Ultrastructure of the spermatozoid in Halimeda tuna (chlorophyceae)

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Abstract
The mature Halimeda tuna spermatozoid was studied under the electron microscope. It is pear‐shaped and biflagellate. The nucleus is an uncondensed structure except for a few opaque (chromatin) aggregations and shows a rounded profile. The endoplasmic reticulum is a rather well‐developed system of rough cisternae engaged in synthesis and storage of proteins. Free ribosomes are numerous. A large mitochondrial apparatus shaped like a horseshoe lies in the anterior gamete region. Only one single plastid is found, and it exhibits a deeply indented outline, a partially structured matrix, osmiophilic globules, and three to four starch grains. The axoneme pattern is 9 + 2. B tubules show septate lumina. A peculiar structure provided with a three‐layered shell covering materials of varying electrondensity lies on the upper surface of both basal bodies. The flagellar root system exhibits a cruciate pattern and sets having an inconstant number of microtubules – ie, three, four, or five.