Microlife: Rotifers

Kingdom Animalia, Phylum Gnathifera

Gnathifera occur in water, sediments, and as parasites of vertebrates. Free-living kinds are mostly less than 1 mm long, using cilia to move or collect food, and have characteristic jaws in the the throat. Rotifers are by far the most common, 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. Most have a retractable corona divided into two parts, which look like spinning wheels when active. They are worm-like and contractile, and variously move by stepping with their head and foot or by swimming.

Rotaria
Puddle sample - about 450 µm

Rotaria

Latin rota, wheel
Angl. roh-TAIR-eea

Rotaria have a forward projection with two eyes, called the rostrum, and a dorsal antenna without them. They are usually long, with two prominent spurs above the toes.

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.

Testudinella
Stormwater ponds - body about 175 µm

Testudinella

Latin testudo, turtle, -ella, dimn.
Angl. te-STOO-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.

Floscularia
Duck pond - case about 125 µm wide

Floscularia

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

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

Limnias
Duck pond - about 325 µm

Limnias

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.

Collotheca
Duck pond - body about 210 µm

Collotheca

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 kinds are sessile and form 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.

Squatinella
Stormwater ponds - about 200 µm

Squatinella

Latin squatinus, 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.

Colurella
Chestermere Lake - body about 95 µm

Colurella

Greek kolouros, truncated
Angl. KOL-yur-EL-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.

Lepadella
Glenmore Reservoir - about 145 µm

Lepadella

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.

Taphrocampa
Fish Creek - about 140 µm

Taphrocampa

Greek taphros, trench, 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
Duck pond - about 120 µm

Notommata

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

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

Monommata
Fish Creek - body about 80 µm

Monommata

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.

Trichocerca
Stormwater ponds - body about 160 µm

Trichocerca

Greek thrix, hair, kerkos, tail
Angl. tri-KOS-er-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.

Euchlanis
Duck pond - about 460 µm

Euchlanis

Greek eus, good, chlanis, mantle
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.

Lecane
Duck pond - about 220 µm

Lecane

Greek lekanē, pan
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.

Trichotria
Fish Creek - body and foot about 315 µm

Trichotria

Greek thrix, hair, tria, three
Angl. tri-KOT-reea

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.

Platyias
Marsh sample - about 370 µm

Platyias

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.

Brachionus
Stormwater ponds - body about 175 µm

Brachionus

Greek brachiōn, arm
Angl. BRAK-ee-OH-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.

Notholca
Stormwater ponds - about 260 µm

Notholca

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

Keratella

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.

Lophocharis
Stormwater ponds - body about 155 µm

Lophocharis

Greek lophos, crest, charis, favour
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.

Mytilina
Stormwater ponds - body about 175 µm

Mytilina

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.

Scaridium
Fish Creek - about 390 µm

Scaridium

Greek skaros, leaping, -idion, dimn.
Angl. skar-ID-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.

Asplanchnopus
Stormwater ponds - about 540 µm

Asplanchnopus

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.

Polyarthra
Puddle sample - body about 90 µm

Polyarthra

Greek polys, 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.

Synchaeta
Stormwater ponds - about 175 µm

Synchaeta

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.