METACONCHOECIINI Chavtur and Angel, 2011

Chavtur, Vladimir G. & Angel, Martin V., 2011, Revision of Metaconchoecia (Ostracoda: Halocyprididae) and the designation of two new tribes Conchoeciini and Metaconchoeciini 2857, Zootaxa 2857 (1), pp. 1-87 : 8-9

TRIBE METACONCHOECIINI Chavtur and Angel new status

Type genus. Metaconchoecia Howe 1955

Synonymy.

1906a Conchoecia ‘ rotundata ’ group—Müller p.79-86.

1920 Conchoecia ‘rotundata’ group—Skogsberg, p.649–658.

1949 Metaconchoecia —Granata & Caporiacco p.5 (nomen nudum).

1955 Metaconchoecia —Howe, p. 118.

1973 Metaconchoecia —Poulsen p. 70.

1978a Conchoecia —Deevey, p 53 (part).

1980 Conchoecia rotundata group—Deevey & Brooks, p. 85 (part).

1981 Conchoecia ‘skogsbergi’ species complex—Gooday p.145.

1986 Metaconchoecia Granata & Caporiacco — Kempf 1986, Index A: 498 (part).

1992 Metaconchoecia —Kock, p. 68.

1995 Metaconchoecia Kock — Kempf 1995, Index A supplement 1, p.149 (part).

Diagnosis. Small to medium sized halocyprids (<2 mm). Pelagic in oceanic waters. Carapace cylindrical to globose, tapered anteriorly in some species. The posterior dorsal corner is unarmed, and either smoothly rounded or obtusely angled. Posterior ventral corner is rounded. Carapace lacks sculpture in the majority of species, but when present is either in the form of longitudinal striae or concentric rings. RAG on posterior margin close to posterior end of hinge between carapace valves. LAG on dorsal face usually posterior to rostrum but always anterior to midlength. Labrum with a deep V-shaped cleft.

Composition and main characters. The new tribe includes all the species previously attributed to the genus Metaconchoecia , i.e. Müller’s (1906a, 1912) “ rotundata ” group. Members of this new tribe are distinguished from all other Conchoeciinae genera by the positions of the asymmetrical glands on the carapace valves. The LAG opens on the dorsal margin in the anterior half of the carapace usually just posterior to the anterior end of the hinge between the two carapace valves. In several of the newly designated genera, the LAG opens closer to mid-length, but in one genus, it opens in front of the anterior end of the hinge (i.e. on the rostrum). The RAG opens on the posterior margin, usually close to the posterior end of the hinge and near the rounded posterior dorsal corner of the carapace. However, in some genera the RAG opens lower down the posterior margin sometimes at the apex of a shallow angle.

There are often only subtle intergeneric and interspecific differences in the morphologies of the limbs, so confirming the identities of specimens is seldom easy. There may be slight variations in the external appearances of species that clearly have very different ecologies. Preliminary results of barcoding the CO1 gene of some of these species have confirmed their separate identities ( Bucklin et al. 2010).

The Metaconchoeciini consists of ten genera, nine of which are newly designated herein. Table 2 compares the previous classification with our revision. In addition to the locations at which the asymmetrical glands open, all the species in the tribe have the following characters in common:

1. They are small in size (≤ 1.9 mm); some are very small (<1 mm). 2. The carapaces are devoid of spines and lack sculpturing in all but two genera, Vityazoecia and Juryoecia ( Figs.

3, 5 ). 3. The shoulder vaults are smooth and are not accentuated. 4. The posterior dorsal ‘corner’ is either rounded or obtusely angled. 5. In females the second segment of the first antenna lacks a dorsal seta. 6. The labrum is deeply notched and is flanked by relatively short, stubby filaments. 7. There is no seta on basale of the maxilla, and the first segment of the endopodite of the maxilla has four anterior setae, one lateral seta, and three posterior setae (e.g. Fig. 7F, G ). (in Conchoeciini there is a seta on the basale and there are six anterior setae on the first segment of the endopodite) 8. The toothed edge of the mandibular basale has two peg teeth, which are bare and slightly offset from each other, and there are six triangular cutting teeth the first of which is offset from the others. The inner tooth is quite tall and narrow (e.g. Fig. 7A, B ) 9. The female frontal organ is fused into a single unit (e.g. Fig. 9H ), so that the capitulum and shaft are undiffer-

entiated. 10. The basal segments of the first antenna of females are fused. 11. In males the c-seta of the first antenna is very short (<6% carapace length), and the base of the a-seta is usually

S–shaped and inflated. In some of the new genera this seta is furnished with one or two side arms (e.g. Fig. 6B,

C) 12. The hook appendages on the endopodites of the male second antennae are relatively small and less dimorphic than in the Conchoeciini .

Distribution. This tribe is almost ubiquitous in the World’s oceans. Its species occur at all depths except either in the uppermost 100m or so at temperate and high latitudes (see Angel et al. 2007), or where dissolved oxygen concentrations are exceptionally low, such as in the North Arabian Sea (unpublished Discovery data; Graves personal communication).

Figures

FIGURE 3. Carapace outlines (lateral and ventral) of males of all Metaconchoecia species redrawn at the same scale from the original species descriptions or redescriptions. M. acuta (redrawn from Gooday 1981, Fig 32A); M. alta (redrawn from Chavtur 2003, Fig. 22A); M. ampla (redrawn from Chavtur, 2003, Fig. 26A); M. australis (redrawn from Gooday 1981, Fig. 37H); M. crassiseta (redrawn from Chavtur 2003, Fig. 36A); M. discoveryi (redrawn from Gooday 1981, Fig. 20A); M. fowleri (redrawn from Gooday 1981, Fig. 11A), M. inflata inflata (redrawn from Gooday, 1981, Fig. 39A); M. inflata lata (redrawn from Chavtur 2003, Fig. 45A); M. obtusa (redrawn from Gooday, 1981, Fig. 23A); M. rotundata (redrawn from Gooday 1981, Fig. 43A); M. longiseta (redrawn from Chavtur 2003, Fig. 2D); M. skogsbergi (redrawn from Skogsberg 1920, Fig. 122-1); M. subinflata (redrawn from Gooday 1981, Fig. 45A); M. wolferi (redrawn from Gooday 1981, Fig. 30A).

FIGURE 5. Carapace outlines of females of the various forms of Muelleroecia macromma reported in the literature reproduced at identical scales. A, sensu strictu (Müller 1906a); B, M. sp.1 aff. C. macromma Deevey 1974; C, M. sp.2 aff. C. macromma Deevey 1982; D, M. sp.3 aff. C. macromma Poulsen 1973; E, M. sp.4 aff. C. macromma Angel 1981b.

FIGURE 6. Juryoecia distoglandula n. sp. Male (Paratype, Museum of Zhirmunsky Institute of Marine Biology, Vladivostok, Russia, IBM 2823, RV Vityaz Cruise 39, Station 5617; 45°49’N, 153°33’E; depth 6000-7000m), A, Lateral view of right valve of carapace; B, First antenna; C, Details of the distal part of first antenna showing the two side arms on a-seta; D, The armature of the first antennal e-seta; E. Second antenna (not showing endopodite); F, Hook appendage of the endopodite of right second antenna; G, Hook appendage of the endopodite of left second antenna; H, Mandible; I, Tooth-lists and masticatory pad of mandible; scales in millimetres.

FIGURE 7. Juryoecia distoglandula n. sp. Male (Paratype, Museum of Zhirmunsky Institute of Marine Biology, Vladivostok, Russia, IBM 2823, RV Vityaz Cruise 39, Station 5617; 45°49’N, 153°33’E; depth 6000-7000m), A and B, Mandible, toothed edge of basale; C, Mandible, proximal and distal tooth lists; D, Mandible, toothed edge of coxale; E, Mandible, exopodite; F and G, Maxillae; H and I, Fifth limbs, left and right; scales in millimetres.

FIGURE 9. Juryoecia distoglandula n. sp. Female. A, Lateral view of carapace of holoytype (Museum of Zhirmunsky Institute of Marine Biology, Vladivostok, Russia (IBM 2822) RV Vityaz Cruise 39, Station 5612, 45°43’N, 153°25’E, depth 5000- 6000m) B, ventral view of carapace of holotype; C, ventral view of carapace of one paratype (RV Vityaz Cruise 39, Station 5617; 45°49’N, 153°33’E; depth 6000-7000m); D, and E, ventral and lateral view of the second female paratype (RV Vityaz Cruise 39, Station 5617; 45°49’N, 153°33’E; depth 6000–7000m), F, Posterior dorsal corner of carapace of holotype, showing the opening of the LAG; G, Capitulum of frontal organ of the holotype; H, Frontal organ and first antenna of the holotype, showing side arms on the a-, b-, c- and d-setae; I, Details of the distal end of the first antenna of the holotype, showing the side arms on the sensory a-, b-, c- and d-setae; J, Second antenna of holotype; K, Details of endopodite of the second antenna of the holotype (note b-seta is broken); scales in millimetres.