Fig. 8 a–c
Ligula substriata Montagu, 1808 (p. 25).
Montacuta substriata Montagu—Jeffreys 1881 (p. 698); Hidalgo 1917 (p. 450). Montacuta substriata (Montagu) — Deroux 1961 (p. 107, fig. 4 M. s.); Tebble 1966 (p. 89, text-figs. 42a–c). Montacuta substriata (Montagu, 1809) — Nordsieck 1969 (p. 93, pl. 14, fig. 52.40). Montacuta substriata (Montagu, 1808) — Poppe & Goto 1993 (p. 87, pl. 14, fig. 13); Repetto et al. 2005 (p. 315, mid right fig.);
Oliver et al. 2016 (online resource).
Diagnostic characters. Oval outline; very long anterior side; hinge of the right valve with an obliquely elongate anterior cardinal tooth; 9–10 weak radial ridges in the middle of the shell. Prodissoconch: shell type ST-2A; length about 210 µm (P-1 about 120 µm); slightly oval outline, somewhat more elongated in posteroventral direction; convex profile; P-1 roughly D-shaped, flattened, elevated with respect to P-2; P-1 surface weakly striated around the cicatrix; P-2 with dense fine commarginal growth welts; transition to the nepioconch well marked (no lip).
Remarks. The elevated P-1 appears to be rather unusual, as well as the dense growth markings on P-2; consequently, the P-1/P-2 transition could also be interpreted as prodissoconch/nepioconch transition. We consider the concentrically sculptured shell as P-2 because of the clear demarcation with the adult shell and the completely different scupltural features of this latter.
Occurrence. Box-corer sample BC72 (1 specimen). Length: 2 mm.
Distribution and habitat. Montacuta substriata is distributed from Iceland to the Mediterranean, at infralittoral depths and down to about 600 m, being a commensal organism living attached to the anal spines of the heart urchins Spatangus purpureus and Echinocardium flavescens (Nordsieck 1969; Poppe & Goto 1993; Oliver et al. 2016).
Fossil record. Plio-Pleistocene of Norway and Italy (Monterosato 1872; Monegatti & Raffi 2001).