Move from sea to fresh water
Maintenance of different concentration of ions inside & outside of the cell.
Reduced size of surface area & contractile vacuoles are quite adequate to remove small amount of water which enters the organism by osmosis: small protozoa.
In large animals:
Body wall composed of some impermeable material through which neither water nor salt can pass: scales of fish & cuticle in Arthropods, mucus secreted by eels,catfish.
Presence of bivalent ions Ca2+,Mg2+ in fresh water also reduces the permeability of semi permeable membranes helps to reduce the loss of salt.
Fresh water animals excrete ammonia has small molecular weight helps to increase the osmotic pressure of the tissues. & it is toxic has to be removed is done by dilution /symbiotic algae in some group.
Eggs of the fresh water animals cannot live long in water. Many fresh water fishes & amphibians have spawning habitats to ensure the simultaneous release of gametes.since less planktonic food is available in fresh water so their eggs have more yolk than marine sp.
Vertebrates (fish) have retained their marine adaptations ;Streamline body, muscles for swimming , fins for balancing ,gills for respiration & scales for protection.
Adaptations seen in the animals migrated from land .
Main group of terrestrial organism which move to fresh water is insect, pulmonate mollusk, water mites & small no of birds & mammals.
1. Adaptation to live on the surface film
Large animals can break through the water surface , but small ones neither sufficient weight nor adequate strength to force their way through surface film.they use the surface tension .
Insects: water bugs belongs to hemiptera.
Warer skater & water strider which are completely on the surface.
2. Adaptation for respiration : : surface & shallow waters of pond & lakes usually contain high concentration of dissolved O2& Co2.in areas of high densities of planktons consentration of O2 achieves supersaturation.
But in deep mud anaerobic condition may exist.
a). Air obtained through the body surfaces & the production of respiratory pigments.
Small ones waterflea(Cladocera) – zooplankton,have large surface area in relation to their bulk body & frequently posses no special respiratory organs, whole body act as gill.
Daphnia are able to synthesis haemoglobin in response to reduced O2 supply .
In some presence of haemoglobin is permanent : burrows in mud have to withstand continuous anaerobic condition :: annelids :square tailed worm(Eiseniella), tube making Tubifex ,Chironomus larvae.
b). Obtaining atmospheric air through the tracheal system
lack of current in pools means less circulation & less O2.in such con they depands on atmospheric O2 have to rice to the surface to obtain fresh supplies through spiracles.
1. Presence of tube & siphons.
Mosquito larvae –Culex pipens, water scorpion:Nepa, stick insect :Ranatra have well developed siphons which enable them to Pearce the surface film,
Bottom living rat-tailed maggot (Eristalsis has telescopic siphon can be extended siphon forms an air lock to prevent the entry of water. By fringing hairs which entrap air bubbles.
2.Presence of compressible & noncompressible gills.
Beetles & water bugs come to surface periodically to obtain air.
The air may be carried as bubbles located close to the openings of tracheal system.::water boatman ,Notonecta traps a single bubble among hairs at the posterior of the abdomen.
Addition to that air may from sheen like layer covering the whole body:water beetle.
Small beetle of family Elimidae & Dryopidae have hydrofuge hairs on the cuticle. Which can trap air .then permanent gas layer taken in by tracheae as physical gills: is known as plastron respiration . further modified in to air bubble :incompressible gill.
Blood gills & tracheal gills
Blood gill are common in many dipteran larvae.they project out of the body has tracheoles in which O2 diffuses from water.
Mayfly nymph has special plate like gills attached to the abdomen.
Their into which water pumps in& out to ventilate the gills.
Respiration in water birds.