Parachiton hylkiae Strack, 1993

Dell’Angelo, Bruno, Landau, Bernard M., Sosso, Maurizio & Taviani, Marco, 2020, Late Pleistocene Red Sea Mollusca: 1. Polyplacophora, Zootaxa 4772 (3), pp. 401-449 : 406-407

Parachiton hylkiae Strack, 1993

( Fig. 3 )

Leptochiton (Parachiton) hylkiae Strack 1993, p. 4 , pl. 1, figs 2–8, pl. 2, figs 1–4; Schwabe 1997, p. 28, 2 figs p. 30; Kaas & Van Belle 1998, p. 92; Anseeuw & Terryn 2004, p. 6, 22; Kaas et al. 2006, p. 18, fig. 2, map 18.

Parachiton hylkiae ; Kaas 1996, p. 373; Saito 1996, p. 165; Sirenko 2015, p. 145.

Leptochiton hylkiae ; Dekker & Orlin 2000, p. 7.

Type material. Holotype RMNH 9313, specimen 9.8 x 4.4 mm. Paratypes in Strack and van der Sman collections.

Type locality. Egypt, Red Sea , southern side of Giftun Kebir Island .

Material examined. Egypt (Hurghada: this study): St. 13: 2 valves (1 head and 1 intermediate), Figs 3 A–G ( MZB 50524); St. 14: 2 valves (1 intermediate and 1 tail), Figs 3 H–I ( BD 180; MZB 50525). Maximum width: 4.5 / 4 / 3.1 mm.

Description. Head valve semicircular, tegmentum sculptured with numerous radiating chains of minute granules, concentrically crossed by several conspicuous growth lines.

Intermediate valves broadly rectangular, L/W = 0.38, highly elevated (H/W = 0.45), anterior profile rounded, front, sides and posterior margins almost straight, apex inconspicuous, lateral areas not raised, poorly defined, sculptured like head valve, central area with similar, longitudinally oriented rows (more than 70) of usually coalesced, minute granules, interstices very narrow.

Tail valve incomplete, mucro overhanging posterior edge, postmucronal slope very steep, straight, postmucronal area narrow, sculptured like head valve, antemucronal area like central areas.

Articulamentum with apophyses small.

Remarks. Detailed descriptions of this species were given by Strack (1993) and Kaas et al. (2006). Two species of Parachiton are living in the Red Sea, P. hylkiae ( Strack, 1993) and P. jordanensis ( Anseeuw & Terryn, 2004) . They are easily separated by the position of the mucro (terminal in P. hylkiae , often overhanging the posterior edge vs situated at about 4/5 of the total length in P. jordanensis ), the number of longitudinal rows of granules in the antemucronal area of the tail valve (ca 85 vs 50) and in the central area of intermediate valves (ca 68–95 vs 45–50), and the number of radiating rows of granules in the lateral areas of intermediate valves (ca 20 vs 10–12).

The material at hand is scarce and consists of only four valves including an incomplete and partially eroded tail valve. All characters support the attribution to Parachiton hylkiae , including the terminal mucro ( Figs 3 H–I), the overhanging the posterior edge, the rounded profile of the intermediate valve ( Fig. 3G ), and the high number of longitudinal rows of granules, more than 70 in the central area of intermediate valve ( Fig. 3D ). The number of longitudinal rows of granules in the antemucronal area of the tail valve cannot be counted accurately, but is high, tending towards that typical of P. hylkiae .

This is the first fossil record of this species.

Distribution. Late Pleistocene: Egypt (Hurghada: this study). Present-day: Indian Ocean: Northern Red Sea ( Strack 1993).

Figures

FIGURE 3. Parachiton hylkiae Strack, 1993, Egypt, Hurghada, Late Pleistocene (last interglacial MIS5e). A–C. MZB 50524a, head valve (St. 13), width 4.5 mm, dorsal, lateral and posterior views. D–G. MZB 50524b, intermediate valve (St. 13), width 4 mm, dorsal view, detail of tegmentum surface of central and lateral areas, ventral and frontal views. H–I. MZB 50525, tail valve (St. 14), width 3.1 mm, dorsal and lateral views. Scale bar: 100 µm (E).