Meristorygma Carter, 1974

Poletaev, Vladyslav, 2024, New and revised taxa of Carboniferous spiriferides (Brachiopoda, Spiriferida) from the Donets Basin (Ukraine) and South Urals (Russia), European Journal of Taxonomy 968, pp. 132-155 : 139

Genus Meristorygma Carter, 1974

Type species

Meristorygma arctica Carter, 1974 ; original designation.

Diagnosis

Medium-sized shell with diverse outline; fold and sulcus moderately developed. Well-defined sulcus with two, rarely four primary ribs and median furrow; uniplicate anterior commissure usually with subquadrate tongue; fold with three distinct ribs; the central with weakly furrow. Ribs on sides are few and weak. Hinge line of short, smooth ventral interarea non-denticulated. Ventral adminicula and dorsal crural plates are absent; vascula ramose, radially arranged with a pair of strong vascular media, which correspond to the pair of costae in the sulcus. Microornament is absent.

Species included

Arctic Canada and southeastern Alaska ( Carter 1974: 674): Meristorygma arctica Carter, 1974 ; Pennsylvanian.

Russia, Northern and Polar Ural ( Kutorga 1844; Kalashnikov 1980): M. panduriformis ( Kutorga, 1844) ; upper Pennsylvanian–Lower Permian; M. pajkchoica Kalashnikov, 1980 ; Moscovian.

South Ural (Bashkortostan)and Middle Asia ( Yanishevsky 1900; Poletaev 2018): M. gracilis ( Yanishevsky, 1900) upper Serpukhovian–lower Bashkirian; (this paper) M. donakovae Poletaev, 2018 ; uppermost Visean–Serpukhovian, Magnitogorsk district.

Ukraine, Donets Basin ( Rotai 1951; Poletaev 2018): M. miussensis ( Rotai, 1951) upper Bashkirian; M. postgracilis ( Rotai, 1951) ; Moscovian.

Remarks

The analysis of the ventral valve of the natural mould of Meristorygma arctica ( Carter & Poletaev 1998) has shown that the species has a ramose, radially arranged vascular system with a twin of strong vascular media, in contrast to Brachythyris ovalis (Phillips, 1836) , which has a weak, simple, pinnate vascular system. The variability of the vascular system of related taxa may mostly be the result of evolution ( Lazarev & Poletaev 1982).