Trilobozoa, from

Ancient Greek Ancient Greek (, ; ) includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Greek ...

τρεῖς (''treîs''), meaning "three", λοβός (''lobós''), meaning "lobe", and ζῷον (''zôion''), meaning "animal", is a phylum of extinct, sessile animals that were originally classified into the

Cnidaria Cnidaria ( ) is a phylum under kingdom Animalia containing over 11,000 species of aquatic invertebrates found both in fresh water, freshwater and marine environments (predominantly the latter), including jellyfish, hydroid (zoology), hydroids, ...

. The basic body plan of trilobozoans is often a triradial or radial sphere-shaped form with lobes radiating from its centre. Fossils of trilobozoans are restricted to marine strata of the Late

Ediacaran The Ediacaran ( ) is a geological period of the Neoproterozoic geologic era, Era that spans 96 million years from the end of the Cryogenian Period at 635 Million years ago, Mya to the beginning of the Cambrian Period at 538.8 Mya. It is the last ...

period.

History and interpretations

Originally, both M.A. Fedonkin and B.N. Runnegar presumed that there were 2–3 families within the Trilobozoa, those families being Albumaresidae and Tribrachididae . Although, affinities with the

Conulariida Conulariida are an extinct group of medusozoan cnidarians known from fossils spanning from the latest Ediacaran up until the Late Triassic. They are almost exclusively known from their hard external structures (alternatively referred to as a the ...

were made because the conulariids possess similar three-fold symmetry. Fedonkin originally classified the Trilobozoa as a class of the

phylum In biology, a phylum (; : phyla) is a level of classification, or taxonomic rank, that is below Kingdom (biology), kingdom and above Class (biology), class. Traditionally, in botany the term division (taxonomy), division has been used instead ...

Coelenterata Coelenterata is a term encompassing the animal phyla Cnidaria (corals, 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 phyla. Th ...

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

jellyfish Jellyfish, also known as sea jellies or simply jellies, are the #Life cycle, medusa-phase of certain gelatinous members of the subphylum Medusozoa, which is a major part of the phylum Cnidaria. Jellyfish are mainly free-swimming marine animal ...

. ''

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. Etymolo ...

'' was once interpreted as a edrioasteroid

echinoderm An echinoderm () is any animal of the phylum Echinodermata (), which includes starfish, brittle stars, sea urchins, sand dollars and sea cucumbers, as well as the sessile sea lilies or "stone lilies". While bilaterally symmetrical as ...

, although with the discovery of the related ''

Albumares ''Albumares brunsae'' is a tri-radially symmetrical fossil animal that lived on 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 S ...

'' and ''

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

'' (along with better-preserved

White Sea The White Sea (; Karelian language, Karelian and ; ) is a southern inlet of the Barents Sea located on the northwest coast of Russia. It is surrounded by Karelia to the west, the Kola Peninsula to the north, and the Kanin Peninsula to the nort ...

specimens), it became apparent to M. Fedonkin that all of the organisms formed one phylum (originally class) of triradially symmetrical enigmatic organisms from the

. The eventual split of

into the phyla

and

Ctenophora Ctenophora (; : ctenophore ) is 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"), and they are ...

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 the Ancient Greek word (), meaning "the depths". ...

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

Description

Trilobozoans had a triradial 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 have corresponded to collapsed chambers that can be observed within the related genera ''Albumares'' and ''Anfesta''. 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 triradial 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 States and territories of Australia, state in the southern central part of Australia. With a total land area of , it is the fourth-largest of Australia's states and territories by area, which in ...

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 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'' are similar and may be a close relative of ''Anfesta.''

''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 about 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 are with the width reaching up to .

''Hallidaya''

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

Northern Territory The Northern Territory (abbreviated as NT; known formally as the Northern Territory of Australia and informally as the Territory) is an states and territories of Australia, Australian internal territory in the central and central-northern regi ...

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 or more 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 flatter although bigger. Wade (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 reinterpreted 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 or sea sponges are primarily marine invertebrates of the animal phylum Porifera (; meaning 'pore bearer'), a Basal (phylogenetics) , basal clade and a sister taxon of the Eumetazoa , diploblasts. They are sessility (motility) , sessile ...

. Ivantstov & Fedonkin (2002) went on to classify ''Rugoconites'' into the Trilobozoa by suggesting it had triradial 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''. 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.

''Tribrachidium''

''Tribrachidium heraldicum'' is a small triradially symmetrical form often preserved on the base of sandstones and often show a three-lobed, circular animal preserved in it. The central part of ''T. heraldicum'' has three hooked ridges (or arms) that make up the lobes; the arms are covered by numerous branched furrows that were interpreted as tentacles.

References

External links

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