Low-growing Cup Coral, Paracyathus humilis

Low-growing Cup Coral, Paracyathus humilis. Underwater photograph taken in Bahía de Banderas, Puerta Vallarta, Jalisco, July 2026. Photograph courtesy of Greg Timms, youtube.com/@CoralmasterdivesPuertoVallarta/videos. Identification courtesy of Bob Hillis, Ivins, Utah.

Phylogeny: The Low-growing Cup Coral, Paracyathus humilis (Verrill, 1870), is a hexacoral in the Caryophylliidae Family of Solitary Stony Corals. This family comprises the highest diversity of hard corals, and contains forty genera. This species is one of twenty-seven species in the Paracyathus Genus. The name Paracyathus comes from the Greek and means “resembling a cup” and refers to the cup-like skeletal structure of these corals. The species name humilis comes from the Latin word meaning “low”, “lowly”, or “grounded”, and refers to the short, flattened, stature of this species. It is also known as the Low Stony Coral and in Mexico as Coral Pétreo.

Morphology: The skeletal structure of the Low-growing Cup Coral is tough, with a horn-like consistency, and a chalice-like shape. They attach to the substrate with a pedicel (stalk-like support system), measuring around 3.7 mm in diameter. The stalk widens at the top into a cup-shaped calicle, or corallite, where the polyp lives. The calicle reaches 5.5 mm in diameter and 10.2 mm in height. The calicle and pedicel are light brown in color. The lower portion of the pedicel is usually encrusted. The polyp has 48 tentacles. Low-growing Cup Corals are solitary, and not linked through stolons, like species in the Polycyathus Genus.

Habitat and Distribution: Low-growing Cup Corals are found attached to rocks, coral, and other hard substrates. They reside at depths between 23 m (75 feet) and 104 m (340 feet). They are a Tropical Eastern Pacific species that are found in all Mexican waters of the Pacific Ocean with the exception that they are absent from the Sea of Cortez and from along the west coast of the Baja Peninsula.

Diet: Low-growing Cup Corals are azooxanthellate suspension feeders. They use their tentacles to capture micro plankton and suspended organic matter from the surrounding water.

Predators: Low-growing Cup Corals are a poorly studied species and their predators are not documented. Similar species are preyed upon by crabs, fish, gastropods and sea stars.

Reproduction: Low-growing Cup Corals are gonochoric (male or female for life). They reproduce sexually through broadcast spawning with external fertilization. The embryos develop into planktonic planula larvae, which eventually settle to the substrate and develop into adult corals.

Ecosystem Interactions: Formal documentation specific ecosysten interactions of the Low-growing Cup Corals has not been formally documented. Similar species host copepods, flatworms and boring sponges as parasites. Any mutualistic or commensal relationships have not been documented.

Human Interactions: Low-growing Cup Corals have a limited impact on human activities. They are utilized by the aquarium trade on a nominal leverl. From a conservation perspective, the Low-growing Cup Coral has not been evaluated.

Synonyms: None