Key character
Small species with the gland on the left valve opening on the rostrum or on the anterior third of the dorsal carapace margin. This difficult genus contains many sibling species which are distinguished mostly by subtleties of carapace shape. Below 19 species are considered.
There are four species in which the asymmetrical gland on the right carapace valve opens on a prominence towards the top of the dorsal margin:
¥ÊMetaconchoecia pusilla (Müller, 1906) (Metaconchoecia pusilla, Metaconchoecia glandulosa 2) is a small (<1 mm) deep mesopelagic species which is often abundant at middle to high latitudes.
¥ Metaconchoecia macromma (Müller, 1906) (Metaconchoecia macromma, Metaconchoecia macromma 2) is larger (>1 mm) with the gland on the left valve opening further back along the dorsal surface and tends to be more abundant at low latitudes.
¥ Metaconchoecia isocheira (Müller, 1906) (Metaconchoecia isocheira, Metaconchoecia isocheira 2) is a small Southern Ocean endemic, occurring at mesopelagic depths in which the male is immediately recognisable by having only a single row of stout spines as armature on the antennular e seta.
¥ Metaconchoecia glandulosa (Müller, 1906) (Metaconchoecia glandulosa, Metaconchoecia glandulosa 2) A much larger (>1.5 mm) deep bathypelagic species, also has the left asymmetrical gland set well back, but the carapace is almost parallel-sided in ventral aspect and it uniquely has a group of large gland cells just below the rostral incisure on both valves.
¥ Metaconchoecia lunata (Deevey, 1982) (Metaconchoecia lunata). Might be confused with M. macromma in that it has the left asymmetrical gland set well back Only the male of this large abyssopelagic species has been found in the Southern Ocean, although in very deep samples from the North Atlantic female specimens which may belong to the same species have been found. The unique feature of this species is the trifid antennular a seta.
There are three small (<1 mm) globous species:
¥ Metaconchoecia kyrtophora (Müller, 1906) (Metaconchoecia kyrtophora, Metaconchoecia kyrtophora 2, Metaconchoecia kyrtophora 3), a shallow mesopelagic to epipelagic tropical species. In ventral profile has clearly visible shoulder vaults, and the male antennular e seta has a unique armature of peg spines.
¥ Metaconchoecia nasotuberculata (Müller, 1906) (Metaconchoecia nasotuberculata, M. nasotuberculata 2), also a tropical to subtropical mesopelagic species, is distinguished by having the left gland opening close to the tip of the rostrum, but most readily by the development of protuberances near the posterior dorsal corner of the carapace.
¥ Metaconchoecia teretivalvata (Iles, 1953) (Metaconchoecia teretivalvata, Metaconchoecia teretivalvata 2) is a shallow mesopelagic species occurring often abundantly in subtropical to temperate waters, it has a broad carapace which curves smoothly in ventral aspect. The male has 10 pairs of spines in the armature of the antennular e seta.
¥ Metaconchoecia arcuata (Deevey, 1978) (Metaconchoecia arcuata, Metaconchoecia arcuata 2) is another small deep bathypelagic species which is deep-bodied relative to the other species and the carapace does not taper anteriorly. The thin-walled setae on the male second antennal endopodite have side branches.
All the remaining species will be difficult to identify without experience, good material and reference to Gooday (1981).
¥ Metaconchoecia skogsbergi (Iles, 1953) (Metaconchoecia skogsbergi, Metaconchoecia skogsbergi 2), the largest species (>1.3 mm). A mesopelagic species abundant in the Southern Ocean.
¥ Metaconchoecia discoveryi (Gooday, 1981) (Metaconchoecia discoveryi, Metaconchoecia discoveryi 2) has the opening of the left asymmetrical gland >15% of the carapace length behind the tip of the rostrum. It is also a slim species with the carapace breadth <40% its length, and the antennular e seta armature consists of 11 pairs of spines.
¥ Metaconchoecia fowleri (Gooday, 1981) (Metaconchoecia nasotuberculata, M. nasotuberculata 2) is slightly longer and broader than the previous species, and has the left asymmetrical gland opening 12-15% of the length behind the rostrum. The male antennular e seta has an armature of 13 pairs of spines.
There are two species with carapaces that strongly taper anteriorly. The largest (1.06-1.26 mm) known only from southern latitudes:
¥ Metaconchoecia wolferi (Gooday, 1981) (Metaconchoecia wolferi, Metaconchoecia wolferi 2) and has 13 pairs of spines in the armature of the male antennular e seta.
¥ Metaconchoecia obtusa (Gooday, 1981) (Metaconchoecia obtusa, Metaconchoecia obtusa 2) is shorter (0.91-1.06 mm) with a rather bluntly rounded anterior edge to the carapace below the rostrum (see M. acuta below) and has 12 pairs of spines in the armature of the male antennular e seta.
Species that are less tapered anteriorly include a very broad species:
¥ Metaconchoecia inflata (Gooday, 1981) (Metaconchoecia inflata, Metaconchoecia inflata 2) in which the carapace breadth is often >50% the length.
¥ Metaconchoecia rotundata (Müller, 1906) (Metaconchoecia rotundata, Metaconchoecia rotundata 2), the smallest species (<0.87 mm) has only 8 pairs of spines in the armature of the male antennular e seta.
¥ Metaconchoecia australis (Gooday 1981) (Metaconchoecia australis, Metaconchoecia australis 2) is superficially like C. teretivalvata, but is slimmer and has 11 pairs of spines in the armature of the male antennular e seta.
¥ Metaconchoecia subinflata (Gooday, 1981) (Metaconchoecia subinflata, Metaconchoecia subinflata 2) is anteriorly broadened, particularly in the male, which also has 11 pairs of spines in the armature of the antennular e seta.
¥ Metaconchoecia acuta (Gooday, 1981) (Metaconchoecia acuta, Metaconchoecia acuta 2) is shorter and has a distinctive acute edge to the anterior edge of the carapace below the rostrum. It has 10 pairs of spines in the armature of the male antennular e seta. These species can be consistently sorted on the basis of their carapace shape, and despite some overlap, show differences in their vertical ranges at any one position.
Metaconchoecia fowleri (Metaconchoecia fowleri, Metaconchoecia fowleri 2) is the type species for the genus.
Species information:
Genus Metaconchoecia.pct