Annelids (Annelida) PDF

Annelids (Annelida) − segmented animals, bilaterally symmetrical, triploblastic animals, have best developed coelom − live mostly in seas, fresh water, in soils (are important for production of humus) − have homonomous segmentation - the external segments,...

Annelids (Annelida) − segmented animals, bilaterally symmetrical, triploblastic animals, have best developed coelom − live mostly in seas, fresh water, in soils (are important for production of humus) − have homonomous segmentation - the external segments, which may be seen in the common earthworm, correspond to the internal segments − can have parapodia (projections looking like limbs) or setae (bristle-like structures, “štetinky”) − many marine species have shells − many species have head region, where sensory organs are concentrated − CS: closed, dorsal and ventral vessels are interconnected − DS – consists of an unsegmented gut that runs through the middle of the body from the mouth, located on the underside of the head, to the anus, which is on the pygidium (=unsegmented terminal region) − RS: gills or by body surface − ES: metanephridia − NS: gangliated, ladder-like, “cerebral” ganglia are the main ones, there are nerve cords running from these ganglia, these cords create pharyngeal nerve ring and some connected nervous ganglia on ventral side of body − SS: different types of eyes, tentacles, statocysts − RS: gonochorists (mostly), reproduction – asexual and sexual, can have internal or external fertilization, (by hermaphrodites – sperms mature first), terrestrial and fresh water species have direct development − can have clitellum (a swelling towards the head of the animal, where the gonads are located) − system: 3 classes: Polychaeta (polychaetes), Oligochaeta (oligochaetes) and Hirudinea (leeches) Class: Polychaeta (Polychaetes) − marine − have parapodia with setae and gills − breathe with gills (on parapodia) − indirect development (larva trochophore) − can have shell (by sessile species) − are carnivorous  member: Palolo worm (Palola viridis) Class: Olighochaeta (Oligochaetes) − segmented body − have setae on each segment − have clitellum − breathe with the whole surface of body − mostly live in soil and fresh water  members: Common earthworm  feeds on (Lumbricus terrestris – remains of dead dážďovka zemná) plants, is important for producing humus Tubifex tubifex (Sludge worm – tubifex bahenný) Class: Hirudinea (Leeches) − fresh water species − the external segmentation doesn´t correspond to the internal arrangement of organs − carnivorous or ectoparasites − have suckers at the ends of body (mouth, terminal sucker) − gut has lateral projections, in which food (blood) is stored Medicinal leech suck out blood, after (Hirudo piercing the skin they medicinalis) inject anti-coagulants (hirudin) and anesthetics into host´s body Fish leech (Piscicola geometra/pijavička rybia) Horse leech (Haemopis sanguisuga/pijavic a konská)