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The bony fish lineage shows more derived anatomical traits, often with major evolutionary changes from the features of ancient fish. They have a bony skeleton, are generally laterally flattened, have five pairs of gills protected by an operculum, and a mouth at or near the tip of the snout. The dermis is covered with overlapping scales. Bony ...
Bony fish can be any type of heterotroph: numerous species of omnivore, carnivore, herbivore, filter-feeder, detritivore, or hematophage are documented. Some bony fish are hermaphrodites, and a number of species exhibit parthenogenesis. Fertilization is usually external, but can be internal.
Many bony fishes have an internal organ called a swim bladder, or gas bladder, that adjusts their buoyancy through manipulation of gases. In this way, fish can stay at the current water depth, or ascend or descend without having to waste energy in swimming. The bladder is only found in bony fishes.
Each gill is supported by a cartilaginous or bony gill arch, [1] which helps to maintain the gill's surface area. Bony fish (osteichthyans, mostly teleost ray-finned fish) have four pairs of arches, cartilaginous fish (chondrichthyans) have five to seven pairs, and the more basal jawless fish ("agnathans") have up to seven.
Conversely, freshwater has less osmolytes than the fish's internal fluids. Therefore, freshwater fishes must utilize their gill ionocytes to attain ions from their environment to maintain optimal blood osmolarity. [6] [10] In some primitive bony fishes and amphibians, the larvae bear external gills, branching off from the gill arches. [11]
It has since been revealed that even if galeaspidans have just one external opening, it has two internal nasal organs. [5] [6] After the appearance of jawed fish (placoderms, acanthodians, sharks, etc.) about 420 million years ago, most ostracoderm species underwent a decline, and the last ostracoderms became extinct at the end of the Devonian ...
The cladogram below shows the evolutionary relationships of the teleosts to other extant clades of bony fish, [15] and to the four-limbed vertebrates that evolved from a related group of bony fish during the Devonian period. [17] [18] Approximate divergence dates (in millions of years, mya) are from Near et al., 2012. [15]
Bony fishes have additional dermal bone, forming a more or less coherent skull roof in lungfish and holost fish. The simpler structure is found in jawless fish , in which the cranium is represented by a trough-like basket of cartilaginous elements only partially enclosing the brain, and associated with the capsules for the inner ears and the ...