Raninella elongata A. Milne Edwards, 1862

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 : 94

Raninella elongata A. Milne Edwards, 1862

( Fig. 27A–E )

Raninella elongata A. Milne Edwards, 1862: 493 .

Palaeocorystes callianassarum Fritsch in Fritsch & Kafka, 1887: 46.

Hemioon cunningtonii Bell, 1863: 10 .

Raninella atava Carter, 1898: 24 .

Material examined. From the upper Cenomanian of Le Mans, Butte de Gazonfier: carapace with both chelipeds preserved (LM3788); carapace and sternum, illustrated by Brocchi (1877: figs. 4, 5), designated lectotype by Breton & Collins (2007: 18) ( MNHN A25922); syntypes, two carapaces ( MNHN R03927); paralectotype, one of two carapaces (see also under Raninella trigeri ) with exposed pleurites 5‒7 preserved ( MNHN R03934, as Raninella trigeri ); one carapace ( MNHN A29413); from the ‘Upper Greensand’, Isle of Wight, southern England ( NHM In. 31302, indicated as ‘new species’ by Woodward 1874; see Wright & Collins 1972: 89).

Remarks. Raninella elongata (see A. Milne Edwards 1862: 493; Fritsch in Fritsch and Kafka, 1887: 46, textfig. 69, pl. 10, fig. 9, as Palaeocorystes callianassarum ; Bell, 1863: 10, pl. 2, figs. 4–7, as Hemioon cunningtonii ; Carter, 1898: 24, pl. 1, fig. 7, as Raninella atava ), from the upper Albian to Coniacian of southern England, Bohemia ( Czech Republic), northern France and Germany, was considered a juvenile form of Raninella trigeri by Van Straelen (1936: 41). Later authors (e.g., Wright & Collins 1972; Tucker 1995; Breton & Collins 2007) did not subscribe to this view and considered these two species distinct. Glaessner (1969: R627) was of the opinion that H. cunningtonii represented juvenile specimens of Raninella elongata and synonymised the two genera. Most subsequent authors (e.g., Wright & Collins 1972; Collins & Wienberg Rasmussen 1992; Tucker 1995, 1998; De Grave et al. 2009; Schweitzer et al. 2010) treated the two genera as distinct, but these authors also included species that are now placed in Bournelyreidus n. gen. Breton & Collins (2007: 18) referred to Raninella elongata , thus relegating Hemioon as a junior synonym of Raninella . We concur.

Direct comparison of the types and additional material of both R. elongata and R. trigeri has revealed ample differences. Both species do exhibit similar carapaces: elongated but rather wide (width [between bases of widest anterolateral spine] 67 % of maximum carapace length in R. elongata , 75 % in R. trigeri ), widest at approximately one-third of total carapace length from the front; posterolateral margin long, continuously arched and sharply rimmed; two anterolateral teeth: flattened, wider in R. trigeri , whereas in R. elongata the posterior tooth is strong, somewhat flattened, not as wide as in R. trigeri ; the anterior lateral tooth being subtler; orbitofrontal margins of both species are nearly identical, only the lateral margin below the outer orbital corner is convex and widened in R. trigeri . The sterna of R. elongata and R. trigeri are remarkably similar in all details, the only difference being that sternite 4 is slightly wider in the latter. The position of the pereiopods, nature of pterygostome, areolation of subhepatic region and construction of the suborbital border are identical. Chelipeds are conspicuously similar, inclusive of the characteristic crest on the outer distal surface of the merus; yet, the chelae of R. trigeri appear to be taller than those of R. elongata . There are many analogues in the cuticle microstructures of the two species.

The differences between R. elongata and R. trigeri match sexual and ontogenetic differences observed in Ranina ranina as well. In the latter, the orbitofrontal margin and anterolateral spines are much more weakly developed in juveniles than in adults, resulting in a wider appearance of the carapace ( Barnard 1950: 397, 398, fig. 75a, b). The orbital margin is nearly equally well developed in adult females as in males, but the two trifid anterolateral teeth are clearly less prominent ( Sakai 1937: 179, text-fig. 45). No juvenile or specimens of intermediate size of either R.elongata or R. trigeri have so far been documented ( Breton & Collins 2007: 18). Raninella elongata was recorded from various localities throughout Europe, whereas R. trigeri is known exclusively from its type locality. So long as no additional material, preferably retaining sternum or abdomen to allow determination of sex, is forthcoming, it is prefered to keep these species apart.

A similar case is known from Alabama (Paleocene, Sucarnoochee Beds, Prairie Creek, Wilcox County), from where R. bidentata (see Rathbun 1935b: 84, pl. 18, figs. 9–12, as Symnista ) and R. eocenica (see Rathbun 1935b: 82, pl. 18, figs. 13–16) have been recorded. In the absence of additional material which preserves thoracic sternum or abdomen, these species are here considered as distinct.

Figures

FIGURE 27. Raninella elongata A. Milne Edwards, 1862 (Raninidae, Ranininae), upper Cenomanian, Butte de Gazonfier, Le Mans (northwestern France); A, C, D, MNH LM3788 (indeterminate sex); dorsal view of carapace and chelipeds; left lateral view of carapace and cheliped (arrow indicating crest on merus of left cheliped), and ventral view showing thoracic sternum and chelipeds; B, E. MNHN R03934 (paralectotype); dorsal view of carapace, and ventral view showing pterygostome. 3, 4, 5, thoracic sternites 3, 4, 5; br, branchiostegite; e4, episternite 4; ml, median line. Scale bars: 10mm.