The Southern Ocean continental shelf fauna is quite well known compared to the bathyal and abyssal faunas (Clarke & Johnston, 2003). Distribution of many species was reported as eurybathyic (Brey et al., 1996) and circum-Antarctic (Clarke & Johnston, 2003). However, an increasing number of publications show that many, previously considered widely distributed, species are actually groups of distinct species, each one with restricted (not circum-Antarctic, nor eurybathic) distributions (e.g. Dahl, 1990; Brandão et al., 2010) and that – at least in the Weddell Sea – the bathyal fauna is significantly different from the shelf and abyssal faunas (Kaiser et al., 2011).

Where benthic Ostracoda from the Southern Ocean are concerned, there are over 100 papers published to date. Kornicker (1993), for the suborder Myodocopina, and Hartmann (1997), for the subclass Podocopa, summarized the taxonomic information on the Antarctic and Subantarctic species recorded up to those dates (i.e. approximately 50 papers). Both authors provided a list of references, identification keys and illustrations down to species level. More recently, all taxonomic and biogeographical information on benthic Southern Ocean Ostracoda (including also the 50 papers published after Kornicker (1993) and Hartmann (1997)) is in the process of being summarized by the senior author of the present paper and will be uploaded soon on the SCAR-MarBIN (Scientific Committee on Antarctic Research-Marine Biodiversity Information Network) website (www.scarmarbin.be), the OBIS (Ocean Biogeographic Information System) node for the Antarctic.

Additionally, Blachowiak-Samolyk & Angel (2008) revised, summarized and provided an identification atlas for the planktonic ostracods of the Southern Ocean, mostly for those belonging to the order Halocyprida, but also for a few species of the myodocopid subfamily Cypridininae.

Based on the 100 publications mentioned above, a total of 334 ostracod species were recorded from the Antarctic and Subantarctic zones of the Southern Ocean. Among these, 284 species are benthic, while 50 species are pelagic (http://www.scarmarbin.be). Approximately 90% of the benthic species were recorded from the continental shelf (S. N. Brandão, unpublished database), while a few studies involve deep samples (e.g. Ayress et al., 2004; Brandão, 2008a, b, 2010; Chavtur et al., 2010).

The present paper studies both live and subfossil benthic ostracods collected from the Atlantic Sector of the Southern Ocean and provides basic information on the species of the thaerocytherid genera Bradleya Benson, 1972, Harleya Jellinek & Swanson, 2003 and Poseidonamicus Benson, 1972, including the description of three new species. The specimens studied here were collected during four cruises of the German Research Vessel Polarstern. Three of these cruises were during the ANDEEP (ANtarctic benthic DEEP-sea biodiversity, colonization history and recent community patterns) project, which aimed to reverse the lack of knowledge on the deep Southern Ocean benthos by analysing bathyal and abyssal samples (see Brandt et al., 2007 for an overview of ANDEEP). The fourth cruise was part of the EASIZ (Ecology of the Antarctic Sea Ice Zone) project and samples were collected from the shelf and continental slope of the Scotia and Weddell seas (for an overview of the EASIZ project, see Clarke & Arntz, 2006).

Previous publications on ANDEEP and EASIZ ostracods are concerned with the macroecology and taxonomy of Macrocyprididae (Brandão, 2010), Bairdioidea (Brandão, 2008a), Platycopida (Brandão, 2008b) and Cypridinidae (Chavtur et al., 2010), and the genetics of Macrocyprididae (Brandão et al., 2010).

The first genus studied in the present paper is Bradleya Benson, 1972, which has a world-wide distribution, from the Paleocene to the Recent, and lives from 496 m to 4675 m depth. At least 166 species have been assigned to Bradleya so far. However, several species actually belong to other reticulated genera, such as Agrenocythere Benson, 1972, Ambostracon Hazel, 1962, Hermanites Puri, 1955, Radimella Pokorny, 1969 and Thaerocythere Hazel, 1967 (Benson, 1972) and the real number of described species is more likely to be around 40. The discovery of Bradleya mesembrina Mazzini, 2005 in our samples extends its geographical and bathymetric distribution to the Antarctic zone of the Southern Ocean and to shallower and to deeper regions.

The second genus studied here is Harleya Jellinek & Swanson, 2003, which has a distribution restricted to Recent sediments from mid-depths (990–2370 m) of the Antarctic zone of the Southern Ocean (Jellinek & Swanson, 2003). This genus includes only two named species. Harleya ansoni (Whatley, Moguilevsky, Ramos & Coxill, 1998) is reported here for the first time from the Weddell Sea.

The three new species described here belong to the genus Poseidonamicus Benson, 1972, a genus inhabiting the continental slopes and mid-oceanic ridges of the world's oceans. The oldest record of this genus is Poseidonamicus major Benson, 1972 from Oligocene deposits (approximately 33 Ma ago) in the northern Atlantic (Benson, 1972). Today, a total of 17 species of Poseidonamicus are known (Benson, 1972; Whatley et al., 1986; Hunt, 2007; Yasuhara et al., 2009), plus the three new species described here. The previously recorded bathymetric range of Poseidonamicus was from 1200 m (Poseidonamicus pintoi Benson, 1972) to 3140 m (Poseidonamicus nudus Benson, 1972). The following four species are known from the Subantarctic zone of the Southern Ocean: P. hisayoae Yasuraha, Cronin, Hunt & Hodell, 2009; P. major; P. minor Benson, 1972; and P. ocularis Whatley, Downing, Kesler & Harlow, 1986 (Benson, 1972, Jellinek & Swanson, 2003; Mazzini, 2005; Yasuhara et al., 2009). However, until now, not a single Poseidonamicus species was known from the Antarctic zone (see definition of Antarctic and Subantarctic zones in the section ‘Material and methods’). As a result of the present study, the bathymetric distribution of Poseidonamicus is extended to the abyssal zone and to slightly shallower depths. Similarly, the geographical distribution of this last genus is extended southwards by 20° of latitude. Finally, we provide the first SEM photo of the lectotype of Poseidonamicus viminea (Brady, 1880) nomen dubium.

The present study examined 165 live (= with soft parts) specimens and 339 subfossils (= empty valves) from 35 samples taken on board the RV Polarstern in the Atlantic Sector of the Southern Ocean, from 41°7.03′ S to 75°26.9′ S, from 9°54.88′ E to 64°39.45′ W and from 231 m to 5194 m depth ( Table 1

Details of sampling localities of the specimens studied.

The subfossil (= empty) valves were transferred to micropalaeontological slides and specimens containing limbs were kept in ethanol (either 70% or 96%). All specimens in the samples were picked. For study under the optical microscope, specimens were dissected in Hydromatrix permanent medium and their valves were transferred to micropalaeontological slides. Each dissected specimen, and a few subfossil specimens, was numbered with the prefix SNB for future study, ensuring the correct assignment of the soft parts (on glass slides) to their appropriate valves (on micropalaeontological slides) and to illustrations (Table 2).

The drawings were made with the aid of a camera lucida attached to a Zeiss microscope, and were digitally inked using the program Adobe Illustrator. Notice that while both SNB and OP are authors of P. yasuharai and P hunti, SNB alone is the author of P. tainae.

The valves selected for scanning electron microscopy were coated with carbon or gold in an evaporation unit PD170AZ from Leybold-Heraeus, and were observed in a LEO 1525 scanning electron microscope (Carl Zeiss SMT).

Identification of specimens was based on descriptions and illustrations of the genera Bradleya, Poseidonamicus and Harleya and their species as presented by Benson (1972), Whatley et al. (1986, 1998), Jellinek & Swanson (2003), Mazzini (2005) and Hunt (2007) and the descriptions of valves follow the nomenclature proposed by Benson (1972) (for the moral loop, anterior and posterior reticular fields) and Hunt (2007) (for the anterior and posterior cardinal angles, anterior and posterior marginal rims, dorsal and ventrolateral ridges). Measurements of the valve length do not include spines.

For the soft part anatomy, we use the terms suggested by Horne et al. (2002): (1) antennula, (2) antenna, (3) mandibula; (4) maxillula ; (5) fifth limb; (6) sixth limb; (7) seventh limb; (8) male copulatory limb; (9) furca.

The chaetotaxy formulae are based on Schornikov & Keyser (2004), with the following modification: ‘d’ denotes carrot-like seta (Pl. 9, fig. G); ‘sfc’ denotes structure supposedly formed by the fusion of a setae and a claw. As Schornikov & Keyser (2004) explained:

figures (i.e. numerals and letters) without parentheses denote segments numbered from proximal to distal; ‘+’ is used when two segments are fused;

In the sections entitled ‘Material’, the stations of the ANDEEP cruises are given as follows: station number according to cruise report, followed by a minus (‘–’) and the deployment number (e.g. “133-2” is the second deployment of station 133). In the case of samples collected with the epibenthic sledge (EBS), these two numbers are followed again by a minus (‘–’) and ‘E’ (for epinet) or ‘S’ for supranet or ‘E+S’ when specimens collected on both epinet and supranet were stored together in one glass or slide or ‘U’ when the animal was outside both nets (for example, on sediment above the metal box of the EBS). For example, ‘133-2-E+S’ means that the EBS was the second gear deployed at station 133 and that specimens collected on both epinet and supranet were placed in one glass or slide.

All specimens are deposited in the Crustacean collection of the ‘Zoologisches Museum Hamburg’, Universität Hamburg, under the abbreviation ZMH K-.

Here a ‘live’ specimen means that the specimen was collected with soft parts, in contrast to subfossils, which were specimens collected as empty valves or carapaces.

The maps were created with the program Ocean Data View (Schlitzer, 2007). We follow SCAR-MarBIN (www.scarmarbin.be) on the operational northern limits of the (1) Antarctic and (2) Subantarctic zones of the Southern Ocean.

Antarctic zone: (1.a) South Atlantic: (1.a.1) between 60°W and 50°W: 57°S; (1.a.2) between 50°W and 30°E: 50°S; (1.b) Indian Ocean: (1.b.1) between 30°E and 80°E: 50°S; (1.b.2) between 80°E and 150°E: 55°S; (1.c) South Pacific: between 150°E and 60°W: 60°S.

(Higher classification based on Horne et al., 2002)

Class Ostracoda Latreille, 1806

Subclass Podocopa Sars, 1866

Order Podocopida Sars, 1866

Suborder Cytherocopina Baird, 1850

Superfamily Cytheroidea Baird, 1850

Family Thaerocytheridae Hazel, 1967

Genus Bradleya Hornibrook, 1952

Type species. Cythere arata Brady, 1880 (by original designation).

Additional species. 166 species have been assigned to Bradleya. For a list of these species, see the ‘World Register of Marine Species’ website (WoRMS, www.marinespecies.org).

Diagnosis. This is slightly modified after Benson (1972). In lateral view, valves ‘subrectangular to subquadrate with broadly rounded anterior margin and squared posterior margin without noticeable caudal process; dorsal and ventrolateral carinae’ present. ‘Surface smooth to strongly reticulate with celate overgrowth (in the type-species); the reticular pattern is grid like rather than radiate and consistent within species, with variation’ in adult ‘due to increased coarseness of some muri and loss of others. Most species have traces of a bridge or box-girder construction within the pattern of the anterior field of the reticulum, extending from the region of the suppressed muscle-scar node (absent in smooth forms) to the ocular ridge, which extends from the position of the eye tubercule (absent in blind species) to join with the ventrolateral ridge. In some species a median ridge, post-adjacent to muscle scar node, is formed from emphasis of one set of longitudinal muri and may be joined with the dorsal carina at the posterior to form a postero-dorsal loop. This feature becomes well developed as the lower element of the bridge decreases in size. Several species having this feature are considered together as the new subgenus Quasibradleya. Hinge hemi- to holamphidont commonly with a lobed posterior tooth; vestibule absent. Muscle-scar pattern thaerocytherid with two frontal scars'. Antennulae with five segments, exopodite of mandibula with 5 setae. Antennae with long exopodite. Distal region of segment I of fifth to seventh limbs strongly sclerotized (= knee apparatus of some authors, e.g. Benson, 1972).

Bradleya mesembrina Mazzini, 2005

(Pl. 1, figs A–G; Fig. 1; Table 2

Specimen catalogue.

2005 Bradleya mesembrina Mazzini: 81–83, figs 47.A–K, 48.B.

2009 Bradleya mesembrina, Yasuhara et al.: 918, figs 4.8, 4.9.

Diagnosis. From Mazzini (2005). ‘Medium-sized Bradleya with thick muri. Fossae fused in the posterior area. Postero-dorsal and anteroventral carinae pronounced. Weak ocular ridge. Surface of the fossae covered with a secondary reticulation, formed by small chains of circular pits.'

Material. 31 live specimens, 14 subfossil valves.

# 42-2-E, ANDEEP I: 1 left valve, ZMH K-42452a. 1 live adult female, 1 live juvenile (?male), in alcohol, ZMH K-42452b. 1 left valve, 1 right valve of the 1 live male (SNB 0890) on a micropalaeontological slide ZMH K-42452d, plus its dissected soft parts on a glass slide, ZMH K-42452c.

Dimensions. Adult males – SNB 0888 (ZMH K-42489a), LV L 0.96 mm, H 0.59 mm. SNB 0889 (ZMH K-42494c) LV L 1.04 mm, H 0.62 mm. SNB 0890 (ZMH K-42452d), LV L 1.00 mm, H 0.62 mm. Adult females – SNB 0891 (ZMH K-42452f), LV L 1.07 mm, H 0.64 mm. (ZMH K-42492b) LV L 0.92 mm, H 0.57 mm. (ZMH K-42491) LV L 1.08 mm, H 0.64 mm. (ZMH K-42490) LV L 0.98 mm, H 0.62 mm. Juveniles – (A-?1) (ZMH K-42452b), LV L 0.84 mm, H 0.55 mm.

Distribution. (Fig. 1) Late Pleistocene to Recent. Antarctic and Subantarctic zones of the Southern Ocean. (1) Holocene, Southern Tasman Rise, 1636–3685 m (Mazzini, 2005). (2) Late Pleistocene and Holocene, Subantarctic zone of the Atlantic Sector of the Southern Ocean, 2532 m (Yasuhara et al., 2009). (3) Recent, Antarctic zone of the Atlantic Sector of the Southern Ocean (off Southern Sandwich Islands, Eastern Weddell Sea and Scotia Sea), 231–4420 m (herein).

Remarks. The geographical and bathymetric distribution of B. mesembrina is herein extended to the Antarctic zone of the Southern Ocean, and to shallower (shelf) and deeper (abyssal) habitats.

Genus Harleya Jellinek & Swanson, 2003

Type species. Harleya davidsoni Jellinek & Swanson, 2003 (original designation).

Additional species. Poseidonamicus ansoni Whatley, Moguilevsky, Ramos & Coxill, 1998.

Diagnosis. From Jellinek & Swanson (2003). A ‘genus with large, subquadrate to sub-rectangular and heavily calcified species, ornamented with fine striae, often forming a polygonal, irregular and internally punctate meshwork, a holamphidont hinge (paramphidont in juveniles) and variable hermicytherid pattern of central muscle scars’.

Harleya ansoni (Whatley, Moguilevsky, Ramos & Coxill, 1998)

(Pl. 1, fig. H; Pl. 2; Fig. 1; Tables 1–2)

1998 Poseidonamicus ansoni Whatley, Moguilevsky, Ramos & Coxill: 132, pl. 5.12–5.16.

Diagnosis. Modified after Whatley et al. (1998: 132). Left valve sub-rectangular in lateral view, with strongly marked dorsal and postero-ventral cardinal angles. Primary reticulation selate but conspicuous, secondary reticulation either slight or covered by selation. Both valves postero-ventrally with one to three long spines, plus four to six short spines.

Material. 10 live specimens, 4 subfossil valves.

# 133-2-E, ANDEEP III: 1 left valve, 1 right valve (coated with gold) of the live adult male SNB 0212 on a micropalaeontological slide, ZMH K-42468a, plus its dissected soft parts on a glass slide, ZMH K-42468b.

Dimensions. Adult males – LV L 1.17–1.20 mm, H 0.59–0.64 mm. RV L 1.24 mm, H 0.61 mm. Adult females – LV L 1.10–1.19 mm, H 0.60–0.66 mm. Juveniles – LV L 0.94–1.00 mm, H 0.52 mm.

Distribution. (Fig. 1) Recent. Atlantic Sector of the Southern Ocean. Scotia Sea, 990–2370 m (Whatley et al., 1998). Weddell Sea, 1581–1639 m (herein).

Remarks. The male specimen SNB 0212 shows four frontal muscle scars on the right valve (Pl. 2, figs F, G) and three frontal muscle scars on the left valve (Pl. 2, fig. H). This adds variability to the original definition of Harleya (Jellinek & Swanson, 2003), which included solely specimens with three frontal scars. Indeed, subdivision of frontal (not to cite the adductor) scars seems to have happened independently in several ostracod lineages as, for example, the Bajocian Progonocytherinae (Pokorny, 1964). The geographical distribution of H. ansoni is herein extended to the Weddell Sea.

Genus Poseidonamicus Benson, 1972

(Pls 3–9; Figs 2–3; Tables 1–2)

Type species. Poseidonamicus major Benson, 1972 (original designation).

Additional species. Poseidonamicus anteropunctatus Whatley, Downing, Kesler & Harlow, 1986; Poseidonamicus dinglei Boomer, 1999; Poseidonamicus hisayoae Yasuhara, Cronin, Hunt & Hodell, 2009; Poseidonamicus minor Benson, 1972; Poseidonamicus miocenicus Benson & Peypouquet, 1983, Poseidonamicus nudus Benson, 1972; Poseidonamicus ocularis Whatley, Downing, Kesler & Harlow, 1986; Poseidonamicus panopsus Whatley & Dingle, 1989; Poseidonamicus pintoi Benson, 1972; Poseidonamicus praenudus Whatley, Downing, Kesler & Harlow, 1986; Poseidonamicus pseudorobustus Coles & Whatley, 1989, Poseidonamicus punctatus Whatley, Downing, Kesler & Harlow, 1986; Poseidonamicus riograndensis Benson & Peypouquet, 1983; Poseidonamicus robustus Whatley, Downing, Kesler & Harlow, 1986; Poseidonamicus rudis Whatley, Downing, Kesler & Harlow, 1986; Poseidonamicus whatleyi Dingle, 2003. Poseidonamicus hunti Brandão & Päplow, sp. nov.; Poseidonamicus tainae Brandão, sp. nov.; Poseidonamicus yasuharai Brandão & Päplow, sp. nov.

Invalid or excluded species. According to Benson (1972), Poseidonamicus viminea (Brady, 1880) is a nomen dubium (see also section below). Following Jellinek & Swanson (2003), Poseidonamicus ansoni Whatley, Moguilevsky, Ramos & Coxill, 1998 belongs to the genus Harleya Jellinek & Swanson, 2003.

Diagnosis. From Benson (1972). ‘Distinguished from other reticulate, holamphidont thaerocytherid genera, principally by its suppressed but wide dorsal carina, the lack of an ocular ridge, the regular, vertically aligned fossae and muri (in reticulate species, or indicated in the pattern of fine structure within the carapace wall of nude forms) of the posteromedian portion of the reticulum, the semipunctate to reticulate aspect of its anterior region, and a characteristic, vertically oriented central mural loop that occurs between these two regions in the area of the muscle-scar pattern. Often there is a conspicuous vertical ridge that joins the posterior of the dorsal carina with the posterior of the ventrolateral carina. Muri and solae are usually featureless except for celate pores, both sieve and murate; few spines other than marginal spines are present. Smooth or nude forms with underlying reticular “ghosts”'.

Poseidonamicus hunti Brandão & Päplow, sp. nov.

(Pl. 3; Pl. 4, figs J–L; Pl. 5; Fig. 2; Tables 1–2)

2005 Poseidonamicus sp. Mazzini: 78, 80, fig. 46.A–N.

Derivation of name. In honour of Dr Gene Hunt, Smithsonian Institution, for his work on the genus Poseidonamicus and on the evolution of deep-sea ostracods.

Diagnosis. Valves sub-oval in lateral view. Anterior cardinal angle higher than posterior cardinal angle. Dorsal ridge inconspicuous. Ventrolateral ridge slightly developed but terminating in 1 robust spine. Fossae shallow; fossae in the anterior field small and rounded. Muri and mural loop weakly developed. Fossae in the posterior field not arranged in sub-vertical rows.

Material. 29 live specimens plus 2 subfossil valves.

Holotype. # 136-4-S, ANDEEP II, live adult male SNB 0886, 1 left valve, 1 right valve on a micropalaeontological slide ZMH K-42466a, plus its dissected soft parts on a glass slide ZMH K-42466b.

Paratypes.

Type locality – # 136-4-E, ANDEEP II: 1 left valve, 1 right valve on a micropalaeontological slide ZMH K-42475c. 5 live adults, 4 live juveniles in alcohol, ZMH K-42475d.

Description. Valves elongate, sub-oval in lateral view. Posterior margin more narrowly rounded than anterior margin. Posterior margin with 5–8 spines; anterior margin with 11–14 spines. Dorsal margin oblique to ventral margin. Anterior cardinal angle higher than posterior cardinal angle. Ventral margin sub-rectilinear. Dorsal ridge inconspicuous. Ventrolateral ridge slightly developed but terminating in 1 robust spine. Fossae shallow; fossae in the anterior field small and rounded. Medial and posterior fossae largest. Muri and mural loop weakly developed. Anterior-most fossae sub-quadrate, large and shallow. Fossae in the posterior field sub-polygonal, not arranged in sub-vertical rows. Pitted secondary reticulation present in some specimens but not in others. Hinge holoamphidont. Maximum-height at anterior cardinal angle. Carapace sub-circular in dorsal view. Two frontal scars. Valves lack both ocular sinus and eye tubercle.

Antennula with 5 articulated segments, segments I and II fused and without setae but with some unarticulated fine, cuticular extensions, segments V and VI also fused. Segment III dorsally with 1 seta and ventrally with 1 very long seta. Segment IV with 1 plumose, dorso-distal seta. Segment V with 4 distal setae, 1 of which slightly shorter than the other 3 setae; plus 1 ventro-distal (possibly sensory) seta. Segment VI with 4 distal setae: 2 normal setae, 1 reduced seta and 1 claw. Segment VII with 1 distal claw, 1 seta and 1 modified structure (i.e. ‘1fsc’ in chaetotaxy formula), this last modified structure is possibly an aesthetasc fused to a claw. The shortest branch of this supposedly fused seta is rounded and flexible.

Segments I and II of antenna without setae. Exopodite 3-segmented and modified as a spinneret seta. Segment III with 1 very long, ventro-distal claw. Segments IV and V fused. Segment IV ventrally with 2 long setae and 1 reduced seta, and dorsally with 2 distal setae. Segment V both dorsally and ventrally without setae, but distally with 1 claw and 1 reduced seta. Segment VI with 2 ventral claws and 1 distal claw.

The mandibula consists of a strongly sclerotized masticatory process (i.e. medial region of the coxa) with about 6 strong teeth (endites), 1 distal seta and a segmented palp. The mandibular palp consists of a basis (basipodite of some authors), a 1-segmented exopodite and a 2-segmented endopodite. Segment II (=basis) ventrally with 1 medium-sized, plumose seta, 1 short, ‘carrot-like’ seta and 1 long, distally plumose seta; ventro-distally with 2 medium-sized, simple setae. Exopodite with 2 distal setae, 1 of which is long, the other plumose. Segment III with 1 dorso-proximal seta, and 7 distal setae. Segment IV with 2 distal setae, 1 of which annulated.

Maxillula with a basis with three endites (or masticatory lobes, or masticatory processes), a 2-segmented endopodite (=palp), and a well-developed exopodite (or vibratory plate). The exopodite with about 14 ‘Strahlen’ plus 1 dorso-proximal, plumose, aberrant ‘Strahl’. Endite I with 4 distal setae and 1 thick, ventrolateral seta. Endite II with 5 distal setae. Endite III with 5–6 distal setae and 1 thick, ventrolateral seta. Segment I of palp with 1 thick, long, lateral seta and 4 dorso-distal setae. Segment II with 3 sub-equally long setae. Palp thicker then endites.

Segment I of the fifth limb dorso-proximally with 1 long, annulated seta and 1 shorter seta; ventrally with ‘carrot-like’ exopodite (Pl. 5, fig. G); distally with 2 annulated setae. Segment II dorso-distally with 1 short seta. Segment III without setae. Segment IV distally with 1 long claw.

Segment I of sixth limb dorsally with 1 long, annulated setae, ventrally with 1 seta-like exopodite, and distally with 2 short setae. Segment II dorso-distally with 1 short seta. Segment III without setae. Segment IV distally with 1 long claw.

Segment I of seventh limb dorsally with 1 long seta; distally with 2 short setae, 1 of them annulated; and ventrally with 1 seta-like, short exopodite. Segment II dorso-distally with 1 annulated seta. Segment III without setae. Segment IV distally with 1 long claw.

Furca reduced to 2 plumose setae.

Basal capsule of male copulatory limb sub-oval with a sharpened, distal end. Labyrinth heavily sclerotized. Copulatory process short and sinuous. Three lobes attached to the basal capsule: (1) smallest one dorsal, and elongated; (2) medium-sized one medially positioned and elongated; (3) largest one laterally positioned and sub-circular.

Chaetotaxy of the holotype. Antennula 1(0/0), 2(0/0), 3(0/0:1l), 4(.1./0), 5(0/0:3,1r,1l) +6(0/0:2,1r,1c), 7(0/0:1c,1s,1sfc). Antenna 1(0/0) +2(0/0), 3-segmented exopodite(0/0), [endopodite] 3(0/1), 4(0/2,1r:2) +5(0/0:1c,1r), 6(0/2c:1c). Mandibula 1(0/6t:1), 2(0/.1.1d.1p:1pl,3l) +[endopodite] +3(.1/0:3,4l) +4(0/0:2), exopodite (0/0:1,1p). Maxillula Palp 1(0/0: 4,1l), 2(0/0:3). Fifth limb 1(.1./0:2), ‘carrot-like’ exopodite, 2(.1./0), 3(0/0), 4(0/0:1c). Sixth limb 1(.1./0:2), seta-like exopodite, 2(.1/0), 3(0/0), 4(0/0:1c). Seventh limb 1(.1./0:2c), reduced, seta-like exopodite, 2(.1/0), 3(0/0), 4(0/0:1c).

Dimensions. Holotype: adult male – SNB 0886, LV L 1.14 mm, H 0.65 mm; RV L 1.14 mm, H 0.60 mm. Paratypes: adult males – SNB 0880, LV L 1.06 mm, H 0.54 mm; RV L 1.03 mm, H 0.544 mm; SNB 0884, LV L 1.15 mm, H 0.62 mm; RV L 1.12 mm, H 0.59 mm; adult females – SNB 0112, LV L 1.04 mm, H 0.59 mm; RV L 1.03 mm, H 0.58 mm; SNB 0885, LV L 1.19 mm, H 0.67 mm; RV L 1.18 mm, H 0.64 mm.

Distribution. (Fig. 2) Recent and subfossil. Southern Ocean, 1690–4978 m. Subfossils, Subantarctic zone of the Pacific Sector (South Tasman Rise, 1690–4067 m) (Mazzini, 2005). Recent, Antarctic zone of the Atlantic Sector (Weddell and Scotia seas, 3681–4782 m) (herein).

Remarks. The small and rounded, anterior fossae of Poseidonamicus hunti sp. nov. (Pl. 3, figs A–F) resemble the fossae of juveniles of other Poseidonamicus species. This may indicate neoteny in the lineage leading to P. hunti. Poseidonamicus hisayoae a late Cenozoic, Southern Ocean species has a similar morphology, which may suggest their common ancestry.

In lateral outline P. hunti is very similar to P. hisayoae, and the two species also share a weak dorsal and ventrolateral ridges. On the other hand, the medial fossae are arranged in conspicuous sub-vertical rows in P. hisayoae, while these fossae are arranged more randomly in P. hunti. The small and rounded, anterior fossae of P. hunti are similar to P. anteropunctatus, P. dinglei and P. punctatus, but the first species is more oval in outline, while the latter two species are sub-polygonal. Poseidonamicus major, P. minor, P. pseudorobustus and P. riograndensis show conspicuous dorsal and ventrolateral ridges, and a sub-polygonal outline, while in P. hunti the dorsal and ventrolateral ridges are weak and the outline is sub-oval. Poseidonamicus miocenicus and P. pintoi show strong muri and sub-rectangular fossae, while the muri of P. hunti are weak and the fossae are rounded. The muri and fossae are conspicuous in P. hunti, but selate in P. nudus. Poseidonamicus ocularis, P. panopsus and P. whatleyi have a sub-rectangular outline, P. praenudus, P. robustus and P. rudis are sub-polygonate, with a V-shaped posterior margin, while P. hunti is sub-oval.

Poseidonamicus tainae Brandão, sp. nov.

(Pl. 4, figs A–H; Pl. 6, figs A–D, G–I; Fig. 2; Tables 1–2)

Derivation of name. In honour of Taina Müller, Universität Hamburg, for her wise words.

Diagnosis. A large, moderately calcified, Poseidonamicus with sub-polygonal outline, except for the dorsal margin which is slightly concave. Dorsal ridge moderately robust. Ventral ridge rounded. Fossae shallow and large, muri low. Only primary ornamentation present on lateral surface. Posterior margin with up to 10 spines, anterior margin with 8 to 18 short, spines. Carapace sub-hexagonal in dorsal view.

Material. 15 live specimens plus 34 subfossil valves.

Holotype. # 129-2-S, ANDEEP I, 1 left valve, 1 right valve of the live adult male SNB 0882 on a micropalaeontological slide ZMH K-42456b, plus its dissected soft parts on a glass slide ZMH K-42456c.

Paratypes.

Type locality – # 129-2-S, ANDEEP I: 1 right valve on a micropalaeontological slide, gold coated, ZMH K-42456a. 4 live adult females, 1 adult live male, in alcohol, ZMH K-42456d.

Description. Valves sub-polygonal in lateral view. Dorsal margin slightly concave. Dorsal ridge conspicuous. Anterior margin with 8 to 18 short spines. Posterior margin with up to 10 spines, some of them long. Ventrolateral ridge well developed and terminating in 1 robust spine. Fossae just dorsal to ventrolateral ridge deep and rounded. Ventral margin convex. Fossae in the anterior field rounded, bounded with well-developed muri, and smaller than those in the posterior field. Anterior-most fossae sub-quadrate, large and deep. Fossae in the posterior field arranged regularly in sub-vertical rows, and sub-polygonate. Mural loop conspicuous. Hinge holoamphidont. Maximum height at anterior cardinal angle. Carapace sub-hexagonal in dorsal view. Valves show ocular sinus but lack eye tubercle.

Antennula with 5 articulated segments, segments I and II fused and without setae but with some unarticulated fine, cuticular extensions, segments V and VI also fused, suture between segments IV and V+VI faint. Segment III dorsally with 1 seta and ventrally with 1 very long seta. Segment IV with 1 plumose, dorso-distal seta. Segment V with 4 distal setae, 1 of which slightly shorter than the other 3 setae; plus 1 ventro-distal seta. Segment VI with 4 distal setae: 2 normal setae, 1 reduced seta and 1 claw. Segment VII with 1 distal claw, 1 seta and 1 modified structure (i.e. ‘1fsc’ in chaetotaxy formula); this last modified structure is possibly an aesthetasc fused to a claw. The shortest branch of this last seta is rounded and flexible.

Segments I and II of antenna without setae. Exopodite 3-segmented and modified as a spinneret seta. Segment III dorsally with some unarticulated fine, cuticular extensions; ventro-distally with 1 very long, claw. Segments IV and V fused. Segment IV medially with a few unarticulated fine, cuticular extensions; ventrally with 2 long setae and 1 modified seta; and dorsally with 2 distal setae. Segment V both dorsally and ventrally without setae, but distally with 1 claw and 1 small seta. Segment VI with 1 ventral claw, 1 ventral seta and 1 distal claw.

The mandibula consists of a strongly sclerotized masticatory process (i.e. medial region of the coxa) with 7 or 8 strong teeth (endites) and several very short, ventral setae, 1 short, distal seta, and a segmented palp. The mandibular palp consists of a basis (basipodite of some authors), a 1-segmented exopodite and a 2-segmented endopodite. Segment II (= basis) ventrally with 1 medium-sized, plumose seta and 1 short, ‘carrot-like’ seta; dorsally with 2 setae; distally with 2 long, plumose setae. Exopodite with 4 or 5 distal setae, 1 of which is long. Segment III with 1 dorso-proximal seta, 1 dorso-distal seta and 5 or 6 long ventro-distal setae and 2 short ventro-distal setae. Segment IV with 3 or 4 distal setae.

Maxillula with a basis with three endites (or masticatory lobes, or masticatory processes), a 2-segmented endopodite (= palp), and a well-developed exopodite (or vibratory plate). The exopodite with 14 ‘Strahlen’ plus 1 dorso-proximal, plumose, aberrant ‘Strahl’. Endite I with at least 4 distal setae and 1 thick, ventrolateral seta. Endite II with 4 distal setae. Endite III with 5 distal setae. Segment I of palp with 1 thick, long, lateral seta and 4 dorso-distal setae. Segment II with 3 sub-equally long setae. Palp thicker than endites.

Exopodite thicker in fifth limb, medium in sixth limb and thin in seventh limb. Segment I of the fifth limb dorso-proximally with 1 long, annulated seta and 1 shorter, annulated seta; ventrally with ‘carrot-like’ exopodite; distally with 2 annulated setae. Segment II dorso-distally with 1 short seta. Segment III without setae. Segment IV distally with 1 long claw.

Segment I of sixth limb dorsally with 2 long setae, ventrally with 1 plumose seta-like exopodite, and distally with 1 annulated seta. Segment II dorso-distally with 1 short seta. Segment III without setae. Segment IV distally with 1 long claw.

Segment I of seventh limb dorsally with 1 reduced seta, and 1 seta; distally with 1 annulated short seta, and ventrally with 1 seta-like, thin exopodite. Segment II dorso-distally with 1 seta. Segment III without setae. Segment IV distally with 1 long claw.

Furca reduced to 2 plumose setae, 1 of them half as long as the other.

Basal capsule of male copulatory limb sub-oval. Labyrinth heavily sclerotized. Copulatory process short and sinuous. Three lobes attached to the basal capsule: (1) smallest one dorsal and elongated; (2) medium-sized one medially positioned and elongated, sub-triangular; (3) largest one laterally positioned and sub-circular.

Chaetotaxy of the holotype. Antennula 1(0/0), 2(0/0), 3(1/1l:0), 4(.1/0), 5(0/0:3,1r,1l) +6(0/0:2,1r,1c), 7(0/0:1c,1s,1sfc). Antenna 1(0/0) +2(0/0), 3-segmented exopodite(0/0), [endopodite] 3(0/1), 4(0/3:2) +5(0/0:1c,1), 6(0/1c,1:1c). Mandibula 1(0/7-8t:1), 2(.1.1/.1d.1p:2lp,2) +[endopodite] +3(.1,1/0:2,5-6) + 4(0/0:3-4), exopodite (0/0:3-4,1l). Maxillula Palp 1(0/0: 4,1l), 2(0/0:3). Fifth limb 1(.2/0:2), ‘carrot-like’ exopodite, 2(.1./0), 3(0/0), 4(0/0:1c). Sixth limb 1(.1.1./0:1), seta-like exopodite, 2(.1/0), 3(0/0), 4(0/0:1c). Seventh limb 1(.1r.1./0:1), reduced, seta-like exopodite, 2(.1/0), 3(0/0), 4(0/0:1c).

Dimensions. Holotype: adult male – SNB 0882, LV L 1.02 mm, H 0.58 mm; RV L 1.01 mm, H 0.54 mm. Paratypes: adult females – SNB 0396, LV L 1.08 mm, H 0.61 mm; RV L 1.08 mm, H 0.63 mm; SNB 0881, LV L 1.20 mm, H 0.69 mm; RV L 1.18 mm, H 0.64 mm; SNB 0883, LV L 0.97 mm, H 0.56 mm; RV L 0.98 mm, H 0.55 mm. Adult with fragmented soft parts: SNB 0302, LV L 0.95 mm, H 0.56 mm; RV broken.

Distribution. (Fig. 2) Recent and subfossil. Atlantic Sector of the Southern Ocean. Weddell and Scotia seas, 2359–4978 m (herein).

Remarks. The limbs of P. tainae are not drawn here because they are very similar to the limbs of P. hunti, which are illustrated in Plate 5.

Poseidonamicus hisayoae is similar to P. tainae sp. nov., but (1) the dorsal and ventral margins are more sub-parallel in the latter species. As a consequence, (2) the anterior cardinal angle is conspicuously higher than the posterior one in P. hisayoae, but not in P. tainae. (3) The posterior margin is more narrowly rounded in P. hisayoae. (4) The dorsal ridge is weak in P. hisayoae but conspicuous in P. tainae.

Poseidonamicus anteropunctatus, P. dinglei, P. major, P. praenudus, P. pseudorobustus, P. riograndensis, P. robustus and P. rudis are sub-polygonal in outline with the dorsal margin oblique in relation to the ventral one. On the other hand, P. tainae is sub-oval with sub-parallel dorsal and ventral margins. Additionally, P. major is lozenge-shaped in dorsal view, while P. tainae is sub-hexagonal. P. minor and P. miocenicus display robust muri and deep fossae, while these features are weakly defined in P. tainae. The ornamentation of P. nudus is selated, while P. yasuharai has conspicuous muri and fossae. Poseidonamicus ocularis, P. panopsus and P. whatleyi display eye tubercles, robust muri and deep fossae, while P. tainae displays low muri and narrow fossae, and lacks eye tubercles. Similar to P. tainae, P. pintoi has a rounded, sub-oval outline, but the latter species is higher in relation to its length, and displays robust muri and deep fossae. In P. tainae the muri are low and fossae shallow. P. punctatus has a rounded dorsal margin, with inconspicuous anterior and posterior cardinal angles, while the dorsal margin of P. tainae is slightly concave and both anterior and posterior angles are easily distinguishable. Additionally, P. punctatus has a secondary reticulation, which is absent in P. tainae. Poseidonamicus hunti is sub-oval in outline, while P. tainae is sub-rectangular.

Poseidonamicus sp. cf. P. tainae Brandão, sp. nov.

(Pl. 6, figs E–F; Tables 1–2)

Material. 3 live specimens plus 1 subfossil valve.

# 16-10-S, ANDEEP III: 1 left valve, 1 right valve of the live adult female SNB 0630 on a micropalaeontological slide ZMH K-42480a, plus its dissected soft parts on a glass slide, ZMH K-42480b. 1 right valve on a micropalaeontological slide ZMH K-42480c.

Dimensions. Adult female – SNB 0627, LV L 1.06 mm, H 0.63 mm; RV L 1.02 mm, H 0.62 mm; LV L 1.02 mm, H 0.62 mm; SNB 0630, RV L 1.02 mm, H 0.59 mm; SNB 0879, LV L 1.04 mm, H 0.62 mm; RV L 1.04 mm, H 0.58 mm.

Remarks. Four specimens collected from stations 16 (Cape Basin) and 43 (Scotia Sea) show a similar outline and ornamentation pattern to P. tainae, but their muri are more strongly developed, the fossae are more rounded (Pl. 6, figs E–F) and their dorsal ridge is weaker than in P. hunti (Pl. 6, figs A–D, G).

Poseidonamicus viminea (Brady, 1880) nomen dubium

(Pl. 4, fig. I)

1880 Cythere viminea Brady: 94.

1972 Poseidonamicus viminea, Benson: pl. 2, fig. 15.

Material. Lectotype (by virtue of monotypy): 1 broken, subfossil, juvenile right valve on a micropalaeontological slide used by H. S. Puri in the 1960s and labelled ‘173, Cythere viminea Brady, H. S. Puri 7/67, T, Lectotype, 116, “Challenger”, No. 146, Depth 1375, 81.5.33’, NHM 81.5.33.

Remarks. Since the lectotype is a juvenile (Pl. 4, fig. I), Benson (1972) considered Poseidonamicus viminea a nomen dubium. We show here, for the first time, an SEM photograph of this lectotype.

An empty, original slide used by Brady (1880) labelled ‘Cythere viminea Brady, Type, 81.5.33, “Challenger”, No. 146, Depth 1,375 faths., G. S. Brady, 173’ is also included in the NHM collection.

Poseidonamicus yasuharai Brandão & Päplow, sp. nov.

(Pls 7–9; Fig. 3; Tables 1–2)

Derivation of name. In honour of Dr Moriaki Yasuhara, Smithsonian Institution, for his work on deep-sea ostracods and climate change.

Diagnosis. A large, moderately calcified, Poseidonamicus with sub-rectangular outline, sub-parallel and sub-rectilinear dorsal and ventral margins and ventrolateral ridge. Dorsal ridge very weak, projecting dorsally and joining the dorsal margin of the valve. Fossae shallow, muri low. Only primary ornamentation present on lateral surface. Posterior margin with up to 10 spines, anterior margin with 8 to 18 spines. Three frontal muscle scars.

Holotype. # 133-2-E, ANDEEP III, live adult male SNB 0211, 1 left valve and 1 right valve (coated with gold) on a micropalaeontological slide ZMH K-42469a, plus its dissected soft parts on a glass slide ZMH K-42469b.

Paratypes.

Type locality – # 133-2-E, ANDEEP III: 13 left valve, 4 right valves (+ 4 broken right valves), 4 closed subfossil carapaces (+ 1 broken but measured), on a micropalaeontological slide (2 valves coated with gold), ZMH K-42453a. 1 left valve, 1 right valve of the live adult female SNB 0210 on a micropalaeontological slide ZMH K-42453b, plus its dissected soft parts on a glass slide, ZMH K-42453c.

Material. 75 live specimens plus 280 subfossil valves.

Description. Valves sub-rectangular in lateral view, males more elongate than females. Dorsal margin slightly sinuous; dorsal ridge very weak; anterior margin with 8 to 18 spines; posterior margin with up to 10 spines, a few of them robust and long. Ventrolateral ridge well developed, with 1 robust and long spine arising on its posterior end. Marginal rims (i.e. anterior-most and posterior-most areas of lateral surface) smooth and wide. Anterior muri more robust than posterior ones. Deep and rounded fossae just dorsal to ventrolateral ridge. Fossae in anterior field smaller, deeper and more rounded than those in posterior field. Posterior fossae polygonal and arranged regularly in sub-vertical rows. Anterior field separated from the posterior field by slight mural loop. Carapace arrow-shaped and rounded in dorsal and ventral views. Hinge holamphidont. Four vertically aligned and undivided adductor muscle scars, plus three frontal scars. Valves lack both ocular sinuses and eye tubercles.

Antennula with only 5 articulated segments; segments I and II fused; segments V and VI also fused. Segment I and II without setae but with some unarticulated barbulae. Segment III terminally with 1 long, ventrolateral seta, unarticulated barbulae also present on dorsal and ventral margins. Segment IV with one dorsal seta. Segment V with 4 distal setae and one lateral, possibly sensory seta (because of its rounded tip). Segment VI (fused to segment V) with 5 distal setae: 2 normal setae, 1 reduced seta and 2 claws. Segment VII with 2 distal claws and 1 modified structure (i.e. ‘1fsc’ in chaetotaxy formula), which is possibly an aesthetasc fused to a claw. Supposedly sensory part of this modified seta is rounded and flexible.

Segments I and II of antenna fused and without seta. Segment III with 1 dorsal seta and 1 very long, ventral seta. Exopodite 3-segmented and modified as a spinneret seta. Segments IV and V fused. Segment IV dorso-distally with 2 setae; ventro-distally with 1 seta, 1 barbed claw, and 1 supposedly sensory, ‘candle-shaped’ seta with a flattened tip. Segment V without setae both dorsally and ventrally, but distally with 1 claw and 1 reduced seta. Segment VI with 2 ventral claws and 1 distal claw.

The mandibula consists of a strongly sclerotized masticatory process (= coxa) with 1 short, distal seta, around 5 strong teeth (endites) and a segmented palp. The mandibular palp consists of a basis (basipodite of some authors), a 1-segmented exopodite and a 2-segmented endopodite. Segment II (= basis) ventrally with 3 setae: 1 normal seta, 1 ‘carrot-like’ seta, 1 plumose seta; ventro-distally with 1 long, plumose seta and 2 simple setae. Exopodite with 5 distal seta, one of these long and plumose. Segment III (= endopoite segment 1) with 5 distal setae, 1 dorsal seta, 3 simple lateral setae, and 1 lateral plumose seta. Segment IV with 4 distal setae, 1 of them annulated.

Maxillula basis with three endites (or masticatory lobes, or masticatory processes), a 2-segmented endopodite (= palp), a well-developed exopodite (or vibratory plate). Exopodite flat and large, with 15 distal ‘Strahlen’ and one proximal, plumose, dorsal, aberrant ‘Strahl’. Endite I with 6 distal setae. Endite II with 5 distal setae and 1 thick, ventrolateral seta. Endite III with 5 to 6 distal setae. Segment I of palp with 1 thick, long lateral seta and 4 dorso-distal setae. Segment II with 2 long setae and 1 short seta. Palp as thick as endites.

Segment I of fifth limb dorsally with 2 annulated setae; distally with 2 annulated setae; ventrally with a ‘carrot-like’ exopodite (dashed and marked with a ‘*’ in Plate 9, fig. F and detailed in Plate 9, fig. G). Segment II dorsally with 1 short, thick, distal seta. Segment III without seta. Segment IV with 1 long, distal claw.

Segment I of sixth limb dorsally with 2 setae, one of which is annulated; ventrally with seta-like exopodite; and distally with 1 short, thick, annulated seta. Segment II dorsally with 1 short, thick, distal seta. Segment III without seta. Segment VI distally with 1 long claw.

Segment I of seventh limb dorsally with 1 long, annulated seta, distally with 1 annulated seta; ventrally with seta-like, annulated exopodite. Segment II dorsally with 1 short, thick, distal seta. Segment III without setae. Segment IV distally with 1 long claw.

Basal capsule of male copulatory limb sub-oval with a sharpened, distal end. Labyrinth heavily sclerotized. Copulatory process short and straight. Three lobes attached to the basal capsule: (1) smallest (dorsal) is elongated; (2) medium-sized one is medially positioned and sub-triangular; (3) largest (laterally positioned) is sub-circular.

Furca reduced to 2 plumose setae, 1 of these long, the other short.

Chaetotaxy of the holotype. Antennula 1(0/0) +2(0/0), 3(0/0:1l), 4(.1./0), 5(0/0:4,1l) +6(0/0:2,1r,2c), 7(0/0:2c,1sfc). Antenna 1(0/0) +2(0/0), 3-segmented exopodite(0/0), [endopodite] 3(.1./1), 4(0/1,1c,1s:2) +5(0/0:1c,1r), 6(0/2c:1c). Mandibula 1(0/5t:1), 2(0/.1,1d,1p:1pl,2l) +[endopodite] 3(.1./0:5,3l,1pl) +4(0/0:4), exopodite (0/0:4,1p). Maxillula Palp 1(0/0: 4,1cl), 2(0/0:3c). Fifth limb 1(.2./0:2), ‘carrot-like’ exopodite, 2(.1/0), 3(0/0), 4(0/0:1c). Sixth limb 1(.1.1./0:1), seta-like exopodite, 2(.1/0), 3(0/0), 4(0/0:1c). Seventh limb 1(.1./0:1) +seta-like exopodite, 2(.1/0), 3(0/0), 4(0/0:1c).

Dimensions. Holotype: adult male – SNB 0211, LV L 1.06 mm, H 0.60 mm; RV L 1.07 mm, H 0.58 mm. Paratypes: adult males – SNB 0626, LV L 1.14 mm, H 0.61 mm; RV L 1.15 mm, H 0.64 mm; SNB 0887, LV L 1.12 mm, H 0.60 mm; RV L 1.10 mm, H 0.59 mm; adult females – SNB 0006, LV L 1.06 mm, H 0.59 mm; RV L 1.05 mm, H 0.60 mm; SNB 0210, LV L 1.00 mm, H 0.57 mm; RV L 1.00 mm, H 0.56 mm. (A-1) – SNB 0315, LV L 0.88 mm, H 0.49 mm; RV L 0.88 mm, H 0.47 mm. Adult subfossils: W 0.50–0.62 mm; (A-1) subfossil W 0.43 mm.

Distribution. (Fig. 3) Recent. Weddell Sea, Atlantic Sector of the Southern Ocean, bathyal and shallow abyssal depths (924–3136 m).

Remarks. A sub-rectangular outline with sub-parallel dorsal and ventral margins of P. yasuharai distinguish this species from P. anteropunctatus, P. dinglei, P. hisayoae, P. hunti, P. major, P. minor, P. praenudus, P. pseudorobustus, which are sub-polygonal, irregular in outline and have dorsal margin oblique in relation to ventral margin. Poseidonamicus miocenicus, P. pintoi, P. punctatus and P. riograndensis have rounded, sub-oval outlines, robust muri and deep fossae, while P. yasuharai is sub-rectangular with low muri and narrow fossae. Additionally, P. punctatus has secondary reticulation, which is absent in P. yasuharai. The ornamentation of P. nudus is selated, while P. yasuharai has conspicuous muri and fossae. Poseidonamicus ocularis, P. panopsus and P. whatleyi have eye tubercles, robust muri and deep fossae, while P. yasuharai is ornamented with low muri and narrow fossae, and has no eye tubercles. The lateral outline of P. robustus, P. rudis and P. tainae is sub-polygonal, the posterior margin is V-shaped and their ventrolateral ridges are curved and robust, while P. yasuharai is sub-rectangular in outline, its posterior margin is slightly rounded and its ventrolateral ridge is sub-rectilinear.

Poseidonamicus sp.

Material. 1 live specimen plus 4 subfossil valves.

# 16-7, ANDEEP III: 1 juvenile right valve on a micropalaeontological slide ZMH K-42609.

Dimensions. Juveniles: SNB 0878 LV L 0.88 mm, H 0.50 mm. RV L 0.70 mm, H 0.38 mm.

Remarks. Only juveniles and adult broken valves were collected in the five ANDEEP stations 16-7, 99-4, 114-4, 140-8 and 141-10 and, since species-level identification of juveniles is not possible, these specimens are left in open nomenclature.