92 Proceedings of the Royal Physical Society. 



IX. — Note on Piona carnea C. L. Koch and Eurycypris pubera (O. F. M.) 



By Wm. Williamson. 



(Received 15th February 1910. Read 28th February 1910.) 



It is generally recognised that watermites prey on Entomostraca ; an 

 instance which recently came under my observation tends to show that the 

 eggs of watermites may be subjected to the same treatment from some of 

 tbe Entomostraca. 



In July 1909, while tow-netting on Kilconquhar Loch, I took a number 

 of specimens of the Hydracarid, 1 Piona carnea C. L. Koch, and of the 

 Ostracod, Eurycypris pubera (0. F. M.). Very often after capture, water- 

 mites deposit eggs in patches on the sides of the tubes containing them, and 

 on this occasion Piona carnea deposited several clusters of eggs. A day 

 or two after, I noticed among these eggs, others of a smaller size and deeper 

 colour. These latter I found to be the eggs of Eurycypris pubera and to have 

 been deposited in the following manner. The female Eurycypris commenced 

 by hacking away, chiefly with the second pair of antennae, but also sometimes 

 by nibbling, at the gelatinous matrix in which hydracarid eggs are often 

 embedded. When a sufficiently large aperture had been made and the cell 

 containing the hydracarid egg had been penetrated, the Eurycypris then 

 inserted the tips of the second pair of antennae. These lying close together 

 formed a track along which the ostracod egg was rolled into the place 

 selected for its deposition. Some little effort appeared to be necessary to 



1 1 have here employed the term hydracarid in preference to hydraclmid for the 

 following reasons. The term Hydracarina is now used to cover all the genera hitherto 

 included in the Hydrachnidre — more correctly Hydrarachnidae— while the latter is greatly 

 restricted in its application, including at the present time only the genera Hydrarachna 

 and Bargena, and, according to Koenike, one other genus. It seems to me, therefore, that to 

 use the word hydrachnid (or hydrarachnid) in anything but the restricted sense would not 

 be proper, and that for use in the wider sense the word hydracarid is preferable. There 

 will thus be available two words from the same stem to denote aquatic acarina, viz., 

 hydracarid, for the fresh-water forms, and halacaiid for the marine forms. 



With regard to the etymological correction indicated above, though Hermann pointed 

 this out in 1804, almost no support was given to the change until Koenike recently 

 substituted Hydrarachna for Hydrachna (Silsswasser fauna Deutschlands, Heft 1 2). Hermann's 

 views are expressed as follows : — " J'ai observerai ;\ cette occasion que le nom d'hydrachna, 

 employe par Muller, n'est point etomologiquement juste. Des contractions de cette ispece ne 

 respondent point au ge'nie de La langue : on ne dit point hippotame au lieu d' hippopotame. 

 Le nom d'hydrachna ne peut §tre approuvd, d'autant moina qu'il exprime toute autre chose 

 qu'une araigne'e aquatique, le mot &.x vr i significant suie, paillette, ecume, et par consequent 

 hydrachna eignifieroit paillette d'eau " (Mem. Apteral). 



