Paradorippe granulata – A crab with external fertilization and a novel type of sperm storage organ challenges prevalent ideas on the evolution of reproduction in Eubrachyura (Crustacea: Brachyura: Dorippidae)

Exceptional preservation of mid-Cretaceous marine arthropods and the evolution of novel forms via heterochrony

“…5 and figs. S5 to S8), as well as those from several recent works on larval, foregut, fossil and extant adult morphology, and molecular data ( 2 , 10 – 12 , 22 , 64 , 65 ), we conclude that podotreme brachyurans (i.e., where males and females have sexual openings at the base of the legs) do not form a natural group but rather a grade. Podotreme clades such as Dromiacea (Homolodromioidea, Dromioidea, and extinct relatives) and Homoloida branch closer to the root of Brachyura, while podotreme clades such as Raninoida, Cyclodorippoida, and extinct relatives, are recovered as sequential sister groups of Eubrachyura (Fig.…”

“…Extinct clades such as Dakoticancroida and Componocancroidea also appear to be closer to some eubrachyurans (e.g., Dorippoidea) than to less inclusive podotreme brachyurans (i.e., Dromiacea and Homoloida). Alternatively, the presence of spermatheca in podotreme crabs may have valuable phylogenetic implications and support a monophyletic Podotremata ( 6 , 66 ), but whether this character alone or other sexual characters were gained or lost several times within total-group Brachyura remains unknown ( 65 ). In addition, although extant heterotreme and thoracotreme eubrachyurans have been considered to form monophyletic assemblages, it is possible that the heterotreme and maybe the thoracotreme conditions had evolved in parallel more than once, but this is yet to be tested.…”

The morphology of the reproductive system in the crab Percnon gibbesi (Decapoda: Brachyura: Grapsoidea) reveals a new combination of characters in Thoracotremata

“…The bursa has previously been regarded as an apomorphy of a few species of Eubrachyura and was mainly discussed in relation to cryptic female choice (Jensen & Bentzen, ; Klaus et al, ). However, with more studies emerging that describe bursae as accessory (Jensen et al, ; Klaus et al, ) or sole sperm storage structures (Vehof et al, ; Vehof et al, ), the question arises whether those bursae are actually homologous and may represent the primary sperm storage structures of Eubrachyura. Future studies should focus on additional representatives closely related to P. gibbesi or belonging to putatively early diverging lineages of Thoracotremata in order to better understand the plesiomorphic character states in the sperm storage systems within this group.…”

“…In contrast to this they are rather uniform in the species of Thoracotremata studied so far (McLay & Becker, 2015). However, heterotremes and thoracotremes have in general been considered as exhibiting internal initiation of fertilisation as each of the paired oviducts is directly connected to the paired internalised sperm storage organs, the seminal receptacles (but see Vehof, Scholtz, & Becker, 2018).…”

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)

“…Hayer et al (2016) discovered in Dorippe sinica Chen, 1980 a separate, ectodermic, sperm-storage chamber, not corresponding to a split between the plates of the intersegmental phragma 7/8 as in all podotreme crabs, but being nevertheless an independent structure (a cuticular invagination of sternite 6), leading to an external fertilisation as in podotremes. In other dorippids, Dorippe quadridens (Fabricius, 1793), Medorippe lanata (Linnaeus, 1767) and Paradorippe granulata (De Haan, 1841), the female reproductive system also shows unique characters, leading to an external fertilisation (Vehof et al 2017(Vehof et al , 2018. This dorippid condition, which is reminiscent of the podotreme spermatheca and could be an evolutionary step or transition, challenges our common concept of reproduction in the Eubrachyura, in which the fertilisation has traditionally been considered internal.…”