Lec 11: Rotifera and Acanthocephala

• Rotifera derive their name from the characteristic ciliated crown, or corona, that, when beating, often gives the impression of rotating wheels
• Rotifers are common inhabitants of freshwater lakes and ponds.
• Pelagic forms of Rotifers are common in surface waters of freshwater lakes and ponds.
• Some rotifers are epizoic (live on the body of another animal) or parasitic
• Floaters are usually globular and saclike; creepers and swimmers are somewhat elongated and wormlike; and sessile types are commonly vaselike, with a thickened outer epidermis (lorica).
• Many species of rotifers can endure long periods of desiccation, during which they resemble grains of sand.
• A rotifer’s body comprises a head bearing a ciliated corona, a trunk, and a posterior tail, or foot.
• Except for the corona, the body of Rotifers are nonciliated and covered with a cuticle.
• The ciliated corona of Rotifers, or crown, surrounds a nonciliated central area of their head, which may bear sensory bristles or papillae
• The trunk of Rotifers contains visceral organs and often bears sensory antennae.
• Their foot is narrower and usually bears one to four toes. The foot is an attachment organ and contains pedal glands that secrete an adhesive material used by both sessile and creeping forms.
• Rotifers are dioecious, and males are usually smaller than females.
• The female reproductive system in the Bdelloidea and Monogononta consists of combined ovaries and yolk glands (germovitellaria) and oviducts that open into the cloaca.
• In Bdelloidea, all females are parthenogenetic and produce diploid eggs that hatch into diploid females.
• In class Seisonidea females produce haploid eggs that must be fertilized and that develop into either males or females
• In Monogononta, however, females produce two kinds of eggs
• Class Seisonidea - marine forms with elongated but vestigial corona and epizoic in gills of crustaceans
• Class Bdelloidea - creeping or swimming form of trochal discs in corona; parthenogenetic with unknown males
• Class Monogononta - sessile and swimming forms with small males and complex egg types
• Acanthocephala as the sister taxon to Rotifera.
• Members of phylum Acanthocephala are commonly called “spiny-headed worms.”
• The phylum Acanthocephala derives its name from one of its most distinctive features, a cylindrical, invaginable proboscis bearing rows of recurved spines, by which it attaches itself to the intestine of its host
• All acanthocephalans are endoparasitic, living as adults in the intestine of vertebrates.
• The proboscis of Acanthocephalans, which bears rows of recurved hooks, is attached to the neck region and can be inverted into a proboscis receptacle by retractor muscles.
• The body wall of Acanthocephalans are syncytial, and its surface is covered by minute crypts 4 to 6 μm deep, which greatly increase the surface area of the tegument.
• Acanthocephalans have no heart, but muscles of the body wall form tubes connected to the lacunar system.
• Acanthocephalans have no respiratory system.
• When present, the excretory system of Acanthocephalans consist of a pair of protonephridia with flame cells. These unite to form a common tube opening into the sperm duct or uterus.
• The nervous system of Acanthocephalans have a central ganglion within the proboscis receptacle and nerves to the proboscis and body
• Acanthocephalans have no digestive tract, so they absorb all nutrients through their tegument.
• The phylogeny of Acanthocephala is largely based on the shape and organization of spines of the proboscis.
• Acanthocephalans are divided into three classes: Archoacanthocephala, Eoacanthocephala, and Palaeacanthocephala.