Internal Anatomy

          The body wall of Stichopus chloronotus is composed mostly of collagen fibres (Menton and Eisen 1970; Matsumura 1974). The body wall can be stiffened as described in the External Morphology section of this webpage, but it is generally soft. The integument can disintegrate quickly, even though it is quite thick (Conand et al. 1998). Echinoderms (spiny-skinned animals) typically have a noticeably spiny skeleton, however in holothurians this is reduced to small ossicles embedded in the body wall (Edgar 2008). The shape of these ossicles is often used for identification of taxons and species (Edgar 2008). The ossicles of Stichopus chloronotus are made of calcium carbonate (Endean 1982) and are often C or S-shaped, hence the name Stichopus (Rowe and Gates 1995).

           The digestive system is made of a long gut, which in Stichopus chloronotus is coiled into three loops (Conand et al. 1998). The walls of the digestive tract are very thin, and the tract has an average length of approximately 30 cm (Conand et al. 1998). The mouth opens into a muscular pharynx and the ring canal (Ruppert et al. 2004). Connected to this ring canal are five longitudinal muscle bands, which also connect to the cloaca and the integument (Conand et al. 1998). The oral tentacles may be retracted into the trunk using pressure from the water vascular system (Ruppert et al. 2004). The water vascular system is also responsible for giving the tentacles their shape (Conand et al. 1998), controlling the movement of tube feet, and transporting liquid throughout the body, while being aided by cilia (Edgar 2008). The intestine leads to the cloaca, a rectum-like chamber that precedes the anus (Ruppert et al. 2004). Two respiratory trees, which are highly branched organs that are used for respiration (Edgar 2008), open into the cloaca and extend into the coelomic cavity (Conand et al. 1998). Respiration is achieved by pumping water in and out of the cloacal chamber at the posterior end of the animal (Endean 1982). This pumping is done using cloacal dilator muscles that contract to bring water into the anus and then expel it (Ruppert et al. 2004).

          The hemal system and coelomic systems are both used for internal transport (Ruppert et al. 2004). There is no true heart, and the vessels are contractile (Ruppert et al. 2004). The nervous system is comprised of a nerve ring near the oral tentacles, and there is no true brain (Ruppert et al. 2004). Genital glands are situated on both sides of the dorsal mesentery, and the gonads appear to be branched tubules (Conand et al. 1998). The gonads look similar in both males and females and are whitish in colour (Franklin 1980). The video below shows a dissected sea cucumber with anatomy that is similar to that of Stichopus chloronotus.