Description 

This is a strongly banded shrimp superficially resembling the Titan Shrimp, but much smaller and less robust. 

Carapace The carapace is pale grey with four well-defined diagonal red-brown bands laterally, the anterior two meeting dorsally to make two dark horseshoes on the dorsum. The posterior two are red and continue into the abdominal stripes. 

The abdomen is pale grey with three or four red-brown stripes on each side, and a dark brown stripe dorsally. This is interrupted by a white patch on the third or fourth segment. There may be a white patch dorsally on segment 1 and a black spot laterally on abdominal segment 4. 

The rostrum is red-tinged grey, as are the antennae. 

The pincers are grey with no clear pattern. The claws have blue and pink areas. 

The chelate second legs are grey proximally becoming red with yellow joints. 

The walking legs are pale grey becoming darker grey or red on either side of the pale yellowish joints. They have a red tinge distally. 

The tail fan has a grey-green telson and a pale-centred endopod and proximal exopod. The distal portion of the exopod is a blue-grey transverse oval 

Identifying Features

The bold diagonal banding on the carapace, when typical, is very distinctive. There is often a small black spot on either side of the fourth segment of the abdomen. 

Similar Shrimps

This shrimp has similar markings to the Titan Shrimp but the Titan Shrimp is much bigger and has a barrel-shaped profile with the abdomen as broad as the carapace. It has more massive pincers, with well-marked transverse bands. The Titan Shrimp may have bands on the side of the carapace but these are reddish and run more horizontally on a background paler and more uniform than the dull grey of the Diagonal Barred Shrimp. 

The Diagonal Barred Shrimp has four bands on the carapace, not two, and the dark stripes on the abdomen are better defined. 

Nomenclature

Ryanskiy (2016) p7. has images of a similar-looking shrimp and gives the name Alpheus rapacida, common name Robber Snapping Shrimp. Length up to 5. 7 cm. Distribution Indo-West Pacific – Red Sea, Thailand, Vietnam, Indonesia, Australia. 

Debelius (2001) Crustacea p151 has images of a shrimp to which he gives the name Alpheus rapax with the common name Marbled Snapping Shrimp. It looks nothing like the Diagonal Barred Shrimp or any other shrimp we have seen. (Image from Marsa Alam, Egypt). 

A rapax and A rapacida are both species complexes (Anker 2001)

We have not seen this shrimp form a pair with the similar-looking Titan Shrimp or any of the other shrimps described in this book.