Fine structure of the nemertean worm Lineus lacteus red blood corpuscles.

In the blood of Lineus lacteus, haemoglobin-containing cells measuring 6-7 micrometer in diameter were seen. Using electron microscopy different cellular components were identified, including a nucleus which contains a nucleolus, mitochondria, rough and smooth endoplasmic reticulum, free ribosomes, osmiophilic deposits, and Golgi apparatus. The morphological appearance of the Lineus lacteus erythrocyte was found to resemble an immature mammalian red cell.