A sperm is the male reproductive cell. When the sperm has the usual single flagellum (or "tail") to propel it along, it is called a spermatozoon and may be described as uniflagellate. Unlike this motile cell, a sperm that lacks a flagellum is not motile and is termed a spermatium.
Spermatia are produced in the spermatangium, which is found in microorganisms, algae, fungi and the gametophytes of plants.
Fungi spermatia, also called pycnidiospores are often confused with conidia. In some fungi however, the spermatia are identical to conidia and actually germinate both with and without fertilization. In addition, one study of the fungi Botrytis cinerea demonstrated that large numbers of microconidia were found in the sexual bodies.
Crossing tests were performed which showed that microconidia are actually able to function similarly to spermatia during reproduction.
In the red alga Erythrocystis montagnei, a particularly dense portion of the spermatial vesicle membrane has a layer of microtubules that is 20 nm thick. Usually, this portion forms two swellings that appear three-shaped cross sectionally.
However, occasionally two separate cylindrical bodies, around 0.3 μm in diameter, have been seen in the vesicles and some have suggested they may be remnants of flagella.
Another red alga called Tiffaniella snyderae has also been studied. Their spermatia are released from the exposed spermatial strands that connect to the spermatangial heads. Individual spermatial strands interact to form multi-spermatial strands that can be as long as 600 μm with as many as 47 spermatia along their length, although mainly the strands are 100-200 μm in length and accommodate 8 to 21 spermatia.
Further Reading
What influence has COVID-19 vaccination had on sperm characteristics?