Temporal range: Cryogenian to Present,
Diversity of various invertebrates from different phyla (including a invertebrate of the phylum Chordata)
Left to right: Chrysaora fuscescens (Cnidaria), Fromia indica (Echinodermata), Caribbean reef squid (Mollusca), Drosophila melanogaster (Arthropoda), Aplysina lacunosa (Porifera), Pseudobiceros hancockanus (Platyhelminthes), Hirudo medicinalis (Annelida), Polycarpa aurata (Tunicata), Milnesium tardigradum (Tardigrada).
Scientific classificationEdit this classification
(unranked): Filozoa
Kingdom: Animalia
Groups included
  • All animal groups not in subphylum Vertebrata

Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a backbone or spine), derived from the notochord. This is a grouping including all animals apart from the chordate subphylum Vertebrata. Familiar examples of invertebrates include arthropods, mollusks, annelids, echinoderms and cnidarians.

The majority of animal species are invertebrates; one estimate puts the figure at 97%.[1] Many invertebrate taxa have a greater number and variety of species than the entire subphylum of Vertebrata.[2] Invertebrates vary widely in size, from 50 μm (0.002 in) rotifers[3] to the 9–10 m (30–33 ft) colossal squid.[4]

Some so-called invertebrates, such as the Tunicata and Cephalochordata, are more closely related to vertebrates than to other invertebrates. This makes the invertebrates paraphyletic, so the term has little meaning in taxonomy.

  1. ^ May, Robert M. (16 September 1988). "How Many Species Are There on Earth?". Science. 241 (4872): 1441–1449. Bibcode:1988Sci...241.1441M. doi:10.1126/science.241.4872.1441. JSTOR 1702670. PMID 17790039. S2CID 34992724. Archived from the original on 15 November 2016. Retrieved 17 June 2014.
  2. ^ Richards, O. W.; Davies, R.G. (1977). Imms' General Textbook of Entomology: Volume 1: Structure, Physiology and Development Volume 2: Classification and Biology. Berlin: Springer. ISBN 978-0-412-61390-6.
  3. ^ Howey, Richard L. (1999). "Welcome to the Wonderfully Weird World of Rotifers". Micscape Magazine. Retrieved 19 February 2010.
  4. ^ Roper, C.F.E. & P. Jereb (2010). Family Cranchiidae. In: P. Jereb & C.F.E. Roper (eds.) Cephalopods of the world. An annotated and illustrated catalogue of species known to date. Volume 2. Myopsid and Oegopsid Squids. FAO Species Catalogue for Fishery Purposes No. 4, Vol. 2. FAO, Rome. pp. 148–178.

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