Adhesive organs of the gastrotricha

Abstract

The lateral and posterior adhesive organs of an undescribed species ofNeodasys can be seen by electron microscopy to have only one gland cell type. This gland has dense spherical secretion granules like secretion granules of the viscid glands of other gastrotrichs, and it extends to the exterior through a tubular extension of the animal's cuticle, the adhesive tubule, as in other gastrotrichs. Each adhesive gland ofNeodasys has a prominent striated rootlet that extends through its full length, attaching at its distal end to a basal-body-like structure at the tip of the gland's neck. Unlike other gastrotrichs,Neodasys has no second gland type that would be equivalent to a releasing gland. The lateral adhesive organs have a sensory cell closely associated with the gland cell but not in direct communication with the lumen of the tubule; it bears a single cilium that projects alongside the adhesive tubule. The posterior adhesive organ has adhesive gland cells whose necks reach to adhesive tubules on toe-like extensions of the animal's body; sensory cells here are not in a one-to-one association with the tubules; a secretory myoepithelial cell extends to the tip of each toe. The adhesive organs ofNeodasys are interpreted as being of a form that would have been found in a common ancestor to the gastrotrichs and from which the duo-gland organs of other gastrotrichs might have been derived.