Identifying Australian Ghost Crabs

According to Sakai & Türkay, 2013, Australia has 5 sp. of Ghost Crab:
O. ceratophthalma
O. cordimana
O. pallidula
O. fabricii
O. convexa

Rae, 2018, The distribution and trophic ecology of Golden ghost crabs (Ocypode convexa) maps all of them except Ocypode pallidula which they describe as "constrained to islands off the Queensland coast, such as Lady Elliot and Heron Islands"

Along with O. pallidula, O. ceratophthalma and O. cordimana are widespread and distinctive. The 2 species endemic to Australia are the Golden Ghost Crab (O. convexa) and the Kimberley Ghost Crab (O. fabricii). I realized that these two species are being confused on iNat with obs of both species being ID'd as O. convexa.

According to Sakai & Türkay, 2013:
O. convexa: Exorbital angles triangular and directed anteriorly.
O. fabricii: Exorbital angles acutely triangular and protruding outward.

I've annotated the images below with arrows pointing at the exorbital angles

Likewise in Sakai & Türkay, 2013 and Table 1 in Jones, 1988, The Occurrence of Ocypode pallidula Jacquinot (Decapoda, Brachyura) in Australia and the Coral Sea
O. convexa:
Ocular styles very short
Median notch of lower orbital deep
Pterygostomial region tuberculate all over its surface.

O. fabricii:
Ocular styles very short
Median notch of lower orbital slight
Pterygostomial region distinctly tuberculate except along lateral sides of buccal cavern.

I've annotated these 3 features in the images below

Its hard to find photos of live crabs in publications but I found 1 in each of Rae, 2018 and Piersma et al., 2016

These photos are consistent with O. fabricii being a more ochre colored, sharper/more angular crab with silver/pale blue eyes while O. convexa is a light yellow colored, rounder crab with jet black eyes.

Thanks to @luccio42, @dariodipas, @possumpete @keirmorse @johneichler and @viviroceania for making their awesome photos available for this post!

Publicado el enero 15, 2023 04:14 MAÑANA por loarie loarie

Comentarios

Great guide, will need to go back and correct my IDs

Publicado por thebeachcomber hace alrededor de 1 año

Yeah fantastic guide Scott, very glad to help out with some pics - we'll need to make a trip a little further north next time Thomas to tick off O.fabricii (@thebeachcomber)!

Publicado por possumpete hace alrededor de 1 año

I'm still struggling with O. pallidula. We have hundreds of obs ID'd as O. pallidula but I think most of them come from guesses or CV suggestions. If anyone finds some good O. pallidula characters please share them

Publicado por loarie hace alrededor de 1 año

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