29 de março de 2021

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:

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 em 29 de março de 2021, 07:56 TARDE por wernerdegier wernerdegier | 0 comentários | Deixar um comentário

08 de outubro de 2020

On the ID of the crabs previously identified (by me) as Calappa galloides from Portugal

Werner de Gier, Naturalis, 08-10-2020

This post was a direct result from an email from @nemalgarve about the following two observations:
https://www.inaturalist.org/observations/56942761 and https://www.inaturalist.org/observations/61933811

The following species within Calappa are known from the Iberian Peninsula
(sensu Marco-Herrero et al., 2015 – most recent list)
• Calappa granulata
• Calappa pelii1
• Calappa tuerkayana2
Following Pastore, 1995, the present species were:
• Calappa granulata
• Calappa pelii1
• Calappa tuerkayana2
• Calappa rissoana3

1: Brockerhoff & McLay (2011) stated Calappa pelii to be an alien species in the Mediterranean Ocean, originating from West Africa. Holthuis (2001) also mentions that lots of decapods have made the switch from West Africa to the Mediterranean, including another species known as Calappa gallus4.
2: Calappa tuerkayana is thought to be a misidentification of Calappa gallus (see Holthuis, 2001), but later was thought to be a misidentification of juvenile Calappa granulata crabs (resulting from DNA studies: see Marco-Herrero et al., 2015). It is safe to say that Calappa tuerkayana is not a valid species, but it is still present in WoRMS.
3: Calappa rissoana is thought to be a coloration-variation of Calappa granulata, but if it is indeed another species, it should be known as Calappa rosea (see Holthuis, 2001 for details).
4: Calappa gallus is known from tropical waters in the Indo-West Pacific, but also from the Caribbean (and West Africa). The ones from the Caribbean (and the entire Atlantic) are relocated to a new species: Calappa galloides, following Manning & Chace (1990). Interestingly, this species is also found around the Canary Islands (González et al., 2000) and might have a larger distribution than thought before. If the identification of González et al. (2000) is correct, is not known.

So, to come back on the identification of these specimens: it cannot be an adult Calappa granulata (and the apparently very similar looking Calappa rosea), but it might be a juvenile one, following the molecular identification of specimens identified in the field as Calappa tuerkayana. In the time I identified the crabs as Calappa galloides, I could not find any figurations of Calappa pelii, the other Calappa gallus-looking species. I now have found a nice figure from “FONDS DE PÊCHE LE LONG DES CÔTES DE LA RÉPUBLIQUE FÉDÉRALE DU CAMEROUN” from Crosnier (1964) (https://core.ac.uk/download/pdf/39892275.pdf). Due to the bumpy texture on the carapace with the two hepato-gastric lines very visible, an ID in the direction of Calappa gallus-like crabs should be in place – so, which one? I think I might be wrong with Calappa galloides as an ID for the Portuguese specimens, and they might be adult Calappa pelii crabs (Calappa pelii is somewhat rounder/square than the triangular Calappa galloides). The posterior spines at the back are somewhat flattened (less spiky) than in Calappa pelii though… In addition, this one (https://www.inaturalist.org/observations/31632718) from West Africa really should be Calappa gallloides.

I think the only way to properly ID these Portuguese crabs is looking at the type specimens (here in Leiden) and make better pics of the found carapace of this one (https://www.inaturalist.org/observations/56942761) and this one (https://www.inaturalist.org/observations/61933811). For a scientific publication, a DNA study of all crabs labelled as Calappa galloides might be very interesting – I believe this species, together with Calappa pelii, Calappa pokipoki and other gallus-like calappas form a taxonomic group (maybe even genus?). I think I still have a DNA barcode of Calappa galloides from Curacao (Caribbean), which might be of interest in a later stage.

Lessons learned today: don't think you can't discover anything on European beaches, there might be a taxonomic issue causing problems in the species-identifications of many animals found on your beach!

-Werner de Gier
iNaturalist Curator of Crabs (Brachyura: mainly Pinnotheridae and Calappidae)
Naturalis Biodiversity Center, Leiden

Publicado em 08 de outubro de 2020, 01:22 TARDE por wernerdegier wernerdegier | 2 comentários | Deixar um comentário