388 BIOLOGY OF THE PROTOZOA 



as to give to the body the effect of a bag or sac. In Condylostoma 

 the peristome is triangular and the peristome is only slightly 

 insimk (Figs 84, p. 160; 171, p. 387). 



Faiiiily 5. Ctenostomidae, Lauterborn.— The genera of this family 

 — Discoviorpha, Sa2)rodinmvi , Pelodiniiim and Epalxis — are pecu- 

 liarly modified forms typical of the sapropelic fauna. The body is 

 laterally compressed and asymmetrical and the cilia are reduced 

 while spines and a peculiar comb-like structure above the mouth 

 distinguish them from all other ciliates. 



Order III. OLIGOTRICHroA, Butschli. 



The organisms included in this Order have greatly reduced cilia 

 or none at all, combinations into membranelles being the sole 

 motile organs. The adoral zone forms a nearly or quite complete 

 ring around the margin of the peristome which is usually at right 

 angles to the long axis of the body. Of the three families included 

 one consists of parasitic forms (Ophryoscolecidse) and two are free- 

 living and usually pelagic (Halteriidse and Tintinnidse) . 



Family 1. Halteriidse, Clap, and Lach.— Small organisms with 

 the characteristic adoral zone of the Order and with no cilia on the 

 peristome which is usually arched. The pellicle is hardened into 

 a test in the genus Lahoea and a zone of protective trichites is 

 present in some species of Stromhidium. Spines, cilia and cirri are 

 generally absent in these two genera but are present in the genus 

 Halteria (for Genera see Key). 



Family 2. Tintinnidse, Clap and Lach. emend.— These are small 

 pelagic forms, usually marine, with frequently highly sculptured 

 tests and spinous processes. Some forms have a few scattered 

 rows of cilia down the body but for the most part cilia are absent. 

 (For genera see Key.) 



Family 3. Ophryoscolecidse, Stein.— Parasitic forms of frequently 

 fantastic shape with a thick periplast and a retractile peristome; 

 cilia are generally absent, the adoral zone is a complete circle and 

 in some forms there is an additional ring of membranelles apart 

 from the peristomial apparatus. The posterior end is often drawn 

 out into spines and processes of peculiar shape and arrangement. 



The genera Entodinvum and Cyclojjosthivm have but one circle 

 of membranelles, the former with posterior spines, the latter with 

 two bundles of latero-posterior appendages. The genera Ophryo- 

 scolex and Diplodinium have two circlets of membranelles, the 

 second circlet forming an incomplete ring posterior to the adoral 

 zone in Opliryoscolex, and a complete ring on the dorsal side in 

 Diplodinium. (For genera see Key.) 



