TY - JOUR

T1 - Ultrastructure of the ciliary pits in the Geocentrophora group (Platyhelminthes, Lecithoepitheliata)

AU - Raikova, Olga I.

AU - Reuter, Maria

AU - Böckerman, Inger

AU - Timoshkin, Oleg A.

PY - 1995

Y1 - 1995

N2 - The ultrastructure of the paired lateral ciliary pits in several endemic species of Geocentrophora from Lake Baikal and in one cosmopolitan species, G. baltica, has been compared and the possible functional significance is discussed. The pit is composed of two distinctive parts; the bottom of the pit is an extensive sensitive area, filled with uni-and biciliary sensory receptors with reduced rootlets and numerous neurotubules. The walls of the pit are formed by several large ‘dark cells’, characterized by a dark cytoplasm with numerous mitochondria, a large nucleus, intracellular canaliculi, basal infoldings of the cell membrane, glycogen granules and a varying number of cilia. A protruding, densely ciliated ridge occurs along the anterior wall of the pit. The cilia have a strengthened rootlet system and seem to provide a strong water current into the pit. Dark cell processes penetrate the basement membrane of the pit and come into the vicinity of large cells with a cytoplasm similar to that of the ‘dark cells’ of the pit. These large cells in their turn come close to the terminal parts of the protonephridial canals, containing a weir. Smaller protonephridial capillaries without a weir seem to open directly into the pit lumen. The morphological data obtained suggest that the ciliary pit in not only a sensory structure, but plays a part in osmoregulation and ion exchange as well.

AB - The ultrastructure of the paired lateral ciliary pits in several endemic species of Geocentrophora from Lake Baikal and in one cosmopolitan species, G. baltica, has been compared and the possible functional significance is discussed. The pit is composed of two distinctive parts; the bottom of the pit is an extensive sensitive area, filled with uni-and biciliary sensory receptors with reduced rootlets and numerous neurotubules. The walls of the pit are formed by several large ‘dark cells’, characterized by a dark cytoplasm with numerous mitochondria, a large nucleus, intracellular canaliculi, basal infoldings of the cell membrane, glycogen granules and a varying number of cilia. A protruding, densely ciliated ridge occurs along the anterior wall of the pit. The cilia have a strengthened rootlet system and seem to provide a strong water current into the pit. Dark cell processes penetrate the basement membrane of the pit and come into the vicinity of large cells with a cytoplasm similar to that of the ‘dark cells’ of the pit. These large cells in their turn come close to the terminal parts of the protonephridial canals, containing a weir. Smaller protonephridial capillaries without a weir seem to open directly into the pit lumen. The morphological data obtained suggest that the ciliary pit in not only a sensory structure, but plays a part in osmoregulation and ion exchange as well.

KW - ciliary pit

KW - Lecithoepitheliata

KW - osmoregulation

KW - protonephridia

KW - sensilla

KW - ultrastructure

UR - http://www.scopus.com/inward/record.url?scp=84951515396&partnerID=8YFLogxK

U2 - 10.1007/BF00036382

DO - 10.1007/BF00036382

M3 - Article

AN - SCOPUS:84951515396

VL - 305

SP - 169

EP - 175

JO - Hydrobiologia

JF - Hydrobiologia

SN - 0018-8158

IS - 1

ER -