Question: Do all animals have red blood cells???

Kevin Mahon answered on 18 Jun 2012:

Great question! If we define animals as anything with the kingdom animalia (silly distinction, but important!) then no – we have several examples of animals that don’t have them.

Antartic Ice Fish (family Channichthyidae) don’t have ‘red’ blood cells because they don’t have hemoglobin – hemoglobin doesn’t work very well at cold temperatures.

Insects (like many other invertabrates) have hemocytes (an equivalent to a red blood cell). They are bluish in color because of the hemocyanin they contain.

Lobsters and crabs (among other crustaceans) use hemocyanin dissolved in their plasma to transport oxygen – they have no red blood cells at all!

There are others but better yet I can give you two WHOLE divisions of animals without blood cells. The Platyhelminthes (Flatworms) and the Nematoda (Nematodes) don’t even have circulatory systems!

It would be interesting to see if more or less species overall have red blood cells – I think less might be the case as insects alone account for nearly 10 million species!