About Pachymatisma johnstonia (Bowerbank, 1842)
Pachymatisma johnstonia (Bowerbank, 1842) is a species of sponge in the family Geodiidae. This sponge is found along the north-eastern Atlantic coasts. It is typically a grey encrusting sponge that has large, prominent oscula and a pale yellow interior. Its overall size and form depend heavily on how much it is exposed to waves. In locations with heavy wave exposure, it is usually small and thin. In more sheltered locations, it can grow to more than 50 cm across and 15 cm thick.
