102 



SCIENCE-GOSSIP. 



BRITISH FRESHWATER MITES. 



By Charles D. Soar, F.R.M.S. 



{Continued from page So.) 



GENUS HYGROBATES KOCH, 1835-41. 



HP HIS genus according to Piersig contains five 

 ■*- species. A much larger number had at different 

 times previously been named, but Piersig proved 

 them to be the same mites under different names, 

 and therefore reduced the number to five. In 

 Britain at present there appears to be only three 

 species. I have had a very large number through 

 my hands from different localities, both my own 

 collecting and from friends ; but can find only 

 two species. There are numbers of variations. 

 No two seem to be exactly alike. They vary a 

 great deal in proportions, no doubt due to the 

 chitinous parts of the mites being nearly fully de- 

 veloped at the time they leave the inert stage pre- 

 ceeding the imago, the soft parts only being left to 

 grow. This growing gradually alters the arrange- 

 ment and position of the epimera and genital 

 plates by pushing the chitinous parts further apart, 

 and thus altering the appearance of the ventral sur- 

 face. I mention this fact because it gave me much 

 trouble, as I had to make a number of drawings, 

 before I could be satisfied the specimens were all 

 the same species. I do not think there is any 

 doubt about it, and hope these remarks will 

 save others working at this genus, some of 

 the labour I have expended to arrive at this con- 

 clusion. 



Fig. 1. — //. hngipalpis, female. 



The mites belonging to the genus Hygrohates 

 are characterised by having the body soft skinned. 

 Legs sparingly supplied with hairs. Claws to all 

 feet. Eyes wide apart. Epimera arranged in 

 three groups. Three comparatively large discs let 

 into each genital plate. 



1. Hygrobates longipalpis Hermann, r8o4. 



Female. — Body: (Fig. 1.) Oval in form, some- 

 times slightly flattened on the anterior margin. 

 Length about 2.0 mm. Width about 1.60 mm. 

 Colour yellow with dark brown markings on dorsal 

 and ventral surface. Over, and in, these brown 

 markings run a quantity of coloured streaks, or 

 veins, of a very light yellow or sometimes white 

 tint. If a tube containing several of these mites is 

 held up to the sunlight they are seen to be of a 

 very brilliant colour. Eyes, pink. 



Legs. — First pair about 1.23 mm., fourth pair 

 about 1.72 mm. They have a number of bristles, 

 or stiff hairs, on each leg (fig. r), but are quite 

 without the long swimming hairs at the joints, we 

 noticed in Curvipts and Limnesia. Nevertheless 

 they are quick and strong swimmers, as it is neces- 

 sary they should be, for I have sometimes taken 

 them in very rapid streams. In colour the legs 

 are a pale blue. 



Fig. 2. — H. longipalpis, epimera. 



Epimera. — Forms three groups. The centre 

 group is formed by the first two pairs being jointed 

 on to the plate which holds the mouth organs as 

 seen in fig. 2. In colour they are pale blue, as are 

 all the chitinous parts of this mite. I say all the 

 chitinous parts, but it is well to note I have taken 

 some specimens with the legs and epimera quite 

 colourless, and others with these parts a pale 

 yellow, though pale blue seems to be the predomi- 

 nant colour. 



Fig. 3. — H. longipalpis, palpus. 

 Palpi. — (Fig. 3.) Is about 0.72 mm. in length 

 This varies in different specimens, but I find the size 

 given is most usual. There are two short bristles, 

 close together, about the centre, on the bow side 

 of the penultimate segment of the palpi, which 

 differentiate this from the next species. 



