The red-lined Calappas

I am tagged more and more in identifications of box crabs (Calappidae; shame-faced crabs) from the IWP, time to clear something up which I am currently looking up every time I get tagged in what I like to call "red-lined Calappas".

Red-lined Calappas are box crabs with distinct red lines between the postero-lateral (or caudal) spines, on the back rim of their carapace. The three species in this "complex" are Calappa lophos, Calappa guerini, and Calappa quadrimaculata. They can be found in the IWP, and two of them have been spotted on iNaturalist before:

As a few examples:
https://www.inaturalist.org/observations/67798539 < C. guerini
https://www.inaturalist.org/observations/61776004 < C. lophos

First and foremost, this species group was studied by Lai, Chan and Ng in 2006, and they dubbed the group the "Calappa lophos group", the results are discussed here below, but if you want to see the paper yourself, check it out here:
https://academic.oup.com/jcb/article/26/2/193/2194856

Calappa lophos can be identified by its intense colouration on the carapace: red to purple-like streaks (lines) between the posterolateral spines, and red spots all over the posterior part of the carapace. Furthermore, the spines on the posterior margin are almost rounded (compared to the spiny margin of C. guerini). If these characters are not visible, the line between the antennular cavities is distinctly white.

Calappa guerini is however often times a bit smaller, and has no additional large spots on the carapace. The line between the antennulae is not distinct and the posterior spines are longer and appear more sharp.

The last and most rare species is Calappa quadrimaculata, which was described due to the lophos-group being split. It is known from Japan and Taiwan and is characterized by having an orange to cream colouration, often with four red blots on the carapace surface (and one spot on the outer surface of the claws).

Hope this clears some things up!

I'll check the other lophos-group ID's on iNaturalist, keep your eyes on the observations!
Until next time!

Publicado por wernerdegier wernerdegier, 29 de marzo de 2021

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