SCIENCE-GOSSIP. 



33 



BRITISH FRESHWATER MITES. 



A SPECIES NEW TO BRITAIN. 



By C. F. George, M.R.C.S. 



IJTETTINA macroplica Piersig is a pretty and 

 ^ ' curious little mite which appears to have 

 escaped the observation of the older writers on the 

 Hydrachnidae. Piersig seems to have first found 

 it, for he described it in 1892 in " Zoologischer 

 Anzeiger." In his large and important work 

 (" Deutschlands Hydrachniden ") now in course of 

 publication, he gives a coloured figure of the dorsal 

 side of the female, a ventral and dorsal figure, 

 uncoloured, and a 

 figure of the ventral 

 side of the larva and 

 nymph, as well as a 

 figure of the palpi ; 

 but he does not figure 

 the ventral side of the 

 male. I first found 

 the male in October, 

 1S95, and it was only 

 this spring that I 

 found the female. 

 The sexes are very 

 much alike in appear- 

 ance at first sight, ex- 

 cepting as to size; the 

 female, as is usual in 

 water mites, being con- 

 siderably the larger. 



The general colour 

 of Wettina macroplica 

 is pale dull yellow, 

 with dark reddy 

 brown caeca, looking 

 almost black when 

 only slightly magni- 

 fied. The Y-shaped 

 portion, between the 

 caeca, is of a deeper 



and brighter yellow. The creature is a very 

 and active swimmer, and gyrates in a curious 

 fashion, somewhat after the manner of some of the 

 smaller male Curvipes. The swimming-hairs on 

 the front legs are rather strong and curved, thickest 

 at their base and gradually tapering to a point at 

 the apex. The mite, after being disturbed, swims 

 only for a short time, and soon buries itself again 

 in the mud, and this may be one reason why it 

 has been seldom noticed. One of the features that 

 first strikes the observer is the curiously enlarged 

 last joint of the first pair of legs, with their 

 tremendous claws, which can be quite retracted 

 into a cavity ; the female possesses them as well as 

 the male. The last two or three joints of all the 

 July, i8g8.— No. 50, Vol. V. 



Fig. I.— Ventral side of male. 

 ,, 2. — Dorsal ,, ,, 



Wettina macroplica Picrsi, 

 F 



legs are more or less coloured a yellowish red; 

 this is the case in some other mites, especially 

 in Acercus and Curvipes. These also have, in 

 some species, the ultimate joint of the first pair 

 of legs enlarged, but in their case the end 

 joints of the second pair of legs have likewise 

 been enlarged in such specimens as I have 

 observed. The anterior portion of Wettina 

 macroplica, especially in the male, has a sort of 

 neck, from each corner 

 of which, or rather 

 from a slight tubercle 

 under each corner, 

 j^^^-~~- projects a rather long 



X:§^ tactile hair, curving 



outwards. The geni- 

 tal area at once serves 

 to distinguish this 

 mite from Acercus or 

 Curvipes, for there are 

 only three cells, or 

 discs, placed on chiti- 

 nous plates on each 

 side of the sexual 

 opening, and these are 

 differently arranged 

 in the sexes. In the 

 male the plates sur- 

 round the sexual 

 opening, and have the 

 cells on them after 

 the fashion of some 

 Limnesia ; in the fe- 

 male the plates have 

 the cells arranged 

 on them in a sort 

 of triangle and are 

 situated at the pos- 

 terior part on each side of the sexual opening, as 

 in Fiona. All this is well shown in the figures so 

 kindly drawn for me by Mr. CD. Soar. 



So far as I know, no other species of this genus 

 has yet been described. The following are its 

 diagnostic characters :— (i) The three basal joints 

 of the first pair of legs are 7iot thicker than the 

 others ; (2) the body skin is soft, not chitinous ; 



(3) the fourth pair of legs are provided with claws ; 



(4) the thigh plates are divided into four groups ; 



(5) the genital discs are three in number and placed 

 on chitinous plates ; (6) the palpi are not so long 

 as the body; (7) the first pair of legs have the 

 distal end thickened and provided with large claws. 



Kirton in Lindsey. 



. 3. — Ventral side of female 

 4. — Last joint of first leg. 



