CENOMANOCARCINIDAE, Guinot & Vega & Van Bakel, 2008

Guinot, Danièle, Vega, Francisco J. & Van Bakel, Barry W. M., 2008, Cenomanocarcinidae n. fam., a new Cretaceous podotreme family (Crustacea, Decapoda, Brachyura, Raninoidia), with comments on related families, Geodiversitas 30 (4), pp. 681-719 : 681-719

Family CENOMANOCARCINIDAE n. fam.

“Uncertain family” – Vega et al. 2007: 410, 412.

TYPE GENUS. — Cenomanocarcinus Van Straelen, 1936 by present designation.

INCLUDED GENERA. — Cenomanocarcinus . With reservation Campylostoma Bell, 1858 .

DIAGNOSIS. — Large size (for C. aff. vanstraeleni estimated maximum length of carapace: 160 mm); females probably larger than males. Carapace subhexagonal to subcircular. Anterolateral margin convex, long, with four to six teeth, the last epibranchial (often broken), may be extremely produced. Posterolateral margins markedly convergent posteriorly and with two teeth, the subdistal (at the extremity of the lateral ridge) may be marked, spiniform. Posterior margin clearly concave. Cervical and branchiocardiac grooves shallow. Three prominent longitudinal ridges (carinae) may bear strong tubercles: one axial (axial ridge) and two branchial (branchial ridges), generally forming a characteristic H with the imaginary horizontal line crossing the cardiac region; an oblique ridge (epibranchial ridge) may be present, ending in the epibranchial tooth. Two transverse ridges, one on protogastric regions and a less marked one on hepatic regions. Front narrow, trilobed. Orbits rounded; supraorbital margin with two notches. Branchiostegite joining the coxae of the pereiopods, thus no exposure of the pleurites. Mxp3 extremely elongate (reaching half carapace length), pediform, with coxae not closely approximated; endopodite: ischium long and developed, subrectangular longitudinally; merus ovate, approximately half the length of ischium; exopodite very

broad and longer than endopodite ischium.

Thoracic sternum relatively narrow, entirely covered laterally by male abdomen, therefore in contact with coxae of pereiopods, and leaving most of anterior sternum exposed between tip of telson and base of mxp3. Sternite 1 elongated between the bases of mxp3, sternites 2 and 3 showing as small, narrow plate (may be crown-shaped) intercalated between mxp3 coxae; sternite 4 long, well developed, with concave borders; sternites 5 and 6 wider and showing fairly expanded lateral flanges. Sternal sutures 4/5 and 5/6 short, forming lateral grooves, curved forwards where they are markedly deeper. Presence of a pair of prominences on sternite 5, being part of abdominal holding system. Sternites 7 and 8 unknown (see Addenda). Presence of a spermatheca (see Addenda). Medially an undivided portion, without median line. Male and female abdomens with all segments free, first segments dorsal, segment 6 much longer. Male abdomen fairly long and broad, completely filling laterally sterno-abdominal depression. Sexual dimorphism not well marked, the abdomen being only slightly narrower in males than in females. Surface of segments may bear several small tuberculate transverse ridges in both sexes.

Chelipeds robust and long, showing homochely and homodonty; fingers elongated, gaping in adult males.Sexual dimorphism including in females smaller, more slender and spinose chelipeds, with propodus much longer than in males and prehensile margins of fingers appressed.

P2-P4 rather long, markedly dissymmetric in both sexes. P2 slender and long; propodus moderately enlarged and flattened. P3 with propodus more developed and flattened, and styliform dactylus. P4 more robust than P3; merus shorter and thick; propodus extremely wide, ovate, and flattened; dactylus semi-ovoid. P5 very dissimilar in position, size and shape, markedly reduced, however rather long, thin, subdorsal, carried horizontally; merus subrectangular, one-third the length of P4 merus; carpus rectangular, two-thirds the length of merus; propodus subtriangular; dactylus nearly as long as propodus, simply curved, without terminal prehensile apparatus.

STRATIGRAPHIC RANGE. — Upper Albian-Santonian and upper Campanian of the Tethyan Province.?Early Eocene (Ypresian) for Campylostoma tentatively assigned herein to the Cenomanocarcinidae n. fam.

Remarks

In the Cenomanocarcinidae n. fam. the relationship between thoracic sternum and abdomen, i.e. the male abdomen filling laterally the sterno-abdominal depression and in contact with the coxae of the legs, conforms to the podotreme organization as

defined by Guinot (1977) and Guinot & Tavares (2001). However, the podotreme condition can only be confirmed by the female gonopore on P3 coxa (and spermatheca at the extremity of suture 7/8; see Addenda) or absence of vulva on sternite 6 in females.

The thoracic sternum described here is based principally on a Cenomanocarcinus sp. from the upper Albian of Colombia ( Fig. 3E , sternum associated with carapace) (Vega et al. in study) and on a very large female C. aff. vanstraeleni from the Coniacian (according to labelling with the specimen) of Colombia, lacking the dorsal carapace ( Fig. 6 ). The pair of prominences on sternite 5 is assumed to lock the abdomen.

Assignment of the Cenomanocarcinidae n. fam. to the subsection Raninoidia (see Discussion) is supported by several features, as follows: cheliped shape, in particular the fixed finger markedly bent; P3 and P4 with enlarged and flattened articles (P3 propodus quadrangular; P4 propodus ovate and P4 dactylus semi-ovoid); P5 reduced, subdorsal, and directed obliquely;mxp3 developed, elongate, with wide exopodite.However, the carapace of cenomanocarcinids differs to such an extent from that of Recent raninoids, that it requires major discussion. Placement of the Cenomanocarcinidae n. fam. in the vicinity of the most primitive raninoids, the Palaeocorystidae , the probable rootstock of the Raninoidea , is tentative (see Discussion).

Figures

FIG. 3. — A-D, F, Cenomanocarcinus vanstraeleni Stenzel, 1945; A, B, C, F, late Cenomanian-Turonian, Eagle Ford Group, Turonian, Múzquiz, Coahuila, Mexico; D, late Cenomanian, Eagle Ford Group, Britton Formation, California Crossing, Dallas County, Texas; E, Cenomanocarcinus sp., upper Albian,Colombia;A, female (MUZ-216),thoracic sternum (anterior portion of sternite 4 exposed) covered laterally by abdomen, mxp3, and pereiopods; at left, inflated P4 propodus (MUZ-212); B, mxp3 (MUZ-212); C, female (MUZ-201), sternite 4 with pair of tubercles, and abdomen;D,?female,paralectotype (BEG-21091-A1),thoracic sternum without abdomen; E, thoracic sternum (associated with carapace) showing a crown-shaped plate,long sternite 4, and deep, curved sutures 4/5 (INGEOMINAS/ Jur-1; Vega et al. in study); F, male (MUZ-215), thoracic sternum (see deep sutures 4/5) and abdomen. Scale bars: 10 mm.

FIG. 6. — Cenomanocarcinus aff. vanstraeleni Stenzel, 1945, Coniacian (according to the accompanying label), Apulo, Colombia, female, 160 × 150 mm (estimated carapace measurements not including lateral spines) (RGM M902):A, ventral view; B, chelipeds.