Leptella (Leptella) inequicostellata, Hansen & Holmer, 2011

Hansen, Jesper & Holmer, Lars E., 2011, Taxonomy and biostratigraphy of Ordovician brachiopods from northeastern Ny Friesland, Spitsbergen 3076, Zootaxa 3076 (1), pp. 1-122 : 85-88

Leptella (Leptella) inequicostellata sp. nov.

Pl. 23, Figs. 5–13; Table 29

Derivation of name. Refers to the unequal costellae.

Plate 23

Pelonomia sulcata sp. nov.

Valhallfonna Formation, Olenidsletta Member.

1. TSGF17084 , paratype, ventral valve exterior. Middle unit. Coll. J. Hansen, 17.07.2008, sample JH-190 .

2. TSGF17061 , paratype, ventral valve interior. 97 m above base. Coll. J. Hansen, 28.07.2008, sample JH-136 .

3–4. TSGF17060 , paratype, ventral valve interior, oblique anterolateral view. 97 m above base. Coll. J. Hansen, 28.07.2008, sample JH-136 .

Leptella (Leptella) inequicostellata sp. nov.

Valhallfonna Formation, Profilbekken Member, 21 m above base. Coll. J. Hansen, 19.07.2008, sample JH-23.

5. TSGF16766 , paratype, ventral valve exterior .

6. TSGF17077 , paratype, dorsal valve exterior .

7. TSGF17078 , paratype, ventral valve exterior .

8–10. TSGF17072 , holotype, dorsal valve interior, oblique anterolateral view and oblique posterolateral view .

11–12. TSGF17071 , paratype, ventral valve interior, oblique anterolateral view .

13. TSGF17073 , paratype, ventral valve interior .

Plectambonitid sp.

14. TSGF16768, fragment of impression of ventral valve exterior. Valhallfonna Formation, Profilbekken Member, 83 m above base. Coll. J. Hansen, 01.08.2008, sample JH-161.

Strophomenid sp.

15. TSGF16767, impression of ventral valve exterior. Valhallfonna Formation, Profilbekken Member, 71 m above base. Coll. J. Hansen, 24.07.2008, sample JH-99.

Protoskenidioides promontorium sp. nov.

Valhallfonna Formation, Olenidsletta Member.

16. TSGF17065 , paratype, posterior view of ventral valve exterior. 97 m above base. Coll. J. Hansen, 28.07.2008, sample JH- 136 .

17. TSGF16870 , holotype, mould of dorsal interior. 90 m above base. Coll. J. Hansen, 20.07.2008, sample JH-45. 18 . TSGF16871 , paratype, mould of dorsal interior. 90 m above base. Coll. J. Hansen, 20.07.2008, sample JH-45. 19 . TSGF16867 , paratype, mould of ventral interior. 90 m above base. Coll. J. Hansen, 20.07.2008, sample JH-45 .

Holotype. Pl. 23, Figs. 8–10; TSGF17072 , dorsal valve; 21 m above base of Profilbekken Member, Valhallfonna Formation, sample JH-23; Profilbekken meltwater stream, Basissletta, Ny Friesland, Spitsbergen.

Material. One whole specimen and 84 dorsal and 76 ventral valves from sample JH-23. The paratypes are TSGF16766 , TSGF17071 , TSGF17073 , TSGF17077 and TSGF17078 .

Diagnosis. Small, slightly concavoconvex to planoconvex Leptella (Leptella) with alate cardinal extremities and an L/W ratio of 0.43–0.74; unequally parvicostellate; dorsal platform extending to 49–65% of valve length with short median septum extending anterior to platform.

Description. Shell small, subangular to semicircular and slightly concavoconvex or planoconvex. Largest measured specimen 4.6 mm long. Angle of cardinal extremities 30–80˚. Anterior margin weakly unisulcate. Normally unequally parvicostellate with two to four finer costellae for each stronger costella and interspaces generally absent; 7–9 rounded costellae per mm at 1-mm growth stage and 17–18 per 2.5 mm at 2.5-mm growth stage. Costellae not or only weakly impressed on valve floor.

Dorsal valve with sulcus. L/W ratio 0.43–0.60. Interarea 8–19% as long as valve, anacline and planar or slightly concave. Notothyrium covered by low chilidium. Deep dental fossettes. Brachiophores thin, diverging at about 110–120˚ proximally and much more distally. Fulcral plates variably developed. Cardinal process absent, but a small, deep notothyrial platform present. Valve floor outside muscle field with rather fine, scattered, circular pustules ordered in concentric and radial rows. Bema absent, but muscle field confined by a low, triangular platform with its anterior point located at 49–65% of valve length. Median septum high, triangular and broad, with apex located at 49–65% of valve length and front rarely reaching anterior to weak diaphragm located at 82–92% of valve length.

Ventral valve normally crested. L/W ratio 0.47–0.74. Interarea apsacline, planar or slightly concave, 11–24% as long as valve. Delthyrium V-shaped, with sides diverging at 40–60˚. Small pseudodeltidium present in larger specimens. Pustules as on dorsal valve. Teeth moderate, triangular, supported by thick, recessive dental plates. Bilobed ventral muscle field raised above valve floor, reaching 19–28% of valve length. A weak median mount or ridge is developed well anterior to the raised muscle field on larger specimens. Valve floor generally with weak peripheral diaphragm located at 7–19% of valve length from margin. Diaphragm covered by coarse pustules.

Remarks. In Benedetto & Cech (2006), Benedetto revised the definition of the subgenus Petroria Wilson, 1946 because he found that the presence or absence of a ventral median callosity and the extent of the dorsal median septum, characters used by Cocks & Rong (1989, 2000), were of little diagnostic value. This revision affects the assignment of the present species. According to the definition of Cocks & Rong (2000), this species should be assigned to the subgenus Petroria . However, it has dense, distinct costellae and lacks comas, contrary to the revised diagnosis, and is therefore assigned to the subgenus Leptella .

The type species, Leptella (L.) sordida (Billings, 1862) , has a well-developed median ventral callosity, a platform that occupies the proximal 80% of the valve floor, and a median dorsal ridge that does not extend anterior to the platform. Leptella (L.) alata Benedetto & Herrera, 1993 from Argentina is moderately concavoconvex, and the platform extends to about 67% of the valve length. Leptella (L.) corbetti Laurie, 1991 from Australia has widely spaced costellae and a maximum width located anterior to the hinge axis. Leptella (L.) costellata Benedetto & Herrera, 1993 from Argentina is about 0.73 times as long as wide and is equicostellate. Leptella ? (L.) exigua Clark, 1924 from Quebec is moderately convex and lacks costellae. Leptella (L.) grandis Xu & Liu in Xu et al., 1974 from China is moderately concavoconvex, and its dorsal septum, although longer, terminates at the margin of the platform. Leptella (L.) hubeiensis Zeng, 1977 from China is strongly concavoconvex and has distinct muscle scars, and its platform occupies the proximal 65% of the valve floor. Leptella (L.) musculosa Williams & Curry, 1985 is morphologically similar but is distinguished by its semi-elliptical outline, moderately concavoconvex profile and smooth or faintly costellate exterior. Leptella (L.?) nevadensis Ulrich & Cooper, 1938 from Nevada is strongly concavoconvex and has a high L/W ratio. Leptella (L.) plana Benedetto & Herrera, 1993 from Argentina is about 0.65 times as long as wide and has 10–12 costellae separated by radial striae, and its platform extends to 85% of the valve length. Leptella (L.) variabilis Benedetto & Herrera, 1993 from Argentina is moderately to strongly concavoconvex and lacks ornamentation except for 8–12 costellae, and its platform occupies 75% of the valve length.

Occurrence. 21 m above base of Profilbekken Member, Valhallfonna Formation, Basissletta in northeastern Ny Friesland, Spitsbergen.