Not only for males: the pleon‐holding mechanism in female calappids (Crustacea: Decapoda: Brachyura)

Adult female Calappidae were examined with light microscopy and microcomputed tomography for the presence of a pleon‐holding mechanism. A typical press‐button consisting of a protrusion on the fifth thoracic sternite and a socket on the sixth pleon segment was found in species of the genera Calappa, Calappula, Cycloes, Mursia, and Paracyclois. Within the genus Calappa, 15 of 17 species showed a complete press‐button mechanism, whereas in two species only a sternal button or none of the holding structures could be observed. The functionality of the mechanism was assessed by manually flexing and opening the pleon. This revealed a lack of function in species with fully developed holding structures, while others exhibited full function. Additionally, signs of abrasive wear could be identified with scanning electron microscopy on the surface of the holding structures of Calappa hepatica. The documentation of pleon‐holding structures of varying degrees of functionality in adult female eubrachyurans provides new insight into a morphological characteristic known exclusively from Brachyura.     

The oldest higher true crabs (Crustacea: Decapoda: Brachyura): insights from the Early Cretaceous of the Americas

Despite the extensive fossil record of higher crabs (Eubrachyura) from Late Cretaceous and Cenozoic rocks worldwide, their Early Cretaceous occurrences are scarce and fragmentary, obscuring our understanding of their early evolution. Until now, representatives of only two families of eubrachyuran‐like crabs were known from the Early Cretaceous: Componocancridae and Tepexicarcinidae fam. nov., both monospecific lineages from the Albian (~110–100 Ma) of North and Central America, respectively. The discovery of Telamonocarcinus antiquus sp. nov. (Telamonocarcinidae) from the early Albian of Colombia, South America (~110 Ma), increases to three the number of known Early Cretaceous eubrachyuran‐like families. The ages and geographical distributions of the oldest eubrachyuran‐like taxa (i.e. Componocancridae, Telamonocarcinidae and Tepexicarcinidae fam. nov.) suggest that the oldest higher true crabs might have originated in the Americas; that they were already morphologically diverse by the late Early Cretaceous; and that their most recent common ancestor must be rooted in the Early Cretaceous, or even the Late Jurassic.     

Notes on the position of the true freshwater crabs within the brachyrhynchan Eubrachyura (Crustacea: Decapoda: Brachyura)

Cladistic and phenetic relationships of 51 eubrachyuran crab genera, comprising 36 genera of marine crabs and 18 genera of true freshwater crabs from 7 families, were investigated using 121 parsimony-informative adult morphological characters. The data matrix was subjected to four different treatments: (1) a cladistic analysis with a combination of unordered and ordered characters, (2) a cladistic analysis with all characters unordered, (3) neighbour-joining, and (4) UPGMA phenetic analyses. The parsimony analysis conducted with a combination of ordered and unordered characters produced a set of hypotheses which supported monophyly of a Pseudothelphusidae+Potamoidea clade. Furthermore, exemplar genera of the Bythograeidae and Pinnotheridae formed an unresolved polytomy with the Pseudothelphusidae+Potamoidea group, the Thoracotremata. The trichodactylid freshwater crabs were positioned as the sister taxon of the basal portunoid Carcinus, but were unresolved relative to other portunoids and geryonids. Second, the parsimony analysis conducted with all characters unordered resulted in a [bythograeid, pseudothelphusid+potamoid, pinnotherid, thoracotreme] group with no hierarchical resolution, which in turn formed a polytomy with a goneplacid+portunoid clade and a polyphyletic Xanthoidea. And third, phenetic groupings of the eubrachyuran genera invariably placed the pseudothelphusids with the potamoids, and this clustered with a group containing the thoracotremes (either in whole or part). Support was thus found for morphological connections among the nontrichodactylid freshwater crabs, thoracotremes, bythograeids, and pinnotherids, and for the placement of the trichodactylids within the Portunoidea. These two latter findings (that used a range of genera from each family) are broadly congruent with a previous cladistic analysis of selected eubrachyuran familial groundpatterns that used a basal exemplar of each marine and freshwater crab family (Sternberg et al., 1999). However, it is clear that the large scale homoplasy identified here may nullify any reliable hypothesis of brachyrhynchan groupings at this stage.     

Presence of Zanthopsis M’Coy, 1849 (Crustacea: Decapoda: Brachyura) in the Early Eocene of Iran,and comments on the different species and/or morphotypes and their palaeobiogeography

In the present work, we report the discovery of several carapaces of Zanthopsis sp. from the Lower Eocene of Central Iran, which represent the easternmost record of the genus. In addition, we discuss on the similarities of the different species and/or morphotypes of the genus, and conclude that the European species could be ascribed to the “Zanthopsis leachii complex”, until future works determine the validity of the species therein contained. In this sense, Zanthopsis jacobi Van Straelen, 1924, in agreement with Artal and Vía (1988), is herein considered a junior synonymous of Z. dufouri (H. Milne Edwards in d’Archiac, 1850). The presence of Zanthopsis in the lower Eocene of Iran suggests homogeneity of the brachyuran fauna on both sides of the Tethys Realm.