Fissurella cumingi

Fissurella cumingii is a large, oval-shelled keyhole limpet that lives from the low intertidal zone down to about 15 m depth on rock, and it can be recognised at a glance by the purplish-red, strawberry-like colour of its foot and mantle ^[1]. WoRMS treats it as an accepted species of the family Fissurellidae, described by Reeve in 1849 ^[2].

On the south-eastern Pacific coast its northernmost verified record is Matarani, in Peru (17°00' S), and it reaches south to Mehuín, in Chile (39°23' S) ^[1]. It is eaten in central and northern Chile and sold together with other limpets, whose catches Chilean fishery statistics record under a single generic name ^[1],[3].

The shell is large (80 to 100 mm long when mature), of medium height, oval in outline and narrower at the front end. The radial ribs are of fine to medium strength and, in young stages, nodulous or beaded; the rays are dark reddish-purple on a dark yellowish-grey ground, and the foremost rays are often split. The margin is very broad and flat in young shells, and the rays cross its full width ^[1].

The living animal is easier to identify than the shell: the foot has a distinctive strawberry-red colour, and the foot and mantle are purplish red, paler in individuals with lightly pigmented shells. McLean notes that this colour is so unlike that of any other species that it is enough to recognise it; juvenile shells have rays that split in two ^[1].

The taxonomy of this group is difficult. For a long time it was regarded as a colour variety of Fissurella latimarginata, and it had not been recognised as a separate species before McLean's 1984 work ^[1],[3]. Molecular analyses published in 2011 place it in a latimarginata complex with Fissurella latimarginata, Fissurella bridgesii and Fissurella oriens, and point out that shell characters do not always agree with genetic relationships ^[3].

Similar species

• Fissurella latimarginata: It has the same size, proportions and narrow front end, but its ribs are finer, sharper and less beaded, and it lacks the strawberry-red foot; an alga-covered shell is told apart by the rayed margin of Fissurella cumingii ^[1].
• Fissurella maxima: Its inner margin is rounded, crenulate and zoned, whereas in Fissurella cumingii it is flat and shows the rays across its full width; in old collections, cleaned specimens of Fissurella cumingii were also often misidentified as this species ^[1].

McLean set the verified northern limit of the species at Matarani, in southern Peru (17°00' S), and the southern limit at Mehuín, in south-central Chile (39°23' S), and noted that the range probably extends farther north and south ^[1]. Its distribution is more southern than that of Fissurella latimarginata and Fissurella maxima, which reach much farther north in Peru ^[1].

It lives from the lowest intertidal zone and the immediate subtidal down to 15 m depth, on the upper surfaces of rocks; at low tide it is found mainly in deep tide pools in surf-exposed areas ^[1]. McLean counts it, with Fissurella latimarginata and Fissurella maxima, among the limpets that commonly occupy the range from the low intertidal to about 5 m ^[1]. At Antofagasta, in northern Chile, he collected living specimens, in smaller numbers than Fissurella latimarginata, at 5 m on rocky bottom; at Iquique he received small, elevated specimens from subtidal mussel beds, and obtained living specimens in the market, evidently taken by divers ^[1].

The microscopic anatomy of the reproductive system was described in this species and in Fissurella latimarginata, which live together on the same coast. In both the gonad is divided into compartments, and the gametes pass by a duct linked to the right kidney into the mantle cavity ^[4].

The authors looked for a reproductive difference that could separate the two species and found no marked anatomical differences between them, so this anatomy does not allow them to be told apart reliably ^[4]. Other work cited by Olivares-Paz and colleagues does, in contrast, report differences in the ultrastructure of the sperm nucleus among Fissurella cumingii, Fissurella latimarginata and Fissurella crassa ^[3].

The shells of limpets from the shallow subtidal, this species among them, usually carry a thick mat of finely branched red algae up to 5 mm high; the surrounding rock, by contrast, is left bare except for encrusting coralline algae by the grazing of the black sea urchin Tetrapygus niger and, probably, of the limpets themselves ^[1].

Its predators include the clingfish Sicyases sanguineus: McLean illustrates a relatively large specimen of this limpet found in the stomach of one such fish, and notes that its prey often have the shell broken at one end, presumably by the fish's strong teeth ^[1]. For the genus Fissurella, McLean also describes an escape response to the seastar Heliaster helianthus, in which the limpet raises its mantle over the edge of the shell and moves quickly away ^[1].

Large individuals of limpets are eaten throughout Chile and Peru, and in the Iquique market they are sold without being sorted by species. McLean saw Fissurella cumingii in that market, considered it exploited for food in central and northern Chile, and described it as a major component of the shell piles of central Chile, that is, of heaps of discarded shells ^[1].

In Chile limpets are recorded under a single name and the share of each species is not separated: according to Olivares-Paz and colleagues, in the 5 years before their study (2011) the artisanal fishery took on average 1900 tonnes a year of Fissurella as a whole, not of this species alone ^[3]. The authors attribute the lack of data by species to the difficulty of identifying them with shell-based keys ^[3].