Sea pens | Oceana Canada

Canadian Marine Life Encyclopedia

Sea pens

Penatulacea

Distribution

Range depends on species, some are circumglobal while others are more restricted

Ecosystem/Habitat

Sandy or muddy bottoms

Feeding Habits

Filter feeder

Conservation Status

Not listed

Taxonomy

Class Anthozoa (corals, anemones & relatives); Order Pennatulacea (sea pens)

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Sea pens are colonial corals. Like their relatives, sea pens are made up of a colony of several polyps (individual animals). What makes them unique among colonial corals is that each polyp is specialized to perform specific functions. One of their polyps develops into a rigid, erect stalk, which anchors the rest of the colony to the ocean floor. This gives many sea pens an appearance similar to a large feather or old-fashioned quill pen, which is how they got their name.

Sea pens come in all shapes, sizes and colours; however each colony and species has a central stem, called the rachis, which anchors and supports the rest of the colony. The rachis is a specialized polyp which develops into an erect stalk. It loses all its tentacles and forms a bulbous root (called the peduncle), which secures the colony to the ocean floor. In some species, this stalk, or rachis, can be more than a metre long. Most sea pens have a skeleton made of calcium carbonate that runs down its length. Branching off of the central rachis are the other polyps, which are used for such things as feeding, taking in water or reproduction. Despite their name, not all sea pens look like old-fashioned quill pens. Some species lack the “feather-like” structure and look more like clubs, umbrellas or pinwheels.