ASTACOCIWTON, A NEW TYPE OF ACARID. 



By W. A. Haswell, M.A., D.Sc, F.R.S., Emeritus Professor oi' Biology, 

 University of Sydney. 



(Plates xxxvi.-xxxvii.) 



[Read 30th August, 1922.] 



Contexts. 



1. Introductory: mode of occurrence; methods, etc 329 



2. Diagnosis 330 



3. General features (female) 330 



4. Capitulum : appendages 331 



5. Coxal or integumentary glands 333 



6. Digestive system 33.^ 



7. Salivary and supposed anti-coagulin glands . . 335 



8. Integument; the so-called fat-body 337 



9. Excretory organ 337 



10. Reproductive system 338 



11. Male ' 340 



12. Conclusion . . . . 340 



1. Introductory ; mode of occurrence, methods, etc. 



The Acarid dealt with in this paper occurs, sometimes abundantly, in the 

 branchial chambers of the common spiny Crayfish {Astacopsis serratus) of the 

 rivers of Eastern Australia. I have found it most numerous in the bright crim- 

 son variety that frequents the larger tributaries of the Grose and Cox in the 

 Blue Mountains; bitt it occurs also, though more rarely, in the Crayfishes of small 

 streams not connected with the Hawkesbury River system.* 



'I'he adult females, which are devoid of eyes, are firmly attached to the gill- 

 filaments of their hosts by means of the chelicerae and pedipalpi, and can only 

 be detached by the use of a certain amount of force. The males, which ai-e 

 comparatively small, and which are provided with a pair of eyes, are not at- 

 tached, but swim very actively. Proba.bly they are intermittently parasitic, 

 though I have no actual direct evidence of this. The same holds good of the 

 young females. Though soft and thin-skinned, Astacocroton is by no means 

 easily acted on by fixing agents. In cold sublimate-acetic or alcohol it remains 



'Astacocroton does not occur on the common bicarinate Crayfish or "Mirami" 

 (Parachaeraps bicarinaius) ; and a number of specimens of the Western Australian 

 Chaeraps teniiimanus , C. quinquecarinaius and C preissii examined by me with the 

 assistance of Mr. F. A. McNeill, Zoologist in charge of Lower Invertebrates at the 

 Australian Museum, proved also to be free from the parasite. 



