Concept

Acetabulum (morphology)

Summary
Acetabulum æsɪˈtæbjʊləm (plural acetabula) in invertebrate zoology is a saucer-shaped organ of attachment in some annelid worms (like leech) and flatworms. It is a specialised sucker for parasitic adaptation in trematodes by which the worms are able to attach on the host. In annelids, it is basically a locomotory organ for attaching to a substratum. The name also applies to the suction appendage on the arms of cephalopod molluscs such as squid, octopus, cuttlefish, Nautilus, etc. Acetabulum literally means "a small saucer for vinegar". It is derived from two Latin words acetum, meaning "vinegar", and -bulum, a suffix denoting "saucer" or "vessel" or "bowl". The name is used because of the saucer-like structure in the invertebrates. In leeches, acetabulum refers to the prominent posterior sucker at the extreme end of the body. In fact it forms a head-like structure, while the actual head is relatively small. It is a thick disc-shaped muscular system composed of circular, longitudinal and radial fibers. In flatworms, acetabulum is the ventral sucker situated towards the anterior part of the body, but behind the anterior oral sucker. It is composed of numerous spines for penetrating and gripping the host tissue. The location and structure of the acetabulum, and the pattern of the spine alignment are important diagnostic tool among trematode species. Acetabulum in molluscs is a circular hollow opening on the arms. It occupies the central portion of the sucker and surrounded by a larger spherical cavity infundibulum. Both these structures are thick muscles, and the acetabulum is specifically composed of radial muscles. They are covered with chitinous cuticle to make a protective surface. Acetabulum is essentially an organ of attachment. In annelids, it is used for adherence to the substratum during a looping locomotion. Annelid worms such as leeches move by repeated alternating extensions and shortenings of the body. This in turn is done by successive attachment and detachment of the oral sucker and the acetabulum.
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Related concepts (3)
Sucker (zoology)
A sucker in zoology is a specialised attachment organ of an animal. It acts as an adhesion device in parasitic worms, several flatworms, cephalopods, certain fishes, amphibians, and bats. It is a muscular structure for suction on a host or substrate. In parasitic annelids, flatworms and roundworms, suckers are the organs of attachment to the host tissues. In tapeworms and flukes, they are a parasitic adaptation for attachment on the internal tissues of the host, such as intestines and blood vessels.
Digenea
Digenea (Gr. Dis – double, Genos – race) is a class of trematodes in the Platyhelminthes phylum, consisting of parasitic flatworms (known as flukes) with a syncytial tegument and, usually, two suckers, one ventral and one oral. Adults commonly live within the digestive tract, but occur throughout the organ systems of all classes of vertebrates. Once thought to be related to the Monogenea, it is now recognised that they are closest to the Aspidogastrea and that the Monogenea are more closely allied with the Cestoda.
Trematoda
Trematoda is a class of flatworms known as flukes or trematodes. They are obligate internal parasites with a complex life cycle requiring at least two hosts. The intermediate host, in which asexual reproduction occurs, is usually a snail. The definitive host, where the flukes sexually reproduce, is a vertebrate. Infection by trematodes can cause disease in all five traditional vertebrate classes: mammals, birds, amphibians, reptiles, and fish. Trematodes are commonly referred to as flukes.