MARINE PROTOZOA FROM WOODS HOLE. 
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Genus TRACHELOCERCA (Ehr. ’83) Cohn ’66. 
(Quennerstedt ’67; Gruber ’87; Entz ’84; Kent ’81; Gourret & Roeser ’88; Biitschli ’88; Schewiakoff ’89; Shevyakov ’96.) 
Tlie only well-known representative is very elongate, large (up to 3 mm. Van Beneden) , and very 
contractile. The main feature of importance in distinguishing it is the 4- part structure of the mouth 
region, which, however, may not be obvious. Pharynx faint and smooth. Contractile vacuole 
terminal. Macronucleus in one central body or in numerous pieces scattered throughout the cell. 
Salt water. 
Tracheloeerca phoenicopterus Cohn ’66. Fig. 30. 
Synonyms: T. sagitta Ehr. ’40, Stein ’59; T. tenuicottis Quennerstedt ’67, Kent ’81; T. minor Gruber ’87, Shevyakov ’96. 
The body is extremely elongate and ribbon-like, and this, combined with its wonderful power of 
extension and retraction, makes it one of the most curious and interesting of microscopic forms. The 
anterior end is square or cylindrical; the type species has a four-sided mouth, but many specimens 
may be found which have a plain cylindrical mouth region. One reason for this may be the fact 
that the extremity gets broken off. In one instance I noticed a very large form with the anterior end 
under some debris, which evidently held it tight, for the body of the ciliate was thrashing back and 
forth and twisting itself into knots, etc., like a nematode worm. Finally, the anterior end broke off 
with about one-tenth of the body; the remainder, in an hour, had regenerated a new anterior end 
with long cilia, but with no indication of four sides. The small anterior piece was also very lively, 
moving about and eating like the normal animal; its history, however, was not followed. This species 
appears to be variable in other ways as well; thus, in some cases the posterior end is rounded (cf. 
Entz ’84); in others it is pointed (cf. Kent ’81, Cohn ’66, et al.) . 
Again, the macronucleus may be a single round body (Entz ’84, Biitschli ’88) or in two parts 
(Kent ’81), or in many parts scattered about the body (Gruber). In the Woods Hole forms the tail 
is distinctly pointed and turned back sharply, forming an angle at the extremity. The cilia on this 
angular part are distinctly longer than the rest. The function of this posterior part is apparently to 
anchor the animal while it darts here and there upon the tail as a pivot, contracting and expanding 
the while. The body is finely striated with longitudinal markings; when contracted there are no 
transverse markings nor annulations. The nucleus is in the form of many fragments scattered 
throughout. Length of large specimen 1.7 mm. 
Genus MESODINIUM Stein ’62. 
(Maupas ’82, ’84; Entz ’84; Shevyakov ’96.) 
The main part of the body is globular or conical, with a short, platform-like oral region, and a 
deep annular groove about the middle of the body. The (esophagus is rather long, and smooth or 
longitudinally striped. One or more rings of cirri rise in the groove. If more than one ring of cirri 
are present, the anterior set usually point forward and lie close to the anterior part of the body. The 
posterior set, on the other hand, cling close to the posterior region of the body and give to it a peculiar 
encapsuled appearance. The most characteristic feature is the presence of four short tentacle-like 
processes which can be protracted and retracted from the oral region. (Mereschowsky says that 
the entire anterior half is more or less contractile. ) The macronucleus is horseshoe-shaped or ovoid 
and is situated in the posterior half of the body. The contractile vacuole is also posterior. 
