Encrusting sponge

Encrusting sponge

Observation - Encrusting sponge - UK and Ireland. Description: A classically textured sponge, albeit encrusting a seaweed frond. Apparently dead, though pliable, not brittle; certainly had infested a good sized frond of Thongweed (Himanthalia elongata) or Egg wrack (Ascophylum nodosum). The closest I can get is A.

A classically textured sponge, albeit encrusting a seaweed frond.
Apparently dead, though pliable, not brittle; certainly had infested a good sized frond of Thongweed (Himanthalia elongata) or Egg wrack (Ascophylum nodosum).
The closest I can get is A.fucorum (old name Esperiopsis fucorum). Half the name itself may be a clue to the correct ID.
I wish I had taken more photos and perhaps brought some home for closer inspection.
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Core edit
Changed elongate to elongata (above)