Raninella 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 : 90-91

Genus Raninella A. Milne Edwards, 1862 (= Hemioon Bell, 1863 )

Raninella A. Milne Edwards, 1862: 492 .

Hemioon Bell, 1863: 10 [as Hemioön ].

Type species. Raninella trigeri A. Milne Edwards, 1862 , by original designation. Type species of Hemioon , by monotypy, is H. cunningtonii Bell, 1863 (= Raninella elongata A. Milne Edwards, 1862 ).

Species included. Raninella ? bidentatum ( Rathbun, 1935b), R. circumviator ( Wright & Collins, 1972) , R. elongata A. Milne Edwards, 1862 (= Palaeocorystes callianassarum Fritsch in Fritsch & Kafka, 1887), R. eocenica Rathbun, 1935b , R. libyca Van Straelen, 1935 , R. novozelandicum ( Glaessner, 1980) , R. quadrispinosum ( Collins, Fraaye & Jagt, 1995) , R. trigeri A. Milne Edwards, 1862 , R. yanini ( Ilyin & Alekseev, 1998) and Raninella ? n. sp. (sensu Lehmann 2004).

Emended diagnosis. Carapace oval, elongated, widest anterior to mid-length, weakly arched in longitudinal cross section, tumid in transversal cross section. Posterolateral margin weakly arched, sharply rimmed; anterolateral margin shorter, with 2 slightly raised, strong, triangular teeth. Orbitofrontal margin concave, slightly narrower (about 45 % in R. trigeri ) or slightly wider (about 55 % in R. elongata ) than maximum carapace width (including lateral teeth), with distinct triangular outer orbital corner, 2 long orbital notches. Rostrum triangular, excavated, with 2 small subdistal teeth. Branchiocardiac grooves weak, cervical groove obsolete. Post-frontal region depressed, coarsely granular. Carapace surface with minute granules; in lateral, posterior regions granules directed anteriorly (inclined nodes), flattened. Suborbital margin with long notch. Pterygostome tumid, granular; posterior corner with distinct semi-circular recess for mxp3 coxa; wide, smooth buccal collar lining buccal cavity; exhalant channels deep, well developed. Mxp3 elongated, in oxystomian condition. Branchiostegite reduced; pleurites exposed, surface smooth (polished). Sternite 3 crown shaped; sternite 4 anteriorly wide, joining pterygostome; episternite 4 small. Sternite 5 extended laterally between P1, P2, reaching exposed pleurites. Sternite 5 with medial line. Sternites 6‒8 distinctly narrow. No abdominal holding mechanism. Chelipeds homochelous, merus with subdistal granulate crest, chelae flattened, fingers weakly downturned, closing, prehensile margin with sharp teeth; lower margin of chelipeds smooth or with small spines. P2 with flattened merus; other pereiopods not studied. Abdomen unknown.

Remarks. Wright & Collins (1972: 87) and Breton & Collins (2007: 18) considered that the description by A. Milne Edwards (1862) of Raninella trigeri , type species of the genus, was meagre, yet valid; we concur. Based upon direct comparison of nearly all key specimens, Hemioon is here considered to be synonymous with Raninella , on account of close similarities in carapace, pereiopods, thoracic sternum and mxp 3 in R. trigeri and R. elongata , the latter being the type species of Hemioon , by synonymy with H. cunningtoni (see below under R. elongata ).

Beurlen (1930: 363) erected the family Raninellidae for a wide array of fossil genera, viz. Eumorphocorystes, Hemioeon [sic], Notopocorystes , Pseudoraninella , Raninella , Raninellopsis and Raninoides . His brief diagnosis was based solely on the developed anterior sternites, a plesiomorphy which cannot be succesfully used within this group, and which is even incorrect for Notopocorystes . The genera he listed are now part of several (sub)families and there is no reason to retain Raninellidae .

Raninella has been used as a waste-basket genus, accommodating numerous, highly diverse species. Some species traditionally referred to Raninella are here transferred to either Bournelyreidus n. gen. or Marylyreidus n. gen. (see above). The higher-level taxonomy of Raninella has also varied, the genus being referred to Raninidae ( Crawford et al. 2006) or Lyreidinae (see e.g., Tucker 1998; Nyborg & Fam 2008; Waugh et al. 2009). Waugh et al. (2009: 27) examined a specimen (NHM In. 63689), which is here confirmed to belong to R. trigeri . Based on a study of its cuticle, these authors suggested that ‘ Raninella … may not fit within the Lyreidinae’, and noted that ‘The front and sternum [of R. trigeri ] resemble Ranina americana ’. Wright & Collins (1972: 87) had earlier remarked that the flattened anterior teeth of Raninella resembled those of Ranina .

Raninella shows typical traits of Raninoidea , such as the possession of exposed pleurites, junction of sternite 4 with the pterygostome, anteriorly widened sternite 5 with junction to exposed pleurites, posterior sternites conspicuously narrow and lack of an abdominal holding system. Raninella is here included in Ranininae on the basis of its rimmed posterolateral margin, strong anterolateral teeth, anteriorly directed granules on the carapace surface and broad sternite 4.

The carapace of Raninella differs from that of Bournelyreidus n. gen. in being wider, in possessing much stronger anterolateral teeth and a continuously arched posterolateral margin. Sternal differences include the presence of a medial line on sternite 5 and the absence of an abdominal holding system. A remarkable character displayed by this genus is the granular subdistal crest of the cheliped merus, which is reminiscent of that in Palaeocorystidae .