1.Monogononta :- The largest group is the Monogononta, with about 1500 species
2. Bdelloidea:- The Bdelloidea, with about 350 species
3.Seisonidea:- (Reproduced by sexually.)
General characters:-
1.Phylum Rotifera are microscopic animal.
2.Mainly found in fresh water rarely in marine and parasitic.
3.Body wall of phylum Rotifer generally lakes a cutical thicken intastiff plates and Lorica into which the head may retrate.
4.Interior end with a cilliated organ called corona.Which helps in swimming and feeding.
5.Posterior food of phylum Rotifera has 2 -toes with cement glands.
6.Cuticale (outer most leayer ) secreated with epidermis and never molted.
7.Digestive system with a highly musculer pharinx called Masterx.
8.No larval stage in the life cycle .
9.Spiral cleavage (mitotically embryonic division).
10.Parthenogenesis largly present in phylum Rotifera. (Fertilisation without union of sperm and ova).
11.Eutelic condition is seen in Phylum Rotifera.
12.Excreatory organ are Protonephridia with Fleme cells.
13.The function of Protonephridia is osmoregulation [Maintenance of water quantity in the body].
14.Body is differentiated into Head, Trunk, and Foot.
15.Body covered by thin , flexible, cuticle, overlaying, thin syncytial hypodermis.
Reproduction and life cycle
1. Rotifers are dioecious and reproduce sexually or parthenogenetically. They are sexually dimorphic, with the females always being larger than the males.
2. In some species, this is relatively mild, but in others the female may be up to ten times the size of the male.
3. In parthenogenetic species, males may be present only at certain times of the year, or absent altogether.
4. The female reproductive system consists of one or two ovaries, each with a vitellarium gland that supplies the eggs with yolk. Together, each ovary and vitellarium form a single syncitial structure in the anterior part of the animal, opening through an oviduct into the cloaca.
5. Males do not usually have a functional digestive system, and are therefore short-lived, often being sexually fertile at birth. They have a single testicle and sperm duct, associated with a pair of glandular structures referred to as prostates (unrelated to the vertebrate prostate). The sperm duct opens into a gonopore at the posterior end of the animal, which is usually modified to form a penis. The gonopore is homologous to the cloaca of females, but in most species has no connection to the vestigial digestive system, which lacks an anus.
6.The phylum Rotifera encloses three classes that reproduce by three different mechanisms:
Seisonidea only reproduce sexually;
Bdelloidea reproduce exclusively by asexual parthenogenesis;
Monogononta reproduce alternating these two mechanisms ("cyclical parthenogenesis" or "heterogony").
Parthenogenesis (amictic phase) dominates the monogonont life cycle, promoting fast population growth and colonization. In this phase males are absent and amictic females produce diploid eggs by mitosis which develop parthenogenetically into females that are clones of their mothers.
7. Fertilization is internal. The male either inserts his penis into the female's cloaca or uses it to penetrate her skin, injecting the sperm into the body cavity. The egg secretes a shell, and is attached either to the substratum, nearby plants, or the female's own body. A few species, such as members of the Rotaria, are ovoviviparous, retaining the eggs inside their body until they hatch.
8. Most species hatch as miniature versions of the adult. Sessile species, however, are born as free-swimming larvae, which closely resemble the adults of related free-swimming species. Females grow rapidly, reaching their adult size within a few days, while males typically do not grow in size at all.
9.The life span of monogonont females varies from two days to about three weeks.
