Tachypleus gigas
Encyclopedia
Tachypleus gigas is one of the four extant species of horseshoe crab
. It is found in shallow water in South East Asia at depths of up to 40 m (131.2 ft). It grows up to 39 cm (15.4 in) long and 17.5 cm (6.9 in) wide, and is covered by a sturdy carapace
, with a long caudal spine (tail).
ous exoskeleton
. In a sample of five individuals, Lazarus et al. recorded maximum and minimum total lengths of 39 centimetres (15.4 in) and 27 cm (10.6 in), respectively. The prosoma is the widest part of the animal, at 14 centimetre and 8.2 centimetre long, while the opisthosoma
is 9 centimetre wide and 6 centimetre long. The caudal spine (the long, pointed part of the tail) is 13.5 centimetre long, bears a crest dorsally, and is concave ventrally. The anterior part of the tail is sharply serrated. Males are smaller than females, have a paler and rougher carapace
, and act as hosts to a greater number of epibionts.
The carapace which shields the prosoma also bears two pairs of eyes – a pair of simple eyes at the front, and a pair of compound eyes positioned laterally. In common with other horseshoe crabs, T. gigas also has ventral eyes near the mouthparts, and photoreceptor
s in the caudal spine.
On the underside of the animal, T. gigas has seven pairs of legs, five of which bear small claws, and five pairs of book gills, which are used for gas exchange
.
of T. gigas is relatively long and involves a large number of instar
s. The eggs
are approximately 3.7 millimetre (0.145669291338583 in) in diameter. The freshly hatched larva
e, known as trilobite larvae, have no tail, and are 8 millimetre (0.31496062992126 in) long. Males are thought to pass through 12 moults
before reaching sexual maturity
, while females pass through 13 moults.
distribution of the three Asian horseshoe crab species, ranging across the western Pacific Ocean
from Japan
to the Philippines
, extending into the Indian Ocean
only on the west coast of Sumatra
.
, detritus
and polychaete
s, which it seeks on the ocean floor. House Crow
s have been observed to turn T. gigas over and eat the soft underside, while gull
s only attack individuals that are already stranded upside-down.
Since horseshoe crabs do not moult
after they have reached sexual maturity
, they are often colonised by epibiont
s. The dominant diatom
s are species of the genera Navicula
, Nitzschia
and Skeletonema. Among the larger organisms, the sea anemone
Metridium
, the bryozoa
n Membranipora
, the barnacle
Balanus amphitrite
and the bivalves
Anomia and Crassostrea
are the most frequent colonists of T. gigas. Rarer epibionts include green algae
, flatworm
s, tunicate
s, isopods
, amphipods
, gastropods, mussel
s, pelecypods, annelid
s and polychaete
s.
T. gigas is listed as Data Deficient
on the IUCN Red List
.
by Otto Friedrich Müller
in 1785. It was originally placed in the genus Limulus, but was transferred to the genus Tachypleus by Reginald Innes Pocock
in 1902.
T. gigas is estimated to have diverged
from the other Asian species of horseshoe crab . While it is clear that the American horseshoe crab Limulus polyphemus is distinct from the remaining extant species of horseshoe crab, relationships within the Asian horseshoe crabs remains uncertain. T. gigas has a chromosome number of 2n = 28, compared to 26 in T. tridentatus, 32 in Carcinoscorpius and 52 in Limulus.
Common name
s for the species include Indo-Pacific horseshoe crab, Indonesian horseshoe crab, Indian horseshoe crab and Chinese horseshoe crab.
Horseshoe crab
The Atlantic horseshoe crab, Limulus polyphemus, is a marine chelicerate arthropod. Despite its name, it is more closely related to spiders, ticks, and scorpions than to crabs. Horseshoe crabs are most commonly found in the Gulf of Mexico and along the northern Atlantic coast of North America...
. It is found in shallow water in South East Asia at depths of up to 40 m (131.2 ft). It grows up to 39 cm (15.4 in) long and 17.5 cm (6.9 in) wide, and is covered by a sturdy carapace
Carapace
A carapace is a dorsal section of the exoskeleton or shell in a number of animal groups, including arthropods such as crustaceans and arachnids, as well as vertebrates such as turtles and tortoises. In turtles and tortoises, the underside is called the plastron.-Crustaceans:In crustaceans, the...
, with a long caudal spine (tail).
Description
Tachypleus gigas has a "sage green" chitinChitin
Chitin n is a long-chain polymer of a N-acetylglucosamine, a derivative of glucose, and is found in many places throughout the natural world...
ous exoskeleton
Exoskeleton
An exoskeleton is the external skeleton that supports and protects an animal's body, in contrast to the internal skeleton of, for example, a human. In popular usage, some of the larger kinds of exoskeletons are known as "shells". Examples of exoskeleton animals include insects such as grasshoppers...
. In a sample of five individuals, Lazarus et al. recorded maximum and minimum total lengths of 39 centimetres (15.4 in) and 27 cm (10.6 in), respectively. The prosoma is the widest part of the animal, at 14 centimetre and 8.2 centimetre long, while the opisthosoma
Opisthosoma
The opisthosoma is the posterior part of the body in some arthropods, behind the prosoma . It is a distinctive feature of the subphylum Chelicerata...
is 9 centimetre wide and 6 centimetre long. The caudal spine (the long, pointed part of the tail) is 13.5 centimetre long, bears a crest dorsally, and is concave ventrally. The anterior part of the tail is sharply serrated. Males are smaller than females, have a paler and rougher carapace
Carapace
A carapace is a dorsal section of the exoskeleton or shell in a number of animal groups, including arthropods such as crustaceans and arachnids, as well as vertebrates such as turtles and tortoises. In turtles and tortoises, the underside is called the plastron.-Crustaceans:In crustaceans, the...
, and act as hosts to a greater number of epibionts.
The carapace which shields the prosoma also bears two pairs of eyes – a pair of simple eyes at the front, and a pair of compound eyes positioned laterally. In common with other horseshoe crabs, T. gigas also has ventral eyes near the mouthparts, and photoreceptor
Photoreceptor
A photoreceptor cell is a specialized type of neuron found in the eye's retina that is capable of phototransduction. The great biological importance of photoreceptors is that they convert light into signals that can stimulate biological processes...
s in the caudal spine.
On the underside of the animal, T. gigas has seven pairs of legs, five of which bear small claws, and five pairs of book gills, which are used for gas exchange
Gas exchange
Gas exchange is a process in biology where gases contained in an organism and atmosphere transfer or exchange. In human gas-exchange, gases contained in the blood of human bodies exchange with gases contained in the atmosphere. Human gas-exchange occurs in the lungs...
.
Life cycle
The life cycleBiological life cycle
A life cycle is a period involving all different generations of a species succeeding each other through means of reproduction, whether through asexual reproduction or sexual reproduction...
of T. gigas is relatively long and involves a large number of instar
Instar
An instar is a developmental stage of arthropods, such as insects, between each molt , until sexual maturity is reached. Arthropods must shed the exoskeleton in order to grow or assume a new form. Differences between instars can often be seen in altered body proportions, colors, patterns, or...
s. The eggs
Egg (biology)
An egg is an organic vessel in which an embryo first begins to develop. In most birds, reptiles, insects, molluscs, fish, and monotremes, an egg is the zygote, resulting from fertilization of the ovum, which is expelled from the body and permitted to develop outside the body until the developing...
are approximately 3.7 millimetre (0.145669291338583 in) in diameter. The freshly hatched larva
Larva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...
e, known as trilobite larvae, have no tail, and are 8 millimetre (0.31496062992126 in) long. Males are thought to pass through 12 moults
Ecdysis
Ecdysis is the moulting of the cuticula in many invertebrates. This process of moulting is the defining feature of the clade Ecdysozoa, comprising the arthropods, nematodes, velvet worms, horsehair worms, rotifers, tardigrades and Cephalorhyncha...
before reaching sexual maturity
Sexual maturity
Sexual maturity is the age or stage when an organism can reproduce. It is sometimes considered synonymous with adulthood, though the two are distinct...
, while females pass through 13 moults.
Distribution
Tachypleus gigas has the broadest latitudinalLatitude
In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...
distribution of the three Asian horseshoe crab species, ranging across the western Pacific Ocean
Pacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...
from Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
to the Philippines
Philippines
The Philippines , officially known as the Republic of the Philippines , is a country in Southeast Asia in the western Pacific Ocean. To its north across the Luzon Strait lies Taiwan. West across the South China Sea sits Vietnam...
, extending into the Indian Ocean
Indian Ocean
The Indian Ocean is the third largest of the world's oceanic divisions, covering approximately 20% of the water on the Earth's surface. It is bounded on the north by the Indian Subcontinent and Arabian Peninsula ; on the west by eastern Africa; on the east by Indochina, the Sunda Islands, and...
only on the west coast of Sumatra
Sumatra
Sumatra is an island in western Indonesia, westernmost of the Sunda Islands. It is the largest island entirely in Indonesia , and the sixth largest island in the world at 473,481 km2 with a population of 50,365,538...
.
Ecology and conservation
T. gigas inhabits sandy and muddy shores at depths up to 40 metres (131.2 ft), and is the only horseshoe crab to have been observed swimming at the surface of the ocean. Its diet is chiefly composed of molluscsMollusca
The Mollusca , common name molluscs or mollusksSpelled mollusks in the USA, see reasons given in Rosenberg's ; for the spelling mollusc see the reasons given by , is a large phylum of invertebrate animals. There are around 85,000 recognized extant species of molluscs. Mollusca is the largest...
, detritus
Detritus
Detritus is a biological term used to describe dead or waste organic material.Detritus may also refer to:* Detritus , a geological term used to describe the particles of rock produced by weathering...
and polychaete
Polychaete
The Polychaeta or polychaetes are a class of annelid worms, generally marine. Each body segment has a pair of fleshy protrusions called parapodia that bear many bristles, called chaetae, which are made of chitin. Indeed, polychaetes are sometimes referred to as bristle worms. More than 10,000...
s, which it seeks on the ocean floor. House Crow
House Crow
thumb|300px|Bangalore, IndiaThe House Crow , also known as the Colombo Crow is a common bird of the Crow family that is of Asian origin but now found in many parts of the world, where they arrived assisted by shipping. It is between the Jackdaw and the Carrion Crow in size but is relatively...
s have been observed to turn T. gigas over and eat the soft underside, while gull
Gull
Gulls are birds in the family Laridae. They are most closely related to the terns and only distantly related to auks, skimmers, and more distantly to the waders...
s only attack individuals that are already stranded upside-down.
Since horseshoe crabs do not moult
Ecdysis
Ecdysis is the moulting of the cuticula in many invertebrates. This process of moulting is the defining feature of the clade Ecdysozoa, comprising the arthropods, nematodes, velvet worms, horsehair worms, rotifers, tardigrades and Cephalorhyncha...
after they have reached sexual maturity
Sexual maturity
Sexual maturity is the age or stage when an organism can reproduce. It is sometimes considered synonymous with adulthood, though the two are distinct...
, they are often colonised by epibiont
Epibiont
An epibiont is an organism that lives on the surface of another living organism. An epibiont is usually considered harmless to the host; in this sense, the relationship between the two organisms can be considered neutralistic or commensalistic. Typical epibionts are barnacles, remoras, and algae,...
s. The dominant diatom
Diatom
Diatoms are a major group of algae, and are one of the most common types of phytoplankton. Most diatoms are unicellular, although they can exist as colonies in the shape of filaments or ribbons , fans , zigzags , or stellate colonies . Diatoms are producers within the food chain...
s are species of the genera Navicula
Navicula
Navicula is a genus of boat-shaped microbes that are a type of Phytoplankton or algae — primarily aquatic, eukaryotic, photosynthetic organisms, ranging in size from a single cell....
, Nitzschia
Nitzschia
Nitzschia is a common pennate marine diatom. In the scientific literature this genus is sometimes termed Nitzchia, this taxon has many species described, which all have a similar morphology.-Occurrence:...
and Skeletonema. Among the larger organisms, the sea anemone
Sea anemone
Sea anemones are a group of water-dwelling, predatory animals of the order Actiniaria; they are named after the anemone, a terrestrial flower. Sea anemones are classified in the phylum Cnidaria, class Anthozoa, subclass Zoantharia. Anthozoa often have large polyps that allow for digestion of larger...
Metridium
Metridium
Members of the genus Metridium, also known as plumose anemones, are sea anemones found mostly in the cooler waters of the northern Pacific and Atlantic oceans. They are characterized by their numerous threadlike tentacles extending from atop a smooth cylindrical column, and can vary from a few...
, the bryozoa
Bryozoa
The Bryozoa, also known as Ectoprocta or commonly as moss animals, are a phylum of aquatic invertebrate animals. Typically about long, they are filter feeders that sieve food particles out of the water using a retractable lophophore, a "crown" of tentacles lined with cilia...
n Membranipora
Membranipora
Membranipora is a genus of bryozoan in the family Membraniporidae. A typical example is the widely distributed species Membranipora membranacea that commonly encrusts seaweeds, particularly fronds of the kelps Laminaria digitata, L. hyperborea, and Saccorhiza polyschides.Colonies of M...
, the barnacle
Barnacle
A barnacle is a type of arthropod belonging to infraclass Cirripedia in the subphylum Crustacea, and is hence related to crabs and lobsters. Barnacles are exclusively marine, and tend to live in shallow and tidal waters, typically in erosive settings. They are sessile suspension feeders, and have...
Balanus amphitrite
Balanus amphitrite
Balanus amphitrite is a species of acorn barnacle in the Balanidae family. Its common names include the striped barnacle, the purple acorn barnacle and Amphitrite's rock barnacle. It is found in warm and temperate waters worldwide....
and the bivalves
Bivalvia
Bivalvia is a taxonomic class of marine and freshwater molluscs. This class includes clams, oysters, mussels, scallops, and many other families of molluscs that have two hinged shells...
Anomia and Crassostrea
Crassostrea
Crassostrea is a genus of true oysters containing the most important oysters used for food.- Species :* Crassostrea ** †Crassostrea alabamiensis...
are the most frequent colonists of T. gigas. Rarer epibionts include green algae
Green algae
The green algae are the large group of algae from which the embryophytes emerged. As such, they form a paraphyletic group, although the group including both green algae and embryophytes is monophyletic...
, flatworm
Flatworm
The flatworms, known in scientific literature as Platyhelminthes or Plathelminthes are a phylum of relatively simple bilaterian, unsegmented, soft-bodied invertebrate animals...
s, tunicate
Tunicate
Tunicates, also known as urochordates, are members of the subphylum Tunicata, previously known as Urochordata, a group of underwater saclike filter feeders with incurrent and excurrent siphons that is classified within the phylum Chordata. While most tunicates live on the ocean floor, others such...
s, isopods
Isopoda
Isopods are an order of peracarid crustaceans, including familiar animals such as woodlice and pill bugs. The name Isopoda derives from the Greek roots and...
, amphipods
Amphipoda
Amphipoda is an order of malacostracan crustaceans with no carapace and generally with laterally compressed bodies. The name amphipoda means "different-footed", and refers to the different forms of appendages, unlike isopods, where all the legs are alike. Of the 7,000 species, 5,500 are classified...
, gastropods, mussel
Mussel
The common name mussel is used for members of several families of clams or bivalvia mollusca, from saltwater and freshwater habitats. These groups have in common a shell whose outline is elongated and asymmetrical compared with other edible clams, which are often more or less rounded or oval.The...
s, pelecypods, annelid
Annelid
The annelids , formally called Annelida , are a large phylum of segmented worms, with over 17,000 modern species including ragworms, earthworms and leeches...
s and polychaete
Polychaete
The Polychaeta or polychaetes are a class of annelid worms, generally marine. Each body segment has a pair of fleshy protrusions called parapodia that bear many bristles, called chaetae, which are made of chitin. Indeed, polychaetes are sometimes referred to as bristle worms. More than 10,000...
s.
T. gigas is listed as Data Deficient
Data Deficient
Data Deficient is a category applied by the IUCN, other agencies, and individuals to a species when the available information is not sufficient for a proper assessment of conservation status to be made...
on the IUCN Red List
IUCN Red List
The IUCN Red List of Threatened Species , founded in 1963, is the world's most comprehensive inventory of the global conservation status of biological species. The International Union for Conservation of Nature is the world's main authority on the conservation status of species...
.
Taxonomy
Tachypleus gigas was first describedAlpha taxonomy
Alpha taxonomy is the discipline concerned with finding, describing and naming species of living or fossil organisms. This field is supported by institutions holding collections of these organisms, with relevant data, carefully curated: such institutes include natural history museums, herbaria and...
by Otto Friedrich Müller
Otto Friedrich Müller
Otto Friedrich Müller, also Mueller was a Danish naturalist.-Biography:Müller was born in Copenhagen. He was educated for the church, became tutor to a young nobleman, and after several years' travel with him settled in Copenhagen in 1767, and married a lady of wealth.His first important works,...
in 1785. It was originally placed in the genus Limulus, but was transferred to the genus Tachypleus by Reginald Innes Pocock
Reginald Innes Pocock
Reginald Innes Pocock F.R.S. was a British zoologist.Pocock was born in Clifton, Bristol, the fourth son of Rev. Nicholas Pocock and Edith Prichard. He began showing interest in natural history at St. Edward's School, Oxford. He received tutoring in zoology from Sir Edward Poulton, and was allowed...
in 1902.
T. gigas is estimated to have diverged
Speciation
Speciation is the evolutionary process by which new biological species arise. The biologist Orator F. Cook seems to have been the first to coin the term 'speciation' for the splitting of lineages or 'cladogenesis,' as opposed to 'anagenesis' or 'phyletic evolution' occurring within lineages...
from the other Asian species of horseshoe crab . While it is clear that the American horseshoe crab Limulus polyphemus is distinct from the remaining extant species of horseshoe crab, relationships within the Asian horseshoe crabs remains uncertain. T. gigas has a chromosome number of 2n = 28, compared to 26 in T. tridentatus, 32 in Carcinoscorpius and 52 in Limulus.
Common name
Common name
A common name of a taxon or organism is a name in general use within a community; it is often contrasted with the scientific name for the same organism...
s for the species include Indo-Pacific horseshoe crab, Indonesian horseshoe crab, Indian horseshoe crab and Chinese horseshoe crab.
See also
- Tachypleus tridentatusTachypleus tridentatusTachypleus tridentatus is a species of horseshoe crab found in China, Indonesia, Japan, Malaysia, the Philippines, Taiwan, and Vietnam....
- Carcinoscorpius rotundicaudaCarcinoscorpius rotundicaudaThe mangrove horseshoe crab, Carcinoscorpius rotundicauda, is a marine chelicerate arthropod. Despite its name, it is more closely related to spiders and scorpions than to crabs. It is the only species in the genus Carcinoscorpius...
- Limulus polyphemus