Abstract
All species of Chilodontidae known to occur in the south-western Indian Ocean are discussed (27 species, of which eight new, belonging to nine genera, of which three new). Keys to genera and species are provided. Observations on protoconch form, shell microsculpture, radula morphology, operculum shape and external anatomy are given, together with summary biological observations. The genus Agathodonta Cossmann, 1918 is not considered to be applicable to the extant species for which it has been recently used and a new genus is proposed for these living forms. Type specimens of a number of extralimital species examined for comparative purposes are illustrated.
Highlights
The taxa discussed in this revision have traditionally been referred to the trochid subfamilies Margaritinae and Monodontinae
AFRICAN INVERTEBRATES, VOL. 53 (2), 2012 these represented Recent descendents of Mesozoic lineages (Amberleyidae) previously thought to have become extinct in the Oligocene or earlier. He later suggested (McLean 1982, 1984) that they be recognised as separate tribes within the Margaritinae, but this idea was subsequently revised in the publication of Hickman and McLean (1990) in which a much modified trochoidean subfamily, the Eucyclinae, was employed for the taxa concerned, based on the extinct families Eucyclidae, Cirridae and Amberleyidae. This subfamily was further divided into three tribes, the Eucyclini, Calliotropini and Chilodontini on the grounds of differing shell morphology, radula form and external anatomy
Warén and Bouchet (1993), on account of uncertainties regarding the affinities of the exclusively fossil Eucyclini, subsequently chose to regard the other two tribes as subfamilies in their own right, this was not followed by Hickman (1998)
Summary
The taxa discussed in this revision have traditionally been referred to the trochid subfamilies Margaritinae and Monodontinae (see for example Keen 1960). Kano (2008) has analysed the relationships of the Seguenzioidea using sequence data from a wider range of taxa and has confirmed that calliotropine and chilodontine species cluster together with seguenziids in a well supported clade, no support was evident for the monophyly of either the Calliotropinae or Chilodontinae, nor for the two treated together as the Chilodontidae He highlighted potentially significant anatomical similarities including a peduncle posterior to the right eyestalk (distinct from the subocular tentacle) and hooded rachidian teeth in the radula, but pointed out that these may be plesiomorphic character states. Morphological and molecular evidence indicates that Synaptocochlea belongs within the Trochidae (Herbert 1998; Williams et al 2008, 2010), in the subfamily Fossarininae Bandel, 2009 Another western Indian Ocean genus which Bandel (2010) referred to the Eucycloidea is Pagodatrochus Herbert, 1989, creating for it a new family, the Pagodatrochidae. It is one of many small, anomalous vetigastropod taxa for which molecular sequence data could provide valuable phylogenetic insights
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