Crab cuticle

Figure 6.6 (Left ) Stained section of a crab cuticle Carcinus maenas), showing the single twist of protein fibres (some indicated by red lines), characteristic of the chiral thermotropic cholesteric mesophase. (Right ) Schematic relation between nested arc texture in the micrograph and the cholesteric mesostructure. Micrograph and drawing adapted from (9. ...

Fig. 3.5 The chitin-protein matrix of the crab cuticle, a Semi-thin section normal to the carapace, from top to bottom epicuticle (cp), pigmented layer (pi), principal layer (pr), membranous layer (mb). Optical microscopy, bar = 50 pm. b Ultrathin section of the principal layer of the cuticle and the underlying epidermal cells. TEM, bar = 5 pm. c Ultrathin section of the principal layer, the chitin-protein fibrils are seen in longitudinal, oblique or transverse view forming well defined strands. TEM, bar = 1 pm. d Aspect of the chitin protein fibrils observed at high magnification in TEM the central electron light chitin crystals are surrounded by a sheath of contrasted proteins [31]...

Christiansen, M.E. 1986. Effect of diflubenzuron on the cuticle of crab larvae. Pages 175-181 in International Conference on Chitin and Chitosan. Plenum Press, New York. 

Christiansen, M.E. and J.D. Costlow, Jr. 1982. Ultrastructural study of the exoskeleton of the estuarine crab Rithropanopeus harrisii effect of the insect growth regulator dimilin (diflubenzuron) on the formation of the larval cuticle. Mar. Biol. 66 217-226. 

Christiansen, M.E., E. Gosling, and M.A. Williams. 1984. Effect of the insect growth regulator diflubenzuron (dimilin) on the uptake of glucose and V-acetylglucosamine into the cuticle of crab larvae. Mar. Biol. 83 225-230. 

Digby, P. S. B. Mobility and crystalline form of the lime in the cuticle of the shore crab Carcinus maenas. J. Zool. Lond. 154, 273 (1968)... 

Striking evidence for chiral liquid crystallisation in vivo has been collected by Bouligand and co-workers. Optical micrographs of stained sections of crab (Carcinus maenas) and insect (Locusta migratoria) cuticle for example, reveal the single twist characteristic of the cholesteric mesophase (Figure 6). 

The main histological changes in the decapod cuticle during moult were described by Travis (1963, 1965, 1970) and are summarized in the beautiful ultrastructural study of the integument of the fiddler crab Uca by Green and Neff (1972). 

Diflubenzuron inhibits several enzyme systems in crab and insect larvae, resulting in disrupted glucose metabolism, reduced AGA incorporation into cuticle, and ultra-structural deformities of chitinous components of the cuticle. Specifically, diflubenzuron inhibits chitin synthetase, a magnesium-requiring enzyme that catalyzes the transfer of A-acetyl-D-glucosamine to chitin the final result is relatively large accumulations of AGAs. 

Chitin and Chitan. Marchessault et al. (1960) have examined the tilting infrared spectra of two chitin samples crab chitin crystallites and larval cuticle chitin of the blowfly. The general principles for interpreting and the practical procedures for obtaining tilted spectra of polymers have been discussed by Liang and Marchessault (1960) and by Pearson et al. (1960). Figure 6.10 presents schematically the tilting... 

Chitosan is a second abundant heteropolysaccharide composed of /3-[l-4]-2-deoxy-2-amino and -2-acetamino D-glucopyranose units [31]. Chitosan is the partial deacetylated (involving alkaline hydrolysis] product of chitin. Chltln is the main component of outer skeleton of small insects, cuticles, and the shells of shrimp, crab, lobster, etc. Chitosan has been expansively investigated in the pharmaceutical industries for the development of various sustained and controlled release drug delivery systems due to its versatile biological activity [as food and non-food items] and excellent biocompatibility. Hirano [22] conducted an experiment with both healthy and infected skin and found the LD50 in case of orally administered mouse to be [>16 g/kg]. Wu et al. [76] worked on... 

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