Critter of the Week - Placogorgia the plexaurid

This delicate little gorgonian coral was collected from around 1300 metres depth from the Louisville seamount chain east of New Zealand.

It has been tentatively identified as Placogorgia, belonging to the gorgonian family Plexauridae.

Placogorgia appears to be a particularly tricky genus to identify confidently, with many a discussion over samples like these between our experts during this year’s coral workshop at NIWA. However, one of the characteristic features of Placogorgia species are the ‘thorn scales’ embedded into the walls of the polyps, which presumably act as a protection. They surround the polyp like a spiky crown – have a look at the closeup to see what we mean.

If it is hard to identify specimens when you can examine them closely with a microscope, giving a positive ID from seafloor images is near impossible. But the DTIS image shows a similar small fan-shaped gorgonian on a nearby seamount between 1200-1600 metres depth, and gives an indication of the habitat these little corals live in. They attach to the volcanic rock and share their habitat with hard corals (top left and right corners), black corals (bottom) and crinoid sea feather stars, and they appear to be hosting a brittle star wrapped around their branches.

Various views of Placogorgia. Scales: left image = 1 cm, sea floor image = 20 cm. Credit: Owen Anderson and DTIS NIWA/ Vulnerable Deepsea Communities voyage TAN1402.