Taxonomy of commonly fossilised invertebrates

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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 / Eukarya[edit]

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 Opisthokonta[edit]

(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 Vertebrates[edit]

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

Sub-kingdom of Parazoa[edit]

(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 / Spongia[edit]

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 Eumetazoa[edit]

(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 Radiata[edit]

(radiates / non-bilaterian eumetazoans)

Phylum Cnidaria / Coelenterata[edit]

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

(cnidarians / coelenterates)

Super-phylum of Lophotrochozoa / Protostomia # 1[edit]

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

Phylum Bryozoa / Ectoprocta / Polyzoa[edit]

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 Brachiopoda[edit]

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 Annelida[edit]

(segmented worms such as earthworms and leeches)

Phylum Mollusca[edit]

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 # 2[edit]

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

Phylum Tardigrada[edit]

(panarthropodic water bears)

Phylum Onychophora[edit]

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

Phylum Arthropoda[edit]

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

(arthropods; jointed legged creatures with an exoskeleton)

Super-phylum of Deuterostomia / Enterocoelomata[edit]

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

Phylum Echinodermata[edit]

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 Hemichordata[edit]

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 Chordata[edit]

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

Invertebrate subphyla[edit]

Subphylum Vertebrata[edit]

Deinosuchus hatcheri at the Natural History Museum of Utah.


  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.

See also[edit]