Pratulum quinarium ( Marwick, 1944 )

Saether, Kristian P., Jingeng, Sha, Little, Crispin T. S. & Campbell, Kathleen A., 2016, New records and a new species of bivalve (Mollusca: Bivalvia) from Miocene hydrocarbon seep deposits, North Island, New Zealand, Zootaxa 4154 (1), pp. 1-26 : 11-12

Pratulum quinarium ( Marwick, 1944)

( Fig. 6 )

Nemocardium (Pratulum) quinarium Marwick, 1944: 266 ; pl. 36, figs. 10, 16.

Material. Sixteen specimens, 12 numbered: two from Moonlight North (Y16/f0694), L4653 ( Fig. 6 A), L4654 ( Fig. 6 D); 14 from Tauwhareparae (Y16/f0539), L4655 ( Fig. 6 C), L4656–4663, L4664 ( Fig. 6 B), UOA.

Remarks. Details of the muscle scars of Pratulum quinarium ( Marwick, 1944) remained unobserved or unreported before this study, and are described here from a single small specimen ( Fig. 6 A). The anterior adductor scar is elongate dorsoventrally, rather thin anteroposteriorly; posterior adductor scar arcuate, about twice as wide (anteroposteriorly) as anterior adductor scar, ca. 50% longer dorsoventrally, situated slightly lower than anterior adductor scar; pallial line entire, parallel to (antero- and postero-) ventral margin and rather distant from it (ca. 60– 70% towards margin from shell centre).

The occurrence of P. quinarium at two Lillburnian-age New Zealand fossil seep sites extends the stratigraphic range of this species back from its previous earliest report in the Tongaporutuan. In fact, none of the species currently assigned to Pratulum have ever been recorded from the Lillburnian, but the genus is known throughout the Cenozoic from Danian to Recent ( Beu & Maxwell 1990). P. quinarium is morphologically close to Pratulum pulchellum ( Gray, 1843) , distinguished from it by the finer and more numerous ribs, and by the narrow interstices, well developed transverse bars and absence of tubercles on the posterior area ( Marwick 1944). At 11–13 mm in length, P. quinarium is among the smallest of New Zealand cardiids. The specimens were predominantly found in a single aggregation at Tauwhareparae, reflecting a gregarious habit that is typical for the genus.

Figures

FIGURE 6. Pratulum quinarium (Marwick, 1944) from Moonlight North and Tauwhareparae. A. Specimen L 4653 from Moonlight North. Scale bar is 1 mm. A 1. Dorsal view. A 2. Anterior view. A 3. Lateral view of right valve. A 4. Lateral view of right valve, muscle scars highlighted. A 5. Lateral view of left valve. B. Specimen L 4664 from Tauwhareparae. Scale bar is 3 mm. B 1. Posterior view. B 2. Lateral view of left valve. B 3. Ventral view. B 4. Anterior view. B 5. Lateral view of right valve. B 6. Dorsal view.