Mazepovacandona, Karanovic, Ivana & Sitnikova, Tatiana Ya., 2017

Karanovic, Ivana & Sitnikova, Tatiana Ya., 2017, Morphological and molecular diversity of Lake Baikal candonid ostracods, with description of a new genus, ZooKeys 684, pp. 19-56 : 20-22

Genus Mazepovacandona gen. n.

Type species.

Mazepovacandona directa (Bronstein, 1947), comb. n.

Other species.

M. godlewski (Mazepova, 1984), comb.n., M. navitarum (Mazepova, 1976), comb. n., M. orbiculata (Mazepova, 1990), comb. n., M. spicata (Mazepova, 1982), comb. n.

Diagnosis.

Shell shape variable, but surface generally smooth or poorly ornamented. A1 7- or 6-segmented. Male A2 with t-setae transformed into sensory setae, z-setae transformed into claws. Female A2 G2-claw considerably shorter than G1 or G3. Exopod of A2 consisting of small plate and three setae of which one is long. Male prehensile palps asymmetrical and both with hook-like fingers. L6 with basal seta and with one seta on each endopodal segment, except on last segment, which carries two setae and one claw. L7 with only d1- and dp-setae on basal segment, e- and f-setae missing, g-seta long; terminal segment with short h1-seta and h2- and h3-setae equally long; penultimate segment divided or incompletely divided. UR with both claws and setae present. Zenker organ with variable number of spine whorls, varying from 3+2 to 5+2; anterior part (cap) hemispherical, lattice-like structure well-developed. Hemipenis with small a-lobe not projecting laterally; M-peace terminally rounded (ball-like); ejaculatory process (bursa copulatrix) terminally pointed.

Etymology.

The genus is named after late Dr. Galina Mazepova as an acknowledgment of her outstanding contribution to the study of Lake Baikal ostracod fauna.

Remarks.

Mazepovacandona currently contains five morphologically diverse species. The carapace shape (from triangular to banana shaped) is only one example of this diversity. The number of segments on the antennule and the way male z-setae on the second antenna are developed is also variable, however all females have G2-claw on the second antenna shorter than the rest of the claws. The number of setae on the second segment of the Md-palp is also variable and it can be either three or four. Prehensile palps are dissimilar among species, although all have clearly pronounced hooked-like fingers on both left and right palp. The basal seta (d1) on the walking leg is shorter in all five species than in two Baicalocandona species redescribed here. The length of this seta relative to the d2-seta (always absent in Candonidae ) is an important taxonomic character in some Cyprididae , such as Cyprinotinae (see the key in Karanovic 2012) and Eucypridinae (see Martens 1989). The d1-seta is often absent in Candonidae , and the importance of its length for the taxonomy of the family has never been studied. In all Mazepovacandona the penultimate segment of the cleaning leg is at least partially subdivided, but this tends to be a variable character, for example in Candona , Fabaeformiscandona (see Meisch 2000), and a few genera from Australia (see Karanovic 2007). The hemipenis morphology in Mazepovacandona is characterized by a rounded distal end of the M-peace. The morphology of this part is an important taxonomic character in Candona (see Petkovski 1960). Also, the ejaculatory process (bursa copulatrix) is pointed in all species of the new genus, but the morphology of this part has not been studied for its taxonomic importance. The hemipenis of the two examined species ( M. directa and M. orbiculata ) was in an erected state and because of that the position of the a-lobe and its shape were not easy to observe. It is interesting to note that all examined males of M. directa had their hemipenis erected. The hemipenis illustrations of these two species in Mazepova (1990) also show an erected copulatory organ. The Zenker organ has a balloon-like anterior end, a characteristic which has been noted in Pseudocandona inaequivalvis baikalensis Bronstein, 1947, some Undulacandona species (see Smith 2011; Karanovicand Cho 2017), and in the families Cyclocyprididae and Paracyprididae (see Danielopol 1982). The morphology and development of the Zenker organ has been studied recently (see Yamada and Matzke-Karasz 2012; Yamada et al. 2014). The phylogenetic importance of its morphology is recognized on the higher taxonomic levels ( Danielopol 1978; Matzke-Karasz 1997), but not well understood at the generic or even family level. Many of the Candonidae genera have the number of whorls of spines as a part of their diagnosis. In the new genus, the number ranges from five to seven, and they all have well-developed spines, which is a sign of the sexual ma turity ( Yamada et al. 2014). Interestingly, Kesling (1957) reported a variability of the whorl numbers in one Candona species, where some individuals have seven and others eight whorls. The latter number is very unusual in the family Candonidae , where the number of whorls never exceeds seven.

Despite the morphological diversity of Mazepovacandona , this genus seems to be most closely related to Candona and Fabaeformiscandona . For example, prehensile palps of M. directa (elongated) are very similar to candida -group of Candona , while female genital lobe bears similarity to the neglecta -group. There is also similarity with Fabaeformiscandona , especially because several of its species have rounded distal part of the M-peace. The breuli-group of the latter genus is particularly similar to Mazepovacandona in sense that the M-peace is not so strongly sclerified and that most species have an UR with a long posterior seta. However, most of the species currently belonging to this group have a completely fused penultimate segment of the cleaning leg.