Oxypleurodon, Miers, 1885

Lee, Bee Yan, Forges, Bertrand Richer De & Ng, Peter K. L., 2019, Deep-sea spider crabs of the family Epialtidae MacLeay, 1838, from Papua New Guinea, with a redefinition of Tunepugettia Ng, Komai & Sato, 2017, and descriptions of two new genera (Crustacea: Decapoda: Brachyura: Majoidea), Zootaxa 4619 (1), pp. 1-44 : 8

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Oxypleurodon sp. 1

( Fig. 1E View FIGURE 1 )

Material examined. 1 juvenile male (6.0 × 4.2 mm) ( ZRC 2018.1478 View Materials , ex. MNHN-IU-2017-11835) [photographed], stn CP4336, Ainto Bay , southeast New Britain, Solomon sea, Papua New Guinea, 06°06’S 149°19’E, 314–341 m, coll. MADEEP Expedition, 7 May 2014 GoogleMaps .

Remarks. Oxypleurodon sp. 1 was collected from the same station as the holotype of Oxypleurodon alisae n. sp. There are, however, several features that are different on this unique juvenile specimen. Oxypleurodon sp. 1 is distinguished by its large supraocular eave, possession of one long gastric plate, a very low, nearly obsolete cardiac plate, a sharp branchial plate, a bifid rostrum with two short pseudorostral spines diverging from their base and bearing rows of hooked setae, and the ambulatory legs have carinate meri. This combination of characters is unique in the genus. The coloration in life is white with orange spots on the shell and ambulatory legs ( Fig. 1E View FIGURE 1 ).

With only a single juvenile specimen, describing a new species is not recommended despite it appearing clearly different from O. alisae n. sp. and from O. stimpsoni Miers, 1885 . If this small specimen is the juvenile of O. alisae n. sp., it would imply that there are substantial ontogenic changes or morphological variations during the development in particular the raising of the plates and reduction of the proportions of the supraocular eave. Some of these major changes during the early stages have been mentioned by Ingle (1979) for the last megalopa of Rochinia carpenteri (Norman, in Thomson, 1873) , but the small specimen here is already the crab stage. It has also been observed that single-rostrum larvae can be modified to form a bifid rostrum during the first juvenile stage ( Tavares 1991; Tavares et al. 2015). In addition to the larval studies that have documented morphological changes, there are also studies on the adult form of some species that have noted the strong ontogenetic changes, notably on the American Scyramathia umbonata (Stimpson, 1871) (see Tavares et al. 2015) and Minyorhyncha crassa (A. Milne- Edwards, 1879) (see Tavares & Santana 2018). Tavares & Santana (2018), however, noted that generally species of Rochinia sensu stricto exhibit only minor ontogenetic changes as they grow. More material will need to be obtained to understand ontogenetic changes in carapace ornamentation.