Surface Area For Attachment Research Articles

Development of a freshwater periphyton community as influenced by diatom mucilages

The function of diatom mucilage in the formation of spatially complex periphyton communities was investigated in McConaughy reservoir (Nebraska, U.S.A.). Seasonal biofilms on natural and artificial substrates revealed high densities of periphytic diatoms (up to 3.5 × 104 cells mm-2). Growth habits of the dominant taxa (short stalk, Achnanthes minutissima; long stalk, Cymbella affinis and Gomphonema olivaceum; rosette, Fragilaria vaucheriae and Synedra radians) depend on the mucilage morphology. The volume of stalk mucilage in late stages of community development was estimated to be more than two times the volume of the cells producing it. When the periphytic biomass exceeded the carrying capacity of its substrate, portions of the community were sloughed, resulting in the loss of the upper story of cells and mucilage. Diatom mucilage affects community structure as follows: (i) it allows cell–surface adhesion; (ii) stalks of Cym. affinis provide increased surface area for attachment by Ach. minutissima; (iii) dense canopies of long-stalked Cym. affinis and Gomphonema olivaceum trap euplanktonic algae which have settled into the periphyton; (iv) mucilage binds detrital particulates; (v) stalked diatoms enable vertical stratification in the community, as spring collections revealed the development of an upper tier composed of Gomphonema olivaceum and Cym. affinis covering a lower tier dominated by F. vaucheriae and Stephanodiscus minutula.

The oral fimbriae of the lamprey Geotria australis

The frond‐like fimbriae surrounding the oral disc of the lamprey, Geotria australis, have been examined in living specimens, and by using histological, histochemical and ultra‐structural techniques. Approximately 57 fimbriae are present in this species, with those at the posterior end of the disc being significantly larger than those in the anterior and lateral regions. The terminal finger‐like projections of the fimbriae possess a stratified epithelium composed solely of a series of rows of mucous‐producing cells. Tests have shown that the mucus of the epithelial cells contains large amounts of N‐acetyl neuraminic acid. Since the adjacent fimbriae are closely apposed when the lamprey is using its oral disc for suction, it is suggested that their flexible shape, mucous secretions and production of an increased surface area for attachment, help to provide a more efficient seal. Since fimbriae are present in all lampreys except those species belonging to the Mordaciidae, it is postulated that their absence in this latter family can be related to known differences in the behaviour of their adult stages.