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 sub-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.

So 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.

If a non-vertebrate animal is mentioned below using its common, vernacular, everyday name, the creature is usually a living, present-day invertebrate. But if, on the other hand, 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.

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), 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 totally – that is, 100 percent – extinct are designated with a bracketed dagger/cross [ † ]:

Domain of Eukaryota / Eukarya

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

• comprises most of the species of life which have been documented by biologists and paleontologists as either living or deceased

• includes a wide variety of single-celled protists, all algae, most plankton, most molds, the green plants, and all animal-related kingdoms
  • but does not include the primal, sub-nuclear, prokaryotic domains of Archaea and Bacteria – nor the enigmatic domain of Viruses

Sub-domain of Opisthokonta

(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

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

• comprises most living and deceased species which have ever been recorded by paleontological and life scientists
  • excludes all unicellular and fungal opisthokonts

Sub-kingdom of Parazoa

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

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

(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

(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

(Porifera may eventually be broken up into separate phyla)

• Sub-phylum Calcarea / Calcispongiae (primitive calcareous poriferans such as yellow lemon sponge, sphinctozoans, pharetronids, Scypha, Leucetta, Gravestockia, Grantia, Astraeospongium, Clathrina, Lelapia, Rhaphidonema, and Girtyocoelia)
  • Class Calcinea
  • Class Calcaronea
  • Class Stromatoporoidea / Stromatoporata / Stromatoporida / Spongliomorphida [†] (lime-layered stromatoporoids / reef-building stromatoporates / button-shaped stromatoporids / disc-shaped spongliomorphids; e.g., Stromatopora, Aulacera, Stromatactis, Actinostroma, Discophyllum, Parallelopora and Amphipora)
  • Class Heteractinida [†] (Paleozoic calcitic heteractinids such as Eiffelia)
• Sub-phylum Silicea / Silicospongia (siliceous poriferans)
  • Class Demospongea / Demospongiae (most living sponges hardened by opaline silica or spongin; for instance, horny sponge, bath sponge, stove-pipe sponge, yellow boring sponge, carnivorous sponge, bristle sponge, chaetids, lithistids, Astroclera, Ceractinomorpha, Clionoides, Hindia, Ventriculites, Laosoiadia, Clionolithes, Tetractinella, and Astylospongia)
  • Class Hexactinellida / Hyalospongiae / Sclerospongiae (siliceous, deep-sea glass sponges, e.g. glassy-latticed Venus flower basket, bird's nest sponge, cloud sponge, Hexactinella, Hydroceras, Dictyonina, Brachiospongia, Titusvillea, and Rhizopoterion)

Sub-kingdom of Eumetazoa

(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

(radiates / non-bilaterian eumetazoans)

Phylum Cnidaria / Coelenterata

(cnidarians / coelenterates)

• Class Hydrozoa (hydra or hydroid group)
  • Subclass Stromatoporoidea [†] (lime-layered stromatoporoids)
  • Subclass Conulata [†] (four-sided, pyramidal conularians)
• Class Anthozoa (corals / polyps)
  • Subclass Octocorallia / Alcyonaria (soft corals and sea pens)
  • Subclass Zoantharia [!] (sea anemones and most extant corals)
    • Order Rugosa / Tetracoralla [†] [!] (wrinkled, horn-shaped tetracorals such as Petoskey coral, Caninia and Heliophyllum)
    • Order Tabulata / Schizocoralla [†] [!] (tabulate corals, for instance, Favosites and Aulopora)
    • Order Scleractinia / Hexacoralla [!] (stony corals such as brain coral, Favia, Meandrina, and most living corals)

Super-phylum of Lophotrochozoa / Protostomia # 1

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

Phylum Bryozoa / Ectoprocta / Polyzoa

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

• 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

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

• Subphylum Linguliformea (inarticulate atremates, such as "living fossil" Lingula) – but mostly extinct
• Subphylum Craniiformea (inarticulate neotremates, such as extant Crania) – but mostly extinct
• Subphylum Rhynchonelliformea [!] (articulate brachiopods with hinged valves; includes most extinct and living brachs)
  • Class Rhynchonellata [!]
    • Order Orthida [†] [!] (orthid brachs such as fossil Orthis)
    • Order Pentamerida [†] (pentamerid brachs such as Conchidium)
    • Order Rhynchonellida [!] (rhynchonellid brachs such as fossils Rhynchotrema and Rhynchonella)
    • Order Spiriferida [†] [!] (spiriferid brachs)
      • Suborder Spiriferinida [†] [!] (spiriferid brachs such as Spirifer and Eospirifer)
      • Suborder Atrypida [†] [!] (atrypid brachs such as Atrypa)
    • Order Terebratulida [!] (most living brachiopods; includes fossil Dielasma)
  • Class Strophomenata [†] [!] (so-called petrified butterflies)
    • Order Strophomenida [†] [!] (strophomenid brachs)
    • Order Productida [†] [!] (spiny or productid brachs)
      • Suborder Chonetidina [†] [!]
      • Suborder Productidina [†] [!]

Phylum Annelida

(segmented worms such as earthworms and leeches)

• Class Polychaeta (marine annelids / polychaetes)
  • Order Scolecodonta [!] (mostly chitinous jaws of scolecodonts)

Phylum Mollusca

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

• Class Monoplacophora (extinct, except for "living fossil" Neopilina)
• Class Bivalvia / Pelecypoda (bivalves / pelecypods) – half of all documented species of Bivalvia are fossils and extinct
  • Subclass Lamellibranchia [!] (clams, oysters, mussels and scallops)
• Class Gastropoda (gastropods / snail group)
  • Subclass Prosobranchia (marine snails and conches)
  • Subclass Opisthobranchia (sea slugs)
  • Subclass Pulmonata (land snails)
• Class Cephalopoda (cephalopods) – 97 percent of all documented species of Cephalopoda are now extinct
  • Subclass Nautiloidea (mostly extinct, but includes "living fossil" Nautilus)
    • Order Orthocerida [†] [!] (long, straight-shelled nautiloids)
  • Subclass Ammonoidea [†] [!] (generally coiled-shelled ammonoids)
    • Agoniatitic (agoniatites) [†]
    • Goniatitic (goniatites) [†] [!] (ammonoids with simple sutures)
    • Ceratitic (ceratites) [†]
    • Ammonitic [†] [!] (the true ammonites, bearing complex sutures)
  • Subclass Coleoidea (includes the living squid, cuttlefish, and octopus)
    • Order Belemnoidea [†] (extinct orthoconic belemnoids)

Super-phylum of Ecdysozoa / Protostomia # 2

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

Phylum Tardigrada

(panarthropodic water bears)

Phylum Onychophora

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

Phylum Arthropoda

(arthropods; jointed legged creatures with an exoskeleton)

• Subphylum Crustacea (crustaceans)
  • Class Ostracoda (ostracods)
  • Class Malacostraca (true crabs, lobster and most shrimp)
  • Class Branchiopoda (brine shrimp)
    • Order Notostraca
  • Class Cirripedia (barnacles)
  • Class Arachnoidea
• Subphylum Trilobitomorpha [†] (extinct trilobite group)
  • Class Trilobita [†] (the armored trilobites)
• Subphylum Hexapoda
  • Class Insecta (insects, best preserved in amber)
• Subphylum Chelicerata
  • Class Arachnida (spiders, best preserved in amber)
  • Class Merostomata ("living fossil" horseshoe crab and extinct eurypterid)
• Subphylum Myriapoda
  • Class Diplopoda
  • Class Chilopoda

Super-phylum of Deuterostomia / Enterocoelomata

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

Phylum Echinodermata

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

• Subphylum Crinozoa (sessile echinoderms) – 91 percent of all documented species of Crinozoa are now extinct
  • Class Crinoidea (crinoids / sea lilies) – See Crinozoa above
• Subphylum Blastozoa [†] (extinct blastoids)
  • Class Diploporita
  • Class Rhombifera
• Subphylum Echinozoa (mobile echinoderms) – 89 percent of all documented species of Echinozoa are now extinct
  • Class Echinoidea (echinoids or sea urchins) – See Echinozoa above
• Subphylum Asterozoa
  • Class Asteroidea (sea stars / starfish)
  • Class Ophiuroidea

Phylum Hemichordata

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

• Class Graptoloidea [†] (extinct graptolites)
  • Order Dendroidea [†]
  • Order Graptoloidea [†]
    • Suborder Didymograptina [†]
    • Suborder Diplograptina [†]
    • Suborder Monograptina [†]

Phylum Chordata

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

Invertebrate subphyla

• Subphylum Urochordata (invertebrate tunicate such as sea squirts)

• Subphylum Cephalochordata (invertebrate lancelets)

Subphylum Vertebrata

• Vertebrates such as hagfishes, lampreys, conodonts [†], ostracoderms [†], placoderms [†], sharks, ray-finned fishes, lobe-finned fishes, amphibians, reptiles, dinosaurs [†], birds and mammals.

See also

• Invertebrate paleontology