Everything about Galeaspida totally explained
Mid
Silurian to Early
Devonian
| image = Galeaspida_1.JPG
| regnum =
Animalia
| phylum =
Chordata
| subphylum =
Vertebrata
| classis =
Galeaspida
}}
Galeaspida ("Helmet shields") is an extinct taxon of jawless marine and freshwater
fish. Their name is derived from a latin word for helmet,
galea, and refers to their massive bone shield on the head. Galeaspida lived in shallow, fresh water and marine environments during the
Silurian and
Devonian times (430 to 370 million years ago) of what is now
China and
Vietnam. Their
morphology is superficially similar to that of the
Heterostraci more than the
Osteostraci, as there's currently no evidence that the galeaspids had paired fins. However, the Galeaspida are regarded as being more closely related to the Osteostraci than Heterostraci as the morphology of the
braincase is more similar to that of Osteostraci than Heterostraci.
Galeaspida had a large opening on the
dorsal surface of the head shield, which was connected to the
pharynx and
gill chamber. It may have served both the
olfaction and the intake of the respiratory water similar to the
nasopharyngeal duct of
hagfishes. Galeaspids are also the
vertebrates which have the largest number of
gills, as some species of the
order Polybranchiaspidida (literally "many gills shields") had up to 45 gill openings. The body is covered with minute scales arranged in oblique rows and there's no other fin besides the
caudal fin. The mouth and gill openings are situated on the
ventral side of the head, which is flat and suggests that they were bottom-dwellers.
There are about seventy species of Galeaspids divided into
Eugaleaspidiformes and
Polybranchiaspidida.
Further Information
Get more info on 'Galeaspida'.
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