The peristomial plates of ophiuroids (Echinodermata: Ophiuroidea) highlight an incongruence between morphology and proposed phylogenies
Fig 10
Familial distribution of IF character states, based on information accumulated to date (S5 Table).
The cladogram is derived from O’Hara et al. [9] (modified by the separation of Ophioplocus januarii from other hemieuryalids and the representation of family Ophionereididae as subfamilies Ophionereidinae and Ophiochitoninae). Characters are numbered as in Table 1. Blue denotes type A and red type B character states. White denotes lack of data. The numbers of species for which information is available are also given. Lower case italicised letters indicate clades to which reference is made in the text. Asterisks and numerals in parentheses refer to the following comments: (1) The dental plates of two species are type A and that of the third (Amphilepis ingolfiana) has a B-like aboral perforation. The teeth of this last species also have an imperforate median cusp (apparently also present in certain other Amphilepis species [26,45]), which may be a vestige of the imperforate cap present in most other families of clade m (suborder Gnathophiurina). (2) There is information on the abradial muscle attachment area of four species, three of which are type B and one type A. (3) There is information on the abradial muscle attachment area of five species, four of which are type B and one type A. (4) The adradial muscle attachment area approaches the type B state, but lacks a pronounced aboral expansion and narrow oral region. (5) Most hemieuryalids have type A dental plates. However, Ophioplocus januarii and four Ophiozonella species have type B dental plates. (6) Although most ophiolepidids have type A dental plates, one species has an “imperfect” perforation and another has distinctly type B perforations. (7) Of the five characters for which there is information, only the type A adradial muscle attachment area is consistent across the three species. All other characters are type A in one species (Clarkcoma australis) and type B in the other two (C. bollonsi and C. canaliculata). (8) The IF traits of the Ophiomyxidae are consistently type A, with the exception of the teeth of the six Ophioconis species for which information was obtained. These have broad teeth with a cap of imperforate stereom, which in most (but not all) species has a denticulate edge. The latter feature suggests that these have evolved from Ophiomyxa-like teeth, which have a proximal edge of imperforate spikes ([36]; Wilkie pers. obs.). The abradial and adradial muscle attachment areas of Ophioconis cincta and O. cupida also approach the B condition. (9) The character states of all ophiocomids are consistently type B, with the exception of Ophiocomella ophiactoides, which has type A peristomial plates. (10) Some ophiohelids have broad, though flattened, teeth, those of Ophiothauma heptactis also having an imperforate proximal edge [46]. (11) The adradial muscle attachment area of a few gorgonocephalid and euryalid species approaches the type B spoon-with-narrow-handle shape.