биота российских вод японского моря - Materials of Alexey Shipunov

Order EUPHAUSIACEA Dana, 1883Viktor V. Petryashov, Artur G. Porodin, Boris M. BorisovGeneral characteristicsEuphausiids are shrimplike higher crustaceans of the superorder Eucarida. Theyare also known as krill. The body is divided into two tagmata (cephalothorax and abdomen)and is composed of five segments of the head, eight thoracic, six abdominalsegments, and the telson (pl. I, figs. 1–4). The eyes are stalked, faceted, usually welldeveloped, with the cornea in some species divided into two lobes. Most part of thehead and thorax, except for the bases of the thoracopods with the gills, is covered by acarapace, dorsally fused with the thoracic segments. Each antennule (antenna 1) consistsof a three-segmented peduncle and two many-segmented flagella. In many generathe antennular peduncle, beside setae, may bear tubercles, spines, and lappets. Eachantenna (antenna 2) consists of a one-segmented (as a result of the fusion of threesegments) protopod, an exopod (antennal scale, or squama), and an endopod with athree-segmented peduncle and many-segmented flagellum. There are eight pairs of thethoracopods. They are biramous (exo- and endopod), relatively similar in arrangement,and not transformed into maxillipeds. One or two distal pairs are shortened(family Bentheuphausiidae) or reduced (family Euphausiidae). In the forms with bilobedeyes the second and/or third pairs of the thoracopods are transformed into elongatedgrasping organs. The coxapodites of the thoracopods bear epipods, forming gillson their outer side, and small blade-shaped endites, best developed on the first thoracopods,on their inner side. There are five pairs of pleopods on the abdomen. They arewell-developed both in males and females, natatory, biramous, with similar arrangement.Pleopods 1 and 2 in males are provided with a copulatory organ (petasma). Thesixth abdominal segment has a pair of flattened biramous (both rami are onesegmented)uropods. The uropods in combination with the telson form a tailfan. Thespecies of the family Euphausiidae have light-emitting organs (photophores). Thereare usually ten of them, two on the lower parts of the eye-stalks, four on the bases ofthe thoracopods 2 and 7, and four on the first to fourth abdominal segments betweenthe pleopods. The species of the genus Stylocheiron are provided with only five photophores:one on each eye-stalk and on the bases of the thoracopods 7, and one on thefirst abdominal segment.Euphausiids are exclusively marine crustaceans living in the pelagic zone, indepths from 0 to 5000 m, sometimes going down to the bottom. At present two familiesof euphausiids are known (Euphausiidae and Bentheuphausiidae), which include11 genera and 86 species. Euphausiids occur in all the oceans, with the species diversitybeing widest in tropical and subtropical waters. Only one family, Euphausiidae, isrepresented in the Sea of Japan.Biology. Euphausiids are usually omnivorous, main types of feeding are predationand filtration. Their ontogenetic development is commonly divided into four periods,viz.: embryonic, larval, juvenile, and adult. Euphausiids have internal fertilization;round eggs are laid in portions; the process of reproduction takes place in the pelagiczone. Nauplii (stages I–III) (pl. III, fig. 1), like the next stage, metanauplii81