Their eponymous genus is Halkieria /hælˈkɪəriə/, which has been found on almost every continent in Lower to Mid Cambrian deposits, forming a large component of the small shelly fossil assemblages.

Later a more thorough description was undertaken in 1995 in the journal Philosophical Transactions of the Royal Society of London and wider evolutionary implications were posed.

Armor plates called "sclerites" had long been known as elements of the small shelly fossils, and detailed analysis showed that some of these belonged to the same animal and how they fitted together.

The first articulated specimens of Halkieria evangelista, with all their hard parts together, were collected in 1989 from the Sirius Passet lagerstätte in Greenland, and were described in 1990 by Simon Conway Morris and John S.

[4] In both genera the sclerites are of the type called "coelosclerites",[4] which have a mineralized shell around a space originally filled with organic tissue, and which show no evidence of growth by adding material round the outside.

In both Halkieria and Australohalkieria the palmate and cultrate sclerites have prominent ribs, and are fairly flat except for 90° bends at the bases, which indicate that they fitted snugly against the animals' bodies.

The rest of the upper surface was covered with about 2,000 sclerites that overlapped each other like tiles and formed three zones with sclerites of different shapes:[8] "palmates", shaped rather like maple leaves, ran along the center of the back between the shell plates; blade-shaped "cultrates" lay on either side of the palmates and pointing towards the middle of the upper surface; and slim, sickle-shaped "siculates" covered the outer edges.

[10] The shellplates and the sclerites were probably made of calcium carbonate originally;[6] it has been suggested on the basis of how they were preserved that they may have been wholly organic, but this is less likely since fossils of non-calcified organisms are usually thin films while Halkeieria fossils are three-dimensional like those of trilobites and hyoliths - in fact several specimens show curvature in the horizontal plane, which suggests that the muscles associated with the sclerites were still present at the time of burial[10] The sole was soft and probably muscular.

Since Halkieria was unsuited to swimming and had no obvious adaptations for burrowing, it must have lived on the sea-floor, "walking" by making its muscular sole ripple.

[10] The name of the most complete and abundant Australian find means "Southern Halkieria the Survivor" because it proves that halkieriids survived the end-Botomian extinction.

Possibly some process after death removed many of the palmates and some of the cultrates, but it is more likely that in A. superstes the part of the scleritome, or "coat of mail", closest to the sea-bed was larger relative to the lateral and dorsal zones further up and towards the center.

[4] The other sclerites from the Georgina Basin are different enough to be excluded from Australohalkieria superstes, but are not sufficiently abundant to provide enough detail for them to be classified.

[12] Hippopharangites[14] has sclerites with a broad central cavity and small pores opening through the shell wall, equivalent to the lateral chambers of other halkieriids (and the aesthete canals of Chitons?

[7] The earliest known occurrences of Halkieriids sclerites, classified as Halkieria longa, date from the Purella antiqua Zone of the Upper Nemakit-Daldynian Stage in Siberia.

[4] It may be significant that the only archaeocyathans known to have survived the end-Botomian extinction also occur in Gondwana, the old super-continent that embraced South America, Africa, India, Australia and Antarctica.

Preservation by a covering of phosphate only seems to have been common during the early Cambrian, becoming rarer with time as a result of increased disturbance of sea-floors by burrowing animals.

Siphogonotuchida MOLLUSCA(crown group) "Siberian halkieriid" ANNELIDA(crown group) Canadia Wiwaxia Thambetolepis(halkieriid) Halkieria evangelista BRACHIOPODA(crown group) In 1995 Conway Morris and Peel presented a cladogram based both on the fossils' features and on early 1990s research in molecular phylogeny, which is the application of cladistic analysis to DNA and RNA:[6] In 2003 Cohen, Holmer and Luter supported the halkieriid-brachiopod relationship, suggesting that brachiopods may have arisen from a halkieriid lineage that developed a shorter body and larger shells, and then folded itself and finally grew a stalk out of what used to be the back.

Their main reason for regarding Halkieria as crown group molluscs is that both possessed armor mineralized with calcium carbonate.

They treated Wiwaxia and Odontogriphus as stem group molluscs because in their opinion both possessed the distinctive molluscan radula, a chitinous toothed "tongue".

[37] Also in 2006, Conway Morris criticized Vinther and Nielsen's (2005) classification of Halkieria as a crown group mollusc, on the grounds that the growth of the spicules in the aplacophorans and polyplacophorans is not similar to the method of growth deduced for the complex halkieriid sclerites; in particular, he said, the hollow spines of various molluscs are not at all like the halkieriid sclerites with their complex internal channels.

Conway Morris and Caron regarded this creature as evidence that the "halwaxiids" were a valid taxon and were monophyletic, in other words shared a common ancestor with each other and with no other organism.

Butterfield and Nicholas (1996) argued that they were closely related to sponges on the grounds that the detailed structure of chancellorid sclerites is similar to that of fibers of spongin, a collagen protein, in modern keratose (horny) demosponges.

[42] However Janussen, Steiner and Zhu (2002) opposed this view, arguing that: spongin does not appear in all Porifera, but may be a defining feature of the demosponges; the silica-based spines of demosponges are solid, while chancellorid sclerites are hollow and filled with soft tissues connected to the rest of the animal at the bases of the sclerites; chancellorid sclerites were probably made of aragonite, which is not found in demosponges; sponges have loosely bound-together skins called pinacoderms, which are only one cell thick, while the skins of chancellorids were much thicker and shows signs of connective structures called belt desmosomes.

In their opinion the presence of belt desmosomes made chancellorids members of the Epitheliazoa, the next higher taxon above the Porifera, to which sponges belong.

[44] The coelosclerites ("hollow sclerites") of halkieriids and chancelloriids resemble each other at all levels: both have an internal "pulp cavity" and a thin external organic layer; the walls are made of the same material, aragonite; the arrangement of the aragonite fibers is in each is the same, running mainly from base to tip but with each being closer to the surface at the end nearest the tip.

It is extremely improbable that totally unrelated organisms could have developed such similar sclerites independently, but the huge difference in the structures of their bodies makes it hard to see how they could be closely related.