Spongocytes make gemmules by wrapping shells of spongin, often reinforced with spicules, round clusters of archeocytes that are full of nutrients.
12.
In species of sponges that use spongin instead of calcaerous and silicaceous spicules, the sclerocytes are replaced by spongocytes, which secrete spongin skeletal fibres.
13.
In species of sponges that use spongin instead of calcaerous and silicaceous spicules, the sclerocytes are replaced by spongocytes, which secrete spongin skeletal fibres.
14.
They are generally characterized by concentric layers of fibers containing spongin ( a collagen-like material ), and by large flagellated chambers that open directly into the exhalant canals.
15.
However Janussen, Steiner and Zhu ( 2002 ) opposed this view, arguing that : spongin does not appear in all Porifera, but may be a defining feature of the demosponges; the silica-based spines of demosponges are filter-feeders.
16.
Along with the Dictyoceratida, it is one of the two orders of demosponges that make up the keratose or " horny " sponges, in which a mineral skeleton is minimal or absent and a skeleton of organic spongin-containing fibers is present instead.
17.
In both Homoscleromorpha and Eumetazoa layers of cells are bound together by attachment to a carpet-like basal membrane composed mainly of " type IV " collagen, a form of collagen not found in other sponges although the spongin fibers that reinforce the mesohyl of all demosponges is similar to " type IV " collagen.
18.
:: As for halogens in amino acids-I was going to say not likely-since most examples I know of tend to appear to be the result of electrophilic attack on double bonds eg terpene like compounds etc . . but no : halogenated tyrosines found in marine animals-spongin in sponges and gorgonin in Gorgonians this time-again marine creatures . talk ) 19 : 49, 18 June 2010 ( UTC)
