''Trilobozoa'' (meaning "three-lobed animals") is a phylum of extinct mobile animals that were originally classified into the Cnidaria. The basic body plan of ''Trilobozoa'' is often a tri-radial or radial sphere-shaped form with lobes radiating from its centre. Fossils of trilobozoans are restricted to marine strata of the Late Ediacaran period.

History and interpretations

Originally, both Fedonkin and Runnegar presumed that there were 2-3 families within the Trilobozoa, those families being Albumaresidae Fedonkin, 1985 and Tribrachididae Runnegar, 1992. Although, affinities with the

Conulariida Conulariida is a poorly understood fossil group that has possible affinity with the Cnidaria. Their exact position as a taxon of extinct medusozoan cnidarians is highly speculative. Members of the Conulariida are commonly referred to as conularii ...

were made because of the conulariids possessing similar three-fold symmetry. Mikhail Fedonkin later classified the Trilobozoa as a class of the

Phylum In biology, a phylum (; plural: phyla) is a level of classification or taxonomic rank below kingdom and above class. Traditionally, in botany the term division has been used instead of phylum, although the International Code of Nomenclature f ...

Coelenterata Coelenterata is a term encompassing the animal phyla Cnidaria (coral animals, true jellies, sea anemones, sea pens, and their relatives) and Ctenophora (comb jellies). The name comes , referring to the hollow body cavity common to these two phyl ...

. Most of the members of what is now the modern day classification for Trilobozoa were thought to have originally been free swimming

Jellyfish Jellyfish and sea jellies are the informal common names given to the medusa-phase of certain gelatinous members of the subphylum Medusozoa, a major part of the phylum Cnidaria. Jellyfish are mainly free-swimming marine animals with umbrella- ...

Tribrachidium ''Tribrachidium heraldicum'' is a tri-radially symmetric fossil animal that lived in the late Ediacaran (Vendian) seas. In life, it was hemispherical in form. ''T. heraldicum'' is the best known member of the extinct group Trilobozoa. Etymology ...

was once interpreted as a

Edrioasteroid Edrioasteroidea is an extinct class (biology), class of echinoderms. The living animal would have resembled a pentamerously symmetrical disc or cushion. They were obligate encrusters and attached themselves to inorganic or biologic hard substrate ...

Echinoderm An echinoderm () is any member of the phylum Echinodermata (). The adults are recognisable by their (usually five-point) radial symmetry, and include starfish, brittle stars, sea urchins, sand dollars, and sea cucumbers, as well as the sea ...

, although with the discovery of the related ''

Albumares ''Albumares brunsae'' is a tri-radially symmetrical fossil animal that lived in the late Ediacaran seafloor. It is a member of the extinct group Trilobozoa. Etymology The generic name ''Albumares'' derives from the Latin ''Mare Album'' (White ...

'' and ''

Anfesta ''Anfesta stankovskii'' is a tri-radially symmetrical fossil animal that lived in the late Ediacaran (Vendian) seafloor. It is a member of the extinct group Trilobozoa. Etymology The generic and specific names of the ''Anfesta stankovskii'' ho ...

'' (along with better-preserved

White Sea The White Sea (russian: Белое море, ''Béloye móre''; Karelian and fi, Vienanmeri, lit. Dvina Sea; yrk, Сэрако ямʼ, ''Serako yam'') is a southern inlet of the Barents Sea located on the northwest coast of Russia. It is su ...

specimens) it became apparent to Mikhail Fedonkin that all of the organisms formed one Phylum (originally class) of tri-radially symmetrical enigmatic organisms from the

Ediacaran The Ediacaran Period ( ) is a geological period that spans 96 million years from the end of the Cryogenian Period 635 million years ago (Mya), to the beginning of the Cambrian Period 538.8 Mya. It marks the end of the Proterozoic Eon, and th ...

. The eventual split of

into the Phylums

Cnidaria Cnidaria () is a phylum under kingdom Animalia containing over 11,000 species of aquatic animals found both in freshwater and marine environments, predominantly the latter. Their distinguishing feature is cnidocytes, specialized cells that th ...

and

Ctenophora Ctenophora (; ctenophore ; ) comprise a phylum of marine invertebrates, commonly known as comb jellies, that inhabit sea waters worldwide. They are notable for the groups of cilia they use for swimming (commonly referred to as "combs"), an ...

led the Trilobozoa to obtain a Phylum level of affinities. The members of the Trilobozoa are now thought to be sessile,

benthic The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from ancient Greek, βένθος (bénthos), meaning "t ...

organisms of unknown affinities, and are a subject open for interpretations and debate.

Description

Trilobozoans had a tri-radial shield-like body that had three antimeres which consisted of a cluster of grooves on their outer surface and within their inner cavity. Most of the members of the Trilobozoa possessed bifurcating concave areas internally that were all separated by sharp ridges. These structures were more likely stiff and culticular rather than elastic internal bodies or membranes even though those structures may have been resistant, they also could've corresponded to collapsed chambers that can be observed within the related genera ''

'' and ''

''. In

, the sediment preserving the animal penetrated from above only within areas between those organs. The spiral-like orientation of the internal bodies of trilobozoans suggests that they were modified from an originally longitudinal to the axis which resulted in the deposition of the organs.

Albumares

''Albumares brunsae'' represents a form first described from the

of Russia by Mikhail A. Fedonkin in 1976. In life, ''Albumares'' most likely had an umbrella-like shape with tri-radial symmetry along with three ridges radiating from its centre. Fossils of ''Albumares'' are known from Russia and

South Australia South Australia (commonly abbreviated as SA) is a state in the southern central part of Australia. It covers some of the most arid parts of the country. With a total land area of , it is the fourth-largest of Australia's states and territories ...

and preserve 100 small ( each) marginal tentacles. From the centre of the lobes arise three canals that split at least 4 times across the body. The then split canals then split until they reach the outer margin of the body. The diameter of the body is , the length of the lobes are maximum. Albumares is similar and may be a close relative of the ''

Anfesta

''Anfesta stankovskii'' represents a small ( hemispherical-shaped form with flattened, three-fold symmetry. Similarly to ''Albumares'', three long sausage-shaped lobes radiate from its centre that are all separated by an angle of 120 degrees. The lobes taper at both their proximal and distal ends, which divide the organism into a number of narrow bodies that are divisible by three. Some specimens from both Australia and Russia preserve tentacles (canals) similar to that of ''Albumares''. Unlike ''Albumares'' and '' Skinnera'', ''Anfesta'' is more oval-shaped and discoidal rather than being dominantly tri-lobate. The length of the lobes is with the width being up to .

Hallidaya

''Hallidaya brueri'' constitutes as a discoidal form that is restricted to Mount Skinner of the

Northern Territory The Northern Territory (commonly abbreviated as NT; formally the Northern Territory of Australia) is an states and territories of Australia, Australian territory in the central and central northern regions of Australia. The Northern Territory ...

of Australia. The fossils were preserved as disc-shaped moulds on the sandstone. The fossils typically range up to in diameter with a height of . Specimens commonly show three central depressions connected by a much smaller, pouch-shaped one around the perimeter of the disk by multiple canals radiating from its centre. ''Hallidaya'' and '' Skinnera'' share common morphological characteristics with each other and are most likely close relatives.

Rugoconites

''Rugoconites'' is a genus of oval- circular-shaped preserved in high relief about six or more centimetres in diameter. The shape of Rugoconites is different in both of its species; R. enigmaticus Glaessner & Wade 1966 is more dome shaped and R. tenuirugosus Wade 1972 is more flatter although bigger.

Wade Wade, WADE, or Wades may refer to: Places in the United States * Wade, California, a former settlement * Wade, Maine, a town * Wade, Mississippi, a census-designated place * Wade, North Carolina, a town * Wade, Ohio, an unincorporated communi ...

(1972) interpreted the multiple lobes of Rugoconites as being tentacles. The multiple bifurcating lobes radiating from a centre served to distinguish Rugoconites from the sponge Palaeophragmodictya the lobes were then re-interpreted as being traces of a Gastrovascular system. However this idea was countered by Sepkoski (2002) who went on to actually classify the genus into the

instead of the

Porifera Sponges, the members of the phylum Porifera (; meaning 'pore bearer'), are a basal animal clade as a sister of the diploblasts. They are multicellular organisms that have bodies full of pores and channels allowing water to circulate through th ...

. Ivantstov & Fedonkin (2002) went on to classify Rugoconites into the Trilobozoa by suggesting it had tri-radial symmetry.

Skinerra

''Skinnera brooksi'' defines small discoidal fossils preserved as composite moulds on sandstone. Fossils are characterized by three radially arranged pouch-shaped depressions that are interpreted as a stomach similar to that seen in

Hallidaya The Ediacaran fossil ''Hallidaya'', a close relative of '' Skinnera'' lived in Belomorian (559-550 Ma) of the Late Ediacaran period prior to the Cambrian explosion and thrived in the marine strata on the ocean floor of what is now considered A ...

. These depressions are then connected to an outer rim by approximately 15 smaller pouches along the disk by canals. ''S. brooksi'' fossils range from to and are slightly domed by being tall. Skinnera and Hallidaya are considered to be close relatives.

References

External links

Ediacara Assemblage
University of Bristol {{Taxonbar, from=Q2334797 Ediacaran life Proterozoic animals Ediacaran first appearances Animal phyla Vendobionta Ediacaran Prehistoric animal taxa Ediacaran Europe