Marine Invertebrate Diversity

Hello interested reader,

This week I have decided to go off the topic of fossils and onto the topic of the diversity of marine invertebrates. Much of the information in this post can be found on the Tree of Life web project: and the World Register of Marine Species:

Another good page for the beginner is:

Using the link above you can find short powerpoint slide shows that illustrate information about marine (and other) invertebrates.

For those of you who are new to the subject, marine invertebrates are all metozoan (multicellular, eukaryotic) organisms that live in the sea and do not have a backbone.

There are specific taxonomic categories that these organisms fall into  (taxonomy in this case is defined as the division of organisms into ordered groups or categories, based on closeness of relation to one another), however the Invertebrata (from which the colloquial term invertebrate is derived) is not a real taxonomic division. It is a term of convenience and would not be found in the systematic description of any organism (systematics is the classification and grouping or organisms based on their evolutionary relationships). Invertebrates, while they hold one similarity between them: that of not having a backbone, may have vastly different evolutionary origins.

The Phyla (Phylum = a high-level taxonomic rank e.g. humans are in the Phylum Chordata, along with other mammals, reptiles, birds, fish, amphibians etc.) that are found to contain marine invertebrates in the present day are as follows:

  • Acanthocephala: Spiny-headed worms
  • Annelida: Segmented worms
  • Arthropoda: Arthropods e.g. Crabs, Lobsters, Shrimps
  • Brachiopoda: Lamp shells
  • Bryozoa: Moss animals or Sea mats
  • Cephalorhyncha: Cephalorynchids (worm and worm-like organisms)
  • Chaetognatha: Arrow worms
  • Chordata: Sea squirts
  • Cnidaria: Jellyfish, Corals, Anemones
  • Ctenophora: Comb jellies or Sea gooseberries
  • Cycliophora: Cycliophorans or Wheel wearers
  • Echinodermata: Sea urchins, Crinoids or Feather stars, Sea stars or Starfish, Sea cucumbers
  • Echiura: Spoon worms
  • Entoprocta: Goblet worms
  • Gastrotricha: Gastrotrichs or Hairy-backs (microscopic worm-like organisms)
  • Gnathostomulida: Unsegmented marine worms
  • Hemichordata: Acorn worms and Sea angels (gill-wings)
  • Mesozoa: Worm-like invertebrate parasites
  • Mollusca: Molluscs e.g. Mussels, Sea snails, Octopuses, Squid, Chitons, Tusk shells, Solenogasters.
  • Myxozoa: Fish parasites (most closely related to the phylum Cnidaria)
  • Nematoda: Nematode worms or Roundworms
  • Nemertea: Ribbon worms
  • Phoronida: Horseshoe worms
  • Placozoa: Placozoans (2-3 mm big, feed on small algae)
  • Platyhelminthes: Platyhelminths or Flatworms
  • Porifera: Sea Sponges
  • Rotifera: Rotifers or Wheel animals.
  • Sipuncula: Sipunculid worms or Peanut worms
  • Tardigrada: Water bears
  • Xenacoelomorpha: Flat worms

So as you can see there are a very large number of different types of marine invertebrate organisms, some you will be familiar with and some you may never have heard of before. I hope you will maybe look up what some of these organisms look like if you haven’t seen them before, and hopefully, along the way, you will gain further understanding of the varied forms of life that have evolved within the marine realm, in all of their weird and wonderful glory.

Until next week,

The Marine Invertebrate


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