Monday, December 28, 2015

[Crustacea • 2015] Macrobrachium xmas • A New Stygobitic Prawn of the Genus Macrobrachium Spence Bate, 1864, from Anchialine Caves in Christmas Island, Indian Ocean; with A Rediagnosis of M. miyakoense Komai & Fujita, 2005 (Decapoda: Caridea: Palaemonidae)


Macrobrachium xmas  Fujita, Davie & Ng.,2015
Y. Fujita, P. J. F. Davie and P. K. L. Ng. 2015. RAFFLES BULLETIN OF ZOOLOGY. 63

Abstract
 A new species of stygobitic palaemonid prawn of the genus Macrobrachium Spence Bate, 1864, is described from Christmas Island, Indian Ocean Territory, Australia. The new anchialine species resembles M. miyakoense Komai & Fujita, 2005, from Japan, but can be distinguished by its relatively longer and more slender rostrum, the proportionately smaller eye cornea with a more swollen eye stalk, and more teeth on the post-rostral margin of the carapace. The taxonomy of M. miyakoense is also discussed based on additional material recently obtained from Japan, and the species rediagnosed. Macrobrachium miyakoense was originally described from two young males collected from Miyako Island, Ryukyu Islands, Japan.

Key words. Palaemonidae, Macrobrachium, new species, anchialine cave, Christmas Island, Indian Ocean, taxonomy

TAXONOMY

Family Palaemonidae


Macrobrachium miyakoense Komai & Fujita, 2005 (Figs. 1–3)
Macrobrachium miyakoense – Komai & Fujita, 2005: 14; De Grave & Fransen, 2011: 327.

Remarks. Macrobrachium miyakoense was originally described from two young males (pocl 14.70 mm and 12.60 mm). The present full-grown specimens are similar in morphology to the type specimens, but some adult characters differ markedly. We have therefore amended the original description of Komai & Fujita (2005) accordingly and provided new figures.


Macrobrachium xmas n. sp.
Macrobrachium microps – Short & Meek, 2000: 83–85, fig. 2
[not Macrobrachium microps Holthuis, 1978].



Color in life. Whole body (carapace, abdomens, and appendages) generally whitish to pale yellow (Figs. 13, 14).

Habitat and Biology. Macrobrachium xmas n. sp. was collected from three anchialine caves (Freshwater Cave, Runaway Cave and Whip Cave). Specific habitat information for these localities has been given by Humphreys & Eberhard (2001). Co-inhabiting decapod crustaceans reported from Christmas Island caves include: a procaridid Procaris noelensis Bruce & Davie, 2006, an alpheid Metabetaeus minutus (Whitelegge, 1897), a barbouriid Parhippolyte cf. uveae Borradaile, 1899, an atyid Antecaridina lauensis (Edmondson, 1935), and three crabs, Karstarma jacksoni (Balss, 1934) [Sesarmidae], Orcovita hicksi Davie & Ng, 2012, and Orcovita orchardorum Davie & Ng, 2012 [both Varunidae] (Anker, 2010; Bruce & Davie, 2006; Davie & Ng, 2012). In this study, two ovigerous females of M. xmas were collected, and the pre-eyed eggs are small, 0.56–0.70 mm (on female pocl 21.66 mm, ZRC 2015.281, average 0.64 mm, n = 10) in size, suggesting an amphidromous life cycle.

Distribution. Only known from Christmas Island thus far. 

Etymology. The new species name is a common arbitrary abbreviation of “Christmas” and is derived from the type locality, Christmas Island. The name is used as a noun in apposition.


Yoshihisa Fujita, Peter J. F. Davie and Peter K. L. Ng. 2015. A New Stygobitic Prawn of the Genus Macrobrachium Spence Bate, 1864, from Anchialine Caves in Christmas Island, Indian Ocean; with A Rediagnosis of M. miyakoense Komai & Fujita, 2005 (Crustacea: Decapoda: Caridea: Palaemonidae). RAFFLES BULLETIN OF ZOOLOGY. 63: 610–625. 


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