Náměty na pokusy a pozorování vodních živočichů ve Školním akváriu (I. pohyb živočichů)

invertebrate and vertebrate animals, which can be kept in a school freshwater aquarium. Demonstrations of various kinds
of animal locomotion are presented in this first part. They are two ways of locomotion of planarians (e.g. Dendrocoelum
lacteum), gliding (beating by cilia) and creeping (muscular activity). Fresh water snails, such as the pond snails (e.g.
Lymnaea stagnalis), can also crawl on the water surface’s underside. The pallial cavity filled with air (pond snails are
pulmonate snails breathing oxygen from the air) gives them buoyancy and together with their slime trace, the water’s surface
tension is sufficient to support their weight. Locomotion in the pond snail is accompanied by rhythmic shell movements,
caused by contractions of the columellar muscles. Special moving is known in some freshwater mussels (e.g. Pseudanodonta
complanata, Sinanodonta woodiana). Their foot is inserted into the ground and then pumped up with hemolymph, so that
it serves as an anchor, after which the mussel can pull body and shell over the ground. Jet-propulsion in dragonfly larvae
(e.g. Aeshna, Libellula) is achieved by the rapid ejection of water from a specialised rectal chamber via the anus. The bell
in freshwater jellyfish (Craspedacusta sowerbyi) can pulsate to acquire propulsion and locomotion. Some insect larvae (e.g.
dragonfly, caddisfly, stonefly) or also adults specimens (e.g. water scorpion, water stick insect) can move using walking on
substrate or plants. The hydra (e.g. Hydra oligactis) also moves from one place to another in search of food. With the help of
glutinant nematocysts the tentacles attach to the substratum. The pedal disc is released and brought up closer to the circlet of
tentacles and attached. The whole process is repeated again and again. Leeches use for motion on substrate their two suckers.
They attach with their front sucker and draws up the hind end, then reach out for a new front attachment using front sucker
(leeches can also swim by undulations of the body). Mosquito larvae swim by jerky movements of their entire bodies. Helical
swimming is typical for the freshwater oligochaete Lumbriculus variegatus. Water striders (Gerridae) move on the water
surface using their central pair of hydrophobic legs in a sculling motion. Most crustaceans, such as shrimp, usually swim by
paddling with special swimming legs (pleopods). Swimming crabs swim with modified walking legs (pereiopods). Daphnia, a crustacean, swims by beating its antennae instead. Water louse (Asellus aquaticus) moves using walking. Some water
insect swim by paddling of three pair of their legs (e.g. water boatman /Corixa sp./, diving beetle /Dytiscus sp./). Many fish
swim through water by creating undulations with their bodies or oscillating their fins. Frogs swim in a similar style as people
doing the breaststroke. They draw their hind legs upward toward their bodies. Then, to proper themselves forward, they
shoot their legs out backwards in a straight lines. They bring their front legs down to their sides to form streamlined shape
(e.g. common frog, Rana temporaria) or their front legs are pointing forwards (e.g. African clawed frog, Xenopus laevis).