ARCHAEOCHIAPASIDAE, Guinot, Carbot-Chanona & Vega, 2019

Guinot, Danièle, Carbot-Chanona, Gerardo & Vega, Francisco J., 2019, Archaeochiapasidae n. fam., a new early Cenomanian brachyuran family from Chiapas, Mexico, new hypothesis on Lecythocaridae Schweitzer & Feldmann, 2009, and phylogenetic implications (Crustacea, Decapoda, Brachyura, Eubrachyura), Geodiversitas 41 (7), pp. 285-322 : 292

Family ARCHAEOCHIAPASIDAE n. fam.

urn:lsid:zoobank.org:act:07C44088-09FD-4D27-A65E-4B3D02BB2BFD

TYPE GENUS. — Archaeochiapasa n. gen. by present designation. Gender feminine.

DIAGNOSIS. — Cuticle very thin. Carapace with lateroposterior and posterior regions expanded, forming all around a narrow, sunken, continuous area (“flange”) bordered by a strongly rimmed, thickened, raised margin. Carapace posterior margin deeply concave. Dorsal surface with a few, small, regularly distributed tubercles; some regions strongly inflated and separated by distinct grooves. Hepatic region conspicuous, delimitated by margin forming right angle; subbhepatic and branchial regions expanded laterally; cardiac region large, extending nearly to posterior border. Cervical and postcervical grooves marked; branchiocardiac groove deep. Rostrum short, sulcate, bifurcate. Chelipeds stout, equal, homomorph, with massive merus, carpus and propodus. P2, P3 very long and slender. Only one last pereiopod (P4 or P5) preserved, straight, and only reduced approximately by about half compared to P3. Thoracic sternum extremely wide compared to the carapace width; sutures 5/6-7/8 reaching margins of pleon, complete on exposed portion of sternum, sutures underneath the folded pleon being not visible. Pleon triangular, of six free somites, plus telson; first three somites dorsal; somite 6 with two lateral prominences, probably at location of sockets for pleonal-locking mechanism; no pleotelson.

REMARKS

In Brachyura the ventral part provides a reliable complex of characters, in particular the thoracic sternum. The organisation of the thoracic sternum and pleon, remarkably well preserved in Archaeochiapasa mardoqueoi n. gen., n. sp. ( Fig. 11 ), is indicative of a non-podotreme crab, in contradiction with what the carapace suggested, and provide evidence of a eubrachyuran affiliation.The new fossil from the lower Cenomanian of Mexico is therefore quite distinct from the podotreme crabs found preserved in Albian-Cenomanian deposits from southern England and France ( Wright & Collins 1972; Breton & Collins 2011; Valentin et al. 2014), from Navarra, northern Spain ( Fraaije et al. 2008; Klompmaker et al. 2011, 2013; Artal et al. 2012), from Tarragona, southern Spain ( Ossó et al. 2018), from Sicilia (Checchia-Rispoli 1917), from Mexico and Colombia ( Vega et al. 2007 a, 2010), from Texas ( Vega et al. 2014), and from a wide range of regions ( Karasawa et al. 2011; Van Bakel et al. 2012).

Figures

FIG. 11. — Archaeochiapasa mardoqueoi n. gen.,n. sp., male 10.3 × 11.1 mm, holotype (IHNFG-5616): thoracic sternum and pleon. Abbreviations:a4-a6, pleonal somites 4-6; t, telson; 3-8, thoracic sternites 3-8; 4/5, 5/6, 7/8, sternal sutures 4/5, 5/6, 7/8. Scale bar: 3 mm.