first teleoconch whorl. Second and last whorls lacking spiral sculpture, even on base. Axial sculpture of very short shoulder costae formed by small spinelets. First whorl: 9–10 costae. Second whorl: 8–9 costae. Third whorl: 11 costae. Aperture narrow, occupying 97% of total height, 15% of diameter. Inner lip straight, columella with five strong folds succeeded posteriorly by one weaker fold, one or two secondary folds intercalated between major folds in a few specimens; inner lip callus narrow. Anal sulcus thin, against suture. No shoulder sinus. Outer lip thin, not thickened externally. Siphonal canal short; siphonal notch shallow; siphonal fasciole low, weak.

Comparisons. In Lyrischapa haimei and in L. sismondai , spiral sculpture consisting of fine threads persists during the whole ontogeny and covers the last whorl, whereas in L. brevispira , the spiral sculpture is obsolete on the first teleoconch whorl and disappears on later whorls. For this reason, this species can be compared with L. vredenburgi and L. blanfordi , with which it shares obsolete or absent sculpture on the last whorl. L. vredenburgi and L. brevispira have a large protoconch of two whorls, up to 10 mm in width, but the apex is globose in L. vredenburgi , whereas it is flat in L. brevispira . L. brevispira differs from L. vredenburgi by its narrower shape, by its poorly developed spines, by its numerous columellar folds (6–8 instead 5–6) and by its anal sulcus against the suture. In its narrow shape, L. brevispira is similar to L. blanfordi , but it is distinguished by its larger protoconch, a very flat spire and poorly developed spines. Because of its poorly developed shoulder spines on the last whorl, L. brevispira retains a juvenile aspect in its adult stage and could be regarded as a paedomorphic species of Lyrischapa .

Stratigraphic range. Lakhra Formation: Lakhra Dome.

Figures

FIGURE 6. A – F. Lyrischapa blanfordi (Vredenburg, 1923), A – C (CPAG. RAN. I. 17, ventral (A), dorsal (B) and apical (C) views, stn 4), D – E (CPAG. RAN. I. 16, ventral (D) and dorsal (E) views, stn 4), F (CPAG. RAN. I. 15, ventral view, stn 4); G – I. Lyrischapa brevispira sp. nov., holotype, CPAG. RAN. I. 18, ventral (G), dorsal (H) and apical (I) views, stn 4. Scale bars: A – H = 10 mm.