Echinodermata

MASHANOV, VLADIMIR; ZUEVA, OLGA; RUBILAR, TAMARA; EPHERRA, LUCÍA; GARCÍA-ARRARÁS, J.E.

Structure and evolution of invertebrate nervous systems

Oxford University Press

Año: 2015; p. 665 - 688

The central nervous system (CNS) of echinoderms is composed of the morphologically distinct ectoneural andhyponeural subsystems (plus the aboral subsystem in crinoids), which are nevertheless highly interconnectedto form a single anatomical entity. In terms of histological architecture, each of these CNS components is aneuroepithelium composed of various types of unmyelinated neurons embedded in a supporting frameworkformed by radial glia. A large diversity of neuronal phenotypes producing a rich array of neurotransmitters havebeen described in both adult and larval nervous systems. Contrary to the general belief, echinoderm nervecells can communicate with each other via ´classical´ chemical synapses. The radial glia are multifunctionalcells, which share some morphological, immunocytochemical, and functional characteristics with radial glia ofchordates. Sensory input to the echinoderm nervous system is mostly mediated through numerous receptorsof various modalities scattered throughout the body. Specialized sense organs are rare and representedby light-sensitive structures and statocysts. The effectors that handle the CNS output include, besides thevisceral and body wall musculature, echinoderm-specific mutable collagenous tissue, which is capable ofchanging its mechanical properties in response to neural stimuli. Indirectly developing echinoderms forma larval nervous system, which is mainly associated with locomotory ciliary bands and the gut. The larvalnervous structures completely degenerate at metamorphosis, and the adult pentameric CNS develops denovo from the oral ectoderm. A hypothesis is discussed that each of the radial nerve cords of the pentamericechinoderm CNS might be homologous to the neural tube of chordates