Description 

This is a very big, strong shrimp commonly found on silty substrate. 

Carapace The dorsum of the carapace is pale grey-brown. There is a brown line in the midline running back from the level of the eyes. Lateral to this a brown patch encircles the eye and runs posteriorly until interrupted by a dorsal pale crescent-shaped mark that slopes forward to terminate in a bright pale patch laterally. Above this point is a horizontal brown line, and below there are two others that run back to become continuous with lines on the abdomen. 

Abdomen The abdomen has a pale grey background with four lines of brown stripes on either side of a darker dorsal midline stripe. These stripes may be so broad that the abdomen looks red-brown with fine broken white lines rather than the other way around. The dorsal rows of white stripes are interrupted at the segment junctions resulting in a repeating segmental pattern of short dorsal white lines enclosing a short dark line. This appearance is characteristic and is most obvious on segments 1 and 4 where there is often a white transverse band as is seen in several Alpheus shrimps, though in this shrimp it is discontinuous. The lowest lateral stripe is red rather than brown. There is a black spot laterally on segment 4. There is sometimes a row of white spots between the second and third lateral stripes. 

The rostrum continues the colour of the upper carapace, usually brown. The antennae are pale red-brown. 

The pincers are broad, brown or grey with three well-marked dark bands the most distal of which may have a blue tinge. Pollex and dactyl are orange. The pincers become very hairy in mature males. 

The chelate second leg is usually purple-blue. 

The walking legs are off-white at the base, becoming red with yellow joints. 

The tail fan is green-brown with a brown border and frequently hairy. 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. 

Variation

The appearance and size may vary even within a couple though the identifying features are constant, as the images show. 

Shrimps living on darker substrates have more pigment, sometimes enough to blur the stripes on the carapace. This can make them look uniformly dark on top and pale below, especially when covered in silt as they usually are. (4315R-9072)

Identifying Features 

A large grey, striped shrimp. 

Lives in silty habitat, away from the reef

The characteristic pattern of interrupted pale lines on the abdomen, particularly segments 1 and 4. 

Similar Shrimps 

Compared to the superficially similar Diagonal Barred Shrimp 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 bars on the carapace are reddish and run more horizontally. on a background paler and more uniform than the dull grey of the Diagonal Barred Snapping Shrimp. 

The Diagonal Barred Snapping Shrimp has four bands on the carapace, not two, and the dark stripes on the abdomen are better defined. In the Titan Snapping Shrimp, they are broken into a repeating series of parallel white and brown stripes on each segment of the abdomen. 

Nomenclature

We have chosen not to attempt a scientific name for this species due to the amount of conflicting information we have found. 

In several journal articles (e.g. Journal of Crustacean Biology vol 32 Page 694) there is a photograph taken by Anker of a similar-looking shrimp which is given the name Alpheus rapax. It corresponds well with our Titan Snapping Shrimp apart from having blue-grey legs with yellow joints instead of yellow joints with a red patch on either side.  

Debelius (2001) p.151 has images of a shrimp to which he gives the name Alpheus rapax with the common name Marbled Snapping Shrimp. It looks nothing like any shrimp we have seen. (Image from Marsa Alam, Egypt). 

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

A rapacida is said to be easily distinguished from A rapax, Fabricius 1798, by a white band, which is not seen in A rapax. (Preston (1978). Unfortunately, the paper is not illustrated and we cannot confirm this. 

Several species have a black spot laterally on segment 4. This may reflect a common ancestry but it is not mentioned in any of the popular textbooks. These “Spot-tail” shrimp are found in a variety of colour patterns. That they are different species is suggested by the fact that they do not form a continuous spectrum and that we have recorded different goby associations for the different forms. 

We have not seen this shrimp form a pair with the Diagonal Barred Snapping Shrimp or any of the other shrimps described on this website.