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Anaspida

Adapted from Wikipedia · Discoverer experience

An artist's reconstruction of Ctenacanthus concinnus, an ancient fish that lived during the Devonian period.

Anaspida ("shieldless ones") is an extinct group of jawless fish that lived from the early Silurian period to the late Devonian period. These small marine fish did not have a heavy bony shield or paired fins, but they had 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 once thought anaspids might be the ancestors of lampreys, but newer studies using phylogenetic analysis are not sure about this. Even so, some studies show that anaspids are at least related to lampreys in some way.

Anaspids are interesting because they help us understand how early fish lived and evolved in the ancient oceans.

Anatomy

Anaspids were different from other early fish called ostracoderms because they did not have a bony shield or armor on their bodies. Instead, their heads and bodies were covered with 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 that opened along the sides of their bodies. One special feature of anaspids was a large, three-pointed spine located behind their gill openings.

Taxonomy

Life reconstruction of Lasanius problematicus

The group Anaspida is made up of two main orders. The first is Lasaniida, which includes just one genus called Lasanius. This group is considered a basic type of anaspid. The second order is Birkeniida, which includes many different 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

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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