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.[2]
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.[4]
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.[5][6]
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.[7][8]
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.[9] In flukes it is used for penetrating the mucosal wall of the gastrointestinal tract for maintaining its parasitic habitat. It is sensory in nature consisting of type 2 sensory receptor, which is a smooth bulb-like non-ciliated papilla.[10]
Molluscans uses it for grasping substratum, catching prey and for locomotory accessory. The best studied acetabular activity is that of octopus. Octopus arms contains 200-300 independently controlled suckers that can grasp small objects and produce high adhesion forces on virtually any non-porous surface. This precise mechanism of high flexibility even has a potential mechanical applications in robotics.[11][12] Each sucker is a tactile sensor for detecting the surrounding. When the sucker attaches itself on an object, the infundibulum mainly provides adhesion while the central acetabulum is quite free. This provides greater suction on the flat surface; hence, making pressure incredibly low. This is why octopus grip is exceptionally firm. Then contraction of the radial muscle of the acetabulum causes detachment of the entire sucker.[7][13]
^Farnesi RM, Marinelli M, Tei S, Vagnetti D (1981). "Morphological and ultrastructural aspects of Branchiobdella pentodonta Whit. (Annelida, Oligochaeta) suckers". J Morphol. 170 (2): 195–205. doi:10.1002/jmor.1051700206. PMID7299828. S2CID21324648.
^Skírnisson K, Kolářová L, Horák P, Ferté H, Jouet D (2012). "Morphological features of the nasal blood fluke Trichobilharzia regenti (Schistosomatidae, Digenea) from naturally infected hosts". Parasitol Res. 110 (5): 1881–92. doi:10.1007/s00436-011-2713-9. PMID22146993. S2CID253976749.
^Cribb TH, Bray RA (1999). "A review of the Apocreadiidae Skrjabin, 1942 (Trematoda: Digenea) and description of Australian species". Syst Parasitol. 44 (1): 1–36. doi:10.1023/a:1006197201426. PMID10619071. S2CID1981959.
^Stern-Tomlinson W, Nusbaum MP, Perez LE, Kristan WB Jr (1986). "A kinematic study of crawling behavior in the leech, Hirudo medicinalis". J Comp Physiol A. 158 (4): 593–603. doi:10.1007/bf00603803. PMID3723440. S2CID9669237.
^Filippi JJ, Quilichini Y, Marchand B (2013). "Topography and ultrastructure of the tegument of Deropristis inflata Molin, 1859 (Digenea: Deropristidae), a parasite of the European eel Anguilla anguilla (Osteichthyes: Anguillidae)". Parasitol Res. 112 (2): 517–528. doi:10.1007/s00436-012-3162-9. PMID23052788. S2CID253978450.