Armed box crab

Platymera gaudichaudii is a decapod crab of the family Calappidae, and its name is the accepted one in the World Register of Marine Species ^[1]. It ranges along the Pacific coast of the Americas from the Farallon Islands, California, to Chile, at depths of 22 to 399 m according to a 1993 revision ^[2]. A 2010 larval description reports that in northern Chile and southern Peru it is exploited locally and sold fresh, and it credits that statement to a 1995 author ^[3].

The 1993 revision describes a transversely oval, convex carapace with an arched, keeled anterolateral margin bearing 15 minute teeth, and a granular lateral spine of nearly one seventh of the carapace width, longer in young specimens ^[2]. The carapace is 1.4 to 1.5 times wider than long and shagreened, with tubercles in juveniles; the chelipeds are massive and nearly equal ^[2]. The species' author described it as reddish ^[2].

A male of 9.75 cm carapace width found at Juan Fernandez had a lateral spine of 2.4 cm, two spines on the distal crest of the cheliped merus, large orbits and eyes on short, thick stalks, and external maxillipeds that do not fully close the mouth cavity ^[4]. The authors also give, as a trait of the family Calappidae, that the chelipeds and walking legs are long and flattened and that the chelipeds fit against the lower front edge of the carapace, protecting the mouth ^[4].

The genus Mursia is very similar. The 1993 revision reinstated Platymera as a distinct genus because its abdominal keel is not divided into three lobes, because the cheliped carries a single-toothed ridge on the outer face of the palm, and because it lacks the stridulating organ that Mursia species have ^[2]. In that paper's key, the inner face of the cheliped dactylus is irregularly granular in Platymera and bears a milled ridge in Mursia ^[2].

The 1993 revision gives a distribution along the west coast of the Americas, from the Farallon Islands (California) to Chile, at 22 to 399 m ^[2]. A 2013 paper cites a range from Punta Año Nuevo, California, to Peru, including the Galapagos Islands, Ecuador and the Chilean coast from Arica to Talcahuano, and a known depth range of 40 to 420 m ^[4]. The same paper mentions the species, under the name Mursia gaudichaudii, on a seamount of the Nazca Ridge ^[4].

For Peru, the 1993 revision examined a female of 28.9 mm carapace length collected at San Lorenzo Island, near Callao, on 10 March 1952 ^[2]. The type locality is Chile ^[2].

In 2012 a male was taken at Juan Fernandez at 550 m depth in a trap set for the golden crab, which was the first record for the archipelago ^[4]. A 2010 larval description gathers depth ranges of 0 to 550 m and notes that the species is more abundant at depth, on fine bottoms with high salinity and little oxygen, although other authors found it on shallow muddy bottoms ^[3].

The larvae were obtained from egg-bearing females caught by bottom trawl at 80 m depth off Punta Teatinos, northern Chile, and newly hatched larvae were reared at 14 °C ^[3]. Zoea I averaged 1.7 mm and zoea II 2.0 mm (the first appeared at 10 days) ^[3]. Zoeae III (2.8 mm on average) and IV (3.6 mm) were described from plankton specimens collected at Caldera and Coquimbo in the spring of 2005, identified by the characters of the reared zoeae I and II ^[3].

What marks the larvae are the small spinules on the lateral spines of the carapace and on the rostral spine, and the spiny processes of the antenna; the 2010 description was the first account of larval development for this genus worldwide ^[3]. The same work reports, from an earlier study, that females outnumber males all year (6.5 to 1 between 0 and 400 m), that egg-bearing females are most numerous in October, and that larvae are released between October and November ^[3].

In northern and central Chile, between regions II and VIII, the species, cited as Mursia gaudichaudi, is among the most frequent and abundant components of the bycatch of the shrimp and prawn trawl fishery ^[3]. The same source states, citing other authors, that it is food for important commercially valuable fishery resources ^[3].

At Juan Fernandez it turned up among the catches of the golden crab Chaceon chilensis fishery, and the authors propose that it lives there in deeper zones than the 2 to 180 m range covered by the lobster fishery, where it had never been recorded ^[4].

In the Chilean trawl fishery the species has no direct economic importance, according to a 1976 study cited in the 2010 larval description, but that same work, citing another author from 1995, states that in northern Chile and southern Peru it is exploited locally and sold fresh ^[3]. The 2010 authors also regard it as a possible fishery resource ^[3].