Callistochiton zitteli (de Rochebrune, 1882 )

Callistochiton zitteli (de Rochebrune, 1882)

Fig. 86 View FIGURE 86

Gymnoplax zitteli de Rochebrune, 1882, p. 59 ; Kaas & Van Belle 1981, p. 82 [nom. nov. pro Chiton fimbriatus Boettger, 1869 , non Sowerby, 1840 (a Recent species from Peru)].

Chiton fimbriatus Boettger, 1869, p. 10 , pl. 1, fig. 13a–g; Boettger 1870, p. 40, pl. 8, fig. 13a–g; de Rochebrune 1882, p. 59; Wenz 1932, p. 14; Kaas & Van Belle 1981, p. 38.

Callistochiton zitteli ; Janssen 1978, p. 224, pl. 16, figs 36–38; Hocht 1986, p. 209; Gürs 1995, p. 25; Dell’Angelo et al. 2011, p. 953, Appendix 2.

Type material. Lectotype SMF 14.28a ( Fig. 86H View FIGURE 86 ) designed by Janssen 1978, tail valve figured by Boettger (1869), pl. 1b, figs 13a–b ( Fig. 86E View FIGURE 86 ). Paralectotypes SMF 14.28b–c ( Figs 86F–G View FIGURE 86 ), valves figured by Boettger (1869), pl. 1b, figs 13c–e ( Figs 86C–D View FIGURE 86 ) and 13f–g ( Figs 86A–B View FIGURE 86 ), respectively.

Type locality. Gienberg ( Germany) .

Type stage. Oligocene (Rupelian).

Material examined. No actual material available, only descriptions and illustrations from the literature.

Description. Head valve semicircular, strongly arched, posterior margin widely V-shaped. Intermediate valve broadly rectangular (W/L = 2.14), moderately elevated, semicarinate in anterior profile, anterior margin slightly sinuose at both sides of jugal area slightly extended forward, side margins slightly rounded, posterior margin almost straight at both sides of well evident apex, lateral areas not raised. Tail valve semicircular/elliptical (W/L = 1.68), mucro small, subcentral.

HV, LA and PMA sculptured with radial granulose ribs (HV 11–14, with some finer secondary ribs, LA 3–4, PMA 11–18). PA and AMA sculptured with granulose longitudinal riblets (CA 7–12 on half valve, usually 9), crossed by few concentric ridges, JA smooth.

Articulamentum with apophyses very large, broad, protruding far, connected in middle, leaving only a narrow sinus free, apical area in intermediate valves triangular and small, insertion plates short, slit formula 25 / 3–4 / 15, teeth strongly furrowed on upper side and thickened at edges.

Remarks. The fossil record of Callistochiton zitteli (de Rochebrune, 1882) is limited to the Oligocene (Rupelian) of Germany.

Chiton fimbriatus Boettger, 1869 could not be mantained as it was already known Chiton fimbriatus Sowerby, 1840 , a species from Peru now considered “taxon inquirendum” by WoRMS.

Comparisons. Callistochiton zitteli is characterized by a number of slits far greater than the other Callistochiton discussed in this study (see Tab. 13).

Distribution. Lower Oligocene: North Europe: Mainz Basin, Germany: Gienberg, Heimberg, Zeilstück ( Janssen 1978; Hocht 1986).