- Book lung
A book lung is a type of
respiration organused for atmospheric gas exchange and is found in arachnids, such as scorpions and spiders. Each of these organs is found inside a ventral abdominal cavity and connects with the surroundings through a small opening. Book lungs are not related to the lungs of modern land-dwelling vertebrates by evolution. Their name describes their structure. Stacks of alternating air pockets and hemolymph-filled tissue gives them an appearance similar to a "folded" book.cite book |title=Biology of Spiders |last=Foelix |first=Rainer F |authorlink= |coauthors= |url=http://books.google.com/books?id=XUgyqxNKhyAC&pg=PA64&dq=book+lung&sig=lcC3sQ_su5vxlM2HezcsA2vCN9I#PPA64,M1 |year=1996 |publisher=Oxford University Press US |location= |isbn=0195095944 |pages=61-64 ] Their number varies from just one pair in most spiders to four pairs in scorpions. Sometimes the book lungs can be absent and the gas exchange is performed by the thin walls inside the cavity instead, with its surface area increased by branching into the body as thin tubes called tracheae. It is possible that the tracheae have evolved directly from the book lungs, because in some spiders the tracheae have a small number of greatly elongated chambers. Many arachnids, like mites and harvestmen ( Opiliones), have no traces of book lungs and breathe through tracheae or through their body surface only.
The unfolded "pages" (plates) of the book lung are filled with
hemolymph(the arthropod blood). The folds maximize the surface exposed to air, and thereby maximize the amount of gasexchanged with the environment. In most species, no motion of the plates is required to facilitate this kind of respiration.
The oldest book lungs have been recovered from extinct
trigonotarbidarachnids preserved in the 410 million year old Rhynie chertof Scotland. These Devonianfossil lungs are almost indistinguishable from the lungs of modern arachnids [Kamenz, C. "et al." (2008) "Biology Letters" 4, 212-215; doi:10.1098/rsbl.2007.0597] .
The absence or presence of book lungs divides the Arachnida into two main groups, but says nothing about the relationships between them: the pulmonate arachnids (book lungs present;
scorpions, whip scorpions, Schizomida, Amblypygi, and spiders), and the apulmonate arachnids (book lungs absent; microwhip scorpions, harvestmen, Acarina, pseudoscorpions, Ricinuleiand sunspiders). One of the long-running controversies in arachnid evolution is whether the book lung evolved once in the arachnid common ancestor [Scholtz, G. & Kamenz, C. (2006) "Zoology" 109, 2-13; doi:10.1016/j.zool.2005.06.003 ] , or whether it evolved in multiple groups of arachnids in parallel as they came onto land.
Book lungs have evolved from book
gills. Although they have a similar book-like structure, they are found in different locations. Book gills are found externally while book lungs are found internally. [cite book |last=Bhamrah |first=H. S. |authorlink= |coauthors=Kavita Juneja |editor= |others= |title=An Introduction to Arthropoda |origdate= |origyear= |origmonth= |url=http://books.google.com/books?id=b_gsiQXNhTUC&pg=PA316&dq=book+lung+book+gills&lr=&sig=Juz6ERoYYY1K9cr8x0XwFwLIibg |format= |accessdate= |accessyear= |accessmonth= |edition= |series= |date= |year=2002 |month= |publisher=Anmol Publications PVT. LTD. |location= |language= |isbn=8126106735 |oclc= |doi= |id= |pages=316 |chapter= |chapterurl= |quote= ] Book gills are still found in horseshoe crabs which have five pairs of them, the flap in front of them being the genital operculum which lacks gills. Book gills are flap-like appendages that are designed for gas exchange within water and seem to have their origin as modified legs. On the inside of each appendage there are attached over 100 thin leaf-like membranes called "lamellae" which appear as pages in a book, and are the areas of the gill where gas exchange takes place. These appendages move with rhythmic movements to drive blood in and out of the lamellae and to circulate water over them. Respiration being their main purpose, they can also be used for swimming in young individuals. If they are kept moist, the horseshoe crab can live on land for many hours.
Wikimedia Foundation. 2010.
Look at other dictionaries:
book lung — bu̇k n a saccular breathing organ in many arachnids containing thin folds of membrane arranged like the leaves of a book * * * book lung a lunglike invagination that functions as a gas exchange organ, found on the underside of the abdomen of many … Medical dictionary
book-lung — (bookґlung″) see under lung … Medical dictionary
book lung — book′ lung n. ivt the respiratory organ of many arachnids, composed of thin, paperlike layers of tissue • Etymology: 1895–1900 … From formal English to slang
book lung — noun organ in many arachnids containing many thin folds of membrane resembling the leaves of a book • Hypernyms: ↑respiratory organ * * * noun : a saccular breathing organ occurring in many arachnids that contains numerous thin folds of membrane… … Useful english dictionary
book lung — the respiratory organ of a spider, scorpion, or other arachnid, composed of thin, membranous structures arranged like the leaves of a book. [1895 1900] * * * ▪ anatomy form of respiratory organ found in certain air breathing arachnid… … Universalium
book lung — noun Date: 1897 a saccular breathing organ in many arachnids containing thin folds of membrane arranged like the leaves of a book … New Collegiate Dictionary
book lung — (ARTHROPODA: Chelicerata) A series of leaf like respiratory pouches of arachnids, located on the internal ventral surface of the abdomen, and believed to be modified insunken gills … Dictionary of invertebrate zoology
book lung — noun A lamellate respiratory organ found in arachnids … Wiktionary
book lung — noun Zoology (in an arachnid) each of a pair of respiratory organs in the abdomen, composed of many fine leaves … English new terms dictionary
lung book — noun : book lung; especially : the functional laminated part of a book lung … Useful english dictionary