References in periodicals archive ?
Observers often assume that seawater is drawn in through the madreporite by the stone canal cilia to hydraulically extend the tube feet.
But in addition to this osmotic uptake, studies with fluorescent microbeads demonstrate that seawater does flow into the madreporite pores of asteroids (Ferguson, 1990b) and, to a lesser extent, of ophiuroids (Ferguson, 1995), and that it is distributed to peripheral parts of the water vascular system.
Their study led Ellers and Telford (1992) to question Fechter's argument that the madreporite is primarily involved in acute pressure equalization.
Thus, the functions of the prominent madreporite system of sea urchins remain unknown, and the normal osmotic differences that might exist between their various body fluids and the media have not been accurately measured.
An effort was made to quantify the influx of seawater through the madreporite with the soluble, high molecular weight tracer, fluorescein isothiocyanate dextran (FID), as was previously done with asteroids (Ferguson, 1989, 1994).
Two sets of experiments tested the effect of long-term obstruction of the madreporite on behavior, tube feet activity, and maintenance of body fluid volume.
Its madreporite cannot be seen externally, and the structure of its water vascular system must be inferred from old descriptions of other ophiuroid species (cf.
To locate the site of the madreporite and examine the organization of the entire system, two small specimens (6-7 mm disk diameter) were fixed in Helly's fixative and decalcified for one week in changes of cold (4 [degrees] C) 5% disodium EDTA.
The extent of seawater entry through the madreporite was evaluated in two sets of experiments.
Further tests were conducted to see if madreporite oblation would lead to diminished functions.
Both pores lead to a discrete lobe of the madreporite "ampulla.
Weight variations (g) of Ophioderma appressum following destruction of the madreporite area, and control animals with a comparable injury to another site