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Abstract. Oviparous animals store yolk proteins within the developing oocyte. These proteins are used in gametogenesis and as a nutritional source for embryogenesis. Vitellogenin and the major yolk protein are [...]

Abstract. Echinoderms have excellent healing and regeneration abilities, but little is known about how they deal with the related challenge of durable foreign bodies that become lodged within their bodies. [...]

Stiffness changes in response to mechanical and chemical stimulation were studied in muscle-free dermal samples from the body wall of the starfish Linckia laevigata. The ultrastructural study showed that the dermis was packed with collagen fibrils between which only a small number of cells were observed. Muscles were found only in the walls of coelomic extensions leading to papulae. Stress-strain tests were performed on isolated dermis containing no muscles. The tangent modulus was 27.5 MPa at 0.04% strain rate in the stress-strain tests. It was increased to 40.7 MPa by mechanical stimulation, which also increased the tensile strength and breaking-strain energy density. Dynamic mechanical tests showed that the increase in stiffness in response to mechanical stimulation was transient. Acetylcholine ([10.sup.-6] - [10.sup.-3] mol [l.sup.-1) and artificial seawater with an elevated potassium concentration (KASW) stiffened the dermis. Mechanical stimulation caused a 12% mass loss. KASW also caused mass loss, which was inhibited by anesthesia. These results clearly showed that the stiffness changes in the starfish dermis were based on a non-muscular mechanism that was similar to that of other echinoderm connective tissues with mechanical mutability., Introduction Starfish change their body stiffness. On one hand they stiffen the body when it is mechanically stimulated (Motokawa and Wainwright, 1991), which is very probably a defensive behavior. On [...]