THE CASPIAN SEA 567 



Derzhavinella, Zernovia, Behningiella and Sowinskya — have only one species 

 each, while Gammarus, Pandorites and Iphigenella have two each. The 

 endemic nature of the two main families of Caspian amphipoda is shown 

 in Table 236. 



Table 236. Endemic nature of Amphipoda of the Caspian fauna (Gammaridae and 

 Corophiidae families) {A. Derzhavin) 



This clear picture of specific endemism is broken only by Stennogammarus 

 ischnus and Corophium curvispinum, which have recently penetrated from the* 

 Baltic Sea through some water systems. Generic endemism is broken (if we 

 except the Arctic immigrants Pseudalibrotus, Pontoporeia and Gammara- 

 canthus) by the genera of the Corophiidae family, widely distributed outside 

 the limits of the Pontic-Caspian region. Thirty-five species of Caspian Amphi- 

 poda have adapted themselves to life in river systems. Of the order Decapoda 

 two species of the Astacidae family (river crayfish) are known in the Caspian 

 (Astacus leptodactylus and A. pachypus) and two species of the Palaemonidae 

 family, brought there by man, while the shrimps Leander rectirostris and L. 

 squilla are found. 



The group of molluscs represented by the classes Gastropoda (according 

 to Lindholm, 37 species) and Lamellibranchiata (21 species) are no less char- 

 acteristic and significant in the fauna of the Caspian Sea. 



Of the Neritidae family (Prosobranchia, Diotocardia) two species are known 

 for the Caspian Sea — Theodoxus pallasi and 77г. schultzii. The latter is strictly 

 endemic to the Caspian Sea, whereas the first has also been recorded in the 

 inlets of the northwestern part of the Black Sea, in Lake Top'yaton, and in the 

 Sea of Azov. The three families of the Monotocardia order — Valvatidae (1 

 species), Hydrobiidae (3 species) and Micromelaniidae (19 species) — are much 

 richer in species.* 



Of the Hydrobiidae family Derzhavin points out 3 species — Lithoglyphus 

 exiguus, Hydrobia pusilla and H. grimmi — and representatives of the Micro- 

 melaniidae family — 19 species, belonging to 4 genera — Micromelania (6 

 species) Nematurella (3 species), Caspia (7 species), and Clessiniola (3 species). 

 All these 19 species are Pontic-Caspian endemic forms, only Gaspia gmelini 

 and Clessiniola variabilis live outside the Caspian in the inlets of the Black and 

 Azov Seas. Thus the strictly Caspian endemic nature of this group is well 

 emphasized. 



* V. Lindholm did not publish a complete description of the gastropod molluscs of the 

 Caspian Sea, and, using the description of Derzhavin, 23 species are given here. 



