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Phylum Arthropoda > Subphylum Crustacea > Class Malacostraca > Order Decapoda > Brachyurans > Superfamily Ocypodoidea
Sentinel crab
Macrophthalmus sp.
Family Macrophthalmidae
updated Dec 2019
Where seen? This inconspicous little crab with eyes on super long stalks are sometimes seen on soft silty and muddy shores such as swimming lagoons. It builds distinctive holes which are either rectangular or oval and seldom circular.

Features: Body width 0.5-1cm. Body is flattened, squarish or somewhat rectangular. The eye stalks are long and in some species can even extend outside the sides of the body. This feature probably gave them their common name. Both pincers of equal size.

Sometimes confused with
fiddler crabs (Uca spp.). Sentinel crabs do not have one enlarged pincer like the fiddler crabs. Sentinel crabs are also not colourful, usually drab brown with darker mottling. Here's more on how to tell apart small crabs with long eye stalks.

What does it eat? It feeds on detritus and small worms.

Pulau Hantu, May 05

Pulau Hantu, May 19
Photo shared by Jianlin Liu on facebook.

Nibbling on a worm.
Pasir Ris, Jan 09

Squarish burrow opening.
Pulau Hantu, Jun 09

Just moulted! Moult has transparent eyes.
Pasir Ris, Dec 08

Sentinel crabs on Singapore shores
On wildsingapore flickr

Other sightings on Singapore shores

East Coast-Marina Bay, Jan 21
Photo shared by Vincent Choo on facebook.

St John's Island, Jan 13
Photo shared by Loh Kok Sheng on flickr.

Kusu Island, Sep 10
Photo shared by Loh Kok Sheng on flickr.

Beting Bemban Besar, Aug 18
Photo shared by Liz Lim on facebook.

Terumbu Pempang Laut, Aug 21
Photo shared by Vincent Choo on facebook.

Family Macrophthalmidae recorded for Singapore
from Wee Y.C. and Peter K. L. Ng. 1994. A First Look at Biodiversity in Singapore
in red are those listed among the threatened animals of Singapore from Davison, G.W. H. and P. K. L. Ng and Ho Hua Chew, 2008. The Singapore Red Data Book: Threatened plants and animals of Singapore.
**from Ng, Peter K. L. & N. Sivasothi, 1999. A Guide to the Mangroves of Singapore II (Animal Diversity)
+from The Biodiversity of Singapore, Lee Kong Chian Natural History Museum.

  Family Macrophthalmidae (previously Ocypodidae)
  +Chaenostoma cf. boscii

+Ilyograpsus sp.
Ilyograpsus paludicola

Macrophthalmus boscii
Macrophthalmus brevis=Macrophthalmus dilatatus
Macrophthalmus convexus
Macrophthalmus crassipes
**Macrophthalmus crinitus
(Little sentinel crab)
Macrophthalmus erato
Macrophthalmus japonicus
Macrophthalmus latreilllei
(Latreille's sentinel crab)
+Macrophthalmus milloti
Macrophthalmus pacificus
Macrophthalmus parvimanus
Macrophthalmus telescopicus
Macrophthalmus travancorensis



  • Ng, Peter K. L. and Daniele Guinot and Peter J. F. Davie, 2008. Systema Brachyurorum: Part 1. An annotated checklist of extant Brachyuran crabs of the world. The Raffles Bulletin of Zoology. Supplement No. 17, 31 Jan 2008. 286 pp.
  • Jones Diana S. and Gary J. Morgan, 2002. A Field Guide to Crustaceans of Australian Waters. Reed New Holland. 224 pp.
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