Pleistacantha ori Ahyong & P.K.L. Ng, 2007

(Figures 13D,E)

Material examined. M07, Stn. 10, 382m, ♂ 33.2× 44.9mm (CW × PRL) (IEO-CD-MZ07/1895); M08, Stn. 24, 402m, ♀ 17.1× 25mm (IEO-CD-MZ08/1760), 16S (MZ 424960), COI (MZ 434806); M08, Stn. 50, 623m, ♀ 17.6× 23.5mm (IEO-CD-MZ08/1905-1), 16S (MZ 424961), COI (MZ 434807); ♀ 17.9× 23.8mm (IEO-CD-MZ08/1905-2), 16S (MZ 424962), COI (MZ 434808); M08, Stn. 57, 366m, ♀ ov. 86.6× 108.5mm (IEO-CD-MZ08/2545); M08, Stn. 62, 467m, ♀ 19.5× 27.6mm (IEO-CD-MZ08/1767), 16S (MZ 424963), COI (MZ 434809); M09, Stn. 4, 258m, ♀ 82.1× 102.3mm (IEO-CD-MZ09/1857); M09, Stn. 27, 543m, ♂ 15.9× 23.4mm (IEO-CD-MZ09/1769); M09, Stn. 31, 457m, ♂ 10.4× 15.4mm (IEO-CD-MZ09/1764); M09, Stn. 60, 304m, ♂ 73× 91.5mm (IEO-CD-MZ09/1856), 16S (MZ 424964); M09, Stn. 63, 617m, ♀ 16.5× 23.5mm (IEO-CD-MZ09/1759), 16S (MZ 424965), COI (MZ 434810) .

Habitat and distribution. Pleistacantha ori had been misidentified and confused with Pleistacantha moseleyi (Miers) for many years, until it was described by Ahyong & Ng (2007) as a new species. It is presently known from off the Natal coast, South Africa, and Madagascar, between 238 and 480m depth (Ahyong & Ng 2007). It was cited by Emmerson (2016c) in waters of Mozambique.

Results and remarks. Several different keys and descriptions were used to identify our specimens: Ahyong & Ng (2007), Griffin (1974), Griffin & Tranter (1986) and Ng e t al. (2017). This was due to the difficult identification of this species because the different sizes of the studied specimens, the common morphological variability between adults and juveniles and the high variability in the size and morphology of the spines found between specimens. Genetic was used to confirm that the smallest specimens analysed belong to the same species than the adults. Eleven specimens, collected between 2007 and 2009, at depths between 258 and 623m, were studied. Our records extend the depth range from 480 to 623m for this species in its complete geographical distribution.

Colouration observed. Our specimens had white carapace, being dark orange in the most prominent zones of the branchial, gastric and cardiac regions. The pseudo-spines were orange, with white tips. The pleon was basically white. The ambulatory legs were whitish orange with long longitudinal spots on merus and carpus, while dactyli looks brown due to the dense tomentum and fouling on them. Smallest individuals had orange carapace with fewer white areas, white legs with many orange transverse stripes and white dactylus, with no fouling on them.

DNA barcodes. There are not 16S and COI sequences available for this species on any public database. Therefore, these are the firsts 16S and COI sequences obtained for this species. The six sequences obtained for 16S belong to a unique haplotype. The BLAST search matches 96.5% (intrageneric distance) with Pleistacantha kannu (MH 384947) from India, submitted by Ravichandran et al. (unpublished), the only species of this genus with a valid sequence in Genbank. There is a sequence of Pleistacantha sanctijohannis (LC 430736) deposited by Komai et al. (2019), but it is noticeably short s (only 164 bp) and does not allow any accurate comparison. Respect to COI, the five sequences obtained for P. ori represent four different haplotypes (differing in one, two and five positions), and the only COI sequence of the genus in Genbank, Pleistacantha kannu (MH 425628) from India, does not match, and look like a bacterial sequence.