The Craspedomonadidae (often called Choanoflagellates, Fig. 40) are a group whose true nature was elucidated some forty years ago by the American zoologist, H. James-Clark. They are attached either to a substratum, by a stalk produced by the base of the cell, or to other members of the same colony; they are distinguished by the protrusion of the cytoplasm around the base of the single flagellum into a pellucid funnel,[[135]] in which the plasma is in constant motion, though the funnel retains its shape and size, except when, as sometimes happens, it is retracted.
Fig. 40.—Various forms of Craspedomonadidae. 2, a, Adult cell; 2, b, longitudinal fission; 2, c, the production of flagellulae by brood-formation; c, collar; c.vac, contractile vacuole; fl, flagellum; l, theca; nu, nucleus; s, stalk. (After Saville Kent.)
The agitation of the flagellum determines a stream of water upwards along the outer walls of the funnel; and the food-particles brought along adhere to the outside of the funnel, and are carried by its streaming movement to the basal constriction, where they are swallowed by the plasma, which appears to form a swallowing vacuole at that point. Longitudinal fission is the ordinary mode of reproduction, extending up through the funnel. If the two so formed continue to produce a stalk, the result is the formation of a tree-like stem, whose twigs bear at the ends the funnelled cells, or "collar-cells" as they are usually called. In Salpingoeca, as in so many other Flagellates, each cell forms a cup or theca, often of most graceful vase-like outline, the rim being elegantly turned back. Proterospongia (Fig. 75, p. [182]) secretes a gelatinous investment for the colony, which is attached to solid bodies. In this species, according to Saville Kent, the central members of the colony retract their collar, lose their flagellum, become amoeboid, and finally undergo brood-formation to produce minute zoospores. This is the form which by its differentiation recalls the Sponges, and has been regarded as a transition towards them; for the flagellate, nutritive cells of the Sponges are provided with a collar, which exists in no other group of Metazoa (see pp. [171], [181], and Fig. 70, p. [176]). The most recent monographer of the family is Raoul Francé, but James-Clark and Saville Kent did the pioneering work.
Fig. 41.—Opalina ranarum. A, living specimen; B, stained specimen showing nuclei; C, stages in nuclear division; D-F, stages in fission; G, final product of fission; H, encysted form; I, young form liberated from cyst; K, the same after multiplication of the nucleus has begun. nu, Nucleus. (From Parker's Biology, after Saville Kent and Zeller.)
Of the life-history of the Trichonymphidae,[[136]] all of which are parasitic in the alimentary canal of Insects, especially Termites or White Ants (Vol. V. p. 356), nothing is known. Some of them have a complete investment of motile flagella, like enormously long cilia, which in Dinenympha appear to coalesce into four longitudinal undulating membranes. Lophomonas inhabits the gut of the Cockroach and Mole-cricket. The Opalinidae have also a complete investment of cilia, which are short, and give the aspect of a Ciliate to the animal, which is common in the rectum of Amphibia, and dies when transferred to water. But despite the outward resemblance, the nuclei, of which there may be as many as 200, are all similar, and consequently this group cannot be placed among the Infusoria at all. Opalina has no mouth nor contractile vacuole. It multiplies by dividing irregularly and at intervals, resolving finally into 1-nucleate fragments, which encyst and pass into the water. When swallowed the cyst dissolves, its contents enlarge, and ultimately assume the adult form.[[137]]
Maupasia has a partial investment of cilia, a single long flagellum and mouth, a contractile vesicle, and a single simple nucleus. It seems to find an appropriate place near the two above groups, though it is free, and possesses a mouth.
Fig. 42.—Longitudinal Fission of Eutreptia viridis (Euglenaceae), showing chloroplasts, nucleus, and flagella arising from pharynx-tube. (After Steuer.)