Elongate Sea Pen, Stylatula elongata

Elongate Sea Pen, Stylatula elongata. Underwater photograph taken in coastal waters off La Jolla, California, August 2019. Photograph courtesy of Bob Hillis, Ivins, Utah.

Phylogeny: The Elongate Sea Pen, Stylatula elongata (Gabb, 1862), is a member of the Virgulariidae Family of Slender Sea Pens. The genus Stylatula is one of six genera in that family, and there are fourteen species in that genus. Sea Pens are colonial animals and are a form of octocoral (soft corals). This species is also known as the Spiny White Sea Pen and the Slender Sea Pen. In Mexico they are known as albanico marino elongado.

Morphology: The Elongate Sea Pen is slender in stature and delicate but rough in texture. The polyp leaves (lateral plumes) have a fluffy appearance. The plumes are salmon to white in color. The plumes attach to a hard white skeletal rod that is made of calcium. This rod attaches to a bulbous holdfast (basal peduncle), which anchors the animal to the sea floor. They are a bioluminescent species that glows in the dark if disturbed. This species is often found in large beds consisting of hundreds of individuals. Elongate Sea Pens reach a maximum of 60 cm (23.6 inches) in length. Those in the Sea of Cortez are smaller in stature reaching only 20 cm (7.9 inches) in length, and may be a different species.

Habitat and Distribution: Elongate Sea Pens reside on mud and sand substrates, at depths between 5 m (16 feet) and 100 m (328 feet). They prefer areas with little water movement, so that they are not dislodged from the sea floor. In Mexican waters the Elongate Sea Pen is a resident of the Pacific Ocean and is found along the west coast of the Baja Peninsula, north of Todos Santos, Baja California Sur. They are also found throughout the Gulf of California.

Diet:  Elongate Sea Pens are suspension feeders that filter plankton and organic matter from the surrounding water.

Predators:  Sea stars and nudibranchs are known to prey on Elongate Sea Pens. The Sea Pen avoid predation by being able to retract into its holdfast before these fairly slow moving predators can do too much damage.

Reproduction: Reproduction of Elongate Sea Pens involves external fertilization. The gametes are spawned through the mouths of the polyps. The fertilized eggs develop into planktonic planula larva. The larva develop fairly quickly, limiting the distance they can spread from the colony before settling to the bottom. Elongate Sea Pens are thought to live in excess of one hundred years, which reduces the need for them to reproduce efficiently.

Ecosystem Interactions:  Other than the role that Elongate Sea Pens play in the food web, no interactions with other species have been documented.

Human Interactions:  Elongate Sea Pens have no significant impact on human activities. From a conservation perspective they have not been formally evaluated however they are common with a fairly wide distribution and should be consider to be of Least Concern.

Synonyms: Stylatula ringei and Virgularia elongata.