Arm autotomy in brittlestars (Echinodermata: Ophiuroidea)

Abstract

Although ophiuroid arm shedding has long been accepted as an example of autotomy, there has been little investigation of the phenomenon to substantiate this. This paper describes the outwardly visible aspects of autotomy and the function of the internal components of the arm during detachment. Observations are focussed on Ophiocomina nigra, some comparisons being made with eight other species. Ophiuroid autotomy is characterized by its occurrence close to the point of stimulation, its rapidity, and by the pattern of intervertebral muscle separation at the insertions which is constant for a given species. Evidence is presented showing the important role played by the intervertebral ligament. Both this and the muscle insertions are collagenous, and it is suggested that they and the other intersegmental connective tissues facilitate autotomy by undergoing a drastic, nervously mediated loss in tensile strength which enables the animal to part from its arm with a minimum of effort. Comparable properties have been ascribed to other echinoderm connective tissues, and their role in asteroid and holothurian autotomy has been acknowledged, but such a mechanism has not previously been suggested for ophiuroid arm autotomy.

Wound healing and arm regeneration in Ophioderma longicaudum and Amphiura filiformis (Ophiuroidea, Echinodermata): comparative morphogenesis and histogenesis

“…There appears to be no speciWc local reservoir of undiVerentiated cells that can migrate through the tissues; this may represent a limitation for ophiuroids. In contrast in crinoids, such reserve elements present extensively around Smith et al (1995) Habitat Epibenthic Infaunal Tortonese (1965), Rosenberg (1995) Depth Shallow (<70 m) Sublittoral (<200 m) Tortonese (1965), Rosenberg (1995) Feeding Carnivorous Suspension feeder Tortonese (1965), Rosenberg (1995) Disc diameter Up to 30 mm Up to 10 mm Disc-arm ratio 1:5 1:12 Dupont and Thorndyke (2006), this study Autotomy: oral muscles separate from Proximal insertions Proximal insertions Wilkie (1978Wilkie ( , 2001 Autotomy: aboral muscles separate from Proximal insertions Distal insertions Wilkie (1978Wilkie ( , 2001 Arm regenerating (%) 40 86 Dupont and Thorndyke (2006), this study…”

Integrating morphology andin vivoskeletal mobility with digital models to infer function in brittle star arms

“…The vertebral ossicles are the most critical for movement as they incorporate the intervertebral muscle attachments and joint interfaces. Four intervertebral muscles, two aboral and two oral, attach to each vertebra surrounding a central intervertebral joint (Wilkie, 1978b; Byrne, ; Clark et al. ).…”

Functional Morphology of the Arm Spine Joint and Adjacent Structures of the Brittlestar Ophiocomina nigra (Echinodermata: Ophiuroidea)

“…Such a loss of tensile strength is undergone by the intervertebral ligament of O . nigra during arm autotomy [38,65,66]. However, arm autotomy is achieved within a timescale of around 1 s after the onset of stimulation [65], whereas spine loss took up to nine days.…”

“…nigra during arm autotomy [38,65,66]. However, arm autotomy is achieved within a timescale of around 1 s after the onset of stimulation [65], whereas spine loss took up to nine days. This difference may be due to the low intensity of irritation caused by the presence of a tag, but more probably signifies that spine loss is not a true autotomy process but an example of opportunistic self-detachment [66], which can be achieved not because the joint is adapted for autotomy but because it is held together by MCT, the primary function of which is to modulate joint mobility.…”