ECTOPARASITIC PROTOZOA 



23 



it. It creeps about over the surface of its host very much as does 

 TricJwdina, apparently causing no injury. 



Description: Diameter 60^; shaped somewhat Hke a crown; lives on 

 fresh-water sponges apparently as a commensal. 



W'allengren (1897) describes another species, C. domergiici 

 from the surface of fresh-water fish. When present in great num- 

 bers this form may cause 

 the death of very young 

 hosts. 



(b) TricJwdina pcdiculns 

 Ehrbg. 



This is perhaps the most 

 commonly encountered ec- 

 toparasitic protozoon. It 

 was first fully described 

 and named by Ehrenberg 

 (1830). He reported it 

 from the outer surface 

 of Hydra, though it has 

 since been reported from 

 sponges, fresh-water med- 

 usoids, planarians, newts, 

 tadpoles, and fish, and also 

 as leading a free-living ex- 

 istence. It is more fre- 

 quently found on fresh- 

 water animals, but has 

 also been reported from 

 marine forms. Rosseter 

 (1886) reported a species, 



m-»' 



Al-^-v 



vc 



cct- 



-urn- 





i 



:":^^r 





Fig. 7. — Kerona pedicidiis. Dorsal view 

 showing {ac) anal cirri, (^3^0 cytostome, 

 {ect) ectoplasm, {end) endoplasm, (w) 

 micronuclei, (M) macronucleus, {mc) 

 marginal cirri, {vd) membranelles, {nem) 

 ingested nematocyst, {vc) ventral cirri, 

 {nm) undulating membrane. X about 650. 

 (From Hegner and Taliaferro, after Uhle- 

 meyer.) 



which he considered sim- 

 ilar to, but apparently not identical with T. pcdicidus, from the 

 kidneys, testes and urinary ducts of male specimens of Triton 

 cristahis. Arnold and Boulenger (191 5) found specimens which 

 show^ed no signs of being digested inside the circular canals of 

 fresh-water medusoids. 



This ciliate is frequently found in company with Kerona pedic- 

 idiis and has been observed to mount upon the back of the 



