Research Article |
Corresponding author: Conni M. Sidabalok ( sidabalok_conni@yahoo.com ) Academic editor: Tammy Horton
© 2020 Conni M. Sidabalok, Helen P.-S. Wong, Peter K. L. Ng.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Sidabalok CM, Wong HP-S, Ng PKL (2020) Description of the supergiant isopod Bathynomus raksasa sp. nov. (Crustacea, Isopoda, Cirolanidae) from southern Java, the first record of the genus from Indonesia. ZooKeys 947: 39-52. https://doi.org/10.3897/zookeys.947.53906
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The giant isopod genus Bathynomus A. Milne-Edwards, 1879, is recorded for the first time in Indonesian waters, from deep waters off southern Java in the Indian Ocean. Bathynomus raksasa sp. nov. is described and notes on juvenile specimens of an unidentified species found in the same locality are also provided. Bathynomus raksasa sp. nov. is characterized by the large size (averaging at 330 mm), narrowly rounded clypeus apex, prominent longitudinal carina on the clypeus, convex lateral margins of the uropodal exopod and endopod, produced distolateral corners of the uropodal exopod and endopod which have acute ends, an uropodal exopod with a setal fringe of medium length (69%), a pleotelson 1.6 times wider than long with the posterior margin medially concave, and the large number (11–13) of spines on the pleotelson.
Bathynomus, Cirolanidae, Indian Ocean, Indonesia, new species, South Java, taxonomy
The genus Bathynomus A. Milne-Edwards, 1879 inhabits the deep sea in the Atlantic, Pacific and Indian Oceans, with some species reaching large sizes in excess of 30 cm length (
The material was collected by the 2018 South Java Deep Sea Survey (SJADES 2018), a joint project between NUS and LIPI, with localities mostly in southern Sumatra and Java (Fig.
The following acronyms are used:
Suborder Cymothoida Wägele, 1989
Family Cirolanidae Da na, 1852
A. Milne-Edwards, 1879: 21.—
The taxonomy of Bathynomus has been reviewed by
Bathynomus giganteus A.
Holotype
, male, 363 mm; Indonesia, Sunda Strait (between Sumatra and Java); 6°00.828'S, 104°49.428'E; 26 Mar. 2018; SJADES exped.; station CP 13, beam trawl 1259 m;
Bathynomus giganteus A. Milne-Edwards, 1879 – 1 male, 354 mm; U.S.A., Virginia, 100 miles off Virginia Beach; 36.483N, 74.8W; 30 May 1962; 73 m depth; ZRC 2014.0837. Bathynomus doederleini Ortmann, 1894 – 6 males, 100, 120, 120, 128, 136, 145 mm; 7 females, 88, 90, 94, 130, 130, 138, 145 mm; 3 juveniles; Taiwan;
Indonesia, Sunda Strait: between Sumatra and Java, 06°00.828'S, 104°49.428'E.
Narrowly rounded clypeus apex (Fig.
Body (Fig.
Antenna 2 (Fig.
Pereopod 1 (Fig.
Pleonite 3 (Fig.
Uropod (Figs
Pleotelson (Fig.
Similar to male.
Robust setae count on female as follows: exopodal lateral margin with 7–10 robust setae, distal margin with 4 or 5, endopodal lateral margin with 3–5 and distal margin with 8–10; pleotelson with 9 distal and 2 lateral straight acute prominent spines along distal margin.
The epithet is the Indonesian word “raksasa” for giant, alluding to its enormous size and the significance of the find. The name is used as a noun in apposition.
Bathynomus raksasa sp. nov. can be readily identified by its large size (330 mm on average), narrowly rounded clypeus apex, produced and acute distolateral corners of uropodal rami, wider rather than long pleotelson with medially concave posterior margin and the presence of 11–13 pleotelson spines. Bathynomus raksasa sp. nov. is the sixth “supergiant” species from the Indo-West Pacific and is one of the largest known members of the genus.
In general appearance, B. raksasa sp. nov. is most similar to B. giganteus and B. lowryi. All three are large, averaging 300 mm in length, possess a prominent longitudinal carina on the dorsal surface of the pleotelson and have acute spines on the distal margin of the pleotelson. The new species is closest to B. giganteus, sharing the relatively medium length of antenna 2 (reaching to between the posterior of pereonite 2 and anterior of pereonite 3), lateral and posterior shape of the uropodal exopod and endopod, and the pleotelson spine count. Bathynomus raksasa sp. nov., however, differs markedly from B. giganteus by its more conspicuous longitudinal carina on the clypeus ventral surface (Fig.
Bathynomus raksasa sp. nov. shares the same general uropodal exopod and endopod shape as B. crosnieri, B. kensleyi and B. richeri but can easily be distinguished from them in its possession of a conspicuous longitudinal carina on the dorsal surface of the pleotelson (Fig.
The appendix masculina is absent on the holotype male of B. raksasa sp. nov. (Fig.
The SJADES cruise also obtained four juvenile and subadult specimens from southern Java (here identified as Bathynomus sp.) (Fig.
Bathynomus sp. superficially resembles the poorly known Bathynomus affinis Richardson, 1910, described from the Philippines from one specimen. There is, however, a problem with what has been identified as “Bathynomus affinis” by
Our material of Bathynomus sp. from Java resembles the “B. affinis” of
Bathynomus sp. differs from B. pelor Bruce, 1986 (from northwestern Australia) in having a longer antenna 2 that reaches to the middle of pereonite 4 (Fig.
Bathynomus sp. shares with B. kapala Griffin, 1975 (from Australia) a similar bifid central pleotelson spine but can easily be distinguished by its relatively longer antenna 2 (Fig.
Compared to B. doederleini, Bathynomus sp. has pereopod 7 coxa more slender (Fig.
Sunda Strait and Indian Ocean, South Java, Indonesia; at depths of 957–1259 m.
The SJADES cruise (chief scientists: Dwi Listyo Rahayu and Peter Ng) was a joint Indonesian-Singapore expedition to southern Java funded by the National University of Singapore and the Research Center for Oceanography, Indonesian Institute of Sciences (LIPI); and supported by their respective Ministries of Foreign Affairs under the RISING 50 program to promote bilateral co-operation. Thanks are also due to Bertrand Richer de Forges and Chan Tin-Yam for their invaluable help in the trawling work and other support. We thank Farid Rifaie and Arid of Research Center for Biology LIPI for the map and some of the photos, respectively. Rene Ong and Muhammad Dzaki Bin Safaruan of LKCNHM are also thanked for assisting us with the photography set up and visits to the collections in LCKNHM. We are also grateful to the reviewers for their constructive comments which significantly improved the quality of this paper.