ON A NEW SPECIES OF MITE OF THE 



FAMILY HALARACHNIDAE FROM THE 



SOUTHERN SEA LION 



By Susan Finnegan, b.Sc, Ph.d. 



Department of Zoology, British Museum (Natural History) 

 (Text-figs. I -1 2) 



A NUMBER of mites of the genus Halarachne were collected by Mr J. E. Hamilton 

 from the posterior nares of the sea Hon, Otaria byronia, at Cape Dolphin, Falkland 

 Islands, while working for the Discovery Committee in 1931. 



The genus Halarachne has a wide geographical distribution, being recorded from 

 the Arctic, the Irish Sea, the North Atlantic, the Californian Coast and the Antarctic. 

 The recorded hosts are seals, sea lions and walrus. 



There are seven known species, three of which were carefully redescribed by Dr 

 A. C. Oudemans in his monograph of the genus (1926). Descriptions of two species 

 not mentioned in the monograph may be found in papers by Steding (1923) and 

 Ferris (1925). 



The Falkland Islands specimens, although bearing a close resemblance to Halarachne 

 rosmari, Oudemans, represent a new species. 



Halarachne magellanica, sp.n. 



Diagnosis. Lateral plates extend from legs I to III. Anal plate pear-shaped. 

 Genital plate oval. Female chelicera with well-developed digitus fixus. Male chelicera 

 with rudimentary sperm-carrier. 



Description. Female (Fig. i). Body long and attenuated. Podosoma with slightly 

 undulating outline, rather pointed anteriorly, convexities over legs II and III. 

 Opisthosoma of mature 9 usually enlarged in anterior third to about the same width 

 as podosoma at broadest, narrowed in posterior two-thirds into cylindrical form and 

 broadened slightly at tip. 



Colour of specimens in formalin a dirty brownish white ; chitinized portions — legs, 

 shield and tracheae — dark yellowish brown to red-brown. 



Dorsal shield (Fig. 2) one and two-third times as long as broad, very much narrower 

 anteriorly than posteriorly, greatest breadth over legs III. Markings very much as in 

 H. rosmari, with six pairs of hairs on shield and one large pair just external to it 

 anteriorly. Lateral shields extending from legs I to III, and, as in the case of all other 

 plates on the body, margins weakly defined. Anal plate (Fig. 3) pear-shaped, situated 

 with apex dorsally and anal aperture posteriorly. Peritrematal plate scarcely visible 

 from dorsal view. 



