Anaspida are a extinct marine subgroup of the agnatha. They lived from the Early Silurian to the Late Devonian times. Anaspida are similar to the Osteostraci and had unpaired fins. Orders Agnatha (Greek, no jaws) is a Super-class of jawless fish in the phylum Chordata, Sub-Phylum Vertebrata. ...
The Anaspida are all narrow-bodied jawless vertebrates characterized by triradiate postbranchial spines.
The Anaspida occur mostly in Norway and Scotland, with some sparse records from eastern Canada, the Baltic area, and a single perhaps dubious record of a "birkeniid" from China.
One of the possible phylogenies of the Anaspida suggests a tendency towards the reduction of the number of gill openings, enlargement of the median dorsal scutes, reduction of anal fin, but is neither corroborated nor refuted by stratigraphy, since most anaspid taxa are of the same age.
The Anaspida, or anaspids, are a group of fossil, jawless vertebrates which lived in the Silurian (-430 to -410 million years ago).
Although the latter two genera share with the Anaspida a strongly hypocercal tail, a characteristic which is unknown in other groups, they have no mineralized exoskeleton and, therefore show no tri-radiate postbranchial spine.
Ritchie, A. New light on the morphology of the Norwegian Anaspida.
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