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 Stylatula genus is one of six genera in the Virgulariidae Family, and there are fourteen species in the Stylatula genus. Sea Pens are colonial animals and are a form of octocoral (soft corals). They are also known as the Spiny White Sea Pen and the Slender Sea Pen and in Mexico 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 Gulf of California are smaller in stature reaching only 20 cm (7.9 inches) in length, and may be a different, yet-to-be described, 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. The Elongate Sea Pen is found in all Mexican waters of the Pacific Ocean with the exception that they absent from south of Mazatlán, Sinaloa, along the central and southwest coasts of the mainland.

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 avoids predation by being able to retract into its holdfast before these fairly slow moving predators can do too much damage.

Reproduction: Elongate Sea Pens reproduce sexually through broadcast spawning, with 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. They are occasionally captured in fishing trawls. 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.