The Enteric Nervous System of Echinoderms: Unexpected Complexity Revealed by Neurochemical Analysis

Abstract

Echinoderms are one of the most important groups of metazoans from the point of view of evolution, ecology and abundance. Nevertheless, their nervous system has been little studied. Particularly unexplored have been the components of the nervous system that lie outside the ectoneural and hyponeural divisions of the main nerve ring and radial nerve cords. We have gathered information on the nervous components of the digestive tract of echinoderms and demonstrate an unexpected level of complexity in terms of neurons, nerve plexi, their location and neurochemistry. The nervous elements within the digestive system consist of a distinct component of the echinoderm nervous system, termed the enteric nervous system. However, the association between the enteric nervous system and the ectoneural and hyponeural components of the nervous system is not well established. Our findings also emphasize the importance of the large lacunae in the neurobiology of echinoderms, a feature that should be addressed in future studies.

Humoral responses during wound healing in Holothuria tubulosa (Gmelin, 1788)

“…Even the Holothuroidea class (sea cucumbers) has an exceptional and unique capacity to regenerate the digestive system and associated organs after evisceration (Garcia-Arraras et al, 2001;Dolmatov et al, 2012). Rapid and efficient repair processes are important for preventing the loss of coelomic fluid, as well as subsequent invasions of external pathogens (Moss et al, 1998;Dolmatov et al, 2012).…”

Morphology and Chemical Messenger Regulation of Echinoderm Muscles

“…The histological structure of the digestive tract in echinoderms consists of three layers: an inner digestive epithelium, a middle layer of connective tissue, and an outer celomic epithelium [28,[40][41][42]. The celomic epithelium is usually a pseudostratified myoepithelium, where most myoepithelial cells are orientated perpendicular to the long axis of the gut, forming the outer circular musculature, and a small portion of myoepithelial cells parallel to the long axis constitutes the inner longitudinal musculature [28,41,43]. The myoepithelial cells in the longitudinal musculature are loosely arranged and partially embedded in the underlying connective tissue.…”

Nervous System Development and Neuropeptides Characterization in Embryo and Larva: Insights from a Non-Chordate Deuterostome, the Sea Cucumber Apostichopus japonicus

“…The development of their body plan is closely associated with the development of the nervous system [ 2 ]. The central nervous system of adult echinoderms includes radial nerve cords (RNCs) and a circumoral nerve ring (CNR) in the oral (mouth) region [ 3 , 4 ]. In most echinoderms, RNCs can be further subdivided into ectoneural and hyponeural systems [ 3 , 5 ].…”

“…The central nervous system of adult echinoderms includes radial nerve cords (RNCs) and a circumoral nerve ring (CNR) in the oral (mouth) region [ 3 , 4 ]. In most echinoderms, RNCs can be further subdivided into ectoneural and hyponeural systems [ 3 , 5 ]. The peripheral nervous system (enteric nervous system, connective tissue plexus, and the neural circuitry of the podia or arm) that connects the RNC with other organs, is considered to be the inner entoneural system [ 3 , 6 , 7 , 8 ].…”

“…In most echinoderms, RNCs can be further subdivided into ectoneural and hyponeural systems [ 3 , 5 ]. The peripheral nervous system (enteric nervous system, connective tissue plexus, and the neural circuitry of the podia or arm) that connects the RNC with other organs, is considered to be the inner entoneural system [ 3 , 6 , 7 , 8 ]. In echinoids, holothuroids, asteroids, and ophiuroids, the ecto and hyponeural components are dominant whereas in crinoids the inner entoneural system is the main part of the adult nervous system [ 8 , 9 ].…”