A colony shaped like a quill, anchored in silt, that withdraws underground when touched.
Not one animal but a colony of them. A single founding polyp forms the central stalk, and secondary polyps grow from it in two ranks of leaf-like branches, giving the quill shape the name records. The base is a swollen bulb buried in sediment as an anchor. Colours run cream, orange, pink and purple, and colonies reach about 40 cm standing clear of the bottom. Several genera occur on Indonesian muck and are not reliably separable underwater, so records are usually left at genus.
Feeds at night, extending the polyps into the current to take plankton, and many colonies withdraw entirely by day — pumping water out and pulling down into the sediment until nothing shows. Touched, a colony deflates and disappears in seconds, and some species emit a wave of green bioluminescence as they do; that is a good reason to look and a poor reason to poke. Sea pens are the food of several sea slugs including Armina, and shelter porcelain crabs, small shrimps and juvenile fish among their branches. Recorded from about 3 to 40 m.
Ratings are per location: 1 means found on most dives that look for it, 5 means a handful of records. Where enough dives have been logged the figure is calculated from them; otherwise it is an editorial estimate, and says so. We publish habitat and destination, not the dive site.
