Conoidasida is a
class of parasitic
alveolates in the phylum
Apicomplexa
The Apicomplexa (also called Apicomplexia) are a large phylum of parasitic alveolates. Most of them possess a unique form of organelle that comprises a type of non-photosynthetic plastid called an apicoplast, and an apical complex structure. Th ...
. The class was defined in 1988 by Levine
and contains two subclasses – the
coccidia and the
gregarines. All members of this class have a complete, hollow, truncated
conoid
In geometry a conoid () is a ruled surface, whose rulings (lines) fulfill the additional conditions:
:(1) All rulings are parallel to a plane, the '' directrix plane''.
:(2) All rulings intersect a fixed line, the ''axis''.
The conoid is a ri ...
. Gregarines tend to
parasitize invertebrate
Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chordate ...
s with the mature gamonts being extracellular, the coccidia mostly infect
vertebrate
Vertebrates () comprise all animal taxa within the subphylum Vertebrata () (chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, with c ...
s and have intracellular gamonts.
Description
A conoid is found in most species and when present forms complete but truncated cone.
Sexual and asexual reproduction are present in
life cycle
Life cycle, life-cycle, or lifecycle may refer to:
Science and academia
*Biological life cycle, the sequence of life stages that an organism undergoes from birth to reproduction ending with the production of the offspring
* Life-cycle hypothesis ...
of all
species
In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...
. Each
zygote
A zygote (, ) is a eukaryotic cell formed by a fertilization event between two gametes. The zygote's genome is a combination of the DNA in each gamete, and contains all of the genetic information of a new individual organism.
In multicell ...
normally forms an
oocyst wall within which it undergoes
meiosis
Meiosis (; , since it is a reductional division) is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, such as sperm or egg cells. It involves two rounds of division that ultimately r ...
. This is sometimes followed by
mitosis. This process of
sporogony produces mobile vermiform infectious
sporozoite
Apicomplexans, a group of intracellular parasites, have life cycle stages that allow them to survive the wide variety of environments they are exposed to during their complex life cycle. Each stage in the life cycle of an apicomplexan organism is ...
s.
Multiple mitotic divisions (
schizogony) also occur during
merogony
Apicomplexans, a group of intracellular parasites, have life cycle stages that allow them to survive the wide variety of environments they are exposed to during their complex life cycle. Each stage in the life cycle of an apicomplexan organism i ...
of the feeding stages (
trophozoite A trophozoite (G. ''trope'', nourishment + ''zoon'', animal) is the activated, feeding stage in the life cycle of certain protozoa such as malaria-causing ''Plasmodium falciparum'' and those of the ''Giardia'' group. (The complement of the trophozoi ...
s) and during
gametogony.
Motility
Microgametes of some species are
flagellated. Locomotion of other
gamete
A gamete (; , ultimately ) is a haploid cell that fuses with another haploid cell during fertilization in organisms that reproduce sexually. Gametes are an organism's reproductive cells, also referred to as sex cells. In species that produce ...
s and any other motile stages is by
gliding or body flexion. Some species possess
pseudopodia but use them only in
phagocytosis
Phagocytosis () is the process by which a cell uses its plasma membrane to engulf a large particle (≥ 0.5 μm), giving rise to an internal compartment called the phagosome. It is one type of endocytosis. A cell that performs phagocytosis is ...
.
References
External links
*
Alveolata classes
{{Apicomplexa-stub