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Anaspida

Adapted from Wikipedia · Adventurer experience

Scientific illustration showing ancient fish-like creatures from the Silurian period with fin structures and spines.

Anaspida ("shieldless ones") was a group of small jawless fish that lived in the ocean from the early Silurian period to the late Devonian period. Unlike some other fish, anaspids did not have a heavy bony shield or paired fins. But they did have a special feature called hypocercal.

Anaspids are characterized by a large, tri-radiate spine (red) posteriorly to the series of branchial openings. It is assumed that the most primitive anaspids, such as Pharyngolepis (top), possessed a long, ribbon-shaped, ventrolateral fin-fold (green). More advanced forms, such as Rhyncholepis (bottom), possessed a shorter paired fin-fold (green) and enlarged, spine-shaped, median dorsal scutes. – Philippe Janvier

Scientists used to think anaspids might be related to lampreys. But newer studies using phylogenetic analysis are unsure about this. Even so, some studies show that anaspids are related to lampreys in some way.

Anaspids are important because they help us learn about how early fish lived and changed over time in the ancient oceans.

Anatomy

Anaspids were different from other early fish because they did not have a bony shield on their bodies. Instead, their heads and bodies had small, thin scales. Along their backs, they had a row of large, bony plates. They also had big eyes on the sides of their heads and many gills along the sides of their bodies. One special feature of anaspids was a large, three-pointed spine behind their gill openings.

Taxonomy

The group Anaspida has two main orders. The first is Lasaniida, which includes one genus called Lasanius. This group is a simple type of anaspid. The second order is Birkeniida, which includes many families such as Birkeniidae, Pterygolepididae, and Rhyncholepididae. Some recent studies suggest that anaspids may be closely related to hagfish and lampreys, rather than to jawed fish.

Images

An artist's reconstruction of Ctenacanthus concinnus, an ancient fish that lived during the Devonian period.
A scientific drawing showing the head area of Pikaia, an ancient sea creature, with its gills.
A scientific illustration of a hagfish (Myxine glutinosa), a unique marine creature known for producing slime.
Scientific illustration of conodonts, ancient marine animals from Earth's past.
Scientific drawing of Coccosteus, an ancient armored fish, as imagined by artist Russell Engelman.
Artist's reconstruction of Ischnacanthus gracilis, an ancient spiky fish from the Devonian period.
An artist’s reconstruction of Cowielepis ritchiei, an ancient fish that lived over 400 million years ago in the Silurian period.
Scientific restoration of Astraspis desiderata, an ancient chordate from the Ordovician period.
Artist's reconstruction of Qingmenodus, an ancient fish from the Devonian period.

Related articles

Silurian
Devonian
Hagfish

This article is a child-friendly adaptation of the Wikipedia article on Anaspida, available under CC BY-SA 4.0.

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