ECOLOGY, COMMENSALISM AND PARASITISM 399 



The other representatives of the group Astomina are characteristic 

 parasites of invertebrates, particularly of the annelids, where they 

 may be found in the digestive tract, the coelom, or in the tissues 

 of diverse organs. Cepede (1910) has given the best monograph 

 on the group but his classification based on habitat has been much 

 improved by Cheissin (1930; see Key, p. 489). Adaptations for 

 attachment have been developed in the form of hook-like chitinous 

 organs which are deeply anchored in the body (Fig. 202, p. 492) 

 and of suckers with or without hooks (Steinella; Sieboldiellina from 

 Turbellaria). Chitinous skeletal bars are also widely distributed in 

 the group. 



Astomida are also found as parasites in medusae (Kofoidella, 

 Cepede), in copepods (Perezella, Cepede), in amphipods and isopods 

 (Collinia, Cepede) and in the gonads of starfish (Orchitophrya, 

 Cepede). 



Mouth-bearing forms of endoparasitic ciliates show great modi- 

 fications and specializations in structure. Taxonomically they are 

 distributed amongst Ilolotrichida and Spirotrichida, the latter 

 including Heterotricha, Oligotrichia (with Entodiniomorpha, Reich- 

 enow). (See Key, p. 508.) 



The Holotrichida are subdivided into Gymnostomina, Hyposto- 

 mina, Trichostomina and Hymenostomina, all of which have para- 

 sitic genera and some groups in which parasites have not been 

 recorded. Among the Gymnostomida are the ectocommensal 

 Ichthyophthirius multifilius and the enterozoic forms Butschlia, 

 Schuberg (in ruminants) ; Bundleia, da Cunha and Muniz; Blepharo- 

 codon, Bundle, Blepharoconus, Gassovsky, Didesmis, Fiorentini, 

 and Blepharoprosthium, Bundle (all from the horse); Buissonella, 

 da Cunha and Muniz (from the tapir); and Protohallia, da Cunha 

 and Muniz (from the capybara). 



Among the hypostomes we have some destructive ectocommen- 

 sals: Chilodon ci/prini, MorofY, for example, causes severe epidemics 

 amongst carp and goldfish. Less destructive, but biologically most 

 interesting, are the ectoparasites known as Foettingeriidae, where 

 the complicated life histories have been carefully followed by 

 Chatton and Lwoff. They appear to be primarily ectoparasites of 

 crabs, where they appear in the encysted condition on the gills. 

 When the exoskeleton of the crab is shed the ciliates leave their 

 cysts and grow apparently on the secretions of the skin. Ulti- 

 mately the fully-developed forms leave the old host and divide, 

 Polyspira in free-swimming condition, Gymnodinioides while en- 

 cysted. 



Foettingeria actiniamm, Clap, lives in the gastral cavity of an 

 actinian; here it divides while encysted and the young forms after 

 emerging from the cyst cannot begin life again in the actinian 

 but become attached to Crustacea of different kinds where they 



