Studies in the anatomy, morphology and taxonomy of extant and fossil craniid and articulate brachiopods

Abstract

Brachiopods have a very long history, from the Cambrian to the present. They were a dominant taxon on the sea floor at times during the Paleozoic but are now considered a minor taxon with ~120 extant genera and ~400 extant species. This thesis investigates the anatomy, morphology and taxonomy of craniid brachiopods from around the world and of articulate brachiopods from New Zealand. Specimens of six species of craniid brachiopod were dissected and the musculature, body wall and mantle examined. New names are proposed for the ‘brachial protractor’ and ‘brachial retractor’ muscles. The ‘brachial elevator’ muscles are part of the anterior adductor muscles, a small bundle of translucent quick-muscle partially enclosed by a larger, curving bundle of dark coloured slow-muscle. A new ring muscle is described. The lophophore arms are extended and retracted by the hydrostatic skeleton and brachial muscles respectively. The valves of Novocrania are possibly opened by the creation of hydrostatic pressure, within a newly described coelomic chamber, by contraction of the oblique lateral muscles. Neoancistrocrania has an extra pair of dorsal mantle canals arising at the posterior and a dorsally directed anterior pouch in the body wall. Specimens of six species (from two genera) of inarticulated craniid brachiopod were dissected and the gut examined and compared. The gut of the five Novocrania species were very similar except for some variations in the configuration of the pylorus-intestine. In contrast, the gut of Neoancistrocrania had two very distinctive features; the pharynx-esophagus-stomach forms a dorsally directed half loop and the pylorus-intestine is straight. Neoancistrocrania has four unique soft-tissue features and should remain a separate genus from Novocrania. There are currently 14 extant species in the craniid genus Novocrania, based on the published literature. Material, or new digital images, of thirteen of these species have been examined. Based on the morphology of the dorsal and ventral valves seven species are synonymized, one species is probably a synonym (but is retained pending more analysis) and one species is not a craniid. The five remaining ‘definite’ species are the same species as those found by molecular analysis by Cohen et al. (2014). Descriptions, figures and illustrations of geographical ranges are provided. Five New Zealand species of fossil craniid (four species of Novocrania and one of Valdiviathyris) are described, figured and their geographic ranges illustrated. Three Australian species of fossil craniid are synonymised and the remaining two species transferred to two different genera (Danocrania and Novocrania), described, figured and their geographic ranges illustrated. The paleoecology is described and possible ancestor – descendant relationships are discussed and illustrated. The two large, closely related, endemic, red, ribbed, New Zealand long-looped Terebratulide brachiopod species (currently placed in Terebratella) have been transferred between the genera Terebratella and Magasella a number of times. However, recently published molecular analysis has shown that New Zealand Terebratella d‘Orbigny, 1847 are not congeneric with southern South American Terebratella, which contains the type species dorsata, therefore the New Zealand species must be removed to another genus. Examination of the convoluted taxonomic history of the species originally described as Terebratula sanguinea Leach in 1814 revealed that only one of the existing generic names, Magasella Dall, 1870, is valid and available. Uncertainty persists concerning whether the two observed morphotypes of Magasella (‘sanguinea’ and ‘haurakiensis’) are truly separate species or two forms of a single morphologically variable species. A statistical analysis of the morphological parameters of several hundred specimens was performed with inconclusive results. However, a cytochrome oxidase I (COI) analysis of the two forms of New Zealand Magasella has shown that they can be accepted as separate species: M. sanguinea (Leach, 1814) and M. haurakiensis Allan, 1949. A diagnosis of the genus and figures and descriptions of the two species are provided. Six brachiopods from the Early Miocene Waitemata and Waitakere Groups, Auckland, New Zealand are described and figured, one at genus level and five at species level. Magadina browni and “Pachymagas” are described for the first time from the Waitemata Group. Terebratella neozelandica is returned to the genus Magasella and is confirmed as a separate species from the Magasella sanguinea fossil lineage. Two morphologies of drillhole, probably attributable to gastropods, have been recognized in specimens of the small extant New Zealand platidiid brachiopod Neoaemula vector, collected from Fiordland, New Zealand. Some of these drillholes have been repaired and these repairs occur in two different ways. The thin replacement shell has both primary and secondary layers, and in some cases is punctate. Drillhole repair is virtually unknown among living brachiopods, but this apparent rarity may be due to successfully repaired drillholes being classified as abandoned or incomplete.