Perplexing Sea Urchin, Hesperocidaris perplexa

Perplexing Sea Urchin, Hesperocidaris perplexa. Urchin collected off the beach at Isla Cosme, Agua Verde, Baja California Sur, March 2020. Size: 6.4 cm (2.5 inches) x 3.2 cm (1.25 inches). Collection and photograph courtesy of Barry Mastro, Escondido, California.  Identification courtesy of Dr. Francisco A. Solís-Marín, Mexico City.

Phylogeny:  The Perplexing Sea Urchin, Hesperocidaris perplexa (Clark, 1907), is a member of the Cidaridae family of Pencil Urchins. The genus Hesperocidaris is one of twenty-four genera in this family, and there are five species in this genus.

Morphology: Perplexing Sea Urchins have a relatively flattened test. Their primary spines are almost as long as the test’s diameter. The spines flatten and widen toward their distal end, which is often damaged. The secondary spines are sculpted with a groove and a brown stripe running the length of the spine. The spines are often encrusted with marine growth, such as sponges, bryozoans, and polychaetes. The tiny pincers between spines (pedicellariae) are globose. These urchins are primarily brown or orange in color. Perplexing Sea Urchins reach a maximum of 14.5 cm (5.6 inches) in diameter.

Habitat and Distribution: Perplexing Sea Urchins are a deeper water species, found at  deptha between 13 m (43 feet) and 1,500 m (4,920  feet). They may be found on rock, sand, or mud substrates. They are sometimes found in sea grass beds, or at the base of corals. They are a tropical Eastern Pacific species. In Mexican waters this species is found throughout the Gulf of California and the Revillagigedos Islands. Some sources extend the range of this species south to Guatemala. They are absent from the west coast of the Baja Peninsula.

Diet:  Perplexing Sea Urchins are omnivores that feed on bryozoans, detritus, foraminifera, sea grass, and sponges.

Predators:  Perplexing Sea Urchins are a poorly studied and understood species. There is very limited documentation regarding predation for this species. Other species in this family are preyed upon by fish including triggerfish and wrasse.

Reproduction: Perplexing Sea Urchins are gonochoric (male or female for life).  Reproduction is sexual, with fertilization taking place externally. Reproduction occurs via broadcast spawning where the females release hundreds of thousands of eggs into the surrounding water concurrently with the release of sperm by males. After fertilization, the larvae will attach to substrate and develop into their adult form.

Ecosystem Interactions: Perplexing Sea Urchins host a large number of colonies of different animals such as bryozoans, tubes of polychaete annelids, sponges or other organisms that live as epibionts.

Human Interactions:  Perplexing Sea Urchins 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:  Dorocidaris perplexa, Stylocidaris perplexa, and Tretocidaris perplexa.