A Sea Pen in Costa Rica…that does not write
Written by: Sandra Baksh
At first, it might look like a feather, leaf or some type of clothing accessory, protruding from the sea floor. If you’re lucky to spot it while diving and have a camera to capture that special image, then this rarely noticed specimen, will have you delving into taxonomy research, as soon as you’re out of the water.
As it gracefully wafts in the ocean current, anchored in just one place, at the bottom of the sea, there’s a simple name for what turns out to be a complex animal—the Sea Pen. They are octocorals or soft corals, belonging to Order Pennatulacea. The name sea pen, derived from the ancient Romans, when these creatures were first recorded centuries ago, then called—penna marina. The sea pen or sea plume, resembles a plume or quill that was used for writing, centuries ago. While sea pens comprise colonies of coral polyps, the morphology is almost plant-like.
The Fleshy Sea Pen (Ptilosarcus undulatus), found at the dive site Tortuga, Guanacaste, Costa Rica, is rarely seen. Structurally, there is one primary coral polyp (the oozoid), that looks like a stalk or midrib of a leaf, which forms a bulb or peduncle at the base, and that keeps it anchored to soft sediment on the sea floor. Secondary polyps then branch off to form a collective structure, called a rachis. Some polyps are for filter-feeding, mainly larvae and zooplankton, while others function in water intake and circulation, to maintain the upright structure. As solitary and benthic as they are, sea pens are the favorite food of certain species of nudibranchs and turtles.