|FREAKS OF NATURE|
|This page is dedicated to organisms with an extraordinary appearance or "life-style"|
|GASTROTRICHA||TARDIGRADA||SPECIES OF THE MESOPSAMMON||APPENDICULARIA|
About 350 species.
These mostly benthic inhabitants of limnic or marine systems (mesopsammon) exhibit hermaphroditic or parthenogenetic propagation. They have a size of 70-500 µm, maximal 1500 µm with spine-like, caudal extensions. Noteworthy is their constant cell number (like rotifers, nematods, tardigrads). The skin is partially syncytial with a thin cuticula; the latter can be organized in scales with thornes, spines, plates or bars. Despite this cuticular organization of the skin, the body remains flexible. The animals exhibit furthermore clinging tubules. The flattened, ventral cuticle is covered with bands of cilia > name, which can be used to glide, crawl or walk. The anterior long cilia serve to swim over short distances. Gastrotrichs usually live isolated. Therefore, finding these organisms may be a diffucult task
TAXONOMY: mainly based on number and localization of clinging tubules:
1. Ordo: Macrodasyida - numerous anterior, lateral and posterior clinging tubules. marine. hermaphroditic.
2. Ordo: Chaetonotida - only two to four caudal clinging tubules. mostly only female sex. mainly limnic, partially marine.
Tardigrads are found in droplets and water films on and in mosses and lichens on old roofs, on leaves, sandy beaches and even on glaciers. They are inhabitants of the mesopsammon and sporadic inhabitants of lakes. Most individuals are females, males become more abundant by the end of the winter. Their size is 50 - 1200 µm and they exhibit constant cell number (like rotifers, nematods, gastrotrichs). They locomote by slow movements of the six paired stump-like extremities each of which end in a double-claw. The body is divided into head plus four body segments. Epidermal cells secrete a proteinaceous cuticle, partially with armour-plates. Tardigrads skin 4-6 times in a lifecycle. Most tardigrades feed on the cell liquids from mossy or lichen cells which are penetrated by stilettoes
CRYPTOBIOSIS: Tardigrads are able to persist dry-out, freezing, and high temperatures by means of a physiological phenomenon called cryptobiosis. Upon seccation of their environment, for example, the animals secrete water and shrink to immobile, knittered can-like structures which now only contain bound water. This way, the animals can persist for over ten years and survive even experimental deep freezing in liquid oxygen. Organs and metabolism maintain their function albeit at a very low rate (anabiosis). Rehydration of cans lead to their revitalization to a normally lively specimen within half an hour.
1.ordo: Heterotardigrada 2.ordo: Mesotardigrada 3.ordo: Eutardigrada
The appendiculates or copelates or larvaceans are ancestors of the vertebrate phylogenetic line with a
chorda dorsalisin their long tail. Together with the Ascidiacea and the Thaliacea the Appendicularia make
up the phylum Tunicata which are all characterized by a large filtration basket with two to numerous gill slits
and the name-giving tunica which is a proteinaceous, delicate or strong body sheath.
Unlike the sessile Ascidiacea (sea squirts) and the planktonic Thaliacea (salps), which show chorda and tail only during ontogenesis, the pelagic appendiculates keep tail and chorda all their live long. Therefore, they are envisaged to be neotenic representatives of the phylum of Tunicates.
Appendiculates are abundant inhabitants of the mediterranean plankton and feed only on microplankton such as Coccolithineae and naked dinoflagellates. Interesting is their mode of feeding: by specialized cells of an adoral field an ultrafine, glassy filter-basket is secreted which covers either the rump (Fritillariidae, Kowalewskiidae) or the whole body (Oikopleuridae). Through this filter, water is pumped via movements of the tail. Food particles are taken up. Upon obstruction, the sheath will be replaced by a new one. Also, in case of flight, the filter-basket is pulled away.
Gastrotricha & Tardigrada & Mesopsammon:
Heinz Streble & Dieter Krauter (1988) Das Leben im Wassertropfen, 8.Auflage. Frankh-Kosmos Verlag, Stuttgart
Hnas-Eckhard Gruner (ed., 1993) Lehrbuch der Speziellen Zoologie; begründet von A.Kaestner, volume I, pt.2 & 3, 5.Auflage. Gustav Fischer Verlag, Jena & Stuttgart & New York
Rupert Riedl (1983) Fauna und Flora des Mittelmeeres, 3.Auflage. Verlag Paul Parey, Hamburg & Berlin.
This page last updated Oct 7th, 2004