Monorhaphis is a monotypic genus of siliceous deep sea Hexactinellid sponges.

The species was described by Franz Eilhard Schulze in 1904 from specimens collected by the German Deep Sea Expedition in 1898–1899.

One study provides substantial evidence that an individual of this deep-sea sponge, that forms giant spicules up to 3 meters long, is about 11,000 years old.

[4] Early growth of the giant spicule is bidirectional, and then unidirectional towards the apex.

[5] The samples were shown to record deep ocean silica geochemistry throughout their lives.