HALOCYPRIDINA Dana, 1853

Graves, Carol, 2011, Redescription of Euconchoecia chierchiae Müller, 1890 and Euconchoecia aculeata (Scott, 1894) (Halocyprididae: Ostracoda) from the Atlantic, and descriptions of two novel species of Euconchoecia Müller 1890, from the Gulf of Oman, Journal of Natural History 45 (31 - 32), pp. 1937-1981 : 1941-1942

Suborder HALOCYPRIDINA Dana, 1853

Family HALOCYPRIDIDAE Dana, 1853 Subfamily EUCONCHOECINAE Poulsen, 1969 Genus Euconchoecia Müller, 1890

Diagnosis

Carapace usually smooth, lacking any sculpture, shape elongate, rostra well-developed but asymmetrical; posterior dorsal corners usually pointed. The “asymmetrical glands” open almost symmetrically just below posterior dorsal corner. Frontal organ long, extends beyond second segment of first antennae ( Skogsberg 1920), but ± length of first antenna. First antennae (A1) show marked sexual dimorphism, in both sexes fourth segment bears ventrally more than 20 bundle setae of similar length and thickness. Terminal A1 segment bears four or five unarmed setae. In males, two setae are long and powerful; the longest seta more than three times the length of bundle sensory setae and 50% carapace length (CL). Protopodite of second antenna (A2) large and powerful. In males A2 is 35–40% CL. A2 endopodite lacks any c-, d- and e-setae (that are typical of other halocyprids), f- and g-setae very long. The male right A2 endopodite with elongate hooked clasping organ, with long proximal shank with h-, i- and j-setae inserted distally, end piece long, curved. Left A2 endopodite has “hook” reduced to just straight basal shank, also carries three setae terminally. Female A2 endopodite without c-, d- and e-setae, f- and g-setae shorter than in male. First segment with small verucca carrying a single seta (similar in length to i-seta of male). Coxale of mandibular protopodite elongate triangular structure contains complex musculature that generates the biting action. Distal end of the coxale has three parallel rows of teeth: pars incisiva, distal tooth list, and narrower proximal tooth list. Basale with distal edge of sub-serrate teeth, one tubular tooth and one dagger-shaped tooth; laterally with four long setae and a plumose seta. The exopodite consists of a long plumose seta. The segmented endopodite with a short, bare dorsal seta sits on first segment plus three spinose ventral setae. Second segment with one spinose ventral seta and two dorsal spinose setae. Terminal segment with seven spinose setae; the longest almost as long as carapace. Basal segment of maxilla with five anterior, one lateral and four posterior setae. Distal segment short and wide with six claw setae, the posteriormost is longer than others, anterior seta with secondary spines, ornamented with short fine hairs. Ventral edge of basale of fifth limb with five spinose pointed setae, and laterally two plumose setae. First endopodite segment with two ventral setae and one dorsal seta; all spinose. Second segment with three curved unequal terminal claw setae; central claw is longest. Main axes of both fifth and sixth limbs in both sexes are endopodites, the dorsal seta on the basale is a remnant exopodite (see Boxshall 1998; Kornicker 2003). In females, basale of sixth limb with ventrally three spinose setae plus one plumose seta, laterally a plumose seta, dorsally a single seta. First endopodite segment with two ventral setae. Second segment with single spinose setae ventrally and dorsally. Terminal segment with three unequal serrate setae. Male sixth limb differs from female’s. Ventral surface of the basale with five spinose setae, terminal setae very long, subequal, smoothly curved with long hairs. Seventh limb in both sexes with two setae one long, one short. Caudal furca with seven pairs of claw setae that diminish in size dorsally, all with secondary spines along trailing edge, plus dorsally small unpaired seta with secondary spines. Between the first and second pairs of claw setae a verruciform process. Intromittent organ broad, widens distally with rounded tip.

Remarks

This genus is exceptional among halocyprid ostracods in that the females retain their eggs in a brood pouch within the carapace, releasing them as they complete the first juvenile instar. The earliest juvenile instar has two pairs of caudal furca spines and at each moult an extra pair is added. Most adult halocyprids have eight pairs of caudal furca spines, whereas Euconchoecia has seven pairs, which poses the question of whether Euconchoecia moult just five times from hatching to maturation rather than the usual six of Conchoecia Dana, 1853 . If Euconchoecia has evolved neotenously from the Conchoecia type of life cycle by a reduction in the number of moults from six to five, such an abbreviated life cycle would enable populations to respond quicker to any changes resulting from upwelling events.