The contractile sponge epitheliumsensu lato– body contraction of the demospongeTethya wilhelmais mediated by the pinacoderm

Abstract

SUMMARYSponges constitute one of the two metazoan phyla that are able to contract their bodies despite a complete lack of muscle cells. Two competing hypotheses on the mechanisms behind this have been postulated to date: (1) mesohyl-mediated contraction originating from fusiform smooth muscle-like actinocytes ('myocytes') and (2) epidermal contraction originating in pinacocytes. No direct support exists for either hypothesis. The question of agonist-antagonist interaction in sponge contraction seems to have been completely neglected so far. In the present study we addressed this by studying sponge contraction kinetics. We also tested both hypotheses by carrying out volumetric studies of 3D synchrotron radiation-based x-ray microtomography data obtained from contracted and expanded specimens of Tethya wilhelma. Our results support the pinacoderm contraction hypothesis. Should mesohyl contraction be present, it is likely to be part of the antagonist system. We conclude that epithelial contraction plays a major role in sponges. Contractile epithelia sensu lato may be regarded as part of the ground pattern of the Metazoa. Supplementary material available online at

Elements of a ‘nervous system’ in sponges

“…Recent work has referred to them as actinocytes and there is some evidence that actinocytes are largely epithelial, i.e. are pinacocytes, and that mesohyl cells play a passive role in contractions (Nickel et al, 2011). Where canals are wide, 'sphincters' made from one or more specialized pinacocytes arise from the canal epithelium, allowing the sponge to constrict a portion of the canal.…”

P05 imaging beamline at PETRA III: first results

“…4,5 Although sponges lack nerve and muscle cells, they are contractile and able to respond specifically upon external stimuli and display endogenous rhythms (for a review see Nickel et.al. 6 ).…”

“…6 The phasic contraction of freshwater sponges is a challenge to this hypothesis and SRµCT at the sub-micrometer resolution will allow for evaluating this particular hypothesis and its alternative hypothesis, the contractility of the sponge mesenchyme (connective tissue). Aiming to test the alternative hypothesis x-ray tomograms were acquired at the BW2 beamline 7 at the former storage ring DORIS III at DESY (shut down in 2012).…”

Predation and the Origin of Neurones

“…Keijzer et al [2013] argue that nervous systems evolved not as an input-output mechanism, but rather as a way to coordinate muscle contraction over large spatial scales. Their argument is based on some of the material we have presented, for example that nervous systems are not necessary for animals to detect stimuli, but does not seem to account for the fact that nervous systems are not necessary for animals to coordinate movement on large spatial scales either [Nickel et al, 2011]. Their point is well taken: a crucial function of the earliest nervous systems was to facilitate quick muscle contractions over the whole body.…”