биота российских вод японского моря - Materials of Alexey Shipunov

far as the Tatar Strait (Bokhan, 1984). The species is also transported by the warmKuroshio Current to the north-eastern tip of Hokkaido Island and to the South KurilIslands (Onbe et al., 1996).Biology and ecology. P. tergestina is a warm-water species of the Peter theGreat Bay fauna, appearing in the middle of summer hydrological season. In 1973 itappeared in Alekseev Bight in August at a temperature of 21.1°C and in September (at17.9°C) reached maximum density (59 sp./m 3 ). As water got colder, the density of thespecies sharply decreased, but it still occurred sporadically until December (Mikulich& Biryulina, 1977).In the south-western part of Peter the Great Bay small numbers of P. tergestinaappear in late August, its density growing in September up to 141 sp./m 3 (Shkoldina &Shevchenko, 2001). In September of 1996 gamogenetic females with one-two developingresting eggs each were recorded in some regions of the bay at a surface watertemperature of 17–19°C.In Vostok Bay P. tergestina usually appears in mid-August when the water iswarmest (22.4°C), reaching a density of 186 sp./m 3 , which decreases to 3.3 sp./m 3 inSeptember (Shkoldina, 2001). It occurs singly until late October, when water temperatureis 13–14°C. At this period gamogenetic females with resting eggs are found, too.The species’ biology and ecology was intensively studied for the Inland Sea ofJapan. Onbe’s records (1974) show that this species appears among the plankton inlatitude about 34°20′N in May or June, reaching maximum abundance in July-Augustand staying in the sea until September-October. Maximum density (8.7–9.4 thousandsp./m 3 ) is registered at a temperature of 22.3–23°C, but in September assemblages upto 30 thousand sp./m 3 were recorded. The bulk of the cladocerans inhabit the upperlayer of water (10–15 m), concentrating at a depth of 3 m in July and nearer to the surfacein August. At night the number of females with mature embryos is maximal, andbefore dawn the young hatch. The same patterns of reproduction were observed in theCaspian Evadne (Rivier, 1969). During a period of gamogenetic reproduction a populationincludes from 2.2 to 12.5% of males and up to 12.4% of females with restingeggs. Females with resting eggs are among the largest specimens in a population(Onbe, 1978b). Japanese scientists observed the hatching of a young P. tergestinafrom a resting egg (pl. VIII, fig. 1). The process begins, like in all the Polyphemoidea,when a rounded egg breaks up into 2 unequal halves; an embryo at this stage alreadyhas a well-pigmented eye. The size of a resting egg varies from 190 to 240 µm (averagesize is 200 µm). Resting eggs are found in sediments all the year round, theirnumber is maximal (7.7 thousand eggs/m 2 ) in July, with the peak density of the cladoceransin the plankton about 3 thousand sp./m 3 (Onbe, 1985).Among the contents of the foregut of P. tergestina large centric diatoms werefound (Kim et al., 1989).3. Genus Podon Lilljeborg, 1853Type species: Podon leuckarti (Sars, 1862).Shell in females rounded, in males small, having irregular shape. Head elongated,anteriorly globular, separated from shell by clearly seen depression. Antennalbranches with well-developed apical segments; number of setae on 4-segmented and3-segmented branches identical (6 setae). Exopods of thoracic limbs weakly devel-19