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Summary | |
Chorisquilla is a genus of shrimp-like crustaceans that falls into the order Stomatopoda . Commonly known as 'mantis shrimp' because of their resemblance to the terrestrial praying mantis, stomatopods are entirely marine organisms encompassing over 500 recognized species. They inhabit shallow waters of coral reef and sandy environments, actively pursuing small prey using spear or club-like appendages. These burrowing crustaceans often hide in coral crevices or mud, where they await prey and defend their territory. Thus, they are rarely seen by divers (Caldwell & Dingle, 1976). Although some stomatopods can reach sizes similar to that of a lobster, most, including many species of Chorisquilla, remain small and only reach lengths of a few centimeters. In addition to their physical strength and impressive predatory skills, stomatopods are unique in that they have the most complex visual sensory system of any organism in the animal kingdom, with the ability to see a wide range of colors and polarized light (Cronin, 2006).
Classified by Raymond Manning in 1969, Chorisquilla is one of six known genera of stomatopods within the family Protosquillidae, which are found most abundantly on Indo-West Pacific reefs. There are currently over 30 known species within the six genera of protosquillids, which include Chorisquilla, Echinosquilla, Haptosquilla, Protosquilla, Rayellus, and Siamosquilla (Ahyong, 2010). However, there is minimal information currently known about any of these groups.
For various reasons discussed throughout this webpage, it is believed that the observed specimen, discovered in rubble from the reef flat at Heron Island in the southern Great Barrier Reef, is post-larval representative of the species Chorsiquilla tweediei. This species is commonly called the 'velcro mantis' for the presence of small hooks on the surface of its telson (Caldwell, n.d.).
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Physical Description | |
As members of the subphylum Crustacea, the Stomatopod body plan is comprised of three main sections: the head, the thorax (person) and the abdomen (pleon). In addition, these organisms have a tail at the posterior end of their body commonly referred to as the telson (Vanhook & Patel, 2008). The stomatopod body can range in size from 15 millimeters over 300 millimeters, with brightly colored, dull, or transparent exoskeletons (Caldwell & Dingle, 1976). C. tweediei range in size from roughly 9-30mm (Caldwell, n.d.).
Distinguishing features among various stomatopods can be observed through differences in their exoskeleton structure, especially in the connectivity of somites. In segmented organisms, somites are typically bilaterally paired divisions of the body formed along the central axis from head to tail. One of the unique and most notable characteristics of the family Protosquillidae is the immovable fusion of the sixth abdominal somite (AS6) with the telson, where AS6 is the abdominal somite directly anterior to the telson (Ahyong, 2001). This fusion forms a pleotelson, a structure formed when one or more abdominal somites fuse together with the telson. However, a groove or demarcation is still usually visible between AS6 and the telson (Ahyong, 2012).
Specific to the Chorisquilla body plan is the division of the posterior end into a U-shaped or V-shaped fissure. Aside from variations in the sixth abdominal somite and the telson, all Chorisquilla species are fairly similar in terms of external morphology (Manning, 1975). As previously mentioned, it is believed that the species under observation is Chorisquilla tweediei. One of the defining features of this species is the external pattern of the eyes. They are white, bilobed, and each contain two vertical black stripes. It has been observed in the field that this species will often sit with its telson blocking the entrance of its burrow, camouflaged by detritus entirely covering the telson surface (Caldwell, n.d.). The dorsal surface of the C. tweediei telson is thickly setose (bristly or covered with setae). Unlike other species of Chorisquilla, they lack spines on the lateral margin of the telson. In addition, the sub-median boss is missing the proximal small, rounded boss that is present in some other Chorisquilla species (Ahyong, 2012).
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Ecology | |
Mantis shrimp are well known for their tendency to occupy and guard burrows in mud and various other sediments. Protosquillidae generally inhabit crevices and holes among reef rocks, sponges, and coral (Ahyong, 2010). Chorisquilla tweediei are typically found in shallow lagoons, reef flats, and reef crests at low intertidal depths of around 15m. Their preferred shelters include small cavities in coralline algae, rock, and coral rubble (Caldwell, n.d.).
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Life History and Behaviour | |
Burrowing
Burrows are excellent shelters for benthic organisms such as stomatopods, providing protection from potential predators as well as a good hiding spot for hunting prey. These crustaceans use their highly functional raptorial appendages, which are primarily used for attacking and capturing prey, to dig holes in soft sediments or hard substrate. By day, C. tweediei are often observed peering out of their cavity spaces. From what little is known about this species, they are known to rarely leave their dwellings (Caldwell, n.d.).
Feeding
Chorisquilla, like other 'smasher' stomatopods, generally feed on invertebrates with body armor such as clams, crabs, snails, and hermit crabs. They select their prey using their incredible and complex vision system and pursue it by stalking. After stunning or killing their prey with repeated blows by the hammer-like raptorial appendage, they drag the organism into their cavity where further shell breakage and consumption of tissues is conducted (Caldwell & Dingle, 1976). The specific diet of C. tweediei is not currently known; however, it is likely they consume small crustaceans (Caldwell, n.d.).
Fighting
Fighting is very common between mantis shrimp, as they are very territorial animals and will aggressively defend their burrows. When 'smashers' fight, they tend to strike at their opponents heavy body armor (the telson), not typically causing fatal injury (Caldwell & Dingle, 1976). Fights for burrows tend to be more violent and aggressive among smashers than stabbers, as stabbers tend to occupy softer substrate and can more easily dig new cavities (Christy & Salmon, 1991).
Mating
Stomatopod sexes are usually very dispersed and separated, which requires actively searching for mates. Smashers are known to be monogamous, and once a male finds a receptive female it will usually fight for entrance into the cavity. Females will sometimes leave their cavities in search of a male, but this is less common. The male will typically defend the female and cavity until the eggs are extruded, and then leave for reasons believed to be lack of space in the cavity once the egg mass is laid (Christy & Salmon, 1991).
Not much is known about the mating system of C. tweediei, but from field observations they are never found in pairs. This indicates that the species likely does not partake in mate guarding as is seen with some stomatopods. It is believed that mating occurs in the female's cavity entrance based on what is seen with other species of Chorisquilla (Roy Caldwell).
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Anatomy and Physiology |
Internal Anatomy | |
Like all crustaceans, a hemal system almost entirely regulates internal transport in stomatopods, complete with a hemocoel, arteries, veins, and a heart. Gills are present and lie in chambers that are formed within the carapace (upper part of the exoskeleton), and are ventilated by thoracic appendage movements (Ruppert et al., 2003). These organisms are gonochoristic, and fertilization occurs internally with sperm being stored in the seminal receptacles of females who lay yolky eggs. Male stomatopods have paired testes and females have paired ovaries that contain cement glands on the ventral side. These glands help hold together the egg during the brooding period (Wortham-Neal, 2002). Excretion is achieved through sac-like paired nephridia located in the thoracic segments; however, the majority of nitrogen excretion is carried out by diffusion of ammonia across the body surface. Stomatopods rely heavily on the use of their major sense organs to interpret their surroundings, in particular their eyes, setae, and statocysts. There is cephalisation of ganglia (brain) in the anterior region of the body, and the nervous system stimulates the digestive ceca, gut, heart and other organs. (Ruppert et al., 2004).
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External Anatomy | |
Stomatopods share the common external features present in most Malacostraca crustaceans. Their body is covered by a hard exoskeleton secreted by the epidermis that functions in defense and protection, and is displayed with various colors and patterns specific to individual species. The body is divided into three main components- the head, the thorax, and the abdomen- and each of these sections contains a certain number of paired segments known as somites. On the anterior end of the body, these segments are fused together, and bear the antennae and feeding appendages (Ruppert et al., 2004). The posterior-most end of the body is known as the telson. In mantis shrimp, the telson acts as an ultra strong body armor for protection during fights with predators and other stomatopods. Since a strike from a mantis shrimp is easily capable of shattering a crustacean shell, the telson's ability to withstand these blows proves that it is nearly impervious to impact (JEB, 2010).
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Raptorial Appendage | |
One of the most notable features of mantis shrimp is the presence of a raptorial (predatory) appendage. These appendages play a large role in predatory prey capture, and function as either barb-like spears or club-like smashers. Like all members of the Protosquillidae family, Chorisquilla falls into the category of smashers. Smashers not only use their club for prey capture, but for fighting with other stomatopods as well. The appendage is highly specialized for these functions, with the ability to break the shells of other organisms with great force. Most animals that use shell-crushing as a means of attacking prey do so by applying continuous force over a period of time (Patek & Caldwell, 2005). Conversely, mantis shrimp generate quick, powerful blows with their hammer-like appendage that can damage or kill prey with extreme strike speeds over 10 m s-1, and in some species strike speeds have been measured at up to 23 m s-1 (Patek et al., 2004). These blows are delivered at forces much greater than the raptorial appendage muscles can generate, which is made possible by a spring and catch mechanism that stomatopods use by storing and eventually releasing muscular energy. In addition to the powerful blow itself, cavitation bubbles are formed between the club and the prey from the intense speed of the strike. When these bubbles collapse, they produce such great force as to play a major role in destroying the hard shells of prey targets (Summers, 2004).
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| Figure 7 |
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A Closer Look: Eyes | |
This section focuses on a group of stomatopods known as Gonodactyloidea. Gonodactyloids are a superfamily that encompasses seven stomatopod families, including Protosquillidae.
Compound eyes are common among arthropods such as insects and crustaceans. They are composed of thousands of individual structural units called ommatidia, which are generally hexagonal in shape and contain a photoreceptor and a lens (Fig. 8). The distribution of these small eye sensors for imaging in exoskeleton-containing invertebrates reduces the weight and energy costs associated with the single eye structure (Völkel et al., 2003), making them evolutionarily beneficial for organisms like stomatopods. The compound eyes of stomatopods fall into the design of apposition compound eyes, which are considered to be the original, ancestral form of compound eyes and are less light sensitive than superposition compound eyes commonly present in nocturnal insects (Völkel et al., 2003). Each ommatidium receptor in apposition eyes acts independently of one another in detecting a portion of an image, which is then brought together with other receptor images in the brain to form a complete figure (Land & Nilsson, 2012).
Mantis shrimp are extremely unique in terms of the complexities of their visual system that combine to form images, especially the range of information channels and movements by different components of the eyes on various levels. Each eye can move quickly and independently of the other, and is characterised by sporadic or discontinuous motion. The ability to view several hundred degrees each second with motile eye stalks and saccidic movement allows stomatopods to place figures of interest into acute zones of surveillance without having to move their entire head or body (Marshall et al., 2014). Thus, targeting moving prey objects is highly advanced in these organisms.
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This video highlights the unique and complex eye movements of the observed specimen, believed to be C. tweediei, obtained from the Heron Island reef flat in the southern Great Barrier Reef. Note the sporadic motion and scanning by the individual eyes.
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In addition to aiming each eye stalk and eye in the direction of interest, gonodactyloid stomatopods can likewise direct each individual ommatidium so that photoreceptors in completely different regions of the eye can detect the same area of visual space (Cronin et al., 1994). Each eye is divided into an upper and lower hemisphere, which are separated by a narrow mid-band (Fig. 9). Since ommatidia in the upper and lower hemispheres also share visual regions seen by ommatidia in the mid-band, there is a resulting section through space that is perceived by three receptor sets. Thus, mantis shrimp can simultaneously view a figure from multiple positions in a single eye (Cronin et al., 1994). However, because the eyes mostly observe a one-dimensional area in space, continuous scanning is necessary to obtain adequate information from the environment and is a unique behaviour of stomatopods (Marshall, 1991).
What is truly special about stomatopods is their ability to see an enormous range of colors and light. In fact, these crustaceans have the most diverse assemblage of color receptors found in any organism. The six rows of ommatidia in the mid-band of stomatopod eyes are very different from those found in either hemisphere, and four of these rows are believed to be involved in color vision (Marshall et al., 1996). The majority of species has ten types of receptor classes for the visible light spectrum (400-700nm), and an additional five or six receptors that function in the ultraviolet spectrum (100-400nm). This can be compared to human eyes, which contain four types of photoreceptors of which only three are used for color sight. This complex system of color vision is thought to be used as a means of enhancing contrast underwater and making detection of prey and other objects easier (Cronin, 2006).
Another unique feature of stomatopod sight is their capacity to see polarized light, an ability that humans do not possess. While this trait is common among arthropods and various other animals, polarized light detection in mantis shrimp is thought to enhance object visibility in underwater environments in addition to their color vision (Cronin, 2006).
As previously mentioned, not much information is known about stomatopods of the genus Chorisquilla. Their eyes function by the same general mechanisms as other gonodactyloids; however, differences in the external structure and patterning do exist. Chorisquilla eyes differ from other stomatopod eyes in that the cornea is dorsally flattened and laterally broadened (Ahyong, 2010). The eyes of the specimen under observation appear to have black and white stripes. According to Roy Caldwell, world expert on stomatopods, this eye pattern is only found in Chorisquilla of the species C. tweediei (Fig.10).
The organism was sectioned and the eyes examined under a microscope. Images show the similarities between eye shape of the post-larval C. tweediei specimen (Fig. 12) and other gonodactyloids (Fig. 11), indicating that the complex features of stomatopod vision systems are present in this species.
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Evolution and Systematics | |
Mantis shrimp are malacostracan
crustaceans that belong to the order Stomatopoda. They are the only
living members belonging to the subclass Hoplocarida (Ahyong &
Harling, 2000). But despite the common name 'mantis shrimp' they are
not very closely related to shrimps or other marine-dwelling
crustaceans. Fossil evidence indicates that before splitting off from
leptostrocans around 400 million years ago, stomatopods were filter
feeders and used their appendages to strain food. The first true
stomatopods are thought to have evolved around 200 million years ago,
when a pair of forward appendages developed into large limbs with the
ability to fold. This is where the name 'stomatopod' came from, as
derived from the Latin word meaning 'mouth foot.' (Caldwell &
Dingle, 1976).
Modern stomatopods are categorized
into four families- Squillidae, Bathysquillidae, Gonodactylidae, and
Lysiosquillidae- which emerged during the Jurassic period, between
190 million and 135 million years ago. They are further categorized
into two functional groups, the spearers and the smashers, based on
the mechanism of prey capture employed by their raptorial appendages.
The spearer functional group includes all species within the
Squillidae, Bathysquillidae, and Lysiosquillidae families, as well
as various genera from the Gonodactylidae. However, the smashers
include only a small number of genera from the Gonodactylidae, including Chorisquilla. (Caldwell & Dingle, 1976).
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Biogeographic Distribution | |
The distribution of mantis shrimp species is very large, as these crustaceans can be found in the shallows of tropical and subtropical waters around the globe. Four of the five stomatopod genera in the family Protosquillidae are found on coral reefs of the Indo-Pacific, and each of these groups has representatives in Australia (Ahyong, 2001). Protosquillids seem to be entirely absent from the Eastern Pacific and Western Atlantic (Ahyong, 2010).
Map showing the Indo-Pacific region where most Protosquillid genera are found. Retrieved 27 May, 2015, from http://www.coral-reef-info.com/image-files/Indo-Pacific-map.png.
C. tweediei are typically found in shallow reefs of New Caledonia and eastern Australia (Caldwell, n.d.).
Map showing Australia and New Caledonia region in the Indo Pacific. Retrieved 27 May, 2015, from http://surftherenow.com/wp-content/uploads/2009/03/new_caledonia.gif.
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Conservation and Threats | |
The ability for stomatopods to disperse throughout shallow coral reef ecosystems is critical for their survival and prosperity. As inhabitants of tropical and subtropical reef systems often battered by storms and hurricanes, these organisms can easily disappear from such devastated areas. It is believed that large stomatopod species are better able to re-inhabit disturbed areas due to higher production of large eggs and wider-ranging geographical distributions than small species. Since small species tend to occupy narrower geographic ranges, produce fewer small eggs, and grow at a slower rate, they are not as likely to be successful in re-inhabiting storm-damaged environments (Reaka, 1980).
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References | |
Ahyong, S. T. (2010). A new genus and two new species of mantis shrimp from the Western Pacific (Stomatopoda: Gonodactyloidea: Protosquillidae). Journal of Crustacean Biology, 30(1), 141-145.
Ahyong, S. T. (2001). Revision of the Australia stomatopod Crustacea. Records of the Australian Museum. Supplement 26, 85-99.
Ahyong, S. T. (2012). The marine fauna of New Zealand: mantis shrimps (Crustacea: Stomatopoda). NIWA Biodiversity Memoir, 125.
Ahyong, S. T. & Harling, C. (2000). The phylogeny of the stomatopod Crustacea. Australian Journal of Zoology, 48(6), 607-642.
Caldwell, R. L. & Dingle, H. (1976). Stomatopods. Scientific American, 80-89.
Caldwell, R.L. Chorisquilla tweediei. Roy's List of Stomatopods for the Aquarium. Retrieved May 19, 2015, from http://www.ucmp.berkeley.edu/arthropoda/crustacea/malacostraca/eumalacostraca/royslist/species.php?name=c_tweediei.
Christy, J. H. & Salmon, M. (1991). Comparative studies of reproductive behavior in mantis shrimps and fiddler crabs. American Zoologist, 31(2), 329-337.
Cronin, T. W. (2006). Stomatopods. Current Biology, 16(7), R235-R236.
Cronin, T. W., Marshall, N. J., & Land, M. F. (1994). The unique visual system of the mantis shrimp. American Scientist, 82(4), 356-365.
Land, M. F. & Nilsson, D-E. (2012). Animal eyes. Oxford Animal Biology Series, 2.
Manning, R. B. (1975). Two new species of the Indo-West Pacific genus Chorisquilla (Crustacea, Stomatopoda), with notes on C. excavata (Miers). Proceedings of the Biological Society of Washington, 88, 253-262.
Mantis shrimp telsons withstand blows like human body armour. (2010). Journal of Experimental Biology (JEB), 213(20).
Marshall, N. J. (1991). Vision in stomatopod crustaceans, University of Sussex (United Kingdom).
Marshall, N. J., Cronin, T. W., & Kleinlogel, S. (2007). Stomatopod eye structure and function: A review. Arthropod Structure and Development, 36(4), 420-448.
Marshall, N. J., Jones, J. P., & Cronin, T. W. (1996). Behavioural evidence for colour vision in stomatopod crustaceans. Journal of Comparative Physiology, 179(4), 473-481.
Marshall, N. J., Land, M. F., & Cronin, T. W. (2014). Shrimps that pay attention: saccadic eye movements in stomatopod crustaceans. Philos Trans R Soc Lond B Biol Sci., 369(1636).
Patek, S. N. & Caldwell, R. L. (2005). Extreme impact and cavitation forces of a biological hammer: strike forces of the peacock mantis shrimp Odontodactylus scyllarus. The Journal of Experimental Biology, 208(19), 3655-3664.
Patek, S. N., Korff, W. L., & Caldwell, R. L. (2004). Biomechanics: Deadly strike mechanism of a mantis shrimp. Nature, 428, 819-820.
Reaka, M. L. (1980). Geographic range, life history patterns, and body size in a guild of coral dwelling mantis shrimps. Evolution, 34(5), 1019-1030.
Ruppert, E. E., Fox, X.S., & Barnes, R. D. (2004). Invertebrate zoology: a functional evolutionary approach (2nd ed.). Belmont, CA: Brooks/Cole.
Summers, A. (2004). Knockout punch: a boxer who could jab like a mantis shrimp could win every match with a single blow. Natural History, 113(6), 22-23.
Vanhook, A. M. & Patel, N. H. (2008). Crustaceans. Current Biology, 18(13), R547-R550.
Völkel, R., Eisner, M., & Weible, K.J. (2003). Miniaturized imaging systems. Microelectronic Engineering, 67, 461-472.
Wortham-Neal, J. L. (2002). Reproductive morphology and biology of male and female mantis shrimp (Stomatopoda: Squillidae). Journal of Crustacean Biology, 22(4), 728-741.
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