Cenomanocarcinidae Guinot, Vega & Van Bakel, 2008

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 : 49-50

Family Cenomanocarcinidae Guinot, Vega & Van Bakel, 2008

Cenomanocarcinidae Guinot, Vega & Van Bakel, 2008: 684 .

Type genus. Cenomanocarcinus Van Straelen, 1936: 37 , by original designation (emend. Stenzel 1945: 447).

Genera included. Cenomanocarcinus Van Straelen, 1936 , Campylostoma Bell, 1858 , and Hasaracancer Jux, 1971 .

Diagnosis (modified after Guinot, Vega & Van Bakel 2008: 684).

Carapace medium to large size (estimated maximum carapace length of 160 mm in Cenomanocarcinus aff. vanstraeleni ); females probably larger than males. Carapace subhexagonal to subcircular, widest about mid-length, weakly arched in all directions, orbits raised (distinct in Cenomanocarcinus , Hasaracancer , weak in Campylostoma ). Anterolateral margin convex, long, with 4‒7 teeth, last epibranchial sometimes conspicuously strong, produced. Posterolateral margins markedly convergent posteriorly, tubercular or with 1 or 2 teeth, subdistal (at the extremity of the lateral ridge) may be marked, spiniform. Posterior margin clearly concave, as wide as or wider than orbitofrontal margin, may be convex in dorsal view. Orbitofrontal margin narrow ( Cenomanocarcinus ) or wider ( Campylostoma , Hasaracancer ). Front narrow, trilobate (orbital corners excluded). Orbits rounded, small ( Cenomanocarcinus ); supraorbital margin with 2 fissures. Cervical groove shallow to acute, branchiocardiac grooves shallow. Three prominent longitudinal carinae may bear strong tubercles: 1 axial (axial carina), 2 branchial (branchial carinae) that are convex or straight, may generally form characteristic ‘H’ with imaginary horizontal line crossing cardiac region; oblique carina (epibranchial carina) may be present, ending in epibranchial tooth. Transverse ridges may be present, nearly in line, one on protogastric regions, less marked one on hepatic regions. Dorsal carapace surface with upright nodes.

Pterygostome deeply grooved, with distinct, blunt crest that extends anteriorly into prominent subantennary lobe. Branchiostegite joining coxae of pereiopods, exposure of pleurites absent. Mxp3 strongly elongated (reaching half carapace length), in oxystomian condition, with coxae large, not close to each other; endopodite ischium long, developed, subrectangular longitudinally; merus ovate, approximately half ischium length ( Cenomanocarcinus ), or slender, as long as ischium ( Campylostoma ); exopodite broad, longer than endopodite ischium ( Cenomanocarcinus ), or shorter than endopodite ischium ( Campylostoma ).

Chelipeds robust, long, homochelous, homodontous; fingers elongated, gaping in adult males; upper, lower margin of chelae spinose, outer surface tuberculate ( Cenomanocarcinus , unknown in others). Smaller, more slender in females than in males, spinose chelipeds, with propodus much longer than in males, prehensile margins of fingers appressed. P2‒P4 rather long, markedly asymmetrical in both sexes. P2 slender, long; propodus moderately enlarged, flattened. P3 propodus more developed, flattened, with styliform dactylus. P4 more robust than P3; merus shorter, thick; propodus wide, ovate, flattened; dactylus semi-ovoid. P5 dissimilar in position, size, shape, markedly reduced, relatively long, thin, subdorsal, carried horizontally; merus subrectangular, length one-third of P4 merus; carpus rectangular, length two-thirds of merus; propodus subtriangular; dactylus nearly as long as propodus, simply curved, without terminal prehensile apparatus. Basis, ischium of pereiopods separated ( Cenomanocarcinus vanstraeleni , Campylostoma matutiforme ).

Thoracic sternum relatively narrow, entirely covered laterally by male abdomen, therefore in contact with coxae of pereiopods, leaving most of anterior sternum exposed between telson, base of mxp3. Sternal plate weakly concave anteriorly, slightly more posteriorly, flatter in females. Sternite 1 elongated between proximal portions of mxp3, sternites 2, 3 showing as small, narrow plate (may be crown shaped) intercalated between mxp3 coxae; sternite 4 long, well developed, with concave borders, its anterior side slightly wider than sternite 3 ( Campylostoma matutiforme , Cenomanocarcinus vanstraeleni ); sternites 5, 6 wider, showing fairly expanded lateral flanges. Sternites 7, 8 weakly tilted, sternite 8 elongated, weakly curved, not much narrower than preceding sternites ( Cenomanocarcinus beardi ). Sternal sutures 4/5–6/7 short, lateral, crescent-shaped. Spermathecal apertures at extremity of suture 7/8, rather small, oval, margins weakly raised ( Cenomanocarcinus beardi ). Thoracic sternum weakly narrowing posteriorly, an undivided portion medially, without medial line ( Cenomanocarcinus beardi , C. vanstraeleni ). Arthrodial cavities evenly spaced, ventro-laterally directed.

Abdomen with all somites free in both sexes, first somites dorsal, somite 6 much longer, sexual dimorphism indistinct. Male abdomen fairly long, broad, completely filling laterally sterno-abdominal depression. Surface of somites may bear several small tuberculate transverse ridges in both sexes. Male telson reaching sternite 4, at same vertical level as gynglymes for P1 ( C. vanstraeleni ); in females, abdomen slightly longer, reaching almost sternite 3, well beyond level of P1 gynglymes ( C. vanstraeleni ).

Double locking teeth on episternite 5 forming abdominal holding system ( C. vanstraeleni , C. aff. vanstraeleni ). No holding structures on coxae of pereiopods.

Remarks. The family Cenomanocarcinidae was erected by Guinot et al. (2008), who discussed the possible relationships with other raninoidean families. The Cenomanocarcinidae is a long-existing family, first appearing during the Albian and becoming extinct in the early Eocene (55.8–46.5 Ma). Only one Mesozoic and one Paleogene (Eocene) genus are so far included. Campylostoma was assigned, albeit with a query, to Cenomanocarcinidae by Guinot et al. (2008); newly examined, better-preserved material confirms this taxonomic placement.

Many characters of the thoracic sternum and appendages of Cenomanocarcinidae are now known ( Guinot et al. 2008); new material illustrated herein substantiates the presence of a prominent, double structure for abdominal holding ( Fig. 40C–F ) and a distinct oxystomian configuration of mxp3 and endostome ( Fig. 50F). The spermathecal aperture described by Guinot et al. (2008: 38), is also illustrated here ( Fig. 58A, B ); the female gonopore has yet to be observed. Karasawa et al. (2011: 550) diagnosed Cenomanocarcinidae as having a complete sternal suture 6/7; this likely was a weakly calcified transverse line, as seen in many podotremes, or a preservational artefact.

In the nature of the anterolateral margin, the narrow orbits and the areolated, tuberculate carapace surface, the family appears closely related to Necrocarcinidae . Necrocarcinids, however, have a very strong sterno-abdominal depression, with the episternites markedly raised, whereas the sterno-abdominal depression of Cenomanocarcinidae is rather flat. The tricarinate carapace is a feature in common with orithopsids, which, however, have concave branchial carinae, rather than the convex branchial carinae seen in cenomanocarcinids. Several sternal differences confirm separation of the two families; sternite 3 is crown shaped in Cenomanocarcinidae , diamond shaped in Orithopsidae ; sternite 4 is relatively flat, gently concave in Cenomanocarcinidae , whereas it is medially strongly excavated, with a deep gutter, in Orithopsidae , and the posterior sternites are of normal shape (plesiomorphic condition) in Cenomanocarcinidae , whereas the configuration in Orithopsidae is different (see below, under Silvacarcinus laurae ).

Cuticle ornament and microstructure in Cenomanocarcinidae is straightforward, with the anterior regions and the branchial crests (not present in Campylostoma ) tubercular, the complete carapace surface being finely granular with upright nodes.

Figures

FIGURE 40. Double peg in Palaeocorystoidea; A, B, Silvacarcinus laurae Collins & Smith, 1993 (Orithopsidae), IRScNB TCCI 6115 (holotype), lower Eocene (Ypresian), Brussels (Belgium); ventral view showing thoracic sternum, and detail of thoracic sternum; C–F. Cenomanocarcinus vanstraeleni Stenzel, 1945 (Cenomanocarcinidae), MAB k. 2909 (C, E), upper Albianlower Cenomanian (Pawpaw Formation), Tarrant County, Texas (U.S.A); details of thoracic sternum; MAB k. 2895 (D, F); same provenance, detail of abdomen and thoracic sternum, and ventral view showing thoracic sternum, abdomen and base of mxp3. 4, 5, 6, thoracic sternites 4, 5, 6; 4/5, 5/6, thoracic sternal sutures 4/5, 5/6; a6, abdominal somite 6; cmxp3, coxa of mxp3; cx2, P2 coxa; dp, distal peg; e4, e5, episternites 4, 5; g2, gynglyme for P2 coxa; p, peg (undifferentiated); sp, subdistal peg; t, telson. Scale bars: A-E: 5mm; F: 10mm.

FIGURE 58. Spermathecal aperture in cenomanocarcinids; A, B, Cenomanocarcinus beardi Schweitzer, Feldmann, Fam, Hessin, Hetrick, Nyborg & Ross, 2003a, MAB k. 2544 (female), Cenomanian (Woodbine Formation), Wagner Park, Texas (U.S.A); ventral view showing thoracic sternum, mxp3 and detail of thoracic sternum showing spermathecal aperture; C, D, Interpretative line drawings of A and B. 3, 4, thoracic sternites 3, 4; 4/5, 5/6, 6/7, 7/8, thoracic sternal sutures 4/5, 5/6, 6/7, 7/8; cx1, cx2, P1, P2 coxae; e4, e5, e6, e7, e8, episternites 4, 5, 6, 7, 8; pt, pterygostome; sa, spermathecal aperture. Scale bars: 5mm.