Oxypleurodon difficilis
Creators: name: Muñoz, Isabel
name: García-Isarch, Eva
name: Cuesta, Jose A.
Publisher: name: Zenodo
Year: 2021
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Epialtidae
Oxypleurodon
Oxypleurodon difficilis

description: Oxypleurodon difficilis (Guinot & Richer de Forges, 1985)
(Figures 9A, 10)
Material examined. M08, Stn. 55, 411m, ♂ 14× 16.5mm (IEO-CD-MZ08/1774), 16S (MZ 424942), COI (MZ 434788); M08, Stn. 107, 549m, ♂ 21× 28.2mm (IEO-CD-MZ08/1897-2); ♀ ov. 18.8× 23.8mm (IEO-CD-MZ08/1897-1), 16S (MZ 424943), COI (MZ 434789); M09, Stn. 9, 540m, ♀ 18.1× 27.3mm (IEO-CD-MZ09/1823- 0a); ♀ 17.9× 25.5mm (IEO-CD-MZ09/1823-0b); ♂ 21.5× 30.1mm (IEO-CD-MZ09/1823-1), 16S (MZ 424944), COI (MZ 434790); ♀ ov. 22.2× 29.3mm (IEO-CD-MZ09/1823-2), 16S (MZ 424945), COI (MZ 434791).
Habitat and distribution. Only one species of Oxypleurodon was previously reported in Mozambican waters, Oxypleurodon holthuisi (Richer de Forges, 2018) while Oxypleurodon difficilis (Richer de Forges, 1984) was recorded in nearby waters of Madagascar (Guinot & Richer de Forges 1986).
Results and remarks. Seven specimens were collected during the M08 and M09 surveys, at depths from 411 to 549m. The keys and descriptions consulted for their morphological revision were Lee et al. (2017), Guinot & Richer de Forges (1984), Richer de Forges (1995, 2010, 2018) and Richer de Forges & Ng (2013). These are the first records of this specie in Mozambique waters.
Following the key for Oxypleurodon of the IP (Guinot & Richer de Forges 1984), these seven specimens could be identified as O. difficilis but there are certain characters that are not coincident with the original description. Guinot & Richer de Forges (1984) described the intraspecific variability in the shape and size of the rostrum. According to them, juvenile males are similar to females in presenting a shorter and thicker rostrum than males. However, the adult males of O. difficilis IEO-CD-MZ08/1774 and IEO-CD-MZ08/1897 present short rostrum, and oppositely, the females IEO-CD-MZ09/1823-0a and IEO-CD-MZ09/1823-2 bear elongated rostrum. In some specimens, the rostra are straight and in others curved upwards. In relation to the size of the channels between dorsal plates, Guinot & Richer de Forges (1984) described wider channels in the juvenile males, but this is also a variable feature in our specimens. Therefore, more similar to O. aurorae respect to this character. In addition, Guinot & Richer de Forges (1984) described the cardiac plates of O. difficilis as: “always transversely oval-shaped”. However, our specimens show great variability in the shape of this plate, from laterally elongated (upward or downward) to inverted triangleshaped (see Figure 10).
Colouration observed. The specimens had a salmon-pink carapace, rostrum dark orange and plates of the dorsal surface white; 4 th- 5 th ambulatory legs white, and the chelipeds and 2 nd and 3 th legs salmon-pink, with propodus and dactyls clearly marked. Legs colour of O. difficilis described by Richer de Forges (2018) was merely white.
DNA barcodes. There are not 16S and COI sequences available for this species in Genbank or BOLD. The four equal sequences of 16S obtained for four specimens from MZ08 and MZ09 are the first ones for this species. There are two COI sequences deposited in BOLD (MDECA 111-10 and MDECA112-10), corresponding to two specimens of O. stuckiae collected in New Caledonia by Bouchet & Richer de Forges (date of collection: 1993-01- 26), and deposited at the MNHN (MNHN-IU 200812259 and MNHN-IU200812261). However, these sequences actually correspond to an unidentified Heterocarpus sp. according to the tree generated in BOLD and to the result of a BLAST search of these sequences in Genbank. The COI sequences obtained for four specimens of O. difficilis present only two haplotypes (differing in two positions). In a BLAST search, the maximum fit was 96% with the sequences of three Plesionaka curvata, and the rest of matches (<90 %) were with several majoid species. The sequences of P. curvata that were uploaded at Genbank (JX 681746, JX681749, JX681750) by Zuccon et al. (2012) belong to specimens deposited in the MNHN (MNHN-IU 200814409, MNHN-IU-2008-14410, MNHN-IU-2008-14412), which were also uploaded to BOLD (MDECA 782-12, MDECA786-12, MDECA789-12), with other sequences of P. curvata that do belong to this species. Therefore, it seems that these three “strange sequences” of P. curvata could correspond to COI sequences of O. stuckiae since they fit 96% (22 mutations) with the sequences of O. difficilis, being in the expected range of intrageneric variability. Therefore, sequences of an unidentified Heterocarpus sp. were deposited instead of the sequences of O. stuckiae while the right sequences of O. stuckiae were deposited under the name of Plesionaka curvata.
description: Published as part of Muñoz, Isabel, García-Isarch, Eva & Cuesta, Jose A., 2021, Annotated and updated checklist of marine crabs (Decapoda: Brachyura) of Mozambique supported by morphological and molecular data from shelf and slope species of the " MOZAMBIQUE " surveys, pp. 1-67 in Zootaxa 5056 (1) on page 28, DOI: 10.11646/zootaxa.5056.1.1, http://zenodo.org/record/5577887