Taxonomic revision of the Devonian genus Pseudonuculana Pojeta, Zhang and Yang, 1986 (Bivalvia: Cucullellidae)
Article
Figures
Metrics
Preview PDF
Reference
Related
Cited by
Materials
Abstract:
After comparing Nuculoidea resupina Guo, 1985, Pseudonuculana zhaoi Pojeta, Zhang and Yang, 1986 and Skyphoconcha beichuanensis Liu and Gu, 1988. There is no doubt that they belong to the same species. This confirms that the genus name Skyphoconcha Liu and Gu is a junior synonym of Pseudonuculana Pojeta, Zhang and Yang. The opisthodetic external ligament of the Pseudonuculana is fully confirmed and its generic diagnosis is revised. Without resilium and pallial sinus, Pseudonuculana is removed from the Nuculanidae and reclassified as a member of Cucullel-linae. According to The InternationalCode of Zoological Nomenclature (4th Edition), Nuculoidea resupina Guo, as a senior synonyms, has priority over the other two junior synonyms but should not be cited as the type species of the genus. As the name-bearing type of the type species, the original designated type species Pseudonuculana zhaoi Pojeta,Zhang and Yang remains unchanged even though it is a junior synonym of Nuculoidea resupina Guo. SYSTEMATIC PALEONTOLOGYClass Bivalvia Linnaeus, 1758 Subclass Protobranchia Pelseneer, 1889 Order Nuculanida Carter, Campbell and Campbell, 2000 Suborder Nuculanina Carter, Campbell and Campbell, 2000 Superfamily Cucullelloidea Fischer, 1886 Family Cucullellidae Fischer, 1886 Subfamily Cucullellinae Fischer, 1886 Genus Pseudonuculana Pojeta, Zhang and Yang, 1986, emend. Fang nov. (= Skyphoconcha Liu and Gu in Liu, 1988) Type species Pseudonuculana zhaoi Pojeta, Zhang and Yang, 1986 (by original designation) (= Nuculoidea resupina Guo, 1985; Skyphoconcha beichuanensis Liu and Gu in Liu, 1988) Revised diagnosis of the genus Shell small to medium, equivalve, inequilateral, elongated but not noticeably attenuated posteriorly; beaks opisthogyrate, shell highest in region of beaks; posterodorsal margin abruptly bent downward behind the umbo, forming a concavity, with its end rising slightly; postero-dorsal and posteroventral margins subparallel as a whole; ventral margin arcuate or nearly straight, anterior margin broadly rounded, posterior margin narrowly rounded, posterior end slightly upturned; teeth taxodont, hinge dentition continuous below beaks, anterior and posterior tooth rows nearly equal in length, or anterior row slightly longer; somewhat larger anterior than posterior taxodont teeth in size; anterior tooth row long and broadly arcuate, occupying the whole anterodorsal margin, its small teeth nearly perpendicular to hinge margin, becoming more slender, more numerous and with narrower interspaces toward the umbo; posterior tooth row concave, descending sharply from under anterior subumbonal teeth and forming an obtuse angle slightly larger than 90o with anterior tooth row, then gradually turning horizontal toward the posterior, not reaching the posterior ends, disappearing before the posterior adductor scar; its small teeth obliquely inclined or nearly horizontal under the umbo, but turning perpendicular to hinge margin and becoming larger with wider interspaces toward posterior ends; a long, opisthodetic, external ligament groove lying above the posterior tooth row, no resilifer; adductor muscle scars subequal, occur-ring at the distal ends of the tooth rows; a single pair of posterior pedal muscle scars located dor-sally and anteriorly to posterior adductor scar, but not confluent with the latter; a single pair of accessory muscle scars occurring anterior to posterior pedal retractor scars; pallial line entire, without sinus; ornament of comarginal growth lines with broad comarginal rugae in mature part of shell, sometimes faint radial traces are barely visible.
