Microlife: Rotifers

Kingdom Animalia, Phylum Gnathifera

Gnathifera occur in water, sediments, and as parasites of other animals. Free-living kinds have characteristic jaws in the throat, and most are less than 1 mm long, using cilia to move or collect food. Rotifers are by far the most common of these, including all but a few kinds from marine sands.

The cilia in rotifers form a corona or crown around the mouth, which ranges from a simple field to complex lobes and bristles. In most the body has a posterior foot, which usually has two or more toes and adhesive glands, used to form temporary or permanent attachments. Some also have sensory antennae and simple eyes.

Reproduction takes place by laying eggs or sometimes live birth. Most individuals are female and parthenogenetic, i.e. have offspring without mating. Normally males are smaller and reduced, and only occur under certain conditions, so are rarely encountered.

Class Bdelloidea

Bdelloids are exclusively female with paired ovaries. They are worm-like and contractile, and variously move by swimming or by alternately stepping with their head and foot. Most have a retractable corona divided into two parts, which look like spinning wheels when active, and two spurs just above the toes.

Stormwater ponds - about 165 µm


Greek a-, without, dinētos, whirled around
Angl. AD-i-NEE-ta

Adineta have an oval head with a neck but no wheels. They move by sliding the head along, collecting food with a rake and cilia underneath, instead of the usual steps.

Spring puddle - about 450 µm


Latin rota, wheel
Angl. roh-TAIR-eea

Rotaria mostly have two eyes on a forward projection, the rostrum, ahead of a dorsal antenna. They are typically long, some kinds extremely so, often with prominent spurs.

Dissotrocha aculeata
Marsh sample - about 60 µm wide


Greek dissos, double, trochos, wheel
Angl. di-SOT-ro-ka

Dissotrocha have long spurs and the body cuticle is stiff, with ventral folds and often dorsal bumps or spines. Eyes are cerebral when present, set behind the antenna.

Philodina megalotrocha
Stormwater ponds - about 110 µm wide


Greek philos, friend, dinos, whirling
Angl. FIL-o-DYE-na

Philodina are more or less pin-shaped with wheels wider than the neck. Most again have cerebral eyes but only smaller spurs and a thin, relatively smooth cuticle.

Class Monogononta

In monogononts females have a single ovary. They come in a great variety of forms, divided into two main groups. Gnesiotrocha usually have a long foot with no toes, though it is occasionally lost, and many live attached or in colonies. Most have a lobed corona and their jaws are adapted for pounding or cutting.

Stormwater ponds - body about 175 µm


Latin testudo, turtle, -ella, dimn.
Angl. tes-TOO-di-NEL-a

Testudinella are flat and nearly circular in outline, except for the head, which has two lobes and can be retracted. There is a small ventral foot with cilia, remaining unattached.

Marsh sample - body about 35 µm wide


Greek ptychē or ptygma, fold, oura, tail
Angl. ti-GYOOR-a

Ptygura have a nearly circular or oval corona without lobes. They usually live in gelatinous cases, in some covered with debris, found most often on aquatic plants and algae.

Duck pond - case about 125 µm wide


Latin flos, flower, -culus, dimn.
Angl. FLOS-kyu-LAIR-eea

Floscularia have a corona with four lobes. Some live in gelatinous tubes but most make them from collected material, rolled into pellets and placed into a regular array.

Duck pond - about 325 µm


Greek limnē, pond
Angl. LIM-neeas

Limnias are sessile with a corona divided into two ciliate lobes. They live inside hardened tubes of secreted material, variously smooth or with sculpted rings.

Duck pond - body about 210 µm


Greek kolla, glue, thēkē, case
Angl. KOL-o-THEE-ka

Collotheca have several knobs or flaps around the mouth, covered in long fine setae which close inward to trap prey. Most are again sessile with clear gelatinous tubes.

Ploima are typically free-swimming rotifers that have either two toes, rarely reduced to one, or sometimes no foot. The jaws are variously adapted for grinding, sucking, or sometimes gripping prey, and in many kinds the cuticle is hardened to form a protective lorica of one or more plates.

Stormwater ponds - about 200 µm


Latin squatina, angel shark, -ella, dimn.
Angl. SKWAT-i-NEL-a

Squatinella are easily recognized by their large head shield, which looks like a halo from above. They have deep bodies with a long foot and often spines.

Chestermere Lake - body about 95 µm


Greek kolouros, truncated
Angl. KOL-yu-REL-a

Colurella are flattened side-to-side with a ventral notch for the foot. The lorica forms a small shield over the head, with a hook that helps them stir up food.

Glenmore Reservoir - about 145 µm


Greek lepas, limpet
Angl. LEP-a-DEL-a

Lepadella also have a ventral notch for the foot, but the lorica is flattened top-to-bottom. The foot itself has 3-4 marked rings, short toes, and serves as a flexible attachment while feeding.

Fish Creek - about 140 µm


Greek taphros, ditch, kampē, caterpillar
Angl. TAF-ro-KAM-pa

Taphrocampa are slender and flexible, with a dorsal eye near the front and short toes at the posterior. The body is divided into marked rings by a series of distinctive grooves.

Notommata tripus
Duck pond - about 120 µm


Greek nōton, back, omma, eye
Angl. noh-TOM-a-ta

Notommata resemble the above but lack the grooves. They are similar to several other genera, but a few species may be recognized by a spine-like tail from between the toes.

Fish Creek - body about 80 µm


Greek monos, one, omma, eye
Angl. mo-NOM-a-ta

Monommata are another kind with one eye and no lorica. The toes are well-developed, with the left normally slightly shorter than the right, but both longer than the body.

Stormwater ponds - body about 160 µm


Greek thrix, hair, kerkos, tail
Angl. TRIK-o-SER-ka

Trichocerca have a cylindrical lorica, often with short spines at the front or ridges. The foot is reduced with mismatched toes, in many kinds with one very long and one very short.

Duck pond - about 460 µm


Greek eus, good, chlanis, fine cloak
Angl. YOO-kla-nis

Euchlanis have their lorica separated into a larger dorsal and flat ventral plate. The former curves over the base of the foot, which has 2-3 weakly marked rings and two toes.

Duck pond - about 220 µm


Greek lekanē, dish
Angl. LEK-a-nee

Lecane have their foot reduced to a flexible base with one or two style-like toes. The lorica is also flattened and separated into dorsal and ventral plates.

Fish Creek - body and foot about 315 µm


Greek thrix, hair, tria, three
Angl. tri-KOH-treea

Trichotria have a thick lorica with ridges on either side. Their foot and toes are long, with a characteristic pair of spines where they meet the body.

Marsh sample - about 370 µm


Greek platys, flat
Angl. pla-TYE-as

Platyias have a flattened lorica with short spines on the front and rear margins. The foot has marked segments and toes, and is attached under the body.

Stormwater ponds - body about 175 µm


Greek brachiōn, arm
Angl. bra-KYE-o-nus

Brachionus have a flexible foot without marked segments. The body is flattened with marginal spines, but unlike Platyias has an eye and sometimes carries external eggs.

Stormwater ponds - about 260 µm


Greek nōton, back, aulax or hōlka, furrow
Angl. no-THOL-ka

Notholca have six short anterior spines and sometimes a pointed tail, but no foot, toes, or carried eggs. The lorica is flattened and typically has lengthwise furrows or a keel.

Keratella with egg
Glenmore Reservoir - body about 150 µm


Greek keras, horn
Angl. KER-a-TEL-a

Keratella also have no foot or toes, but the lorica is divided into several facets rather than striated. They often have attached eggs and some have one or two posterior spines.

Stormwater ponds - body about 155 µm


Greek lophos, crest, charis, grace
Angl. lo-FOK-ar-is

Lophocharis have an oval to rhombus-shaped lorica with a thin raised crest along the back. The foot emerges behind the end, with 3 marked rings and short toes.

Marsh sample - body about 185 µm


Latin mitulus or mytilus, mussel
Angl. MIT-i-LYE-na

Mytilina have a lorica with a dorsal furrow. The front and rear margins often have spines and cover the base of the foot, which is typically short with pointed toes.

Fish Creek - about 390 µm


Greek skaros, leap, -idion, dimn.
Angl. ska-RID-eeum

Scaridium are long rotifers with a thin cylindrical lorica. The foot and toes are each about the same length as the body, and can act as a spring for sudden movement.

Stormwater ponds - about 540 µm


Greek asplagchnos, without innards, pous, foot
Angl. a-SPLANK-no-pus

Asplanchnopus are sack-like rotifers that eat other animals, using their jaws to seize and swallow them whole. The body is hollow and contractile, with a small foot on its underside.

Dirt puddle - body about 90 µm


Greek polys, much or many, arthron, joint
Angl. POL-ee-AR-thra

Polyarthra are set apart by blade-shaped appendages in four groups around the front, used in a rapid jumping motion. There is no foot but some carry attached eggs.

Stormwater ponds - about 175 µm


Greek syn, together, chaitē, long hair
Angl. sing-KEE-ta

Synchaeta have a more or less conical body ending in a short foot and toes. The head has a ciliated projection on either side, with four spines and one eye between them.