Eglonaspididae is a

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

of extinct amphiaspidid heterostracan

agnatha Agnatha (; ) or jawless fish is a paraphyletic infraphylum of animals in the subphylum Vertebrata of the phylum Chordata, characterized by the lack of jaws. The group consists of both extant taxon, living (Cyclostomi, cyclostomes such as hagfish ...

ns whose fossils are restricted to Lower Devonian marine strata of

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near the

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. In life, all of the amphiaspidids are thought to be benthic animals that lived most of their lives mostly buried in the sediment of a series of hypersaline lagoons. Amphiaspids are easily distinguished from other heterostracans in that all of the plates of the cephalothoracic armor are fused into a single, muff-like unit, so that the forebody of the living animal would have looked, in the case of elgonaspidids, very much like a hot water bottle with or without a pair of small, degenerated eyes and a simple, slit-like mouth positioned at the anteriormost portion of the cephalothoracic armor.

Taxonomy

''Eglonaspis''

''Eglonaspis'' has a flattened, triangular-shaped cephalothoracic shield with large, crenulated fringes at the posteriolateral ends, and an elongated, tube-like head. Unlike most of its close relatives, has no trace of eyes, nor preorbital openings whatsoever (though, none of the other eglonaspidid genera have preorbital openings, either). The head of ''Eglonaspis'' has degenerated into a tube-like mouth which, according to researchers, is hypothesized to have permitted the living animal to filter-feed particles in the water column just above the surface of the substrate while the animal stayed buried beneath the substrate.

''Gerronaspis''

''Gerronaspis'' was originally described as a species of ''Putoranaspis'', as "''Putoranaspis dentata''," by Obruchev in 1964. In 1971, Novitskaya reappraised the species and separated it into a new genus. ''Gerronaspis'' has an oval-shaped cephalothoracic shield with crenulated fringes near the posteriolateral ends. The head is short, and has small orbital openings, albeit that are quite large when compared to the orbital openings of other eyed eglonaspidids like ''Empedaspis''.

''Lecanaspis''

''Lecanaspis'' is very similar in anatomy to ''Eglonaspis'', that is, it has a triangular, plate-like cephalothorax. Although the head is missing in the holotype, later, more complete specimens show that, like ''Eglonaspis'', ''Lecanaspis'' had an elongated, tubular head with no eyes.

''Empedaspis''

''Empedaspis'' is thus far known only from a large fragment of the anterior portion of a large cephalothoracic shield. Enough of the fragment permits researchers to hypothesize that the complete cephalothorax would have been shaped like a

hot water bottle A hot-water bottle is a bottle filled with hot water and sealed with a Bung, stopper, used to provide warmth, typically while in bed, but also for the application of heat to a specific part of the body. Early history Containers for warmth in b ...

, possibly with crenulated lateral wing-like extensions, and would have had a small tab-shaped head with small eyes.

''Pelurgaspis''

''Pelurgaspis'' is known from an incomplete cephalothoracic shield that is triangular in shape. The intact shield may have been shaped like a corn kernel or a guitar pic. The small eyes of ''Pelurgaspis'' are positioned at the anterior-most end of the small head.

References

{{Taxonbar, from=Q20686632 Amphiaspidida Devonian jawless fish Early Devonian fish Prehistoric jawless fish families Fauna of Siberia Fossils of Russia Early Devonian first appearances Devonian extinctions