world of amoeboid organisms


Rotifers inhabiting shells of testate amoebae

De Smet W. H.

Laboratory of Polar Biology, Limnology and Palaeobiology, University of Antwerp

The Phylum Rotifera are a group of microscopic pseudocoelomate metazoans. They have a widespread distribution in water’s and limno-terrestrial habitats of all kinds. Many of them are known to live in close association, whether synoecious, commensal or parasitic, with a large and diverse number of animal taxa, including testate amoebae of which both empty shells and shells of live amoebae have been reported to be inhabited.

The first report on rotifers dwelling in empty tests was by Gosse (1886) who created the rotifer genus Eretmia and described two species, which judging from his description were bdelloid rotifers inhabiting tests of Euglypha acanthophora (Ehrenberg ) var. flexuosa Penard. Empty tests of Nebela, Dffflugia and other genera are known to be inhabited by the bdelloids Habrotrocha annulata (Murf) and Hangusticolfis (Murr). Habrotrocha angusticolfis is a case builder, and secretes its own case even when occupying amoebal tests, whereas Hannulata is unable to secrete a case for itself. Habrotrocha incola Bartos has so far only been reported from empty tests of Centropyxis aerophila Deflandre.

Records on rotifers inhabiting tests of live amoebae are scarce. Habrotrocha angusticollis has been observed in shells of live Difflugia, Nebela and others as well. A single monogonont, Dicranophorus diffluglarum Penard, was described as parasitizing Difflugia acuminata Ehrbg.. Two new, apparently parasitic species of monogononts are reported here. A new family, Asciaporrectidae, and genus, Asciaporrecta, was created to accomodate the new species A. arceflicola sp. nov. and A. diffflugicola sp. nov., and A. hyalina (Wulfert) comb. nov. (Zootaxa, in press). The presumed parasite-host relationship seems quite specific, despite the diverse and numerous co-occurring testate amoebae. This suggests that both rotifers find and select their appropriate host by chemotaxis and/or size and shape of the amoebal test. Some testate amoebae have been recognized as predators of rotifers or as feeding on immobile senescent and dead animals (Gilbert et al 2000, 2003). In the present study Lesquereusia spiralis (Ehrbg ) and Difflugia labiosa were found feeding on Mytilma and on Testudinella and bdelloids respectively. It thus is puzzling why Asciaporrecta spp. nov. and their eggs are not consumed. Are foreign bodies inside the shell not recognized as such by the amoebae, or have rotifers and eggs become unattractive or inedible by some chemical adaptation?

Sexual reproduction in monogonont rotifers is induced by endogenous clues or specific environmental factors, e.g. periodic drying, which results in an encysted diapausing embryo, called resting egg, that can withstand harsh conditions. Depending on the species, several resting eggs can be produced or the resting egg is retained within the female, which dies after its production. lt thus is possible to imagine, that the shell-dwelling behavior of parasitic monogonont rotifers eventually began, with undigested resting eggs remaining inside the shell of testate amoebae behaving as predators or scavengers The evolution of the amoeba shells, and in particular the region of the pseudostome as well as the development of and internal diaphragm, have been explained as adaptive processes related to the availability of water and protection against predators. In some cases it also may be an adaption avoiding penetration into the test by parasitic rotifers.

(Text copied with permission of Prof. Dr. Willem De Smet, from a poster on the International Symposium on Testate Amoebae, Antwerp 2006.)

Recent posts

Rhizaspis armata

R. armata, 68 µm long, excl. spines – Laegieskamp Rhizaspis armata (Lauterborn, 1901) Dumack et al., 2021 Basionym: Pamphagus armatum Lauterborn, 1890 Diagnosis: Theca membranous,

Read More »

Rhizaspis spinosa

The original description with original drawings, Penard, 1890. Rhizaspis spinosa (Penard, 1890) Dumack et al., 2021 Basionym: Trinema spinosum Penard, 1890 Diagnosis: Theca membranous, ovoid

Read More »

Difflugia “pseudoclaviformis”

Difflugia “pseudoclaviformis”, front and side view, 424 µm Difflugia “pseudoclaviformis” Diagnosis: Shell pyriform, compressed, with a more or less pronounced aboral protuberance; shell composed of

Read More »

Difflugia from Lolo Pass

Shells 461-448 µm, stacked image. I found this large en remarkable shells in sediment of a small mountain lake near Lolo Pass, Montana USA. It differs

Read More »

Foraminifer drome

Unknown species, collected from the river Drôme, France, 2021 Unknown species September 2021, I found about ten specimens of an agglutinated foraminifer in a sample

Read More »

Cyclopyxis spec

Cyclopyxis spec., 168 µm Cyclopyxis spec. Diagnosis: Shell circular in ventral and dorsal view, more or less hemispherical in lateral view (height/diameter ≈ 0.5); lateral

Read More »

Difflugia fallax

Difflugia fallax, from Penard, 1902 Difflugia fallax Penard, 1890 Diagnosis: Shell hyaline or yellowish-greenish, black at low magnification, round in cross section, formed of a

Read More »

Zivkovicia compressoidea

Z. compressoidea, a-b after Chardez, 1958; c after Jung, 1942 Zivkovicia compressoidea  (Jung, 1942) new.comb. Basionym: Pontigulasia compressoidea Jung, 1942 Diagnosis: Shell ovoid and compressed,

Read More »

Zivkovicia flexa

Z. flexa, from Cash and Hopkinson, 1909 Zivkovicia flexa  (Cash and Hopkinson, 1909) Ogden, 1983 Basionym: Pontigulasia compressa var. flexa  Cash and Hopkinson, 1909 Diagnosis:

Read More »