Hisingerella maniformis, 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 : 56-59

Hisingerella maniformis sp. nov.

Pl. 14, Figs. 1 –15; Pl. 15, Fig. 1 ; Table 14–15

Derivation of name. Latin ‘ mane ’ and ‘ forma ’, early and form; refers to the early occurrence of the species.

Holotype. Pl. 14, Figs. 7–11; TSGF17008 , ventral valve; 26 m above base of Profilbekken Member, Valhallfonna Formation, sample JH-184; N79°50.570’ E17°42.406’, Profilbekken meltwater stream, Basissletta, Ny Friesland, Spitsbergen.

Material. 11 dorsal and 123 ventral valves from samples A84208, F5032, F5268, F5273, F5316, JH-23, JH- 24, JH-95, JH-104 and JH-184. The paratypes are TSGF16825 , TSGF16826 , TSGF17009 , TSGF17011 , TSGF17013 and TSGF17014 .

Diagnosis. Hisingerella with L/W ratio about 0.80–1.05 and pseudointerarea about 50% of valve width; gently to moderately convex posterior margin; procline to steeply apsacline ventral pseudointerarea with weak interridge; weak or absent apical process; weakly developed median buttress; planar dorsal valve.

Description. Shell transversely oval to subcircular with gently to moderately convex posterior margin. Pseudointerarea normally 43–52% as wide as valve. L/W ratio 0.79–1.04. Largest specimen 1.0 mm long and 1.1 mm wide. Larval shell subcircular to transversely oval and about 0.15–0.17 mm long. Larval shell with microornamentation consisting of dense pits. Pits rather shallow, circular and highly variable in size, reaching a maximum size of about 2 µm. Postlarval shell with growth lines.

Dorsal valve planar or weakly convex. Weak sulcus often developed. Umbo not strongly defined. Pseudointerarea planar and slightly to moderately anacline. Median groove broad, about 29–37% as wide and 10–17% as long as valve, with straight or slightly concave anterior margin. Cardinal muscle scars weakly impressed, located relatively close together. Median buttress not strongly developed. Median septum very thin, generally moderately low, subtriangular, with apex at 53–78% of valve length and front at 77–85% of valve length. Median septum with septal rod often extending as short spine in front and commonly with up to four spines along steep anterior edge.

Ventral valve moderately conical with nearly straight to gently convex lateral and anterior slopes. H/L ratio 0.48–1.00. Pseudointerarea poorly defined, slightly concave to gently convex, procline to steeply apsacline. Interridge broad, almost always weak, 20–25% as wide as valve. Foramen rather small, extending on short tube constituting apex of valve. Foramen enclosed by larval shell. Larval shell conical. Vascula lateralia obscure to moderately impressed, laterally directed. Apical process normally absent or poorly developed but occasionally forming a subtriangular platform or wide rim.

Plate 14

Hisingerella maniformis sp. nov.

Valhallfonna Formation, Profilbekken Member.

1–3. TSGF16826 , paratype, exterior of fragment of dorsal valve, oblique lateral view, and detail of larval shell. 67 m above base. Coll. J. Hansen, 24.07.2008, sample JH-95 .

4. TSGF17009 , paratype, dorsal pseudointerarea. 26 m above base. Coll. J. Hansen, 04.08.2008, sample JH-184 .

5–6. Dorsal valve interior, oblique lateral view (specimen lost by accident). 67 m above base. Coll. J. Hansen, 24.07.2008, sample JH-95.

7–11. TSGF17008 , holotype, ventral valve exterior, oblique anterolateral view, oblique posterolateral view, larval shell, and detail of larval micro-ornamentation. 26 m above base. Coll. J. Hansen, 04.08.2008, sample JH-184 .

12. TSGF16825 , paratype, ventral valve exterior. 67 m above base. Coll. J. Hansen, 24.07.2008, sample JH-95 .

13–14. TSGF17013 , paratype, ventral valve exterior, oblique lateral view. 21 m above base. Coll. J. Hansen, 19.07.2008, sample JH-23 .

15. TSGF17014 , paratype, ventral valve interior. 21 m above base. Coll. J. Hansen, 19.07.2008, sample JH-23 .

Remarks. This species is currently the oldest known within the genus. Among the other described species placed in this genus, Hisingerella billingensis Holmer, 1989 from the Darriwilian of Sweden is distinguished by having a distinct apical process, a slightly stronger interridge, and a mean L/W ratio of about 0.93. H. ciliensis Zhang, 1995 from the Darriwilian of China differs by having a distinct apical process, orthocline dorsal propareas, and a highly robust median buttress. H.? davidsoni ( Reed, 1917) from the Sandbian of Scotland differs by having strongly raised dorsal Cardinal muscle scars, a more procline ventral pseudointerarea, and a strong interridge. H. hetera ( Percival, 1978) from the Katian of Australia is distinguished by having a distinct Mantle canal system, a pronounced interridge, and a gently convex dorsal valve. H. nana Hadding, 1913 (in Harper et al. 1984) from the Katian of Norway differs by having a pseudointerarea occupying well over half of the valve width, a ventral valve about 35% as high as long, and a robust apical process. H. nitens ( Hisinger, 1837) from the Katian of Sweden is distinguished by having a well-developed interridge and by being about twice as large. H. tenuis Holmer, 1986 from the Katian of Sweden differs by having a stronger interridge and a more depressed ventral apex. H.? unguicula Holmer, 1989 from the Darriwilian of Sweden is distinguished by having a moderately convex dorsal valve and larval pitting consisting of large, superficial, circular pits that generally do not overlap, with numerous smaller pits of variable size in between. Hisingerella sp. ( Mitchell 1977) from the Ashgillian of Ireland differs by having a distinct apical process, an L/W ratio of about 0.67, and a ventral valve that is about 40% as high as long. Hisingerella sp. ( Candela 2003) from the Katian of Ireland is distinguished by being about 66–74% as long as wide and by having a gently convex dorsal valve and a strong interridge. The similar Hisingerella sp. a ( Holmer 1986) from the Katian of Sweden differs by having a markedly more pronounced dorsal umbo and a straighter posterior margin.

One of the illustrated specimens, the dorsal valve in Pl. 14, Figs. 5–6, has an atypical pseudointerarea in that it is relatively long and the median trough is more prominent. However, compared with the other specimens available, this deviation appears to be intraspecific.

Occurrence. 18, 21, 26, 30, 34, 50, 52, 61 and 67 m above base of Profilbekken Member, Valhallfonna Formation, Basissletta in northeastern Ny Friesland, Spitsbergen.

Figures

FIGURE 1 Locality maps of the Svalbard Archipelago. a) Locations of sites yielding Lower Palaeozoic fossils mentioned in this paper. b) Geological map of the Basissletta plain, northeastern Ny Friesland; redrawn from Fortey & Bruton (1973). The base map is based on aerial photos made available by the Norwegian Polar Institute and on field observations made by the authors in 2008.