Give the characteristis features of the following citing one example of each (a) Chondrichthyes and ostichthyes
(b) Urochordata and cephalochordata

Explanation

(a) Chondrichthyes is characterised by: Always marine, ventral mouth, cartilagenous exoskeleton, uncoverd gills slits, an exoskeleton of placoid scales, two-chambered heart, ureotelic excretion, cold-blooded nature,etc. e.g. Scolidon (Dog fish). Ostechthyes is characterised by: frash-water or marine, terminal mouth, exoskeleton mostly bony, operculated gill slits, exoskeleton of cycloid scales, two-chambered heart, presence of air bladder, mostly ammonotelic excretion, cold-blooded nature. e.g. Labeo (Rohu) and Hippocampus (sea horse). (b) Urochordata is characterised by: Marine habitat, body covered by a test of tunicine, notochord only in tail of larva, undergo retrogressive metamorphosis, etc. e.g. Ascidia, Herdmania, etc. Cephalochordata is characterised by: Marine habitat, notochord extends from head to tail region and persists throughout life, unpaired fins present, etc. e.g. Branchiostoma (Amphiboxus - lancelet).