The body wall of cheilostome Bryozoa. II. Interzoidal communication organs

Abstract

Communication organs (septulae) of cheilostome Bryozoa are more complex than perviously believed. Annuli, present only in lateral septulae, are thickenings of the intercalary cuticle. Each communication pore is filled with a ring-like "pore cincture," through which project a pair of "special cells." Septulae of all species examined (10 species from 6 families) can be considered modifications of the same structure, varying only in degree of calcification and number of communication pores.External walls, including basal and laternl walls, are best defined as reinforcements of the ectocyst, which is derived by intussusception from the primary cuticle of the ancestrula. The lateral ectocyst must be considered a double layer formed by invagination of the distal ectocyst. Internal walls are developed by apposition from inner parts of the ectocyst; they include pore plates and transverse walls.External walls are laid down first. Lenticular masses develop unilaterally an the uncalcified lateral ectocyst; the pore plate develops by apposition from the interior part of the ectocyst. Depending on the species, the pore plate may or may not be calcified at the time of its formation. Communication pores are formed when the developing pore plate abuts against embryonic special cells. The septular ectocyst never cab cifies; it breaks down when the pore plate is complete.Some ascophorans undergo "reparative budding," in which new zoids are formed within dead zoecia. Hollow, ectocyst-covered buds lined with blastemic epithelia are produced from septulae of live zoids; adjacent buds may fuse.These findings are consistent with the view that lateral septulae are aborted zoids and that pore plates represent transverse walls.Without exception, bryozoans are colonial. The association between individuals is most obvious in the Phylactolaemata, in which body cavities of adjacent zoids are confluent. In the Eurystomata, however, zoids are separated by septa pierced by holes plugged with specialized cells. Despite the fact that there is no actual confluence, these holes are called "communication pores."There is evidence that the cells associated with communication pores ("rosette cells") are involved in transport of materials from one zoid to another (Bobin, '64, '65).Communication pores differ in number, arrangement, and the morphology of accessory structures, but there are underlying similarities. The similarities were emphasized by Silen, who based much of his complex theory of evolution of eurystome Bryozoa on the structure and development of interzoidal communication organs. Silkn ('42, '44a, '44b) proposed that all J. MORPII., 129: 149-170Eurystomata were derived from a common ancestral form similar to the "protocheilo. stome,"' Labiostomella gisleni (Silkn). He emphasized budding patterns in eurystomes, especially as related to the structure of zoecial walls and communication organs. Siliin's theory requires that lateral communication organs in cheilostome are to be considered aborted zoid buds. As S i l h himself points ou...

Gametogenesis and embryonic brooding in the cheilostome bryozoan Celleporella hyalina

“…It is therefore possible that sperm enter the colony through the expanded lophophores of the autozooids, and migrate to the female zooids along the funicular system. However, it is doubtful whether the cellular plugs described in bryozoan pore plates (Banta, 1969;Gordon, 1975) would allow the interzooidal passage of sperm. Unfortunately, none of the sections made in the present study passed through these structures, so that it is not possible to say whether they are of the same type as those described in other cheilostonies.…”

Comparative ultrastructure of the bryozoan funiculus: A blood vessel homologue

“…Associated with these pores are complexes of cells known as "communication organs" or "sepda" which have been described by a number of workers (SILEN 1944;BOBIN 1958BOBIN a, b, 1962BOBIN , 1964BOBIN , 1965BOBIN , 1971BOBIN , 1977BANTA 1969;GORDON 1974). Cheilostome gymnolaemates show the most complex funicular system with a series of branching cords which connect various parts of the polypide to numerous communication organs which bridge the walls shared by neighboring zooids (LUTAUD 1961;BANTA 1969). The cheilostome funicular system apparently serves a placenta-like function, as well.…”

Adaptive architectural trends in encrusting ectoprocts

“…Pore plates, which occur in many cheilostomes, are porous septa that aid in establishing communication between zooids and are found in lateral walls (Ryland 1970:87). Each pore plate is separated from its neighbor by 'calcareous shelves extending like buttresses between lateral and transverse walls' (Banta 1969). The thickening of the intercalary cuticle into a gasket-like ring (annulus) may also be an antistress adaptation (see Banta 1969).…”

“…Each pore plate is separated from its neighbor by 'calcareous shelves extending like buttresses between lateral and transverse walls' (Banta 1969). The thickening of the intercalary cuticle into a gasket-like ring (annulus) may also be an antistress adaptation (see Banta 1969). TranJverse pore chambers form a tiny partition between a diagonally placed true septum and a second septum derived by invagination of the exterior walls (see Ryland 1970:89, Fig.…”