Pyramid Sea Star, Pharia pyramidata

Pyramid Sea Star, Pharia pyramidata. Sea Star collected from the El Tule Tidal Pool, km 17, Baja California Sur, August 2009.

Pyramid Sea Star, Pharia pyramidata. Underwater photograph taken in Zihuatanejo Bay, Guerrero, March 2020. Photograph courtesy of Ron Wonteau, Zihuatanejo.

Pyramid Sea Star, Pharia pyramidata. Underwater photographs taken in Zihuatanejo Bay, Guerrero, January 2020. Photographs courtesy of Ron Wonteau, Zihuatanejo.

Phylogeny:  The Pyramid Sea Star, Pharia pyramidata (Grey, 1840),  is a member of the Ophidiasteridae family of Sea Stars. The genus Pharia is one of twenty-three genera in this family, and this is the only species in this genus. The Pyramid Sea Star is also known as the Yellow-spotted Sea Star and in Mexico as Estrella de Mar Piramide. The family name is based on the Greek word for “small snake”, referring to the snake-like appearance of the arms. Pharia pyramidata schmiederi is an accepted subspecies.

Morphology:  Pyramid Sea Stars have a small central disk and five long arms that have rounded tips. The arms are rounded in cross section, and there are two rows of tube feet, with suckers, on the underside of each arm. They have conspicuous ossicles (calcareous particles that are part of the endoskeleton) along their margins.  There are flattened spines running along the ambulacral grooves on the underside. The aboral (dorsal) surface is smooth, with granular skin. These stars may be tan, brown, gray, or lavender in color, with yellow to orangish spots on the disk and, in rows, along the arms.  Pyramid Sea Stars reach a maximum of 30 cm (12 inches) in diameter.

Habitat and Distribution:  Pyramid Sea Stars are found on, and under, rocks within the low intertidal zone, and at depths up to 140 m (460 feet).  They are a tropical Eastern Pacific species that in Mexican waters are found from Punta Eugenia, Baja California Sur south to Guatemala including the Revillagigedos and Tres Marias Islands. They have been found as far north as Santa Catalina Island in Southern California.

Diet:  Pyramid Sea Stars are opportunistic omnivores that feed on algae, bryozoans zand soft-bodied invertebrates.

Predators:  Predation of the Pyramid Sea Stars has not been documented. Other members of this family are preyed upon by eaten by crabs, fish, gastropods, marine mammals, sea turtles, shrimp and other sea stars. This species is most vulnerable to predation when it is in its larval or juvenile stages.

Reproduction: Pyramid Sea Stars are gonochoric (male or female for life). They can reproduce asexually, by both clonal and by regenerative methods. They can also reproduce sexually, through broadcast spawning, with external fertilization. Embryos hatch into planktonic larvae and later metamorphose into pentamorous juveniles, which develop into young sea stars.

Ecosystem Interactions:  The Pyramid Sea Star and the Tan Sea Star, Phataria unifascialis   are known to be parasitized by the Parasitic Cup Shell, Thyca callista. The cup shell attaches to the underside of the sea star’s arms and sucks fluids from the sea star host. The male Parasitic Cup Shell is much smaller (3 mm) than the female (10 mm) and is enclosed within the shell. The Sea Star Shrimp, Zenopontonia soror, is an epibiont associated with Pyramid Sea Stars that will change its color to match the sea star host.

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

Synonyms: Ophidiaster (pharia) pyramidatus,  Ophidiaster porosissimus, and Ophidiaster pyramidatus.