Organization of the coelomic lining and a juxtaposed nerve plexus in the suckered tube feet of Parastichopus californicus (Echinodermata: Holothuroida)

Abstract

The coelomic lining of the water-vascular canal in a suckered tube foot from the sea cucumber, Parastichopus californicus, is a pseudostratified myoepithelium consisting of flagellated adluminal cells and myofilament-bearing retractor cells. The bodies of adluminal cells flank the water-vascular canal and send basal processes between the underlying retractor cells to confront the podial connective tissue. Retractor cells have a contractile apparatus of unregistered thick and thin myofilaments. The contractile apparatus is confined to the medullary sarcoplasm and oriented parallel to the primary axis of a tube foot. The bodies and processes of retractor cells intermingle with the basal processes of adluminal cells at the basal lamina of the coelomic lining. A ganglionated nerve plexus in the podial connective tissue approximates the basal lamina. Neuronal connectives link the ganglia to one another and to the nerve plexus in deep sectors of the podial epidermis. External laminae enveloping the ganglia and connectives in the podial connective tissue are continuous with the basal lamina of the epidermis. The adventitial nerve plexus, since it merges with the epidermal nerve plexus, is a component of the ectoneural division of the echinoderm nervous system.

Neurosensory and neuromuscular organization in tube feet of the sea urchin Strongylocentrotus purpuratus

“…This led to the speculation that neuromuscular interactions required neurotransmitter diffusion from the outer subepithelial neuronal layer through the connective tissue layer to the adluminal muscles Cahill, 1977, 1980). Ultrastructural analysis of the tube feet of the holothurian Parastichopus califonicus has recently confirmed the presence of a neural plexus close to the adluminal surface in the stalk (Cavey, 2006). Our analysis of S. purpuratus tube foot neural organization indicates that there is an adluminal nerve plexus in S. purpuratus in addition to the previously described subepithelial plexus.…”

Neuroanatomy of the tube feet and tentacles in Holothuria glaberrima (Holothuroidea, Echinodermata)

“…The same markers that label the radial nerve and lateral nerves (RN1, anti- β -tubulin, 1E11, anti-Sp-SynB, anti-GFSKLYamide, anti-galanin, anti-NGWIYa-L1), also label the podial nerve; supporting the idea that the podial nerve is an elongation of the ectoneural component of the radial nerve (Flammang and Jangoux 1992; Inoue et al 1999; Cavey 2006; Tamori et al 2007). Interestingly, very few RN1 immunopositive cells were observed in the main podial nerve, although neuronal bodies have been well documented in ultrastructural studies (Smiley 1994; Cavey 2006). This is somewhat troublesome, but it can be explained by the same phenomenon observed in the radial nerve that RN1 fails to label the neuronal soma (Díaz-Balzac et al 2007).…”

“…They only branch to give rise to the podial nervous system. Interestingly, the presence of a neural plexus underneath the epidermis has been reported in the sea cucumbers Parastichopus californicus (Stimpson, 1857) (Holothuroidea, Aspidochirotida) (Cavey 2006) and Holothuria forskali (Chiaje, 1841) (Holothuroidea, Aspidochirotida) (Flammang and Jangoux 1992) through TEM studies and named the basiepithelial plexus. Description of this plexus using immunofluorescence in H. glaberrima shows that, although it is more conspicuous underneath the epidermis or in the ECT , the plexus, called the connective tissue plexus, is found throughout the dermis (Díaz-Balzac et al 2007).…”

“…The podial nerves in the tube feet and tentacles are the component of the podia that have been best described in the literature (Hyman 1955; Flammang and Jangoux 1992; Bouland et al 1982; Smiley 1994; Inoue et al 1999; Cavey 2006), as they are conspicuous and easily identifiable. These are formed by extensions of the ectoneural component of the radial nerve known as lateral nerves.…”

“…Almost all of the current knowledge of the podial and tentacular nervous system is based on classical histological descriptions done early during the last century (see Hyman 1955) or on more recent studies done with electron microscopy (Wood and Cavey 1981; Cavey and Wood 1981; Rieger and Lombardi 1987; Flammang and Jangoux 1992; Pentreath and Cobb 1972; Smiley 1994; Cavey 2006). These studies reveal the detail of cells and fibers, but the overall view of the circuitry and anatomical structures is still lacking.…”