The largest and most diverse group of chondrichthyans includes the sharks, rays, and skates. The nerve cord of a chordate embryo develops from a plate of ectoderm that rolls into a tube dorsal to the notochord.They are marine suspension feeders. It provides propelling force in many aquatic species. Other characters common to gnathostomes include Enhanced sensory systems, including the lateral line system An extensively mineralized endoskeleton Paired appendages 16 Chondrichthyans Sharks, Rays, and Their Relatives Members of class Chondrichthyes Have a skeleton that is composed primarily of cartilage The cartilaginous skeleton Evolved secondarily from an ancestral mineralized skeleton The lateral line system is a row of microscopic organs sensitive to changes in the surrounding water pressure — enables animal to detect minor vibrations. The allantois is a disposal sac for certain metabolic wastes pro- duced by the embryo. The chorion and the membrane of the allantois exchange gases between the embryo and the air. The reproductive tract, excretory system, and digestive tract empty into a common cloaca. These pharyngeal slits function as suspension-feeding structures in many invertebrate chordates; are modified for gas exchange in aquatic vertebrates; develop into parts of the ear, head, and neck in terrestrial vertebrates. The cartilaginous skeleton evolved secondarily from an ancestral mineralized skeleton. The young of marsupials are born very early in their development. Monotremes are a small group of egg-laying mammals consisting of echidnas and the platypus. Other derived characters of primates: A large brain and short jaws. Figure A sea lamprey 18 Origins of Bone and Teeth Mineralization appears to have originated with vertebrate mouthparts. Fishes control their buoyancy with an air sac known as a swim bladder. It completes its embryonic development while nursing in a maternal pouch called a marsupium. It provides skeletal support throughout most of the length of a chordate.
Fishes control their buoyancy with an air sac known as a swim bladder. In many species, the tail is greatly reduced during embryonic development.
The yolk sac contains the yolk, a stockpile of nutrients. Birds are endothermic, capable of keeping the body warm through metabolism. Figure A sea lamprey 18 Origins of Bone and Teeth Mineralization appears to have originated with vertebrate mouthparts.
In most vertebrates, a more complex, jointed skeleton develops and the adult retains only remnants of the embryonic notochord.
They are marine suspension feeders. Monotremes are a small group of egg-laying mammals consisting of echidnas and the platypus. Reptiles have scales that create a waterproof barrier.
The animals called vertebrates get their name from vertebrae, the series of bones that make up the backbone. Gnathostomes jaws might have evolved from skeletal supports of the pharyngeal slits.