Viarhynchiinae Manceñido and Owen, 2002

Radulović, Barbara, Motchurova-Dekova, Neda & Radulović, Vladan, 2007, New Barremian rhynchonellide brachiopod genus from Serbia and the shell microstructure of Tetrarhynchiidae, Acta Palaeontologica Polonica 52 (4), pp. 761-782 : 762-766

Subfamily Viarhynchiinae Manceñido and Owen, 2002

Genus Antulanella nov.

Type species: Rhynchonella pancici Antula, 1903 , monotypic; Barremian (Early Cretaceous) of Crnoljevica, Svrljiške Planine Mountains, eastern Serbia .

Derivation of the name: In honour to the Serbian geologist and palaeontologist Dimitrije Antula (1870–1924), who first described the species R. pancici and other fauna from Crnoljevica. His Ph.D. thesis was published in Austria−Hungary under the name Anthula ( Anthula 1899) and some later authors followed this spelling. In Serbian, the spelling of his surname is Antula, therefore we recommend using this spelling.

Diagnosis.—Small to very rarely medium−sized, costate, subglobose, variable in outline, symmetrical, acutely biconvex rhynchonellides. Beak suberect, hypothyrid auriculate foramen, beak ridges well developed. Squama and glotta present, but not well developed. Anterior commissure uniplicate. Fold and sulcus poorly developed. Ornamented by 32–36 simple costae. Deltidial plates disjunct. Dental plates short, ventrally divergent. Hinge plates slightly ventrally deflected in the juvenile stage, becoming subhorizontal to horizontal, slender and wide, straight to rarely ventrally convex. Dorsal euseptoidum low. Crural bases crescent−shaped. Crura with widened distal ends, rarely typically raduliform or canaliform. Shell composed of two calcitic layers. Secondary layer built up of

predominantly anisometric anvil−like fibres. Secondary layer microstructure fine fibrous, homogeneous.

Antulanella gen. nov. differs from Viarhynchia Calzada Badía, 1974b in its smaller size and variable outline (see also Table 1 ). Internally both genera share widened distal ends of the crura (with diabolo−like sections). Data about Hemithyropsis Kats, 1974 are incomplete, no serial sections being available for comparison. However, the new genus differs externally from Hemithyropsis in having a more circular outline and internally in having subhorizontal to horizontal, rarely ventrally convex hinge plates. Antulanella differs from Septatoechia Lobacheva and Titova, 1977 in its smaller size, more poorly developed fold and sulcus, and much thinner shell wall. Internally Antulanella is characterized by ventrally divergent dental plates, reduced dorsal euseptoidum and crura with generally widened distal ends (see later discussion suggesting revising the taxonomical position of Septatoechia ). In addition to the above−mentioned differences, the three genera presently assigned to the Viarhynchiinae are stratigraphicaly younger than the new genus.

Discussion.—Some external and internal shell features, such as a nearly equibiconvex and subspherical shell with ill developed dorsal fold, and incurved beak, lack of a septalium and type of crura, suggest placement of the new genus in the subfamily Viarhynchiinae , family Tetrarhynchiidae within the Hemithiridoidea .

Dorso−ventrally widened distal ends of crura (giving rise to diabolo−like sections) among the Mesozoic rhynchonellides are reported only in members of the superfamily Hemithiridoidea . This term was introduced by Ager (1967: 143) who stated that the diabolo−like sections, however, do not correspond to the “various processes that are sometimes found at the distal ends of crura in the rhynchonellids”. Among Cyclothyridinae , these types of crural sections are known in the Early Jurassic Squamirhynchia Buckman, 1918 , the Middle Jurassic Globirhynchia Buckman, 1918 , the Late Jurassic Bicepsirhynchia Shi, 1990 , the Middle Jurassic to Early Cretaceous Septaliphoria Leidhold, 1921 , the Early Cretaceous Lamellaerhynchia Burri, 1953 , the Early to Late Cretaceous Cyclothyris McCoy, 1844 , the Late Cretaceous Almerarhynchia Calzada Badía, 1974a and in Owenirhynchia Calzada in Calzada and Pocovi, 1980. Within Viarhynchiinae , they are present in the Late Cretaceous Viarhynchia Calzada Badía, 1974b and in the Barremian Antulanella .

The diabolo appearance of the crura is sometimes accompanied by distal splitting of the crura into two, approximately parallel, plates. This feature has been noted so far in a few species of the above−mentioned genera: the Sinemurian–Pliensbachian Squamirhynchia squamiplex ( Quenstedt, 1871) , the Aalenian Globirhynchia subobsoleta ( Davidson, 1852) , the Oxfordian Septaliphoria paucicosta Childs, 1969 , S. arduennensis ( Oppel, 1858) , S. sobolevi Makridin, 1964 , S. pectunculoides ( Etallon, 1860) , S. moeschi donetziana ( Makridin, 1952) , and Bicepsirhynchia asperata Shi, 1990 , the Cenomanian Cyclothyris sp. of Nekvasilova (1973), the Turonian Cyclothyris zahalkai Nekvasilova, 1973 , and the Campanian– Santonian Almerarhynchia reigi Calzada, 1989 .

Smirnova (1972) also reported crura with widened distal ends in three Early Cretaceous (Valanginian–Late Barremian) species of Belbekella (= Cyclothyris ) from the Crimea and Caucasus: B. rectimarginata Smirnova, 1972 , B. irregularis ( Pictet, 1872) , and B. adducta Smirnova, 1972 . Other species of Belbekella have simple raduliform crura. No parallel plates are observed.

It is worth noting that in Cyclothyris irregularis ( Pictet, 1872) , the crura may be raduliform (Lobacheva in Bogdanova and Lobacheva 1966: 40, fig. 11) or distally widened (i.e., diabolo−type) ( Smirnova 1972: 39, fig. 12).

In Cyclothyris? globata ( Arnaud, 1877) from the Campanian of Guča, western Serbia and from the Early Campanian of Nanos, Slovenia, the crura have widened distal ends ( Radulović and Motchurova−Dekova 2002) but those from other localities in north−eastern Bulgaria ( Motchurova−Dekova 1995), and Croatia ( Radulović and Motchurova−Dekova 2002), have narrow distal ends (i.e., typical raduliform crura).

Recently, Simon (2003) described a new species Almerarhynchia kunradensis from the Upper Maastrichtian of Limburg, the Netherlands. He figured serial sections of two specimens. In one specimen the crura are clearly canaliform but in the other specimen, the crura display very close to diabolo−like sections; moreover they terminate with two approximately parallel plates. These plates are also known in Almerarhynchia reigi Calzada, 1989 .

The above examples suggest that crura in different specimens of one species may be narrow (typically raduliform) or widened and incurved at the distal ends (diabolo shape). Thus, this may be considered as an intraspecific variation and should not be given taxonomical weight.

The distal splitting of the crura into two plates does not always occur in the forms with diabolo crura. The non−occurrence of these plates is most likely a morphogenetic feature. It should also be noted that the plates are very short and that they might be overlooked when sectioned.

Stratigraphic and geographic range.—The Barremian of eastern Serbian Carpatho−Balkanides (Crnoljevica, Prekonozi, Novo Selo, Skrobnica, Bežište).

Tables

Table1. Summary ofthe external,internal and shell microstructurecharacters of Antulanella gen.nov.and all other generaincludedin the subfamily ViarhynchiinaeManceñido and Owen,2002.Data for Septatoechia are taken onlyfrom its type species.* charactersin Septatoechia,which seem to deviate from the norm in the subfamily Viarhynchiinae are shown in italics.

Genera		Antulanella gen. nov.	Viarhynchia Calzada Badia, 1974b	Hemithyropsis Kats, 1974	Septatoechia Lobacheva and Titova, 1977 (based on S. inflata from the type locality)
External morphology	Size	small, rarely medium	large	small to medium	medium to large
	Outline and shape	subcircular, roundly pentagonal or slightly transversely elliptical; subglobular	elongate oval; subglobular	roundly pentagonal, elongate oval, roundly triangular; subglobular	subtriangular, subpentagonal or oval; subglobular to globular
	Convexity Beak Foramen Deltidial plates Ribs	acutely and subequally biconvex, subglobose suberect hypothyrid disjunct subangular (26–32)	acutely and equibiconvex, subglobose slightly incurved hypothyrid disjunct rounded (26–36)	acutely and equibiconvex, acutely and dorsibiconvex, subglobose globulose suberect slightly incurved * to erect hypothyrid hypothyrid disjunct subangular, bifurcating rounded or subangular (25–40) (28–40)
	Fold and sulcus	poorly developed	poorly developed	poorly developed	* well developed
Internal morphology	Dental plates Hinge plates Euseptoidum or dorsal median septum Crura	ventrally divergent subhorizontal to horizontal, rarely ventrally convex euseptoidum widened distal ends, rarely raduliform or canaliform	ventrally divergent dorsally directed euseptoidum raduliform, concave distal ends	hinge plates and socket ridges fused absent raduliform?	* parallel to ventrally convergent ventrally divergent * very high dorsal median septum, slender, short, possible septalium raduliform
Shell microstructure and texture	Shell thickness (in ̊m) Primary layer thickness (in ̊m)	150–480 20–30			* 1000–2000>30
	Fibre shape Fibre size (in ̊m) Microtexture	predominantly anvil−like to elongate rhombic w = 15–30; t = 5–10 homogeneous, thin myotest			rhombic, rarely anvil like or subhexagonal w = 15–32; t = 8 –12 * not homogeneous, built of several sublayers, very thick myotest
Age		Barremian	Upper Campanian– Maastrichtian	Campanian– Maastrichtian	Maastrichtian