Chaetopleura peruviana

Chaetopleura peruviana is a chiton (class Polyplacophora) in the family Chaetopleuridae. Lamarck described it in 1819 as Chiton peruvianus, and it is the type species of the genus Chaetopleura ^[1],[2].

The specimens examined at Caldera (Chile) reached 45 mm in length; it has an oval, slightly flattened body, and stands out for the horny bristles that cover the girdle and protrude between the plates ^[1]. A reference work cited by Araya and Araya places it along the south-eastern Pacific coast from Ecuador to southern Chile ^[1], and a survey carried out between 2013 and 2016 recorded it at Callao, Peru ^[3].

In the specimens examined at Caldera (Chile) it measured up to 45 mm long. The body is oval to elongate-oval and slightly depressed, and the surface of the plates ranges from greenish brown to dark brown ^[1]. The head valve is semicircular, with a straight front slope and a V-shaped rear margin; the intermediate valves are broadly rectangular, and the tail valve is less than semicircular and almost as wide as the head valve ^[1].

The most striking feature is the girdle: it is covered with thick, long horny hairs, up to 10 mm, that are not only scattered over all of it but protrude at the sutures and extend over the valves ^[1]. The plate surface is pustulose, with tiny, well-separated pustules arranged in radiating rows on the end valves ^[1]. The authors also quote, from another work, a mean width/length ratio of 0.66 and a mean height/length ratio of 0.22 ^[1].

Similar species

• Chaetopleura benaventei: It is slightly smaller, differs in overall colour and lacks the horny bristles ^[1].
• Chaetopleura hennahi: Its plate surface is wine-red to reddish brown and lacks the blackish hairs that protrude at the sutures of Chaetopleura peruviana; it is cited between El Callao (Peru) and Arica (Chile) ^[1].

According to a reference work cited by Araya and Araya, the species lives on the western coast of South America, between Cape San Lorenzo (Ecuador, 1°04' S) and the Chonos Archipelago (Chile, 45° S) ^[1]. The same work gives it from the intertidal zone down to 40 m depth ^[1]. It is a marine species ^[2].

A quantitative survey at 12 localities of the Peruvian Province, between Callao (Peru, 12° S) and Valdivia (Chile, 39° S), carried out between 2013 and 2016, found it at all 12, so it occupies several ecoregions ^[3].

At Caldera (Chile, 27° S) it turned up at almost all sampling points, which included rocky coast with tidal pools, pebble beaches, loose boulders on sand, and rocks with large brown-algal holdfasts; sampling there did not go deeper than about 2 m ^[1].

In the 2013–2016 survey its relative abundance, measured in chitons per hour per person, was low at every locality: from 0.3 at Antofagasta to 5.1 at El Sauce, with 1 at Callao ^[3]. The authors treat species scoring below 10 on that measure as rare ^[3].

At 18 wave-exposed sites in central Chile (29–36° S), using 0.25 m² quadrats in the mid and low intertidal zone, Chaetopleura peruviana appeared in 1.02 % of the 1863 quadrats, whereas Chiton granosus appeared in 39.99 % ^[4].

In Antofagasta Bay (northern Chile), a study of the mid-intertidal community listed it among the macroinvertebrates found only in the matrices of the introduced ascidian Pyura praeputialis, and not on neighbouring rock without it ^[5].

The Peruvian-coast literature reviewed here records it at Callao (12° S) in a 2013–2016 survey, at an abundance of 1 chiton per hour per person, which is to say scarce ^[3]. That source does not give the exact collecting site or say whether it is hard to reach or restricted, so it is not enough to guide a search ^[3].