A brown algae with a thallus (body) with multiple holes of varying sizes. The algae is said to be about 10 cm in diameter. But in the one that was washed ashore it was a loose mesh like a woolen hair net. The whole mass was compressible and soft.
Found on the inter-tidal zone off Western Port Bay (Balnarring Beach). They are said to grow in the tidal zone.
'Hydro' = water, 'Clathrus' = mesh
This species forms dense mats.