The Crayfish: An Introduction to the Study of Zoology.

by Thomas Henry Huxley

It is a remarkable circumstance that this crayfish not only thrives in the brackish waters of the estuaries of the rivers which debouche into the Black Sea and the Sea of Azov, but that it is found even in the salter {302} southern parts of the Caspian, in which it lives at considerable depths.

FIG. 75.—Astacus leptodactylus (after Rathke, ¹⁄₃ nat. size).

In the north, Astacus leptodactylus is met with in the rivers which flow into the White Sea, as well as in many streams and lakes about the Gulf of Finland. But it has probably been introduced into these streams by the canals which have been constructed to connect the basin of the Volga with the rivers which flow into the Baltic and into the White Sea. In the latter, the invading A. leptodactylus is everywhere overcoming and driving out A. nobilis in the struggle for existence, apparently in virtue of its more rapid multiplication.[26]

[26] Kessler (Die Russischen Flusskrebse, l. c. p. 369–70), has an interesting discussion of this question.

In the Caspian and in the brackish waters of the estuaries of the Dniester and the Bug, a somewhat different crayfish, which has been called Astacus pachypus, occurs; another closely allied form (A. angulosus) is met with in the mountain streams of the Crimea and of the northern face of the Caucasus; and a third, A. colchicus, has recently been discovered in the Rion, or Phasis of the ancients, which flows into the eastern extremity of the Black Sea.

With respect to the question whether these Pontocaspian crayfishes are specifically distinct from one another, and whether the most widely distributed kind, A. leptodactylus, is distinct from A. nobilis, exactly the same difficulties arise as in the case of the west European {303} crayfishes. Gerstfeldt, who has had the opportunity of examining large series of specimens, concludes that the Pontocaspian crayfishes and A. nobilis are all varieties of one species. Kessler, on the contrary, while he admits that A. angulosus is, and A. pachypus may be, a variety of A. leptodactylus, affirms that the latter is specifically distinct from A. nobilis.

Undoubtedly, well marked examples of A. leptodactylus are very different from A. nobilis.

1. The edges of the rostrum are produced into five or six sharp spines, instead of being smooth or slightly serrated as in A. nobilis.

2. The fore part of the rostrum has no serrated spinous median keel, such as commonly, though not universally, exists in A. nobilis.