Cristafrons Feldmann, Tshudy & Thomson, 1993

Van Bakel, Barry W. M., Guinot, Danièle, Artal, Pedro, Fraaije, René H. B. & Jagt, John W. M., 2012, A revision of the Palaeocorystoidea and the phylogeny of raninoidian crabs (Crustacea, Decapoda, Brachyura, Podotremata) 3215, Zootaxa 3215 (1), pp. 1-216 : 100

Genus Cristafrons Feldmann, Tshudy & Thomson, 1993

Cristafrons Feldmann, Tshudy & Thomson, 1993: 31 .

Type species. Cristafrons praescientis Feldmann, Tshudy & Thomson, 1993 , by monotypy.

Remarks. Cristafrons shows an unusual set of characters. Feldmann et al. (1993: 31) remarked that the general form was similar to species of Notopocorystes . Cristafrons can be readily distinguished from Palaeocorystidae by the prescence of only a single lateral spine and a narrow, non-bifurcate rostrum. The well-defined cervical groove and the hepatic and postfrontal areolations, however, are unusual for Raninoidea , whereas those features are commonly found in Palaeocorystoidea . The thoracic sternum of Cristafrons is ‘not cleft longitudinally’, i.e., the medial line is absent (sternites 1‒5 are described), members of Raninoidinae typically having a medial line up to sternite 5 ( Fig. 44C, D ). It is unlikely that Cristafrons belongs to Ranininae , which has wider carapaces and two wide lateral teeth. Exposed pleurites are not described in the type series: they may be concealed by matrix or were overlooked in the original description, which states that the type specimens ‘are deposited in the Natural History Museum, London’ ( Feldmann et al. 1993: 33), where only two specimens could be traced by us. The majority of the type series appears to have been forwarded to the British Antarctic Survey (BAS), under ‘ Cretiscalpellum praescientis ’ (see also http://www.antarctica.ac.uk/bas_research/data/access/fossildatabase/filter.php?taxonKeyword= CRUSTACEA). A re-examination of the type series is called for in order to resolve the precise taxonomic placement of Cristafrons .

Figures

FIGURE 44. Fossil raninids; A, Raninoides hollandica (Collins, Fraaye, Jagt & van Knippenberg, 1997) (Raninidae, Raninoidinae), MAB k. 2004 (holotype; indeterminate sex),?upper Oligocene, Winterswijk-Miste (eastern Netherlands); right lateral view showing exposed pleurites; B, D, Raninoides glabra (Woodward, 1871), IRScNB TCCI 6120 (indeterminate sex), lower Eocene (Ypresian), Brussels (Belgium); right lateral view showing exposed pleurites and ventral view showing thoracic sternum and appendages; C, Raninoides glabra (Woodward, 1871), IRScNB TCCI 6122 (indeterminate sex); ventral view showing thoracic sternites. pl5, pl6, pl7, exposed pleurites 5, 6, 7; og, outgrowth on exposed pleurite. Scale bars: 5mm.