Late Quaternary deep-sea ostracod taxonomy of the eastern North Atlantic Ocean

Taxonomic revision and re-evaluation of the eastern North Atlantic deep-sea ostracods are conducted based on late Quaternary sediments from Ocean Drilling Program (ODP) Hole 982A, Rockall Plateau, eastern North Atlantic. Twenty-one genera and 51 species were examined and (re-)illustrated with high-resolution scanning electron microscopy images. Six new species are described: Polycope lunaris, Argilloecia labri, Bythoceratina nuda, Cytheropteron colesoabyssorum, Cytheropteron colesopunctatum and Cytheropteron paramediotumidum. Excellent fossil ostracod preservation in this sediment core enabled us to provide a robust taxonomic baseline of the eastern North Atlantic deep-sea ostracods for application to palaeoceanographical, palaeoecological and biogeographical studies.


IntroductIon
North Atlantic deep-sea ostracods have been well investigated (e.g. Brady, 1880;Whatley & Coles, 1987;   remarks. Polycope martinezi is very similar to the Arctic species Polycope arcys, but distinguished by lacking obvious lateral spines and having finer reticulation. P. martinezi was originally reported from the equatorial Atlantic (Karanovic & Brandão, 2012) and is also known from the North Atlantic , 2001Yasuhara et al. 2009b remarks. ODP 982A specimens have better developed reticulation compared to the specimens from the western North Atlantic (Yasuhara et al., 2009b), considered here to be intraspecific variation. This species is similar to P. bireticulata, but the latter has a more evenly rounded outline and different alignment of muri (Yasuhara et al. in press b
Order Podocopida Sars, 1866 Suborder bairdiocopina Gründel, 1967 Superfamily bairdioidea Sars, 1866 Family bairdiidae Sars, 1866 remarks. We follow Maddocks' (1969) genus-level taxonomy for this family.  Colalongo & Pasini, 1980, Bairdoppilata conformis (Terquem, 1878) and Macrocyprissa arcuata (Colalongo & Pasini, 1980 Aiello et al. (2000) and supplemented herein. Our specimens are identical to that shown in Aiello et al. (2000). Our specimens are also very similar to the specimens in Terquem (1878) and Bonaduce et al. (1976), but the latter specimens have a more heavily calcified carapace and slightly more upturned caudal process. Other authors have also reported this species, but with a slightly different outline (Sciuto, 2003) or without images (Faranda et al., 2008;Aiello & Barra, 2010). We consider all of these differences as intraspecific variation and include them in Bairdoppilata conformis. Slight differences in outlines may be due to intraspecific variation in calcification. No SEM or microscopic image of type specimens has been published.
remarks. Comprehensive synonymy lists are given in Aiello & Szczechura (2004), Yasuhara et al. (2009b) (in Ruan & Hao, 1988, but distinguished by having a much more slender outline. A. caju was originally reported from the western North Atlantic (Yasuhara et al., 2009b) and is here confirmed in the eastern North Atlantic.
( Fig. 5D-E) derivation of name. From Latin nuda (adjective, nominative singular, gender feminine or neuter) = stripped, with reference to its carapace without any spine or reticulation.

diagnosis.
A large, moderately calcified Bythoceratina species without spines or reticulation.
holotype. LV, USNM 603660 (ODP982073) (Fig. 5D remarks. We think that this species has considerable intraspecific variation. A comprehensive synonymy list and detailed discussion are given in Yasuhara et al. (in press b).

remarks.
Reliable occurrence records of this species with SEM image(s) or sketches are known only from the eastern North Atlantic as listed in the synonymy list above. Detailed discussion of this species can be found in Yasuhara et al. (in press b).
Cytheropteron colesoabyssorum sp. nov. (Fig. 7A) 1996 Cytheropteron cf. abyssorum Brady;Coles et al.: 136,pl. 3, derivation of name. In honour of Graham P. Coles for his contribution to deep-sea ostracod research; and with reference to its similarity to Cytheropteron abyssorum as indicated by him.

diagnosis.
A large, moderately calcified Cytheropteron species with finely punctate carapace, upturned caudal process, and relatively rounded outline.
type locality and horizon. ODP 982A, 1/2/37-39.  Passlow & Ayress, 1994) in certain aspects, such as presence of a median sulcus on alae and punctate carapace, but easily distinguished by having much finer punctation covering entire carapace, thinner and longer alae, and upturned caudal process and presence of dorsolateral ridge. C. colesoabyssorum sp. nov. is similar to C. cf. tenuialatum of Coles et al. (1996), but distinguished by having a dorsolateral ridge and more strongly upturned caudal process, and by the absence of primary reticulation on the caudal process.

diagnosis.
A large, moderately calcified Cytheropteron species with coarsely punctate carapace and horizontally long, well-developed alae.

Paratype. LV, USNM 603678 (ODP982083).
type locality and horizon. ODP 982A, 1/1/30-32. description. Carapace moderately calcified, large, highest at midlength. Outline rhomboidal or almond-like in lateral view; anterior margin evenly rounded; caudal process prominent and upturned; dorsal margin arched and slightly sinuous; ventral margin curved; alae curved, horizontally long and well-developed, reaching to anterior margin and extending slightly below ventral margin, with a small spine at apex. Anterodorsal margin slightly angular; posterodorsal margin weakly angular. Lateral surface coarsely punctate; primary and secondary reticulation developed in posterior one third. Internal features as for genus. remarks. Cytheropteron colesopunctatum sp. nov. is similar to C. punctatum Brady, 1868 in certain aspects, such as punctate carapace and general outline, but is distinguished by having smoothly curved and horizontally longer alae reaching to anterior margin and well-developed primary and secondary reticulation in posterior one-third. C. punctatum has sinuous and horizontally shorter alae and no or only poorly developed reticulation, according to the sketches and SEM images shown in Brady (1868), Sars (1928) and Whatley & Masson (1979). C. colesopunctatum sp. nov. is similar to C. paracarolinae Zhao et al., 2000(see Zhao et al., 2000, but the latter is larger, lacks punctation in anterior one-third, and has more slender outline and stronger caudal process. Yasuhara, Okahashi & Cronin 2009 ( Fig. 7D-H) 2009 Cytheropteron didieae Yasuhara,Okahashi & Cronin: 900,pl. 6,[8][9][11][12] remarks. This is the first record of the species from the eastern North Atlantic.  fig. 15.  1996 Cytheropteron omega Aiello, Barra & Bonaduce: 170,pl. 2, remarks. Detailed comparison with similar species such as C. garganicum  can be found in Aiello et al. (1996a). Our specimens have relatively weakly developed dorsal ridges compared to the type specimens and thus the 'upside-down omega' structure is unclear, but otherwise identical. We consider this difference as intraspecific variation. Wellpreserved specimens shown here indicate that there are two spines at the apex of alae. A paratype specimen of C. syntomoalatum of Whatley & Coles (1987, pl. 2, fig. 27) is not conspecific with C. syntomoalatum Whatley & Coles, 1987 and is considered here and by Aiello et al. (1996a) as C. omega Aiello, Barra & Bonaduce, 1996, although this specimen has only one spine at the apex of the alae and a slightly more slender outline.
derivation of name. With reference to its similarity to Cytheropteron mediotumidum.

diagnosis.
A large, moderately calcified Cytheropteron species with finely punctate carapace and straight-sided alae.
description. Carapace moderately calcified, large, highest at midlength. Outline subrhomboidal in lateral view; anterior margin rounded; caudal process moderately prominent; dorsal margin arched; ventral margin slightly curved; alae straight, thin and horizontally long, almost reaching to anterior margin, and extending slightly below ventral margin; a small subcentral depression present on alae. Anterodorsal margin slightly angular; posterodorsal margin weakly prominent. Lateral surface finely punctate in posterior two-thirds; primary and secondary reticulation weakly developed in posterior one-third. Internal features as for genus. remarks. Cytheropteron paramediotumidum sp. nov. is very similar to C. mediotumidum Zhao, Whatley & Zhou, 2000, but distinguished by having a less upturned caudal process, finer punctation, less distinct primary reticulation and straight-sided alae. C. paramediotumidum sp. nov. is also similar to C. colesopunctatum sp. nov., but the latter has more prominent caudal processes, coarser and more distinct punctation, and curved-sided alae. remarks. Our specimens have two spines (instead of one) at the apex of alae and slightly more ventrally-extended alae, but are otherwise identical. We consider these differences as intraspecific variation, at least for now.
remarks. This species was known only from the western North Atlantic, but this record confirms its presence in the eastern North Atlantic.