Diploblasts such as Cnidaria and Ctenophora lack the mesodermal layer but possess a layer of mesoglea
, an acellular gel-like matrix of connective tissue, that separates the gastrodermis and the epidermis (Burton, 2008).
For species with a thin mesoglea
layer (<100 [mu] column), such as A.
5a) embedded in the octocoral mesoglea
, which also included some sections in the gastrodermis (Fig.
These cell types were differentiated by their enzyme reactivity and their location within the mesoglea
is remarkable in its ultrastructural similarity to the extracellular matrix of chordates (Tucker et al., 2011), and a number of homologs of chordate extracellular matrix genes have been identified, many of which are known to be integrin ligands in other organisms (Koehler et al., 2009; Ozbek et al., 2010; Tucker et al,, 2013; Tucker and Adams, 2014).
The apex of the cnidocyte with its cnidocil apparatus projects from the surface of the tentacle, while the basal pole, embedded in the ectoderm of the cnidosac, is inserted into the mesoglea
by its basal stalk and basal pad of the fibrillar system (Cormier and Hessinger, 1980).
Individual tentacles responded to electrical stimulation with local and propagated contractions of the longitudinal smooth musculature located within the tentacular mesoglea
. When the stimulating electrode was placed close to the recording electrode and the stimulus voltage was adjusted to just above threshold, each local contraction was accompanied by a short burst of 3-10 extracellularly recorded impulses (5.3 [+ or -] 1.7, n = 19 recordings from 3 animals; Fig.
Although the mechanisms of dinoflagellate symbiont transmission remain unknown, it is likely that symbionts enter through follicle cells surrounding the oocytes in temporary gaps formed in the mesoglea
(Hirose et al., 2001).
Multiple mechanisms are probably involved and include the allocation of food reserves to cells and mesoglea
(Winters et al., 2009; Thornhill et al., 2011), the addition of cells to tissue layers, variation in polyp size and density (Lasker, 1981), and changes in the extent to which tissue permeates the skeleton (Lough and Barnes, 2000).
aurita podocysls (Chapman, 1970), may be made from polyp mesoglea
pinched off by the cyst cells, as described in C.
The polyps, which populate all of the branches, are embedded in mesoglea
, a gelatinous, highly hydrated layer (Lewis and Wallis, 1991) that surrounds the axis.