59 Octocorals – corals with eight internal walls instead of six

Octocorals, as the name suggests, are corals with eight internal walls instead of the usual six. About 240 species of octocorals live in New Zealand waters today but as of 2009, 185 of these were still undescribed. Octocorals are some of the more unusual fossil corals and are sometimes hard to recognize. They are distinguished by the possession of a calcareous skeletal axis which can be preserved in fossils.

One of the most distinctive octocorals is a long thin, pencil-like fossil – hence the name Graphularia longissima – which is common in the Eocene to Miocene limestones and greensands of the Waitaki Whitestone Geopark and at other sites. Superficially like a long piece of bone, the coral can reach 30 cm in length, but is more often found as broken segments.

Its identity as a coral can be seen in cross-section, where the radial structure is visible as fine concentric layers of calcite, surrounding a central nucleus, though on close examination the cross-section may be subquadrangular. One of the figured specimens is from the now closed Balfour Quarry in Southland which has yielded many interesting fossils including brachiopods and molluscs.

—Written by Daphne E Lee