In this group are placed various parasites with reproductive similarities. The trophozoite is large and feeds in the lumen of the host’s gut or between cells Genetic exchange is achieved by a union of two sporonts (mature trophozoites) prior to gametogenesis.
This union and the formation of gametocysts ensures that gametes can find each other. When gametes develop they do so in a gametocyst and fuse in pairs
These are considered to be primitive gregarines because some species display schizogony, which is lost in the eugragarines. The trophozoites of Selamiin are found in the gut wall of various marine annelid worms and are about 80px 25p.
The elongate body has numerous longitudinal myonemes and the nucleus is situated anteriorly, The extreme anterior carries a knob-like process which serves to attach the parasite to its host’s cells. Very little is known about these common parasites.
The parasites of the two suborders making up this order are morphologically very different but neither displays asexual reproduction by means of schizogony.
Numerical increase occurs by sporog ony, that is, the development of eight sporozoites from each zygote, and also by the production of several to numerous gametes from each gametocyte.
Cephalines (Suborder Cephalina) Many insects have these highly developed parasites as gut parasites. Species of Dermestes and Tenebrio are often heavily infected.
There are many species of the genus Gregarisa. The body of the trophozoite (cephalont) which may be up to 400μ long, has a marked knob (epimerite) on the anterior up and the remaining part in two-jointed. The epimerite is lost when the trophozoite in mature and is no longer.
anchored by it to intestinal cells. This stage (sporont) moves slowly in the gut contents and unites with another sporont. Whether these are symbionts or parasites and harm their hosts is not clear. In some species of Dermestes the proportion of beetles infected can be variable. No difference in health or reproductive capacity of the hosts is noted.
Sometimes a host benefits from a symbiont (as in Trichonympha) and sometimes it may be weakened, as with poorly-adjusted parasites. That neither advantage nor disadvantage is known in this instance indicates a condition of apparent neutrality. Transmission between hosts is by contamination of food with gametocysts containing mature sporocysts.
Acephalines (Suborder Acephalina)
As the name suggests these gregarines are without either epimerite or two-jointed body. The mature trophozoite (sporont) is large by comparison with other stages but seldom exceeds 200μ long. A typical genus is Monocystis which has its life-history in the seminal vesicles of earthworms. The sporont is elongate and has a small distention of the anterior which is used as an anchoring device.
The life history is similar to that of the cephalines and need not be repeated here. A characteristic feature is the invasion of a sperm mother cell of the host by a sporo zoite at a time when the nuclei have just divided.. The young trophozoite is intracellular and takes up a central position surrounded by the host’s sperm nuclei.
The latter continue to develop and at a later stage the trophozoite is seen in sections or smears to be covered with sperm tails. Having grown as large as possible in this cell the parasite escapes and continues to feed between the cells of the seminal vesicles. Sporogony is started when two sporonts come together and form a single gameto cyst around themselves. Infection is believed to be by ingestion of soil infected with sporocysts.