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Vertebrate Zoology
Chondrichthyans
Question | Answer |
---|---|
Skeleton of Chondrichthyans | Cartilaginous; Dermal carapace in scales; Placoid scales; Origin of teeth |
Teeth of Chondrichthyans | Teeth whorls; Continuous replacement; Loosely attached to connective tissue in dermis; Replaced every eight days |
Soft Tissue of Chondrichthyans | Large, lipid-filled liver; High urea concentration |
Stem Elasmobranchs | Extinct; Terminal mouth; Cladoselache in predatory form; Stethacanthus with scaled fin and head plates; Damocles and Falcatus with dorsal spines hinting at sexual selection |
Neoselachii includes | Selachii, with chemosensory organs, topetum lucidum;(Galeomorph and Squalomorph); Batoidea with pectoral wings, four gills, spirode gills, no scales and crushing teeth |
Galeomorph | Selachii; Shallow water; Great size; |
Squalomorph | Selachii; Dark, deep water; Small and less derived body; Small brain |
Holocephali | Diverged well before Neoselachii; Basic features like the liver, skeleton, and high urea content; Only four gills covered with operculum and no spiracle |