Characters: Colonies are upright, irregular, usually contorted, anastomosing bifacial plates. They are often over one metre across. Columellae are wall-like lobes.
Colour: Deep bluish-grey or brown.
Similar species: Pachyseris gemmae. See also P. involuta.
Habitat: May develop into large mound-shaped colonies in shallow water but smaller colonies occur in a wide range of habitats including those exposed to strong wave action.
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