Leptochiton chatticus ( Janssen, 1978 )

Leptochiton chatticus ( Janssen, 1978)

Fig. 32 View FIGURE 32

Lepidopleurus chatticus Janssen, 1978, p. 220 , pl. 15, figs 18–19; Van Belle 1981, p. 27; Gürs 1995, p. 19.

Lepidopleurus ( Leptochiton) chatticus ; Dell’Angelo & Palazzi 1989, p. 75, pl. 22, figs 1–2, pl. 25, figs 4–5.

Leptochiton chatticus ; Dell’Angelo et al. 2011, p. 953, Appendix 2.

Lepidopleurus jansseni Gürs, 1995, p. 21 , pl. 2, figs 1–4; Schwabe 2005, p. 96; Dell’Angelo et al. 2011, Appendix 2 p. 953. Type material. Holotype SMF 250021, tail valve, Fig. 32A View FIGURE 32 . Paratype SMF 250022, tail valve ( Fig. 32B View FIGURE 32 ) (both figured in Janssen 1978: pl. 15, figs 18–19). Types of Leptochiton jansseni figured by Gürs: Holotype, tail valve ( Fig. 32H View FIGURE 32 ) and paratypes, head ( Fig. 32E View FIGURE 32 ) and intermediate ( Figs 32F–G View FIGURE 32 ) valves.

Type locality. Höllkopf , near Glimmerode ( Germany) .

Type stage. Oligocene (Chattian).

Material examined. Oligocene (Chattian): Paratype SMF 250023 About SMF /1E, Figs 32C–D View FIGURE 32 (from R. Janssen, see Dell’Angelo & Palazzi 1989: 76). Maximum width of the valves: 4 mm .

Description. Head valve semicircular, posterior margin widely V-shaped, slope straight. Intermediate valves broadly rectangular, width more than three times the length, flat, rounded in anterior profile, anterior margin almost straight, side margins rounded, posterior margin straight, apex not developed, lateral areas not raised. Tail valve semicircular (W/L = 1.86–1.95), flat, anterior margin straight, mucro slightly protruding, in anterior position.

Tegmentum with growth lines clearly marked. HV, LA and PMA sculptured with radial series of dense, minute, roundish granules (LA 10–13, PMA 63–68). CA and AMA sculptured with 16–20 longitudinal series of granules barely visible.

Articulamentum lacking insertion laminae to girdle, with large and triangular apophyses.

Remarks. Leptochiton chatticus ( Janssen, 1978) is only known for the original description, based on the three types of valves (head, intermediate and tail), 15 in total. It shows, according to the author, remarkable affinities with L. maguntiacus de Rochebrune, 1882 , from which it differs to be flatter, for the more elliptical shape of the tail valve and the mucro less protruding and more displaced anteriorly. Unfortunately, the original description is rather short, so as to leave many uncertainties, and the iconography presented is insufficient. Fortunately, Janssen sent a paratype to the senior author, illustrated in the drawing, Figs 32C–D View FIGURE 32 ( Dell’Angelo & Palazzi 1989: 77), which made possible to better define some characteristics of the species.

Gürs (1995) did not report Leptochiton chatticus in his Thesis, considering the paratype SMF 250022 as a juvenile specimen of Lepidopleurus virgifer (Sandberger, 1859) ( Gürs 1995, p. 19: “ in juvenile individuals the granules not yet fused into radial ribs ”.

Gürs (1995) described in his Thesis a new species ( Lepidopleurus jansseni ) from the lower Oligocene of Eckelsheim ( Germany), based on the three valves. The thesis was not published, and the taxon Lepidopleurus jansseni was not formalized. The material of Lepidopleurus jansseni , not present at SMF (R. Janssen, pers. comm., 2020) is possibly kept in the Gürs collection. The “ type ” material (with the three types of valves) was figured by Gürs (1995) and we report here these same illustrations ( Figs 32E–H View FIGURE 32 ). Based on the descriptions and iconography, Lepidopleurus jansseni is morphologically indistinguishable from L.chatticus , and we prefer therefore to synonymize the two taxa.

Comparisons. The characteristics of the sculpture of Leptochiton chatticus Janssen, 1978 agree with the belonging of the species to the Leptochiton cancellatus group, see Tab. 2. The species is strongly depressed, which differentiates it from L. cancellatus ( Sowerby, 1840) and L. sarsi Kaas, 1981 , more similar for the shape and size of the granules. Very characteristic is the tail valve, whose mucro is very displaced anteriorly, so that the antemucronal area is reduced to a narrow strip with longitudinal striae of granules formed by a few coarse granules (from 2 to 6) which tend to coalesce.

Distribution. Lower Oligocene (Rupelian): North Europe: Germany: Steigerberg ( Gürs 1995). Upper Oligocene (Chattian): North Europe: Germany: Glimmerode ( Janssen 1978).