Invertebrate Classification
Articles Showing Typical Characteristics of Some Invertebrate Phyla
Sep 19, 2007
Each species of animal on earth is given a ‘Scientific Name’ (see: Binomial Nomenclature) as soon as it has been discovered and studied by specialists. It is assigned to one of the thirty-five or more ‘Phyla’ and then to a Class, Order, Family and Genus. The new animal is then given its own species name. (Taxonomy is an ever-evolving attempt to group animals as ‘naturally’ as possible and occasionally creatures are discovered that cause a major re-think. In rare cases they will be considered members of a new Class or even Phylum.)
Three well-known Phyla
1 - Phylum Arthropoda
- Insects. The most numerous arthropods on land are in the Class Insecta. They all have six legs, and usually wings at some stage in their life-cycle. Moths and Butterflies are good examples of insects (see: Hummingbird Hawk Moth, Saddleback Caterpillar, Monarch Butterfly, Eastern Tiger Swallowtail, and Red Admiral). More primitive (and wingless) are the Silverfish and Firebrats. (N.B. Millipedes and Centipedes are not insects - they each have a Class of their own).
- Arachnids. These have four pairs of legs and are represented by the Ticks, Scorpions and Spiders - and sea spiders also fit in somewhere here.
- Crustacea. Most live in water (see: European Crayfish), but a few can be found on land (see: Woodlouse Behaviour). See also: crabs
2 - Phylum Annelida. These are the ‘True Worms’, probably the best known being the Earthworm which is unfortunately not a very typical annelid.
3 - Phylum Mollusca. Once again the most familiar examples (Slugs and Snails) are unlike many of the other molluscs. (See 'Octopus Biology')
Natural Classification
Taxonomist attempt to reflect the evolutionary process in the way they are classified. Thus all the Species in any Genus are thought to be more closely related to one-another than to members of a different Genus. (And so on up the hierarchy – related Genera are put into the same Family etc.) In this way the way any creature is classified will show how closely it is related to other animals, and give some idea of how it might have evolved.
‘Artificial’ Groups of Animals
We often speak of ‘Fish’ or ‘Worms’, but these group names do not reflect any evolutionary or genetic relationship. For example ‘Worm’ simply tells you that the animal looks a bit like a member of the Phylum Annelida. ‘Bugs’ is an even looser grouping, saying only that the creature is a bit ‘creepy-crawly’ and that you have no idea what it might be related to. Probably worst of all is ‘Shellfish’ which indicates simply that the animal lives in water and can be eaten!
(See also: Animal Classification)
Other articles by John Blatchford
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