Lumpers and Splitters

Posted by John Blatchford May 19, 2009

Taxonomists give strange animals their own group until evidence of relationships is found.

When a new animal is discovered it is usually possible to see where it fits in the ‘tree of life’, but occasionally something weird turns up. Taxonomists (people who decide how to classify living things) often use body plans to decide how animals are related, and when something novel, or very simple, is found, it is sometimes given its own phylum. Further research (often molecular studies) usually either confirms the novelty, or suggests unforeseen relatives.

Echiura or Spoon Worms

The Spoon Worms were originally give their own phylum (Echiura), but evidence from studies of their DNA suggests that they are related to the annelids and modern practice is to include them in the phylum Annelida.

Entoprocts or Goblet Worms

The Goblet Worms are still problematic – some consider them to be a kind of bryozoan (ectoproct). Others consider the fact that the exit from their alimentary canal is located within the ring of their cilia (as opposed to the ectoprocts, where it is outside the ring) is sufficient to show that these animals are not closely related.

Acoelomorpha

Very simple creatures that look like small blobs! They are so simple that they all look alike – there may be one species or hundreds. Even so, many taxonomists think they are probably a type of highly simplified flatworm (phylum Platyhelminthes).

Taxonomy (how things are classified) reflects the evidence available, and how different specialists interpret it. Some prefer to ‘lump’ all sorts of animals together whenever there is a whiff of kinship (the ‘Lumpers’), while others keep them in separate groups until there is overwhelming evidence of relationships (the ‘Splitters’).