Fleshy Sea Pen, Ptilosarcus undulatus

Fleshy Sea Pen, Ptilosarcus undulatus. Underwater photographs taken in Zihuatanejo Bay, Guerrero, March 2018 and February 2020. Photographs courtesy of Maude Jette, Dive Zihuatanejo, www.Divezihuantanejo.com.

Phylogeny:  Fleshy Sea Pens, Ptilosarcus undulatus (Verrill, 1865), are octocorals in the Pennatulidae Family of Sea Pens. The genus Ptilosarcus is one of eight genera in this family, and there are two species in this genus. This species is also known as the Pacific Sea Pen and in Mexico as abanico marino carnoso and pluma del mar.

Morphology:  Fleshy Sea Pens are colonial animals. They have a flattened central stalk, which anchors them in soft substrates. The stalk also provides the rigidity required to hold the colony upright. The lobes or “leaves” are thick and fleshy. The pen is about three times as high as it is wide. They are off-white in color with brown to orange around the periphery. Fleshy Sea Pens reach 30 cm (12 inches) in height.

Habitat and Distribution:  Fleshy Sea Pens live on mud and sand and are found at depths between 10 m (33 feet) and 50 m (165 feet).  Fleshy Sea Pens are limited to the Eastern Pacific and in Mexican waters they are found from Magdalena Bay south to Guatemala including the entire Sea of Cortez.

Diet:  Fleshy Sea Pens are suspension feeders, using their tentacles to capture suspended plankton and organic matter from the surrounding water.

Predation:  While Fleshy Sea Pens can quickly withdraw into the sand if disturbed they are still prey for the Green Sea Turtle, Chelonia mydas, and the Convoluted Nudibranch, Histiomena convolvuli.

Reproduction: Fleshy Sea Pen colonies are gonochoric (male or female for life). They may reproduce asexually, through fragmentation or budding, or sexually. Sexual reproduction involves broadcast spawning with external fertilization. The fertilized eggs hatch into planular larva. The larva settle onto soft substrate and metamorphose into a polyp, with the polyp’s base becoming a stem, anchoring in the substrate. Secondary polyps then grow laterally from this structure.

Ecosystem Interactions: There are no documented examples of parasitism, commensalism, or symbiosis involving Fleshy Sea Pens.

Human Interactions:  Fleshy Sea Pens are seldom seen by humans and have limited impact on human activities. They a occasionally caught as bycatch in shrimp trawls that may lead to localized population declines. From a conservation perspective they have not been formally evaluated.

Synonyms: Leioptilum solidum, Leioptilum undulatum, Leioptilum verrilli, Leioptilus undulatus, Leioptilus verrillii, Lioptilum verrillii, and Pennatula undulata.