Taxonomy of commonly fossilised invertebrates

The Ordovician cystoid Echinosphaerites (an extinct echinoderm of the Class Rhombifera) from northeastern Estonia; encrusted by a graptolite (black branches).

Although the phylogenetic classification of non-vertebrate animals (both extinct and extant) remains a work-in-progress, the following taxonomy attempts to be useful by combining both traditional (old) and new (21st-century) paleozoological terminology.

The paleobiologic systematics which follows is not intended to be all-inclusive or completely comprehensive. For practical reasons and relevancy, the below classification and annotations emphasize invertebrates that (a) are popularly collected as fossils and/or (b) no longer continue alive on this planet. Therefore, as a result, some phyla, classes, and orders of invertebrates are not listed.[1]

If a non-vertebrate animal is mentioned below using its common, or vernacular name, the creature is usually a living, present-day invertebrate. But if a non-vertebrate is cited below by its scientific, taxonomic genus (in italics), then it is typically an extinct invertebrate, known only from the fossil record.[2]

Invertebrate clades that are (a) very important as fossils (for example, ostracods frequently used as index fossils), and/or (b) very abundant as fossils (for example, crinoids easily found in crinoidal limestone),[3] are highlighted with a bracketed exclamation mark [ ! ].

Invertebrate groups that (a) are now substantially extinct, and/or (b) contain a large proportion of extinct species, are followed by a dashed notation [ such as this ]. But invertebrate clades which are now completely extinct are designated with a bracketed dagger [ † ]:

Domain of Eukaryota / EukaryaEdit

Quinqueloculina, a foraminiferan (a type of protist) from Donegal Bay, Ireland.

(eukaryotes / eukaryans / all cellular organisms bearing a central, organized nucleus with DNA)

Sub-domain of OpisthokontaEdit

(opisthokonts / the animal-related kingdoms / the proto-spongal choanoflagellates, proto-fungal microsporidians, true fungi, and true animals

  • comprises most life forms documented as either living or deceased
    • excludes many molds, all one-celled protists (or protoctists), all algae, and all green plants

Kingdom of Animalia / Metazoa --- All Invertebrates and VertebratesEdit

(metazoans / many-celled true animals / multi-cellular creatures that grab and ingest their organic food)

Sub-kingdom of ParazoaEdit

(parazoans / typically sessile, basal non-eumetazoans / the most-primitive animals / the simplest, colonial, attached, bottom-dwelling, marine invertebrates)

Phylum Archaeocyatha / Archeocyatha / Archaeocyathida / Archeocyathida / Pleospongia [†]Edit

(cone-shaped archaeocyathids/archeocyathids / cup-shaped archaeocyathans/archeocyathans / reef-building pleosponges / calcareous "ancient-cups")

(includes fossil genera such Archaeocyathus, Cambrocyathus, Atikonia, Tumuliolynthus, Kotuyicyathus, Metaldetes, Ajacicyathus and Paranacyathus)

(Archaeocyatha is sometimes classified as a class of Porifera below)

Phylum Porifera / Nuda / SpongiaEdit

Pattersonia ulrichi Rauff, 1894; an Ordovician hexactinellid sponge from near Cincinnati, Ohio.

(quintessential true sponges / marine, colonial, pore-bearing animals / organized collar-flagellates / poriferans; today mostly siliceous) – half of all documented species of Porifera are fossils and extinct [4]

(Porifera may eventually be broken up into separate phyla)

Sub-kingdom of EumetazoaEdit

(eumetazoans / true metazoans / typically mobile, multicellular animals)

(Eumetazoa contains most of the living and deceased species of recorded life, including most invertebrates (alive and extinct), as well as all vertebrate animals)

Super-phylum of RadiataEdit

(radiates / non-bilaterian eumetazoans)

Phylum Cnidaria / CoelenterataEdit

Aulopora (a tabulate coral) from the Silica Shale (Middle Devonian), northwestern Ohio.

(cnidarians / coelenterates)

Super-phylum of Lophotrochozoa / Protostomia # 1Edit

(lophotrochozoan bilaterians, such as flatworms, ribbon worms, lophophorates, and molluscs)

Phylum Bryozoa / Ectoprocta / PolyzoaEdit

Heterotrypa, a trepostome bryozoan from the Corryville Formation (Upper Ordovician) in Covington, Kentucky.

(bryozoans / moss animals) – half of all documented species of Bryozoa are fossils and extinct [5]

  • Class Stenolaemata / Gymnolaemata [!] (mostly marine, calcareous bryozoans)
    • Order Cheilostomata [!] (living, rimmed-mouthed moss animals)
    • Order Cyclostomatida (uncontracted, round-mouthed bryozoans including fossil Stomatopora)
    • Order Cystoporata [†] (extinct, minor group of moss animals)
    • Order Trepostomata [†] [!] (changed-mouthed bryozoans such as extinct Constellaria and Monticulipora)
    • Order Cryptostomata [†] [!] (round hidden-mouthed bryozoans such as Archimedes, Fenestrellina and Rhombopora)
    • Order Ctenostomata [†] (uncommon, comb-mouthed bryozoans)
    • Order Phylactolaemata (living, fresh-water bryozoans)

Phylum BrachiopodaEdit

Rhynchotrema dentatum, a rhynchonellid brachiopod from the Cincinnatian (Upper Ordovician) of southeastern Indiana.

(lampshells, brachiopods or "brachs," not to be confused with the hard-shelled marine mollusks below) – 99 percent of all documented species of Brachiopoda are now extinct

Phylum AnnelidaEdit

(segmented worms such as earthworms and leeches)

Phylum MolluscaEdit

Peltoceras solidum ammonite from the Matmor Formation (Jurassic, Callovian) in the Matmor Formation, Makhtesh Gadol, Israel.
Vermetid gastropod Petaloconchus intortus attached to a branch of the coral Cladocora; Pliocene of Cyprus.

(molluscs or mollusks, not to be confused with the hard-shelled marine brachiopods above)

Super-phylum of Ecdysozoa / Protostomia # 2Edit

(ecdysozoans, such as nematodes, horsehair worms, and molting bilaterians / panarthropods))

Phylum TardigradaEdit

(panarthropodic water bears)

Phylum OnychophoraEdit

(panarthropodic velvet worms, including proto-arthropodic fossils of Arthropleura and Aysheaia)

Phylum ArthropodaEdit

Elrathia kingii (trilobite) from the Wheeler Shale (Middle Cambrian), Utah.

(arthropods; jointed legged creatures with an exoskeleton)

Super-phylum of Deuterostomia / EnterocoelomataEdit

(second-mouthed bilaterians called deuterostomians, such as chordates and echinoderms)

Phylum EchinodermataEdit

Middle Jurassic (Callovian) crinoid pluricolumnals (Apiocrinites) from the Matmor Formation in Hamakhtesh Hagadol, southern Israel.

(echinoderms) – 72 percent of all documented species of Echinodermata are fossils and extinct [7]

Phylum HemichordataEdit

Pendeograptus fruticosus graptolites from the Bendigonian Australian Stage (Lower Ordovician) near Bendigo, Victoria, Australia. Two overlapping, three-stiped rhabdosomes.

(hemichordates such as extant acorn worms) – Less than half of the documented species of Hemichordata are fossils and extinct

Phylum ChordataEdit

(both invertebrate and vertebrate chordates; animals possessing a notochord)

Invertebrate subphylaEdit

Subphylum VertebrataEdit

Deinosuchus hatcheri at the Natural History Museum of Utah.

See alsoEdit


  1. ^ For superb anatomical illustrations and much-more comprehensive information, see Volume E (Archaeocyatha / Porifera) through Volume V (Graptolithina), published 1953 to 2006 (and continuing), of the Treatise on Invertebrate Paleontology, long-edited by Raymond C. Moore and Roger L. Kaesler (Boulder, Colorado: Geological Society of America; and Lawrence, Kansas: University of Kansas Press). But be warned that some terms therein employed – such as supersubphylum – can be unnecessarily wordy or abstruse. Incidentally, revised volumes have been recently published regarding the sponges/archaeocyatha (2004, ISBN 0-8137-3131-3) and the brachiopods (2006, ISBN 0-8137-3135-6).
  2. ^ The names of genera, orders, classes and phyla have been culled from dozens of sources, both current and decades-old. See the International Code of Zoological Nomenclature (ICZN), as well as Volume 1 and Volume 2 of Grzimek's Animal Life Encyclopedia (Farmington Hills, Michigan: Gale Group), edited by zoologists Michael Hutchin, Dennis A. Thorney and Sean F. Craig (2003).
  3. ^ For correspondingly ancient ecosystems, see the Treatise on Ecology and Paleoecology, Volume 2: Paleoecology, edited for years by Harry S. Ladd (1957 / 1971), and published by both the Geological Society of America (Boulder, Colorado) and the Waverly Press (Washington, D.C.).
  4. ^ The rates of extinction for sponges and other phyla are derived from W. H. Easton, 1960, Invertebrate Paleontology (New York: Harper and Brothers) and various modern sources.
  5. ^ For bryozoans and brachiopods, the same footnote as above.
  6. ^ For bivalves and cephalopods (both mollusks), see the above notation.
  7. ^ For the echinoderms, see the above footnote regarding W. E. Easton, 1960, Invertebrate Paleontology, and other sources.