Mantis Shrimp

The etymology of the name has already been discussed earlier in the article, an important question that arises now is what is the use of such a strong appendage? This appendage or pair of limbs and the complex anatomy of eyes are the primary reason for the fascination of marine biologists with the animal. The appendages are used by animals to hunt and protect themselves from predators. The crustacean has a carapace that covers the rear part of the head and some segments of the thorax. The carapace is defined as a hard protective shell-like covering, it is the dorsal part of the exoskeleton. This is also an important feature of their morphology.

The body length of the animal is about 10 cms which are approximately 4 inches in length. Some species of the order are known to have body lengths ranging from 46 cms which are 18 inches to 48 cms long.  Marine shrimps are solitary animals, they are rarely seen in groups, they are also considered to be very territorial. They are excellent swimmers and are found in great depths of the sea. The recorded depth at which the creature is found is about 1,300 metres which are about 4,300 feet.  They live in burrows. 

A very fact about these animals is that they have the most complex eyes in the complete kingdom of Animalia; this will be further evident in the article.

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Figure: illustrating mantis prawn

Taxonomical Classification

The study of the taxonomy of these animals is important as it lays the basic framework of understanding the anatomy, morphology and behaviour of the animal. Taxonomic classification is also very important to understand the phylogenetic relationship between other species. It also helps in understanding the adaptations during the evolutionary course. 

It is very important to note that mantis shrimp is a common name used to define a group of marine animals and is used in the taxonomic classification. Another important point to understand is that the taxonomic classification mentioned here is the general classification system that is used to define the creature, there are various different species of the creature that have a more detailed classification. The taxonomic classification of mantis prawn is described below. 

The animal is classified under the kingdom Animalia, the primary characteristic of the kingdom is that the organism must be multicellular and have eukaryotic cell type, both these requirements are fulfilled by the mantis prawn. The kingdom is further classified into phylum, these animals belong to the phylum called Arthropod. 

Although the phylum Arthropoda is largely known to have members of the insect family, some of the marine creatures like mantis prawn are classified under this phylum. The characteristic feature of this phylum is that the members are invertebrates (lacks notochord) with segmented bodies. The mantis shrimp is known to have a segmented body. The body is generally divided into three regions, the head, the thorax and the abdomen, which holds true in the case of the mantis.  Another essential feature of this phylum is the presence of an exoskeleton, the mantis shrimp is known to have a strong exoskeleton.

They are further classified in the subphylum called Crustacea, the common members of this subphylum comprise crabs, lobsters, crayfish, shrimps, prawns, krill, woodlice, and barnacles. The general anatomical feature of this subphylum is the presence of a segmented body as mentioned in the phylum Arthropoda, the essential difference is that some of the members of the subphylum are known to have cephalothorax, which can be defined as a feud structure of head and thorax. The cephalothorax is converted by the protective layer of the carapace.  The carapace is a significant body part of the mantis shrimp.

They are further classified into the Malacostraca class. This is the largest class of phylum containing about 16 different genera which consist of 40,000 living species. The class has the highest body shape diversity.  Mantis shrimp are categorized into the subclass called Hoplocarida. They are further classified into Stomatopoda order. The order is estimated to have  17 families, 109 genera, and about 450 species. The most common species of the mantis shrimp are as follows,

• Smith's Mantis Shrimp, Gonodactylus smithii.

• Chiragra Mantis Shrimp, Gonodactylus chiragra

• Ciliata Mantis Shrimp, Pseudosquilla ciliata.

• Zebra Mantis Shrimp, Lysiosquillina maculata.

• Peacock mantis shrimp, Odontodactylus scyllarus

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Figure: illustrating peacock mantis.

Morphological Features

Some of the species of mantis shrimp-like peacock mantis shrimp are known for their vivid colours, this the reason they are also referred to as rainbow shrimp. Apart from the rainbow colour, they are available in a variety of colours which includes, orange, tangerine, red, green and brown.  A typical mantis prawn length is 10 cm but there is some reported case where the length of the body can extend up to 25 cm. 

The body of a mantis prawn is segmented and has a hard exoskeleton. The complete anatomy of the body can be divided into head, thorax and abdomen regions. The carapace is a protective covering that covers the rear part of the head and the initial four segments of the thorax.  The most unique morphological feature that is responsible for the etymology of the animal is the presence of the second pair of enlarged limbs. 

Apart from these, they are also known to have a shock-absorbent core. The chitin exoskeleton is the outermost layer beneath which there are multiple layers of elastic polysaccharide chitin. This structure is called a bouligand structure, it is primarily responsible for preventing them from rupturing

Another intriguing fact about the morphology is the eye, they have complex compound eyes. The eyes are located at the base of the stalk, which is joined at the head region. Since they are present at the end of the stalk they can move independently. Mantis prawns are known to have 12 to 16 different photoreceptors in their eyes for colour identification.

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Figure: illustrating eyes of a mantis shrimp

Classification Based on the Morphology

It is evident from the earlier discussion that the most intriguing feature is the presence of strong legs. These second pairs of limbs are indeed named raptorial. This is the term specifically used to define the forelegs of the arthropods, like mantis prawns. The sole purpose of this anatomical modification is to grasp prey, they are strong appendages that are also used for defence. This second pair of thoracic appendages is commonly known as claws. Based on the nature and use of claws the mantis prawn is divided into categories, they are called smashers and spearers. 

Smashers- They are much more rudimentary as compared to their counterparts, the club is used to bludgeon and smash their meals apart. The inner anatomical of the appendage is sharp. The preferred prey of the animal include snails, crabs, molluscs, and rock oysters.

Spearers- They are armed with spiny appendages topped with barbed tips, the elementary mode of attack includes stabbing. The preferred prey type for this category is the meat of softer animals, such as fish. 

Habitat and Ecology

There are about 450 species estimated to be categorized as mantis prawns, they are all classified under the Unipeltata suborder. These animals are estimated to be older than the dinosaurs, they evolved about 193 million years ago from the suborder. 

The highest species diversity is found in the tropical and subtropical waters in the Indian and Pacific Oceans between eastern Africa and Hawaii. They are also found in temperate regions.  They are also found in the Mediterranean Sea and in nearby regions of the Atlantic Ocean. The habitat range of smashers and spearers differ from each other. Spearers are found in the soft sediments of the sea, while the smashers are found in the hard substrata or coral cavities. 

The mantis shrimp is found living in burrows, they reproduce in the burrows. The burrows are made of silt or mud, which can be expanded. They are also found in coral cavities. 

Behaviour

Mantis shrimp are known for their aggressive nature. They live a solitary life, they are not migratory in nature. They are not generally seen outside their burrows. They hunt the prey by stabbing and smashing. Most of the species of mantis are nocturnal in nature, they are most active in the twilight hours. Some of the species are active during the day, but they are rare. 

Diet 

Mantis shrimp are primarily carnivorous animals, the prey of the mantis prawn includes the following: 

• Snails

• Oysters

• Crabs

• Shelled molluscs

• Small fish

• Worms 

• Shrimps 

Reproduction

They reproduce by sexual reproduction. The fertilization process is internal, that is the male and female gametes fuse inside the body of the female. A specific sexual behaviour observed in the peacock mantis shrimp is the creation of a U-shaped burrow. During mating, they dig these burrows near the reef’s edge and attract the male members by their vibrant colour.

After fertilization, they lay eggs. The eggs are carried by the female member of the species on the back until they are hatched. The average time taken to hatch is about 40 days, but depending upon the species the hatching can take 9 to 60 days.

Most of the species are monogamous in nature, that is they mate with the only individual throughout their life span, there are some species that mate with an individual for a specific period of time, which is usually around 20 years. The lifespan of the mantis shrimp varies from species to species, but the average lifespan of the aquatic animal is 20 years. 

Uses and Conservation Status

Mantis shrimp are under threat of population decline. They are designated as species of least concern by IUCN in the red list of threatened species. Although they are considered to be aggressive in nature, some of the species of the mantis are hunted by humans. They are part of the culinary dishes. They are majorly consumed in Asian countries like Japan, the Philippines, and Vietnam. The most common species that are part of the human diet include the following:

• Striped Harlequin or Bumblebee Shrimp

• Red Cherry Shrimp

• Blue Tiger Shrimp

• Blue Bolt Shrimp

• Snowball Shrimp

• Crystal Shrimp

• Glass or Ghost Shrimp

• Caridina Babaulti Shrimp.

Summary at Glance

• They are classified under order Stomatopoda.

• There are about 450 species of shrimp.

• The peacock mantis shrimp is the most important species.

• They are found in tropical seas.

• They are carnivorous in nature, the diet includes shelled molluscs and soft fish.

• They are solitary and monogamous animals.

• The presence of a strong exoskeleton and raptorial are the most important features

• The average lifespan is about 20 years.

• They are categorized among the species of least concern.