ganglion cells below invertebrate sense-organs. Moreover, the body
cavity of the Rotifers is a primitive archicoele; the persistent or
accrescent cleft between epiblast and hypoblast, traversed by
mesenchymal muscular bands. Thus we regard Rotifers as an
independent stem branching off at the outset of the rise from the
Platode type to higher Invertebrata. The Polyzoa (q.v.) which in
many ways recall Rotifers, appear to be equally independent.
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From H. S. Jennings in American Naturalist, vol. xxxv., by permission of Ginn & Co. |
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Fig. 9.—a, Microcodon clavus, showing corona, lateral antennae and jointed foot; b, Rhinops vitrea, corona from below, showing proboscidiform extension containing eyes; c, Philodina megalotrocha; d, head of Rotifer macroceros, postero-ventral view, showing lobes of corona, and antero-dorsal median antenna, telescopic with setae; e, Rotifer (Actinurus) neptunius, showing head with retracted corona, and protruded dorsal proboscis bearing median antenna, and telescopic foot with toes and spurs; f, Asplanchnopus myrmeleo, showing horseshoe-shaped germanium (left), blind saccate stomach (right), apical bladder, foot, &c.; g, Asplanchna ebbesbornii—the coiled tube at left is a kidney; h, i, incudate jaws of Asplanchna brightwellii and girodii chiefly formed of rami, with the rudimentary mallei parallel and external to them; j, Ascomorpha hyalina. |
The following classification of Rotifers is our modification of that of Hudson and Gosse, further altered through considerations put forward by C. Wesenberg-Lund, which, however, we do not consider wholly convincing. He notably regards an oblique disk with uniform ciliation as primitive, a view which we cannot adopt.
Classification:—
(A.) Disk usually with well-marked strong trochus, ciliated groove and more delicate cingulua interrupted by an antero-dorsal median gap, usually more or less bilobed.
(i.) Trophi incudate:
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1. Asplanehnaceae; trochus circular; foot absent or minute; trophi incudate; stomach blind; males frequent, not very dissimilar to females. Asplanchna Gosse (fig. 9, g-i); Asplanchnopus Deguerne (fig. 9, f); Ascomorpha Perty (fig. 9, j). |
(ii.) Trophi malleoramal:
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2. Melicertaceae; females tubicolous, usually attached, or forming spherical floating social aggregates; males free swimming. Melicerta Schranck (fig. 3, e, f); Oecistes Ehrenberg; Lacinularia Schweigger; Conochilus Ehrenberg, with gap postero-ventral and mouth antero-dorsal (fig. 2, 5). 3. Trochosphaeraceae; female footless; sub spherical, the corona bulging into a hemisphere which may equal the hemispherical body; anus apical; male as in Melicertaceae, Trochosphaere Semper (fig. 8, D). 4. Ploimoidaceae; subconical; corona bilobed; retractile foot absent or ciliated; motile appendages present in two families. |
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(a) Pterodinidea; foot a ciliated cup; cuticle forming flat lorica. Pterodina Ehr. (fig. 7, d). (b) Triarthridae; body with a pair of long cervical spines pointing distally and serving for leaping movements or to extend the body and make it too big for small enemies to swallow; Pedetes Gosse (no median spines); Triarthra Ehr., one postero-ventral spine; Tetramastix Zacharias, two unequal median spines. (c) Pedalionidae, foot represented by two styles, sometimes ciliated; body provided with six hollow-jointed muscular fins for swimming and leaping. Pedalion Hudson (fig. 5). |
(iii.) Trophi ramate:
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5. Bdelloidaceae; foot with two toes and accessory spurs or a simple perforated disk; body telescopic at either end, with an antero-dorsal proboscis ending in a ciliate cup and bearing the proximal antenna; corona usually bilobed, very wheel-like. Males if present probably like the females. Germary and ovary paired; oviduct absent; young viviparous. Rotifer Schrank (fig. 9, d, e); Philodina Ehr. (fig. 9, c); Callidina Ehr. (eyeless); Adineta Hudson is eyeless with the corona uniformly ciliated, and proboscis adnate, hooked. |
(iv.) Trophi uncinate:
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Flosculariaceae; disk a contractile cup, often lobed, the cingulum of long vibratile cilia, of very long motionless bristles or absent, rarely with an outer zone of fine cilia. Trochus a pair of ridges or horseshoe open in front. Oral funnel roduced into a fine tube hanging freely into a pharyngeal cup, containing the uncinate trophi. Body-wall usually traversed by a network of canals serving by their contraction to expand the disk. Males and larvae with a ciliated pedal cup and a simple ciliated disk. |
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(a) Floscularidae; tubicolous, with a lobed disk, bearing stiff or vibratile setae. Floscularia Oken (fig. 3, b); Stephanoceros Ehr. (fig. 3, a). (b) Acyclidae. Disk entire or tentaculate, not setiferous; Acyclus Leidz (fig. 3, c). Foot represented by a button-like disk, carried far from the posterior surface; Apsilus Metchnikoff (fig. 3, d); Atrochus Wierzezski (fig. 3, c). |
(B.) Ploimaeae; disk variable, often circular, sometimes with a lobed trochus bearing membranelles (vibratile styles); trophi complete, malleate, submalleate, virgate, or forcipate; anus subapical; foot usually short, and usually bearing two toes which may be much elongated.
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Illoricata, cuticle soft; ciliated exsertile auricles above the disk sometimes present. Albertia Dujardin; Drilophagus Vejdovsky; Microcodon Ehr. (fig. 9, a); Rhinops Hudson (fig. 9, b); Synchaeta Ehr. (fig. 7, c); Hydatina Ehr. has no eye; Notommata Ehr. (restricted by Gosse); Copens Gosse; Notops Hudson (fig. 6, 3); Proales Gosse; Gastroschiza; Diglena Ehr. (fig. 6, 4). Loricata, cuticle hardened armour-like, often sculptured; Polyarthra Ehr.; Pedetes Gosse; Euchlanis Ehr. (fig. 6, 1); Anuraea, Ehr. (fig. 7, b); Notholca Gosse (fig. 7, a); Distylis Eckstein (fig. 7, e); Rattulus Ehr. (fig. 7, f); Colurus Ehr. (fig. 6, 2); Taphrocampa Gosse. |
(C.) Seisonaceae. Body elongated with a narrow neck above the disk; foot ending in a terminal perforated disk. Trophi virgate exsertile; germary paired; genito-urinary cloaca opening above the neck in the male, subapically in the female. Gut blind (Paraseison), or opening into cloaca (Seison). Males resembling females, common. All known species are parasitic on the Crustacean Nebalia; Seison Claus; Paraseison Plate.
Habitat and Habits.—The Rotifera are all aquatic, the majority dwelling in fresh water with Protozoa and Protophyta, as well as Entomostracous Crustacea. This association with Protophyta accounts for their study by many distinguished botanists, such as W. C. Williamson and F. Cohn. Some are moss-dwellers, inhabiting the surface film of water that bathes these plants: such especially are the Bdelloids, with their exceptional capacity for resisting desiccation. Others—the majority—live among weeds, the tubicolous ones mostly upon them. A few are sapropelic, haunting the looser debris that forms the uppermost layer of the bottom ooze of quiet waters: we may cite the aberrant Floscularian Atrochus. Widely different are the habits of the plankton forms, which float or swim near the surface, and are often provided with long
