Elsevier

Revue de Micropaléontologie

Volume 56, Issue 1, January–March 2013, Pages 2-19
Revue de Micropaléontologie

Original article
Challenging cosmopolitanism in the deep sea: The case of “Cythere acanthoderma Brady, 1880” (Crustacea, Ostracoda)Remise en question du cosmopolitisme en milieu marin profond : le cas de « Cythere acanthoderma Brady, 1880 » (Crustacea, Ostracoda)

https://doi.org/10.1016/j.revmic.2012.11.001Get rights and content

Abstract

Cythere acanthoderma Brady was described from Recent sediments collected from all world's oceans during the HMS Challenger expedition in the 1870s. Subsequently, this species has been recorded in at least 27 publications, extending its stratigraphical range from the Recent back into the Upper Eocene, its zoogeographical range from Atlantic, Indian, Pacific, Arctic and Southern oceans, and its bathymetric range from the continental shelf (> 400 m) to deeper regions of the abyss (> 5000 m). Importantly, C. acanthoderma was erected the type species of the widespread and abundant, deep-sea genus Legitimocythere Coles and Whatley, 1989. For the present publication, all the specimens of Legitimocythere acanthoderma housed in the Natural History Museum in London were re-studied. Based on the type material and on previous publications, L. acanthoderma is revised, re-diagnosed and re-illustrated with scanning electron microscopy. Twenty-two specimens are, herein, as Henryhowella, Trachyleberididae gen. nov. and cf. Legitimocythere. Finally, comparisons based on illustrations from earlier publications show that only a few of the over 70 previous records (i.e., fossil and Recent samples) of L. acanthoderma could be confirmed; the remaining records either involved distinct species or genera or are dubious. As a consequence, the revised distribution of L. acanthoderma includes only Recent sediments from bathyal depths of the Subantarctic region of the Southern Ocean, and so it can no longer be considered to be cosmopolitan, eurybathic and to have existed for over 30 million years.

Résumé

Cythere acanthoderma Brady a été décrite à partir des sédiments actuels de tous les océans du monde lors de l’expédition du HMS Challenger dans les années 1870. Depuis, 27 publications discutent de cette espèce, ce qui a permis d’accroître son extension stratigraphique de l’actuel jusqu’à l’Éocène supérieur, son extension zoogéographique de l’océan Atlantique, à l’Indien, au Pacifique, à l’Arctique et aux mers du Sud, et son extension bathymétrique du plateau continental (> 400 m) aux régions profondes des abysses (> 5000 m). C. acanthoderma est devenue l’espèce type du genre Legitimocythere Coles et Whatley, genre répandu, abondant, et habitant les eaux profondes. Pour la présente publication, tous les spécimens de L. acanthoderma conservés au musée d’histoire naturelle de Londres ont été réétudiés. En se basant sur le matériel type et sur les publications antérieures, L. acanthoderma est révisée, elle bénéficie d’un nouveau diagnostic et elle est nouvellement illustrée par microscopie électronique à balayage. Vingt-deux spécimens sont ici re-identifié comme Henryhowella, Trachyleberididae gen. nov. et cf. Legitimocythere. Enfin, les comparaisons basées sur les illustrations de publications antérieures montrent que seulement quelques-unes des plus de 70 occurrences précédentes (échantillons fossiles et récents) de L. acanthoderma ont pu être confirmées ; les enregistrements restants concernant soit des espèces ou genres distincts, soit étant douteux. Par conséquent, la répartition révisée des L. acanthoderma ne comprend que les sédiments récents de profondeurs bathyales de la région subantarctique de l’Océan Austral, et cette espèce ne peut donc plus être considérée comme cosmopolite, eurybathic et exister depuis plus de 30 millions d’années.

Introduction

Brady (1880) when studying the ostracods collected during the H.M.S. Challenger Expedition from 1873 to 1876 described “Cythere acanthoderma n. sp.” and 142 other novel species. Brady (1880) neither designated holotypes nor gave information on the specimens he had illustrated. Many of these new species, especially those from the deep-sea (e.g., Cythere dasyderma Brady, 1880, Cytheropteron mucronalatum Brady, 1880), he recorded from several distinct basins. However, subsequent taxonomic reviews have shown that of these cosmopolitan species were confused groups of distinct species (e.g., Maddocks, 1990, Jellinek et al., 2006, Brandão, 2008, Brandão and Yasuhara, in press; Brandão et al., in review).

Brady (1880) recorded “C. acanthoderma n. sp.” from the Northern Atlantic (stations 64 and 73), the Southwestern Indian Ocean (station 146), the Indo-Pacific (station 191a), the Northern Central Pacific (station 246), and the Southeastern Pacific (stations 296 and 302) (Brady, 1880: pp. 104–105; Jellinek and Swanson, 2003: p. 33) (Fig. 1 and Table 1). The recorded depth ranges were also very wide, ranging from the shallow slope to deep abyssal depths (1061 to 5029 m). Moreover, Brady's (1880: pl. 18, figs. 5a-e) drawings are schematic and it is not even possible to recognise which genera he had illustrated. This not only led to C. acanthoderma being recorded from all oceans, from the Upper Eocene to Recent, and from shelf to abyssal depths (Table 1, Table 2, Table 3 and Fig. 1) but also to it being assigned to several genera, as noted by Jellinek and Swanson (2003): “Echinocythereis (Puri, 1954, Levinson, 1974), Henryhowella (Puri, 1971), Thalassocythere nomen nudum (Ducasse and Peypouquet, 1979, Malz, 1987), Trachyleberis (Ruan and Hao, 1989) and Legitimocythere (Coles and Whatley, 1989, Dingle and Lord, 1990)”.

Below I discuss key publications on C. acanthoderma, for more detailed information see the taxonomic section and Table 1, Table 2, Table 3.

Bate (1963) reported on material of C. acanthoderma housed in the Natural History Museum (NHM) in London and in the Hancock Museum (Newcastle upon Tyne). Puri and Hulings (1976) designated as lectotype a single (unfortunately) juvenile left valve from the Southwestern Indian Ocean (Challenger station 146, 46°46'S, 45°31’E, 2515 m). They also re-sorted the sediment from the type locality (i.e., sample M-170, station 146) and found one complete carapace (NHM 1974.277) and one right valve (NHM 1974.276). But my re-examination of these latter three valves has shown that they actually belong to the genus Henryhowella (see taxonomic section).

Coles and Whatley (1989) described the cosmopolitan, deep-sea genus Legitimocythere and selected C. acanthoderma as its type species. But, as noted by Jellinek and Swanson (2003), they illustrated a distinct species from the Upper Oligocene sediments from the Northern Atlantic, which they misidentified as Legitimocythere acanthoderma.

Dingle et al. (1990) subsequently assigned C. acanthoderma to the genus Trachyleberis and, based on the previous studies of Brady (1880), Benson et al. (1983) Ducasse and Peypouquet (1979) and Whatley and Coles (1987), stated that “Trachyleberis acanthoderma” occurs in the Atlantic, Indian and Pacific oceans, from the Miocene to the Quaternary and from 1600 to 3884 m water depth.

Jellinek and Swanson (2003: pp. 33–34) discussed the taxonomic confusion prevailing with Legitimocythere acanthoderma, and provided comparisons between what they believed to be the “real” L. acanthoderma and the specimens studied by previous authors. However, they did not study any specimens of L. acanthoderma and until then only three optical microscope photos of the juvenile lectotype were available (Puri and Hulings, 1976: pl. 1, figs. 13–18). Therefore, it is not clear where they obtained the information about the adult valve morphology of L. acanthoderma from. Consequently, the validity of their comparisons must be considered doubtful.

Mazzini, 2005 (fig. 23) studied the type material of L. acanthoderma and proposed new diagnostic characters for the genus Legitimocythere. She sorted again the sediment of the original sample of Challenger's station 146 (i.e., sediment sample M-170) and found two more adult right valves and one adult left valve. She also provided SEMs of the external, internal and dorsal views of the juvenile lectotype and one of the re-sorted adult right valves, and compared the morphology of Lacanthoderma with other Legitimocythere species.

The purpose of this study is to complement Mazzini (2005) work on L. acanthoderma and provide:

  • a diagnosis, an emended description Lacanthoderma ‘sensu stricto’;

  • detailed illustrations of valves, i.e. left and right valves’ internal and external views, hinge, muscle scars, external ornamentation of Lacanthoderma ‘sensu stricto’ (Plate 1, Plate 2);

  • an extensive synonymy of L. acanthoderma ‘sensu stricto’;

  • a revised geographical and stratigraphical distribution for this important deep-sea species (Fig. 1; Table 1, Table 2, Table 3);

  • a full list of specimens and slides (included in the syntypes of Lacanthoderma), but herein re-identified as Henryhowella sp., cf. Legitimocythere sp., “Taracythere” sp. nov. aff. “T.” dasyderma and Trachyleberididae sp. (Table 3).

  • SEM photos of the taxa misidentified by Brady (1880) as C. acanthoderma (Plate 3).

Section snippets

Material and methods

The specimens studied herein are all included in the ostracod Challenger collection from the Natural History Museum, London (NHM), mostly from the Zoology Department (for details see Table 3).

Four of the 11 NHM slides had no NHM collection number and, following the curator's (Miranda Lowe) advice, I added a “SNB” number (e.g., SNB-1 020, SNB-1 022, SNB-1 040, SNB-1 056b). These slides have also belatedly received a NHM collection number, i.e., NHM 2012.1468 (SNB-1 020); NHM 2012.1469 (SNB-1

Results and discussion: challenging the deep-sea cosmopolitanism

According to the present taxonomic revision (below), the distribution of L. acanthoderma ‘sensu stricto’, is restricted to Recent sediments from bathyal depths (1636 to 2931 m) of the Subantarctic region of the Southern Ocean (Fig. 1). This replaces the previous distribution from all oceans, and from geological epochs ranging from the Upper Eocene to the Recent, and bathymetrically from shelf to the abyss (341 to 3754 m) (for references see Table 1 and synonymy below).

Most of the previous records

Taxonomy

Remarks: In order to clarify the biogeography of L. acanthoderma ‘sensu stricto’, I include in the taxonomic sections below all specimens contained in the syntype series of “C. acanthoderma”, i.e. the following taxa: cf. Legitimocythere sp., Henryhowella spp. and Trachyleberididae gen. and sp. nov. Finally, the specimens identified by Brady and Norman (1889) as C. acanthoderma, which cannot be identified beyond the family level (i.e., Trachyleberididae spp.) are also listed below.

Higher

Acknowledgements

Miranda Lowe (NHM, London) carefully assisted me during five visits to the NHM and also kindly provided access to and permission for studying the Challenger and other ostracod specimens housed in the NHM. Martin V. Angel suggested revisions to the English. “This research received support from the SYNTHESYS Project http://www.synthesys.info/ which is financed by the European Community Research Infrastructure Action under the FP7 Integrating Activities Programme.” The author thanks the Alexander

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