Pennatulidae Family of Sea Pens

One Sea Pen from the Pennatulidae Family can be found in this website:

Fleshy Sea Pen, Ptilosarcus undulatus.  A representative example of a Sea Pen from the Pennatulidae Family.

Phylogeny: Sea Pens are an octocoral that are members of the Pennatulidae family and like hydroids, jellyfish and sea anemones they belong to the phylum Cnidaria.  They are the subphylum Anthozoa, the class Octocorallia, the order Scleralcyonacea, and the superfamily Pennatuloidea. The Pennatulidae family is one of sixteen families in this superfamily. The Pennatulidae family contains seven genera and fifty-five species. The name Pennatulidae comes from the Latin word meaning “feathered” or “winged”, and refers to the feather-like appearance of species in this family. Sea Pens have been known since the ancient Romans, who called them “penna marina” (sea feather or sea pen) and also “mentula alata” (winged penis). Their common name Sea Pen refers to their resemblance to the quill pens of antiquity.

Morphology: As Cnidarians, Pennatulid Sea Pens have polyps with radial symmetry, a hollow digestive cavity, and specialized stinging structures in tentacles surrounding the mouth. Their polyps have a flower-like appearance. As octocorals, they are colonial organisms, with polyps that have 8-fold radial symmetry. Their 8 tentacles are pinnate (having a feather-like appearance). Octocorals lack the hard calcium carbonate skeletons of Stony Corals. Sea Pen colonies of the Pennatulidae Family differ from other octocorals in that they consist of a single large polyp (initial polyp or oozooid) that anchors the colony in soft substrate. This oozooid supports the feeding polyps (autozooids) and water circulation polyps (siphonozooids). The autozooids are located on well-developed “leaves”. The siphonozooids are located on the rachis (axis). In most pennatulaceans, the anchoring stalk has an axis composed primarily of calcium carbonate. This axis may be circular or quadrate in cross-section. In a few species, the end of the peduncle is shaped like a suction cup, allowing the animal to anchor to hard substrate. Not all Sea Pens have the feather-shaped outline, some are club or umbrella shaped. Some Pennatulaceans exhibit bioluminescence. Most Pennatulid Sea Pens are around 20 cm (3.8 inches)- 40 cm (7.6 inches) in height, but some species can exceed 2 m (79 inches).

Habitat and Distribution: Pennatulid Sea Pens are usually found anchored in soft substrates , but some are found attached to hard surfaces. Most are found at depths between 10 m (33 feet) and 20 m (66 feet), though some deep water species exceed 2,000 m (6,560 feet). Sea Pens are found worldwide in polar to tropical seas. At least two species from this family are found in Mexican waters.

Reproduction: Pennatulid Sea Pen colonies are gonochoric (male or female for life). They reproduce sexually, through broadcast spawning, with external fertilization. The eggs develop into planular larvae before they settle to the substrate and metamorphose into their adult form. They may also reproduce asexually, by budding. Some species have life spans that exceed 100 years.

Ecosystem Roles:  Sea Pens are suspension feeders that use their tentacles to capture suspended plankton from the surrounding water. In turn they are preyed upon by nudibranchs and sea stars.