Fresh and salt water; more common in the latter.

Strombidium caudatum Fromentel '74. Fig. 46, a, b, c.

Fromentel described a fresh-water form of this genus with a caudal appendage. The body is pyriform, broadly truncate on the anterior end, in the middle of which rises a papilliform process (Schnabel). On this process is a heap of pigment granules, which, however, are not constant. A ring of long cirri surround the anterior end and pass into the peristome, and from the left edge of this line of cirri a large adoral zone continues down to the mouth. The peristome is elongate and sac-form, and the mouth lies at the posterior extremity. With the exception of a caudal filament there are no other motile organs; this is about half as long as the body, structureless, hyaline, and sharply pointed. It splits up into a bundle of fine fibers upon treatment with caustic potash (c). The cirri emerge from minute hollows in the edge of the anterior border. The cortical plasm contains peculiar rod-like bodies, which look more like lines or markings than like rods or trichocysts. The nucleus is large, spherical, and placed in the center of the body. The contractile vacuole is posterior.

Length without appendage is about 35µ; greatest diameter 15 to 18µ. In decaying vegetable matter. Common.


Fig. 46.—Strombidium caudatum.
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Although Fromentel's species is incompletely described, it is very evident that the organism corresponds fairly well with the Woods Hole variety. His was a fresh-water type; this is marine, but the caudal filament and the contractile vacuole are similar. Certainly in this case the organism can not be regarded as a Vorticella broken off its stalk, as Kent '81 suspected. The anterior process with its pigment spot; the cirri, the spherical nucleus, the position of the vacuole, etc., are all opposed to such an interpretation which Kent applied to the original species. Neither can it be a Tintinnoid. I place it provisionally as S. caudatum.

Key to the marine genera of Tintinnidæ.
Diagnostic characters: Body attached by a stalk to a cup. Inside the zone of membranelles is a ring of cilia (par-oral).
1. The test is gelatinous and more or less covered by foreign particles Genus Tintinnidium
2. The test is chitinous and clear. No foreign particles. Genus Tintinnus
3. The test is chitinous; covered by foreign particles, growth rings frequent Genus *[Tintinnopsis]
4. The test is chitinous, often covered by foreign particles. The test is marked by discoid, circular, or hexagonal spots. Genus Codonella
5. The test is perforated by pores of circular or hexagonal form. Genus Dictyocysta
* Presence at Woods Hole indicated by asterisk.