LITHOPHYLACIDAE Van Straelen, 1936

Guinot, Danièle & Breton, Gérard, 2006, Lithophylax trigeri A. Milne-Edwards & Brocchi, 1879 from the French Cretaceous (Cenomanian) and placement of the family Lithophylacidae Van Straelen, 1936 (Crustacea, Decapoda, Brachyura), Geodiversitas 28 (4), pp. 591-633 : 600-601

Family LITHOPHYLACIDAE Van Straelen, 1936

Lithophylacidae Van Straelen, 1936: 43 . — Stenzel 1953: 215. — Glaessner 1969: R514.

TYPE GENUS. — Lithophylax A. Milne-Edwards & Brocchi, 1879 by monotypy. No other genus included.

DESCRIPTION

Carapace broad, hexagonal to inverted trapezoidal, widest at outer-orbital angles, each marked by strong tooth. Antero-lateral margins strongly diverging anteriorly, markedly slanted. Dorsal surface lobulated throughout surface. Cervical, gastro-cardiac, branchio-cardiac grooves deep, resulting in H-shaped depression on each side. Gastric pits deep.

Front long, straight, not toothed, projecting medially in narrow, ventrally deflected, non-grooved rostrum. Frontal and orbital margins forming same line, with only minute fissure at mid- of supra-orbital margin. Orbits extremely broad (long orbital margins posteriorly sloping), deep, obliquely directed towards the axis of carapace, divided into two fossae. Eyes with stout stalks, basophthalmite thick; podophthalmite presumably much developed, presumably with inflated cornea.Well defined area (“shutter”) beneath suborbital region. Endostome wide. Mandibles extremely strong. Mxp3 clearly diverging, directed obliquely, with large gap between. Endopodite with rectangular ischion and wide merus; palp articulating on anteromesial corner of merus; exopodite broad. Pleural line typically ventral. Thoracic sternum wide. Sternal sutures 1/2 and 2/3 marked, complete; suture 3/4 replaced by sinuous ridge; sutures 4/5 to 7/8 marked by depressions, deep for 4/5 and 5/6, terminal for 4/5 and 7/8; suture 4/5 interrupted axially; suture 5/6 prolonging beyond deep depressions, thus presumed to be complete; suture 6/7 not interrupted axially, complete; suture 7/8 extremely short, only lateral. Sternites 1 and 2 narrow, not fused; sternites 4-6 widened; most of sternite 7 covered by male abdomen; sternite 8 subdorsal, reduced, narrow, covered by abdomen in both sexes, not visible dorsally. Median line on sternite 7. Wide sterno-abdominal cavity. Male and female abdomens only weakly dimorphic. Male abdomen with all segments free, covering most part of sternite 4, widely triangular; first segments (1-3) completely filling space between coxae of pereopods; telson triangular. Sexual openings typically heterotreme: vulvae on sternites 6; male gonopores located on P5 coxae. G1 long, slender, with simple apex; G2 relatively long, only slightly shorter than G1. Configuration of press-button type for abdominal maintaining. Chelae massive, clear heterochely, weak homodonty; hand not carinated. P2-P4 markedly long, elongated, merus thick, enlarged, compressed. P5 subdorsal, markedly reduced; merus narrow, slender; other articles not preserved. Specialized stridulatory apparatus may be present: pars stridens on merus of P1 consisting of well defined, elongated area bearing several prominent striae; plectrum consisting of row of spaced tubercles on the suborbital region.

REMARKS

The family Lithophylacidae was established by Van Straelen (1936: 44, pl. 4, fig. 9) for the sole Lithophylax , with a small illustration of a topotype, showing the large orbits. It was characterized by a subhexagonal carapace, straight fronto-orbital margin and grooves on the branchial regions. Van Straelen (1936: 44) placed the family close to the Goneplacidae , in remarking however: “Il peut paraître étrange de trouver déjà au Cénomanien une forme se rattachant aux phylums les plus élevés parmi les Brachyrhyncha”.

In absence of any new records of Lithophylax trigeri , the placement of this Cenomanian fossil was rarely evoked. The family has remained poorly known because of the insufficient illustration, and the relationships of the family have not been discussed in the carcinological literature. Lithophylax was initially attributed to the Goneplacidae by A. Milne- Edwards & Brocchi (1879) and later included in the tribu “Goneplacidea” by Van Straelen (1936), then considered incertae sedis by Glaessner (1929: 236), and finally placed with reservation within the Carcineretidae Beurlen, 1930 by Glaessner (1969: R514: “Wide carapace and narrow front, comparable with the distinction of Podophthalminae among Portunidae ”), Bishop (1988: 247), Vega & Feldmann (1991: 172, 173), Vega et al. (1995: 345) and, with confidence, by Schweitzer et al. (2002a: 21; 2003a: 44), based on wide carapace, dorsal areolation, narrow and deflected front, large orbits, developed eyestalks and massive chelae. According to Feldmann & Villamil (2002: 721), who followed Rathbun (1935: 52), Lithophylax was “probably a portunid”. Presently, Lithophylax is referred to the Carcineretidae , one of the heterotreme families that appeared during or before the Cretaceous and became extinct during the Late Cretaceous ( Schweitzer & Feldmann 2005: 35, 42, tables 4, 7).

Main characters of the Cenomanian crab studied herein support the recognition of a distinct family, Lithophylacidae , and its relationships with other known fossil and extant brachyuran families are reviewed (see Discussion).