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Animal Biodiversity
Published in Malcolm S. Gordon, Reinhard Blickhan, John O. Dabiri, John J. Videler, Animal Locomotion, 2017
The process of developing cladistic classifications that are widely agreed to and accepted is not always fast or easy. One problem is that some widely recognized taxa turn out not to be clades. In vertebrate biology that has turned out to be the case with what most people call reptiles. Cladistic analyses indicate that turtles may have derived from a different ancestral basal form than the form that was basal to the snakes and lizards. A named taxon that contains representatives of more than one clade is called a paraphyletic group.
A new large mound dwelling chiton (Mollusca), from the Late Ordovician Boda Limestone of central Sweden
Published in GFF, 2020
Anette E. S. Högström, Jan Ove R. Ebbestad, Yutaro Suzuki
Fossil polyplacophorans are generally placed in the Palaeoloricata of Bergenhayn (1955), characterised by the absence of the articulamentum layer with exposed apophyses typical of neoloricates. Vendrasco & Runnegar (2004) and Pojeta et al. (2010) regarded the Palaeoloricata as a convenient morphological grouping that most likely is paraphyletic, containing stem members of the clade Aculifera that encompass both Polyplacophora and Aplacophora (Sigwart & Sutton 2007; Smith et al. 2011; Vinther et al. 2011, 2012; Sutton & Sigwart 2012 and references in these). The aculiferan divergence may have happened in the Ordovician where palaeoloricates with a narrow morphology potentially represent stem-aplacophorans, in that they do not possess a foot, e.g. the typical creeping sole of modern chitons. Rather these stem forms have a spiculate girdle surrounding the dorsal valves and a vermiform body plan (Vinther et al. 2011; Sutton & Sigwart 2012). Two such forms from the Late Ordovician (Katian) of Scotland, Septemchiton grayiae (in reality S. vermiformis) and Phthipodochiton thraivensis (see Table 1), were discussed as possible stem-aplacophorans (Vinther et al. 2011; Sutton & Sigwart 2012), but assessing whether other Ordovician palaeoloricate taxa are stem-aplacophorans or stem-polyplacophorans is difficult without special preservation or articulated specimens (see discussion in Sutton & Sigwart 2012). Thus, the position of Crassaplax remains unclear, although the large size (uncertain character) and thick valves (compared to the thin valves of the before mentioned forms) may suggest a polyplacophoran affinity. Support for the clade Aculifera today comes from both molecular and fossil data, for example Giribet (2014), Vinther et al. (2017) and Kocot et al. (2020).