биота российских вод японского моря - Materials of Alexey Shipunov

Order MYSIDACEA Boas, 1883Viktor V. PetryashovGeneral characteristicsThe order Mysidacea is a subdivision of the superorder Peracarida. Mysids areshrimplike higher crustaceans (pl. I, fig. 1). Their body is divided into two tagmata:the cephalothorax and the abdomen. The body consists of six-seven segments of thehead (five segments of the protocephalon and one to two segments of the maxilliped),six-seven thoracic segments, six abdominal ones, and the telson. The eyes are facetedand borne on movable stalks; visual elements sometimes more or less reduced, oftenresulting in the reduction of the eyes. Most part of the head and the thorax is coveredwith a well-developed head shield, or carapace, fused to the dorsum of three to four(rarer) anterior thoracic segments. The antennules (antennae 1) are well developed;they consist of a three-segmented peduncle and two many-segmented flagella. Thethird segment of the peduncle in males may bear a setaceous appendix masculina atthe distal margin. The antennae (antennae 2) are also well developed; they consist of athree-segmented protopod, a scaled exopod (antennal scale, or scaphocerite), and anendopod. The endopod of the antenna is composed of a three- to four-segmented basalpart and many-segmented flagellum. The mysids have eight pairs of thoracic limbs(thoracopods), one or two anterior pairs of which are transformed into maxillipeds. Allthoracopods are biramous; they are composed of an exopod and an endopod, attachedto a common base – protopod. Three constituent segments of the protopod are a precoxa(basal one), a coxa, and a basis (distal one). The coxa in several anterior thoracopodsis provided with a process (epipod). The segments of the endopod, from the baseto the apex, are a preischium, ischium, merus, carpus, propodus, and a dactylus. Theend of the dactylus is often armed with a claw-like spine. There is often a knee-likeprominence between the merus and the carpus. The mysids belonging to the tribeErythropini and to the genus Inusitatomysis of the tribe Mysini have the carpus and thepropodus joined obliquely, and the knee-like prominence is the feature inherent mainlyto these groups. Members of the above-mentioned groups from the Sea of Japan,plus the species of the subfamily Gastrosaccinae may have the propodus further dividedinto subjoints, usually two in number. In many species the carpus and the propodusare fused and have secondary division into several small subjoints (this is characteristicof the most species of the tribe Mysini from the northern half of the Sea ofJapan). The Sea of Japan species lack branchiae (podobranchs). Posterior two, or, rarer,three or seven pairs of the thoracopods in females are provided with welldevelopedplates (oostegites) on their inner sides. The oostegites form the marsupium,in which embryos develop; the development is full and direct. The mysids have fivepairs of abdominal limbs (pleopods). The pleopods may be uniramous or biramous.They are often reduced or absent in females and better developed in males. In manyspecies the fourth or, rarer, the third pair of the pleopods in males is elongate andmodified, as it is used in copulation. One pair of flat biramous uropods and the telsonform a tailfan. The species from the Sea of Japan are provided with the statocyst onthe basal part of the endopods of the uropods.42