Callichimaeroidea, Luque & Feldmann & Vernygora & Schweitzer & Cameron & Kerr & Vega & Duque & Strange & Palmer & Jaramillo, 2019

Luque, J., Feldmann, R. M., Vernygora, O., Schweitzer, C. E., Cameron, C. B., Kerr, K. A., Vega, F. J., Duque, A., Strange, M., Palmer, A. R. & Jaramillo, C., 2019, Exceptional preservation of mid-Cretaceous marine arthropods and the evolution of novel forms via heterochrony, Science Advances 5 (4), pp. 1-15 : 2

Callichimaeroidea superfam. nov.

Included family. Callichimaeridae fam. nov. Tentatively Retrorsichelidae Feldmann et al. ( 20).

Diagnosis. Crabs with carapaces longer than wide, small and fusiform ( Callichimaeridae ), or large and ovate ( Retrorsichelidae ). Sternites 1 to 4 are fused and visible ventrally, forming an elongated sternal crown; sternite 4 is not mesially depressed; sternites 5 to 7 are unfused and axially sulcate by linea media; sternite 5 is very wide, almost as wide as the carapace; suture 5/6 is complete, but lacks a true sterno-pleonal cavity. Thepleon is symmetrical, sexually dimorphic, narrower in males than females, and in both sexes narrower than sternite 6 ( Callichimaeridae ). Pleonal somites are not fused, lacking articulating rings and bearing dorsal median tubercle or crest; pleonites 1 to 3 are exposed subdorsally; uropods or uropodal plates areabsent. True orbits, orbital fissures, or any protective structures are absent. Eyes are large in Callichimaeridae but are likely small and reduced in Retrorsichelidae . Chelipeds (claws) are isochelous, and the manus is stout, with pollex or fixed finger slightly ( Retrorsichelidae ) or strongly ( Callichimaeridae ) deflected downward; chelipedsarefoldedventrallyandposteriorlybeneath carapace. Pereopods (legs) P2 and P3 are much larger than P4 and P5; P4 and P5 are situatedsubdorsallyand directed posteriorly, lacking spines, neither subchelate nor modified for carrying or grasping. In Callichimaeridae , P2 and P3 are large and wide and positioned laterally, withdistal podomeres flattened and paddle-like; P4 and P5 are shortand narrow, withthedorsallongitudinalkeelneitherflattenednor paddle-like; P5 isthe smallest, well developed butreduced, and carried subdorsally. In Retrorsichelidae , P2 and P3 areapparentlylarge andpositioned ventrally; atleastone pereopod bearsflattened distal articles.