A new type of brachyuran seminal receptacle in the masked crab Ethusa mascarone (Brachyura, Ethusidae)

Abstract

The reproductive system of the female Ethusa mascarone was studied with a combination of histological and MRI-techniques. The study reveals a completely new type of eubrachyuran seminal receptacle. This receptacle consists of two largely separate chambers that engage with each other in a manner similar to shaking hands. One chamber facing the medial axis is lined by cuticle while the second chamber consists of a thick holocrine epithelium. Both chambers are connected by two openings of a unique structure. First, the glandular chamber opens ventro-laterally to the cuticle chamber via a laterally flattened connective duct that is lined by a highly folded cuticle. A second opening connects both chambers dorsally with the oviduct orifice. A distinct character is the cuticular hook-like projection that is situated in between the connection of oviduct opening, the glandular chamber and the cuticle chamber of the seminal receptacle. The complete seminal receptacle exhibits a combination of plesiomorphic and apomorphic characters. The arrangement of the receptacles featured in two separate chambers, including the ventro-lateral connection of the glandular chamber to the cuticle chamber, presumably reflects an early evolutionary stage of an eubrachyuran receptacle. In contrast, the dorso-lateral opening between both chambers, including the hook-like projection, appears to be an apomorphic character of at least E. mascarone. J. Morphol. 277:1497-1508, 2016. © 2016 Wiley Periodicals, Inc.

A new subfamily classification of the highly diversified Dorippidae H. Milne Edwards, 1837 (Crustacea, Decapoda, Brachyura, Dorippoidea), using morphological, molecular and palaeotonlogical data, with special emphasis on its unique female reproductive system

“…The ethusid seminal receptacle consists of two connected chambers in addition to the ovary + oviduct, instead of the dorippid seminal structure + vagina independent of the ovary + oviduct. The topographic arrangement of ethusids deviates from all other currently known patterns in eubrachyurans, and is reported as apparently derived from that of dorippids (Hayer et al 2016b, 2017). In a molecular phylogeny for the order Decapoda combining nuclear and mitochondrial sequences, a close affiliation of the Majoidea and Ethusidae has been suggested (Bracken et al 2009: fig.…”

“…A recently discovered novel organisation in the two families of Dorippoidea, Dorippidae and Ethusidae (Hayer et al 2016a, b; Vehof et al 2017; 2018a, b; Vehof 2020), using both histology and magnetic resonance imaging (MRI) and microcomputed tomography (µCT) analyses, presents a new challenge by revealing that the female reproductive system of Dorippidae not only shows an amazing diversity across genera but also deviates from known types in the Brachyura. It is surprising to find such a variety of fundamentally different sperm storage organs in a family as small as the Dorippidae.…”

“…35D), without seminal receptacle, the fertilisation occurs externally in vulva opening (according to Vehof et al 2018b: fig. 3; Vehof 2020); C , in Ethusa mascarone (Ethusidae), with glandular and cuticle chambers largely independent of the seminal receptacle (according to Hayer et al 2016b: fig. 8); D , in a generalised eubrachyuran (one of several patterns), with seminal receptacle directly connected to ovary via oviduct, with vulvar opening on sternite 6 and with internal fertilisation.…”

“…The Ethusidae, the sister family to the Dorippidae, exhibits another new type of female reproductive system, exemplified by Ethusa mascarone (Fig. 36C) (Hayer et al 2016b: 1497-1508, figs l-7, 8B). The seminal receptacle is separated into two largely independent, laterally positioned chambers: a cuticular chamber that opens via a concave vagina through the vulva onto the cuticle of sternite 6; and a glandular chamber, interpreted as the modified portion of the oviduct.…”

“…According to the functional model proposed by Hayer et al (2016b: 1506), spermatophores, first stored in the cuticular chamber and then relocated to the glandular chamber via the dorsolateral opening, can be retained at moult process, allowing trans-moult retention. An external sperm plug, located at the opening of the vagina to the seminal receptacle and blocking the vaginal lumen, has been found in E. mascarone (Hayer et al 2016b).…”