A cystoid with two left facets: the significance of Tetracystis in the evolution and classification of the Callocystitidae (Echinodermata, Glyptocystitoida). (30th July 2014)

• Record Type: Journal Article
• Authors: Paul, Christopher R. C.
• Is Part Of: Geological journal. Volume 50:Number 5(2015)
• Page Start: 607
• Page End: 633
• Publication Date: 2014-07-30
• Subjects: Geology -- Periodicals; 551
• DOI: 10.1002/gj.2578
• Languages: English
• ISSNs: 0072-1050

Abstract

<abstract abstract-type="main"> <title> <x xml:space="preserve">Abstract</x> </title> <p>Revision of some North American Silurian callocystitid cystoids shows that <italic>Tetracystis</italic> Schuchert has the first two brachioles to the left in ambulacra B and D (B D different pattern), whereas <italic>Troosticystis</italic> Paul and <italic>Lovenicystis</italic> Regéll have only the first brachiole to the left in all four ambulacra (B–E the same pattern). '<italic>Apiocystites</italic>' <italic>elegans</italic> Hall is transferred to <italic>Tetracystis</italic> because it has the B D different pattern. <italic>Lovenicystis kopfi</italic> sp. nov. is characterized by four short ambulacra. <italic>Salirocystis</italic> gen. nov. has the B D different pattern and two hydropores. All callocystitids that lack ambulacrum A are assigned to a new subfamily, the Tetracystinae; those with five ambulacra are referred to informally as 'lepadocystines'. The previously recognized subfamily Callocystitinae is reduced in rank to a tribe within the 'lepadocystines'. Preliminary character analysis suggests that the loss of ambulacrum A was the most significant evolutionary event within the family Callocystitidae, but has been overlooked in taxonomy. Character analysis also shows that all 'lepadocystines' had the B D different pattern of primary brachioles, which is retained in four tetracystine genera, <italic>Lepocrinites</italic> Conrad, <italic>Sphaerocystites</italic> Hall, <italic>Tetracystis</italic> and <italic>Salirocystis</italic>. Since <italic>Salirocystis</italic> has the plesiomorphic B D different pattern plus the apomorphic double hydropore, one cannot define a monophyletic taxon characterized by the B–E the same pattern plus one characterized by a double hydropore. Both alternatives are equally parsimonious. Here a new monophyletic tribe Lipsanocystini is defined characterized by a double hydropore. The B–E the same pattern evolved independently twice. Among current characters the loss of ambulacrum A, development of the B–E the same pattern and development of two hydropores are the most significant evolutionary events. Number of periproct border plates, length and structure of ambulacra are less significant. Copyright © 2014 John Wiley & Sons, Ltd.</p> </abstract>