Pentaceraster cumingi

Pentaceraster cumingi is a sea star of the family Oreasteridae, described by Gray in 1840 as Pentaceros cumingi ^[1]. It ranks among the most common sea stars of the tropical eastern Pacific, with five arms and a large, inflated body ^[2]. In Peru it is called «estrella dura» ^[3]. According to the management plan of the Reserva Nacional Mar Tropical de Grau, collection to sell dried specimens as souvenirs has brought it to the edge of extinction, and it has not been seen on the Peruvian coast for at least 20 years ^[3].

It is a fairly large star with five-armed symmetry, a swollen body wall and fixed, immovable spines on the upper surface ^[2]. Its colouring varies widely: some individuals are reddish orange or reddish green, others have a grey ground covered by a bright red network ^[2]. An archaeological study lists it among the brightly coloured echinoderms, describing it as deep red in life ^[4].

Although five arms is the rule, at Bahía Chamela on the Mexican Pacific coast 28 of 849 individuals examined (3.29 %) had a different count: four arms turned up in 0.82 %, six in 1.06 % and a forked arm in 1.41 % ^[2]. The authors suggest two origins: errors during larval metamorphosis, and an arm that grows back abnormally after being lost, for instance to a predator ^[2].

It lives from the Gulf of California, Mexico, to northern Peru, on rocky reefs, reef patches and sandy bottoms, from the lower intertidal down to 183 m ^[2]. Another study gives a range of 2 to 92 m, on coral reefs and rock or sand bottoms, with records from Mexico, Costa Rica, Panama, Colombia, the Galápagos Islands and Peru ^[4]. In El Salvador it was documented for the first time in 2022, from photographs of a reef in that country taken since 2017 ^[5].

In Galápagos, counts repeated twice a year between 2006 and 2014 at 12 sites, at 6 to 8 m and at 12 to 15 m, showed it to be one of the two most abundant of the six sea star species studied ^[6]. In the preliminary version of that study it was more abundant at 15 m than at 6 m, and the authors often found it on sediment-covered flat rock and on sand next to the reefs ^[7].

For the Peruvian coast, the management plan of the Reserva Nacional Mar Tropical de Grau describes the estrellas duras as slow animals of rocky or sandy bottoms ^[3].

Between 2016 and 2019 a population was followed off an islet in Bahía Chamela, on the central Pacific coast of Mexico, over sand and rubble some 7 to 10 m deep ^[2]. Five-armed individuals averaged 123.8 mm from the centre of the mouth to an arm tip and weighed 326 g; the largest reached 160 mm, and the commonest sizes ran from 110 to 120 mm ^[2]. Weight and arm length changed between the cold and the warm season, and the star seemed to grow more in the months of warmer water ^[2].

Recruitment is thought to take place between June and August, although juveniles hide and are hardly ever seen: the only one found, under 10 mm, was stuck beneath a reef rock far from the adults, and the authors suppose that young stars later move to the rubble where adults feed ^[2]. The species gathers in large groups, which have been explained as feeding gatherings or as part of its reproduction ^[2].

In Galápagos it had one of the most restricted diets among the sea stars studied, and in field experiments it preferred small pencil urchins Eucidaris galapagensis over large ones ^[6]. In the preliminary version of the work it was the only one of the six species analysed that ate a mobile invertebrate: those urchins made up 8.1 % of its diet; in 462 observations, 51.48 % of the stars were eating, and it often had its stomach turned outwards over encrusting coralline algae ^[7].

The same authors propose that by eating young urchins hidden in cracks and rubble, where fish cannot reach them by day, it may, together with other predators, keep those cohorts from reaching larger sizes; they also saw damselfish biting its tube feet ^[7].

Recorded densities vary greatly from place to place: 0.02 individuals per square metre in the Gulf of Chiriquí, Panama, against 0.66 to 2.03 at Bahía Chamela, where the population stayed all year; in the southern Gulf of California groups of up to 3 individuals per square metre were seen that lasted only a few days ^[2].

The management plan of the Reserva Nacional Mar Tropical de Grau singles it out among the estrellas duras of special conservation interest: because they move slowly they are taken by divers collecting by hand, with traps made for them or with dredges adapted to the seabed, and sold dried as ornaments, which has brought them close to extinction ^[3]. The same document notes that it has not been seen on the coast of Peru for at least 20 years, whereas it is abundant in marine protected areas of Ecuador where taking it is forbidden ^[3].

The reserve counts it among the rocky-reef invertebrates heavily threatened by bad practice in spearfishing and other fishing gear ^[3]. It forbids taking it in the Arrecifes de Punta Sal ^[3] and Cabo Blanco – El Ñuro ^[3] sectors, and it placed its recovery zones at Punta Sal where healthy populations of this and other now seriously threatened species once lived, with the goal of restoring them ^[3].

In El Salvador, the authors who recorded it warn that it is at risk of being caught in trawl nets ^[5].

Today it is sold dried as an ornament in the souvenir market ^[3].

The Mexica buried it in the offerings of the Templo Mayor of Tenochtitlan, in today's Mexico City: 10,000 remains of this species have been counted in 13 offerings, and among sea stars only Nidorellia armata appears more often ^[4]. The offerings with echinoderms date from the reigns of Axayacatl to Motecuhzoma II, between 1469 and 1520, and the authors connect them with Tlaloc, the Mexica deity of rain and earth, and with the watery underworld that such marine animals stood for ^[4].

Today it is very hard to see in Peru. The 2026 management plan of the Reserva Nacional Mar Tropical de Grau, drawing on a 2012 work, states that the species has not been seen on the Peruvian coast for at least 20 years ^[3]. The reserve keeps it among the protected species of two of its sectors, Arrecifes de Punta Sal ^[3] and Cabo Blanco – El Ñuro ^[3].