Definition of blood gill in English:

blood gill

noun

Zoology
  • (In some invertebrates) a diverticulum of the body wall containing a blood-filled space but few or no tracheae, through which gases or ions may pass to or from the surrounding medium; especially such a structure in the aquatic larvae of certain insects (e.g. chironomid midges), originally supposed to be a respiratory organ but now thought to be concerned mainly with osmoregulation; usually in plural.

Origin

Late 19th century. After German Blutkiemen (plural, 1889 or earlier).