Wednesday, July 03, 2013

Caridean Shrimps (Phylum Arthropoda: Infraorder Caridea) of Singapore

Caridean shrimps (phylum Arthropoda, subphylum Crustacea, class Malacostraca, order Decapoda, suborder Pleocyemata, infraorder Caridea) appear very similar to penaeid prawns, with their elongate abdomen. However, unlike the latter, their third pair of walking legs do not have pincers at the tips. Also, the "shell" of the second abdominal segment is enlarged, overlapping and covering part of the first segment and the third segment. Unlike penaeid prawns that release their eggs into the water, caridean shrimps brood their eggs under their abdomen until they hatch.

In addition, caridean shrimps are of the suborder Pleocyemata, and all members of this suborder have leaf-like gills or gills made up of unbranched filaments. Penaeid prawns, on the other hand, are of the suborder Dendrobranchiata, and have gills that are branch-like.

Caridean shrimps are decapods, and like other members of the order Decapoda, they have five pairs of walking legs ("deca" means "ten", while "poda" means "feet"). And as with other crustaceans from the class Malacostraca, their body comprises three main parts - a head with five segments, a thorax with eight segments, and an abdomen with six segments. The head is fused with the thorax to form a cephalothorax. They have a tough exoskeleton strengthened with calcium carbonate, and the carapace covers the gills but not the abdomen. The abdomen is elongate, bearing five pairs of swimming appendages (or pleopods) and ends off with a tail fan comprising a pointed, tail-like structure (or telson) in the middle and a pair of flattened appendages (or uropods) by the sides. The pleopods are used for brooding the eggs and for swimming, while the uropods are used for steering while swimming.

They generally have separate sexes, and reproduce sexually. However, some species are known to first undergo a male phase and later transform into females.

Here are some of the marine species that I have photographed in local waters. I will elaborate on the freshwater shrimps in a separate page.

A) Snapping Shrimps (Family Alpheidae)

Snapping shrimps (family Alpheidae) typically have one claw much larger than the other. The huge claw is structured such that it has a moveable finger and a fixed finger. When it wants to snap, it opens its pincer, separating the moveable finger from the fixed finger, and a special mechanism in the claw locks the moveable finger in position. The moment the mechanism is released, the moveable finger will snap very rapidly towards the fixed finger, creating a tremendous pressure on the water trapped in between. The pressure is so great that it causes bubbles in the water to implode, and generates heat of almost 5000 degree Celsius! The implosion generates a loud snapping sound, a dim flash of light, and also, a powerful shockwave resulting in a strong water jet. This jet of water is so powerful that some snapping shrimps use it to stun their prey (hence they are also called pistol shrimps), such as small fishes or other crustaceans. Some snapping shrimps use this ability mainly to deter predators though, and feed on decomposing organic matter on the substrate.

Snapping shrimps generally have very poor eyesight, making them rather vulnerable to predators. As a result, many species avoid predation by living in burrows or form relationships with other organisms for protection. For example, some snapping shrimps may live among corals and sponges, while others share their burrows with gobies that have better eyesight.

Snapping Shrimps (Alpheus sp.)
The pair of Snapping Shrimps (Alpheus sp.), for example, shares its burrow with the White-saddled Shrimp-goby (Cryptocentrus maudae). One snapping shrimp will always keep one of its antennae on the goby, and when the latter senses any danger and retreats back into the burrow, the snapping shrimps will follow. They are about 6cm long each.

Snapping Shrimp (Alpheus sp.)
Here is another example of a burrowing Snapping Shrimp (Alpheus sp.) with a plain exoskeleton. I have seen several varieties of burrowing snapping shrimps in Singapore, but they are generally rather difficult to identify to the species for regular nature guides like me, and so I guess I will just stick to the genus. The one above is about 8cm long.

Snapping Shrimp (Alpheus sp.)
This burrowing Snapping Shrimp (Alpheus sp.) has very intricate patterns on its shell. This rather huge shrimp was about 10cm long.

Commensal Snapping Shrimps (Synalpheus sp.)
Commensal Snapping Shrimps (Synalpheus spp.) are usually found seeking shelter and protection in/on other invertebrates, including sessile ones such as corals and sponges, or motile ones such as feather stars and sea urchins. The above picture features a white commensal snapping shrimp living in a soft coral. It is quite small, about 1cm long.

B) Cleaner Shrimps (Family Hippolytidae)

Cleaner shrimps (family Hippolytidae) got their common name from the fact that many species from this family feed on parasites and dead skin materials of fishes. It is not uncommon to see these shrimps cleaning the mouth and gills of large fishes, while the latter remain still and do not attempt to eat the former. Most cleaner shrimps also feed on decaying organic matter and small fishes.

Despite the common name, not all shrimps of this family are cleaners, and some scavenge or feed on tiny organic matter.

Hippolytid Shrimps can usually be differentiated from other caridean shrimps by a combination of features: the first pair of walking legs are broader than the second pair, and have obvious pincers at the tips; the carpus (the segment joining the last segment to the upper segments of the leg) of the second pair of walking legs are divided into 3-7 units; the lack of movable spines on the rostrum; and the eyes are not covered dorsally by the carapace.

Cleaner Shrimps (Lysmata sp.)
Lysmata Cleaner Shrimps (Lysmata spp.) can usually be recognised by the three extremely long pairs of antennae. It is about 4cm long.

Marble Shrimps (Saron sp.)
Marble Shrimps (Saron spp.) are not cleaners, despite being in the family Hippolytidae. They can be recognised by the patchy patterns on their relatively short and fat body, and the prominent rostrum (the nose-like structure at the front of the head). Some species can be quite colourful. These shrimps are more active at night, and mostly scavenge for dead animals or other organic matter. The Marble Shrimps I have seen grow to about 5cm long.

Medusa Shrimp (Latreutes anoplonyx)
The Medusa Shrimp (Latreutes anoplonyx) is occasionally seen taking a ride either on or inside the bell of jellyfishes. This translucent shrimp has white and brownish stripes on its body, and is about 3cm long.

C) Palaemonid Shrimps (Family Palaemonidae)

Palaemonid are among the commonest shrimps seen in the intertidal area. They are characterised by having pincers on the first two pairs of walking legs, with the first pair being more slender than the second pair or at most as broad. The carpus (the segment or "waist" joining the last segment to the upper segments of the leg) of the second pair is cylindrical and not divided smaller units. Also, the claws lack hair on them. The rostrum (the pointed nose-like structure at the front of the head) is not hinged, but rigid. There are two main subfamilies in this group - the rock shrimps (subfamily Palaemoninae) and commensal shrimps (subfamily Pontoniinae).

Rock Pool Shrimps (Palaemon spp. or Macrobrachium spp.)
The Rock Pool Shrimps (Palaemon spp. & Macrobrachium spp.) are commonly seen in the intertidal areas, such as tidal pools. I unfortunately do not know anyone who can share with me how to differentiate the two genera in the field as yet, though I understand that many Macrobrachium spp. have big and prominent pincers. The common name is the result of them being commonly seen in rock pools. Unlike most other free-living caridean shrimps found in the intertidal areas, their legs with pincers are not dramatically enlarged. They are usually transparent, often with darker lines on the body. The ones I have seen often have yellow patches on their legs. Most rock shrimps scavenge or feed on algal and decaying animal materials. They are usually quite small, about 2cm long at most.

Cuapetes Shrimps (Cuapetes spp.)
The Cuapetes Shrimps (Cuapetes spp.) are another group of transparent shrimps commonly seen in intertidal areas. They can be distinguished from the previous group by the very much enlarged pincers, and they are mostly commensals, living in corals and sponges. They are quite small, about 1-2cm long.

Caridean Shrimps
Free-living shrimps with enlarged pincers are also commonly seen on our shores. However, I am not sure if they are Cuapetes spp. or other shrimps such as Macrobrachium spp., which may also have huge pincers.

Glass Anemone Shrimps (Periclimenes brevicarpalis)
Glass Anemone Shrimps (Periclimenes brevicarpalis) live on sea anemones. Studies suggest that they avoid being stung by the tentacles by coating themselves with a layer of the host anemone's mucus. They can be recognised by the five orange spots on the tail fan and white blotches on the body. The females are usually bigger with bigger white blotches on the body, while the males are smaller with fewer blotches. They are believed to be commensals, feeding on the leftover food particles of the host. However, they have also been observed to nibble on the tentacles of the sea anemone when food is scarce. They are not host-specific, and can be seen on a variety of sea anemones, such as the Phymanthus Anemones (Phymanthus spp.), Adhesive Anemones (Cryptodendrum adhaesivum), Haddon's Carpet Anemones (Stichodactyla haddoni), Gigantic Carpet Anemones (Stichodactyla gigantea), Magnificent Anemones (Heteractis magnifica), Leathery Anemones (Heteractis crispa) and Bulb-tentacled Anemones (Entacmaea quadricolor). The female grows to about 5cm long, while the males to about 3cm.

Green Coral Shrimp (Coralliocaris graminea)
The Green Coral Shrimp (Coralliocaris graminea) is usually found living among the branches of branching corals, such as Acropora Corals (Acropora spp.). It is often found in pairs, and can be recognised by the green body covered in numerous fine blue stripes. It also has a pair of large claws, which give strong snaps, much like the snapping claw of the snapping shrimps. However, the snap is not as powerful as the ones made by the latter. This small shrimp is about 1cm long.

D) Processid Shrimps (Family Processidae)

Processid shrimps (family Processidae) are typically small nocturnal shrimps. They are often found in shallow waters, such as seagrass meadows. They have claws on their first pair of walking legs, but in most species only the right first walking leg has pincers, while the left one has just a simple claw. The eyes are relatively large, while the rostrum is short with no teeth or other protruding structures on the underside.

Red Shrimp (Processa sp.)
The Red Shrimp (Processa sp.) is the only processid shrimp that I have seen in Singapore so far. It can be recognised by the reddish coloration, with numerous tiny iridescent spots. Other reddish caridean shrimps in Singapore lack the small spots. The Red Shrimp is often seen in seagrass meadows or among seaweed, and it is usually not more than 3cm long.

  • De Grave, S., N. D. Pentcheff , S. T. Ahyong, T.-Y. Chan, K. A. Crandall, P. C. Dworschak, D. L. Felder, R. M. Feldmann, C. H. J. M. Fransen, L. Y. D. Goulding, R. Lemaitre, M. E. Y. Low, J. W. Martin, P. K. L. Ng, C. E. Schweitzer, S. H. Tan, D. Tshudy & R. Wetzer. 2009. A classification of living and fossil genera of decapod crustaceans. The Raffles Bulletin of Zoology, supplement 21, pp. 1-109.
  • Carpenter, K. E. & V. H. Niem (eds), 1998-2001. FAO species identification guide for fishery purposes. The living marine resources of the Western Central Pacific. Volumes 1 to 6. FAO, Rome. pp. 1-4218.
  • Debelius, H. 1999. Crustacea - Guide of the world. IKAN, Frankfurt. 321pp.
  • Manning, R. B. & F. A. Chace, Jr. 1971. Shrimps of the family Processidae from the Northwestern Atlantic Ocean (Crustacea: Decapoda: Caridea). Smithsonian Contributions to Zoology 89.
  • Ng, P. K. L., S. S. L. Lim, L. K. Wang & L. W. H. Tan. 2007. Private lives: An exposé of Singapore's shores. The Raffles Museum of Biodiversity Research, Department of Biological Sciences, National University of Singapore. 212 pp.
  • Ng, P. K .L., R.T. Corlett & H.T.W. Tan (eds.). 2011. Singapore biodiversity: An encyclopedia of the natural environment and sustainable development. Singapore: Editions Didier Millet. 552 pp.
  • Riek, E. F. 1951. The Australian freshwater prawns of the family Palaemonidae. Records of the Australian Museum 22(4): 358–367. 
  • Tan, L. W. H. & P. K. L. Ng. 1988. A guide to seashore life. Singapore Science Centre. Singapore. 160 pp. 
  • World Register of Marine Species. 2012. Retrieved Jul 01, 2013, from

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