TARDIGRADA AND PENTASTOMIDA
BY
ARTHUR E. SHIPLEY, M.A., F.R.S.
Fellow and Tutor of Christ’s College, Cambridge, and Reader in Zoology in the University
CHAPTER XIX
TARDIGRADA
OCCURRENCE—ECDYSIS—STRUCTURE—DEVELOPMENT—AFFINITIES—BIOLOGY—DESICCATION—PARASITES—SYSTEMATIC
The animals dealt with in this chapter lead obscure lives, remote from the world, and few but the specialist have any first-hand acquaintance with them. Structurally they are thought to show affinities with the Arachnida, but their connexion with this Phylum is at best a remote one.
Tardigrades are amongst the most minute multicellular animals which exist, and their small size—averaging from ⅓ to 1 mm. in length—and retiring habits render them very inconspicuous, so that as a rule they are overlooked; yet Max Schultze[[374]] asserts that without any doubt they are the most widely distributed of all segmented animals. They are found amongst moss, etc., growing in gutters, on roofs, trees or in ditches, and in such numbers that Schultze states that almost any piece of moss the size of a pea will, if closely examined, yield some members of this group, but they are very difficult to see. The genus Macrobiotus especially affects the roots of moss growing on stones and old walls. M. macronyx lives entirely in fresh water, and Lydella dujardini and Echiniscoides sigismundi are marine; all other species are practically terrestrial, though inhabiting very damp places.
In searching amongst the heather of the Scotch moors for the ova and embryos of the Nematodes which infest the alimentary canal of the grouse, I have recently adopted a method not, as far as I am aware, in use before, and one which in every case has yielded a good supply of Tardigrades otherwise so difficult to find. The method is to soak the heather in water for some hours and then thoroughly shake it, or to shake it gently in a rocking machine for some hours. The sediment is allowed to settle, and is then removed with a pipette and placed in a centrifugaliser. A few turns of the handle are sufficient to concentrate at the bottom of the test-tubes a perfectly amazing amount of cryptozoic animal life, and amongst other forms I have never failed to find Tardigrades.
