What's the smallest known animal with hemoglobin running in its veins?

Here I mean an animal that on its own is able to produce the hemoglobin that is running in its veins. For that reason this excludes mosquitoes that have filled themselves with blood from another creature, for example.

With smallest I mean either by mass or by spatial dimensions. Either would be interesting.

  • $\begingroup$ Smallest by mass? $\endgroup$
    – Alan Boyd
    Jul 20, 2017 at 15:08
  • $\begingroup$ thanks @AlanBoyd, I have now updated that in my question:-) $\endgroup$
    – alec
    Jul 20, 2017 at 15:11
  • $\begingroup$ What kind of googling have you done? It sounds like a "homework" question to me (not that it comes from actual homework) $\endgroup$ Jul 20, 2017 at 17:59
  • $\begingroup$ The scope of the question is still unclear. Some definitions of 'haemoglobin' include proteins found in invertebrates and even in microbes. By using the expression 'running in its veins' do you aim to exclude such organisms? $\endgroup$
    – Alan Boyd
    Jul 20, 2017 at 18:07
  • $\begingroup$ Why do you want to know this? What will it tell you? Anything other than an entry in the Guinness Book of Records? $\endgroup$
    – David
    Jul 20, 2017 at 23:52

2 Answers 2


It depends how different from human hemoglobin it can be and still count as hemoglobin. Here is a cool evolutionary tree of globins. enter image description here http://www.mhhe.com/biosci/genbio/enger/student/olc/art_quizzes/genbiomedia/0329.jpg

Here is the worlds smallest fish. Fish have hemoglobin similar to that of humans. from Wikipedia: The world's smallest fish is Paedocypris progenetica1 from Indonesia, with mature females measuring 7.9 mm (0.31 in).

enter image description here

But I think bloodworms are even smaller. They have hemoglobin too. It is evolutionarily more distant from us but they use it for the same reason we do.

enter image description here from https://www.prestoninnovations.com/img/media/Seq-7.jpg


Blood worms are red because their blood plasma contains haemoglobin, like human blood. Also spelled “hemoglobin,” haemoglobin increases its ability to take up oxygen. The larvae commonly burrow in the oxygen-poor mud bottom of pools and rivers, so haemoglobin is of great value to the larvae.

If you are going to allow very distant relatives, I think this snail is even smaller than the smallest bloodworm. Less than 1 mm. Molluscs have hemoglobin too.

enter image description here from https://www.slideshare.net/fmoretzsohn/texas-seashellsmore-than-you


Paedophryne amauensis, the world's smallest vertebrate by length, 7.7mm. The coin by the way is an American dime.

enter image description here


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