The Gymnostomaceae are predaceous, feeding for the most part on smaller Ciliates. We have described the peculiar character of the mouth and pharynx in this group, and the mail-like pellicle of Coleps (Fig. 54). Loxophyllum is remarkable for the absence of cilia from one of the sides of its flattened body, and the tufts of trichocysts studding its dorsal edge at regular intervals. Actinobolus has numerous tentacles, exsertile and retractile, each bearing a terminal tuft of trichocysts, which serve to paralyse such active prey as Halteria. Ileonema has one tentacle overhanging the mouth; and Mesodinium has four short sucker-like projections around it.[[170]] It has only two girdles of cilia, which are stout and resemble fine-pointed cirrhi. In Dysteria the cilia are exclusively ventral, and the naked dorsal surface has its pellicle condensed into a bivalve shell; a posterior motile process ("foot") and a complex pharyngeal armature add to the exceptional characters of the genus.
The Aspirotrichaceae are well known to every student of "Elementary Biology" by the "type" Paramecium (Fig. 55), so common in infusions, especially when containing a little animal matter. P. bursaria often contains in its endosarc the green symbiotic Flagellate Zoochlorella. Colpoda cucullus, very frequent in vegetable infusions, usually only divides during encystment, and forms a brood of four. Pleuronema chrysalis (Fig. 57) is remarkable for its habit of lying for long periods on its side and for its immense undulating membrane, forming a lip on the left of its mouth; Glaucoma has two, right and left.
Fig. 56.—Trachelius ovum. A, general view; B, section through sucker; C, section through contractile vacuole and its pore of discharge. al, Alveolar layer of ectoplasm; cil, cilia; c.v, contractile vacuole; m, mouth; N, meganucleus; s, sucker, from which pass inwards retractile myonemes. (After Clara Hamburger.)
Fig. 57.—Pleuronema chrysalis (Aspirotrichaceae). A, Unstimulated, lying quiet; B, stimulated, in the act of springing by the stroke of its cilia. (From Verworn.)
The Heterotrichaceae present very remarkable forms. Spirostomum is nearly cylindrical, and, a very giant, may attain a length of 4 mm. (1⁄6"). Stentor can attach itself by its hinder end, which is then finely tapered and prolonged into a few pseudopodia; its body is trumpet-shaped, with a spiral peristome forming a coil round its wide end, and leading on the left side into the mouth. Many species when attached secrete a gelatinous sheath or tube. S. polymorphus is often coloured green by Zoochlorella (p. [125]); S. coeruleus[[171]] and S. igneus owe their names to the brilliant pigment, blue or scarlet, deposited in granules in lines between the conspicuous longitudinal myonemes. From their large size and elongated meganucleus accompanied by numerous micronuclei, these two genera have frequently been utilised for experiments on regeneration. In Metopus sigmoides the peristomial area forms a dome above its wreath of membranellae; and in M. pyriformis this is so great as to form the larger part of the cell, which is top-shaped, tapering behind to a point. Caenomorpha (Fig. 58) has the same general form, with a peg-like tail, and possesses a girdle of cirrhi.[[172]] The converse occurs in Bursaria; the cell is a half ellipse, something like a common twin tobacco-pouch when closed: a deep depression thus occupies the whole ventral surface, and opens by a wide slit extending along the anterior end. The peristomial area occupies the dorsal side of the pocket so formed, and the mouth is in the hinder left-hand corner. Blepharisma sp. is parasitic in the Heliozoon Raphidiophrys viridis (Fig. 20, 1, p. [74]).
Fig. 58.—Caenomorpha uniserialis. crh, Zone of cirrhi; c.t, cilia of tail; c.v, contractile vacuole; c.w, ciliary wreath; g, granular aggregate; m, zone of membranellae; N, meganucleus; n, micronucleus; oe, pharynx; t, tail-spine; t1, accessory spine; u.m, undulating membrane; v, vacuole; z, precaudal process. (After Levander.)
Among Oligotrichaceae, Halteria, common among the débris at the bottom of pools in woods containing dead leaves, is remarkable for an equatorial girdle of very long fine setae, and for its rapid erratic darting movements, alternating with a graceful bird-like hover. The Tintinnidae are mostly marine, pelagic, with the general look of a stalkless Vorticella; some have a latticed chitinous shell.[[173]]