Amphistomium aequabile Schrammen 1924 Amphistomium aequabile is a rare, funnel-shaped sponge with conspicuous tube-like extensions around the pores on the inside and particularly the outside surfaces (see pictures). The outer tube diameter is little more than one millimeter, and the tubes are up to 3 mm long.
The wall of the sponge is about 10 to 12 mm thick. The surfaces are covered with a smooth siliceous cortex. The margin (outer 5 mm) is rounded and wedge-shaped and does not carry any rimmed oscules. Instead, it is free from cortex and shows tiny pores and anastomosing channels.
The species is distinguished from A.spinatum by the greater wall thickness and regular open funnel-shape.
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