Cloaca lacking.
Anus absent.
Respiration by four pair of gill on bony gill arches, covered by a common operculum on either side.
Ventral heart
Sinus venosus and conus arteriosus present.
Adult kidneys mesonephric.
Excretion ureotelic.
Brain with very small olfactory lobes, small cerebrum and well developed optic lobes and cerebellum.
Cranial nerves 10 pairs.
Well developed lateral line system.
Internal ear with three semicircular canals.
Sexes seperate.
Gonads paired.
Fertilization usually external.
Mostly oviparous,rarely ovoviviparous or viviparous.
Eggs minute to 12 mm.
Cleavage meroblastic.
Development direct, rarely with metamorphosis.
Claspers absent.
Anus absent.
Respiration by four pair of gill on bony gill arches, covered by a common operculum on either side.
Ventral heart
Sinus venosus and conus arteriosus present.
Adult kidneys mesonephric.
Excretion ureotelic.
Brain with very small olfactory lobes, small cerebrum and well developed optic lobes and cerebellum.
Cranial nerves 10 pairs.
Well developed lateral line system.
Internal ear with three semicircular canals.
Sexes seperate.
Gonads paired.
Fertilization usually external.
Mostly oviparous,rarely ovoviviparous or viviparous.
Eggs minute to 12 mm.
Cleavage meroblastic.
Development direct, rarely with metamorphosis.
Claspers absent.
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