The juxtaligamental cells of Ophiocomina nigra (Abildgaard) (Echinodermata: Ophiuroidea) and their possible role in mechano-effector function of collagenous tissue.

The intervertebral ligament of the brittlestar Ophiocomina nigra contains numerous cellular processes which belong to perikarya located on the outer surfaces of the ligament. These are described as the juxtaligamental cells and have been studied by light and electron microscopy. The cells are mainly concentrated in four pairs of ganglion-like nodes associated with the intervertebral ligament and in similar nodes adjacent to every other major connective tissue component of the arm. Although their histochemistry and ultrastructure indicate a neurosecretory function, they are anomalous in containing unusually large electron-dense granules probably associated with calcium. The ganglion-like nodes are innervated by hyponeural nerves, though synaptic contacts with the juxtaligamental cells have yet to be demonstrated. The function of the cells is discussed and it is suggested that they may be involved in the rapid loss of tensil strength which the intervertebral ligament sustains during arm autotomy. They may achieve this by controlling the availability of Ca2+ ions to the extracellular compartment of the ligament.