Amphithyris parva MacKinnon, Hiller, Long & Marshall 2008

Amphithyris parva MacKinnon, Hiller, Long & Marshall, 2008

(Fig. 4; Table 3)

Amphithyris parva Logan, 2007: p. 3108 nomen nudum (erroneously cited original description as of 2007, citation pre-dates the original publication)— MacKinnon et al. 2008: p. 329, fig. 2A–E; table 1 (original description)

Type material. Holotype: NMNZ Br 1455, Paratypes: NMNZ Br 1069

Type locality. Cook Strait, near Wellington, New Zealand.

Material examined. Paratypes (10): NMNZ Br 1069

Additional material. NZGS BR 2288

Diagnosis. Dorsibiconvex shell, weak capillae on dorsal valve exterior and ventral valve exterior. Dorsal median septum absent.

Description. Very small species of Amphithyris. Shell dorsibiconvex, roundly subquadrate, transparent. Dorsal valve more inflated than ventral valve and without median septum (Fig. 4 A). Large amphithyrid foramen (Fig. 4 B), short socket ridges reach beyond posterior shell edge (Fig. 4 C). Exterior surface smooth with weak capillae (Fig.

4C). More inflated than ventral valve (Fig. 4 C and F). Ventral valve with small emergent hinge teeth not parallel to long straight hinge line (Fig. 4 D). Very weak muscle impressions visible (Fig. 4 E). Exterior surface smooth with weak capillae (Fig. 4 F).

Remarks. A. parva was described by MacKinnon et al. (2008) on the basis of apparent 'topotypic' material of A. buckmani. Both Foster (1974) and Campbell & Fleming (1981) were unable to locate Thomson's holotype of A. buckmani (NMNZ Br 80) for comparison with their new species (A. hallettensis Foster, 1974 and A. richardsonae Campbell & Fleming, 1981) and instead used what were assumed to be immature specimens collected later (NMNZ Br 1069) and "five additional juveniles attached to a concretionary boulder from the Outer Island Bay Bank (NZGS BR 2288)" (Campbell & Fleming 1981: p. 147–148). After their re-discovery of the holotype of A. buckmani at NMNZ, MacKinnon and co-workers came to the conclusion that the immature specimens assigned to A. buckmani by Foster (1974) and Campbell & Fleming (1981) belong to a new species, A. parva, which according to our study differs from the other species by its dorsibiconvex shells, the absence of a dorsal median septum and the presence of capillae on the outside of both dorsal and ventral valve. The material from Outer Island Bay Bank (NZGS BR 2288) was assigned to A. parva (MacKinnon et al. 2008), but not listed as type material.