Their nearest relations seem to be certain genera of Crustacea that are found in jurassic strata, in the lias, and more particularly in the lithographic slates of Solenhofen.
They have a very wide bathymetrical range extending from a depth of 250 fathoms (Polycheles crucifera) to a depth of 2,000 fathoms (Willemoesia).
Fig. 18.—Polycheles baccata, one of the Eryonidæ. The eyes and eye-stalks are absent, and the margin and sides of the carapace armed with spines. (After Spence Bate.)
But there are many other curious forms of the macrurous crustacea that deserve a passing mention. The graceful Nematocarcinus gracilipes, distinguished by the extraordinary length of the antennæ and last four pairs of legs, these appendages being three or four times the length of the body, is by no means rarely met with in depths of over 400 fathoms.
The genus Glyphus captured by the ‘Talisman’ is remarkable for the development of a peculiar pouchlike arrangement on the abdomen for the protection of the larvæ during the younger stages of their existence.
The proof of the existence of a peculiar cray-fish, Thaumastocheles zaleuca, at a depth of 450 fathoms, was one of the most important contributions to carcinology made by the ‘Challenger’ Expedition. The chelæ of this remarkable form are of great but unequal length and armed with long tooth-like spines giving it an appearance not unlike that of the jaws of some carnivorous fish. The shell is soft and the abdomen broad and flattened. There are no eyes nor even eye-stalks, but ‘in front of the carapace,’ as Sir Wyville Thomson remarks, ‘between the anterior and upper edge and the insertions of the antennæ, in the position of the eyes in such forms as Astacus fluviatilis, there are two round vacant spaces, which look as if the eye-stalks and eyes had been carefully extirpated and the space they occupied closed with a chitinous membrane.’ The deep-sea prawn, Psalidopus, recently taken in 500 fathoms of water by the ‘Investigator,’ affords us an example of a common bathybial character, the whole body being covered with an extraordinary array of sharp needle-like spines.
Among the crabs many curious forms have been found in deep water extending down to depths of over 2,500 fathoms. They are nearly all characterised by blindness and a remarkable development of tooth-like spines covering the carapace and limbs.
The remarkable Lithodes ferox, from a depth of from 450 to 800 fathoms, is perhaps the most perfectly armed crab—in the way of spines—that exists. Every part of the body and limbs is so covered with spines that one has to be extremely careful in handling even a dead specimen.
This is only one of the many examples that might be given to illustrate this curious feature of the deep-sea Crustacea. Among the crabs alone we have such forms as Galathodes Antonii, Pachygaster formosus, Dicranodromia mahyeuxii covered with a fierce armature of spines or bristles; but there are nevertheless some species in which this character is not particularly noticeable, and in these we usually find some other protection against their enemies. An interesting example of this has been described by A. Agassiz in a crab allied to the Maiadæ, ‘in which the dorsal face appears like a bit of muddy area covered by corals, with a huge white arm resembling a fragment of an Isis-like gorgonian.’ It is evident that this is a case in which the animal is protected by its resemblance to the surroundings.