Tachypleus gigas

Source: Wikipedia, the free encyclopedia.

Tachypleus gigas
Female, off the Bay of Bengal

Data Deficient  (IUCN 2.3)[1]
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Chelicerata
Order: Xiphosura
Family: Limulidae
Genus: Tachypleus
Species:
T. gigas
Binomial name
Tachypleus gigas
(Müller, 1785)
Synonyms[2]
  • Limulus gigas Müller, 1785
  • Limulus moluccanus Latreille, 1802

Tachypleus gigas, commonly known as the Indo-Pacific horseshoe crab,

extant (living) species of horseshoe crab. It is found in coastal water in South and Southeast Asia at depths to 40 m (130 ft).[2]

Description

Illustrations of male from above and below. Notice that the illustration from below incorrectly shows all walking legs as scissor-like, as in females (in males, the two frontal pairs of walking legs have hooks)

It grows up to about 50 cm (20 in) long, including the tail, and is covered by a sturdy carapace that is up to about 26.5 cm (10.4 in) wide.[7]

Tachypleus gigas has a

book gills are located on the underside of the opisthosoma.[9][11] They have a long spiny tail known as the telson. The tail bears a crest dorsally and is concave ventrally,[2] giving it an essentially triangular cross section.[9]

Despite the scientific name T. gigas, the close relative

Carcinoscorpius rotundicauda.[12]
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 photoreceptors in the caudal spine.[13]

Sexual difference

Like the other species, females of T. gigas grow larger than males. On average in Sarawak, Malaysia, females are about 42 cm (17 in) long, including a tail that is about 20 cm (7.9 in), and their carapace (prosoma) is about 22 cm (8.7 in) wide. In comparison, the average for males is about 34 cm (13 in) long, including a tail that is about 17.5 cm (6.9 in), and their carapace is about 17.5 cm (6.9 in) wide.[7] There are some geographic variations in the average size, but most are similar to, or somewhat smaller, than the ones from Sarawak. An outlier are individuals from West Bengal in India where the average carapace width only is about 17 cm (6.7 in) and 14 cm (5.5 in) in females and males respectively.[9] The largest females of the species reach a total length of more than 50 cm (20 in) and can weigh more than 1.8 kg (4.0 lb).[7]

In addition to their smaller size, males have a paler and rougher carapace, act as hosts to a greater number of epibionts,[8] have six (instead of three) long spines on either side of the rear carapace, and their two front pairs of walking legs, prosomal appendages two and three, have hooks (they are scissor-like in females).[6] Juveniles (both sexes) also have six long spines on either side of the rear carapace, similar to adult males.[6]

Distribution and habitat

Male found dead in Bako National Park, Malaysia
Individual found dead on Indonesian shore

Tachypleus gigas is one of three living species of horseshoe crabs in Asia, the others being Tachypleus tridentatus and Carcinoscorpius rotundicauda. The fourth living species,

Limulus polyphemus, is found in the Americas.[12] T. gigas is found in tropical South and Southeast Asia, ranging from the Bay of Bengal to the South China Sea, with records from India, Malaysia, Singapore, Indonesia, Thailand, Vietnam and the Philippines.[1][14][15][16] Although records are lacking, it likely also occurs in Myanmar.[15]

Tachypleus gigas inhabits

salinities down to 15 PSU, but their eggs only hatch above 20 PSU.[15]

Breeding

The

eggs are about 3.7 mm (0.15 in) in diameter.[18] The freshly hatched larvae, known as trilobite larvae, have no tail, and are 8 mm (0.31 in) long.[19] Males are thought to pass through 12 moults before reaching sexual maturity, while females pass through 13 moults.[20]

Ecology

The diet of T. gigas is chiefly composed of molluscs, detritus, and polychaetes, which it seeks on the ocean floor.[21] House crows have been observed to turn T. gigas over and eat the soft underside, while gulls only attack individuals that are already stranded upside-down.[3]

Since horseshoe crabs do not moult after they have reached sexual maturity, they are often colonised by

pelecypods, annelids, and polychaetes.[8]

Conservation

Tachypleus gigas is listed as

Data Deficient on the IUCN Red List.[1]

Taxonomy

Tachypleus gigas was

first described 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.[2]

Tachypleus gigas is estimated to have

chromosome number of 2n = 28, compared to 26 in T. tridentatus, 32 in Carcinoscorpius, and 52 in Limulus.[24]

References

  1. ^
    doi:10.2305/IUCN.UK.1996.RLTS.T21308A9266907.en
    . Retrieved 20 November 2021.
  2. ^ a b c d e S. Lazarus; V. Narayana Pillai; P. Devadoss & G. Mohanraj (1990). "Occurrence of king crab, Tachypleus gigas (Muller), off the northeast coast of India" (PDF). Proceedings of the First Workshop on Scientific Results of FORV Sagar Sampada, 5–7 June 1989, Kochi: 393–395.
  3. ^
    ISBN 978-0-674-01159-5
    .
  4. ISBN 978-0-674-01159-5
    .
  5. ISBN 978-0-306-46681-6
    .
  6. ^ a b c "Identification guide". Horseshoe Crab monitoring site. Retrieved 26 June 2018.
  7. ^ a b c A. Raman Noor Jawahir; Mohamad Samsur; Mohd L. Shabdin; Khairul-Adha A. Rahim (2017). "Morphometric allometry of horseshoe crab, Tachypleus gigas at west part of Sarawak waters, Borneo, East Malaysia". AACL Bioflux. 10 (1): 18–24.
  8. ^
    doi:10.1007/s002270050730
    .
  9. ^
    ISBN 978-0-387-89959-6
    .
  10. ^
    ISBN 978-9971-69-150-9
    .
  11. ^ "COAST / Horseshoe crabs" (PDF). Project Oceanography. University of South Florida. 2001. pp. 81–91.
  12. ^ a b "About the Species". The Horseshoe Crab. Retrieved 26 June 2018.
  13. ^ Liza Carruthers. "Horseshoe crab". The Internet Encyclopedia of Science. Retrieved January 22, 2011.
  14. ^ "Tachypleus gigas (Müller, 1785)". Horseshoe Crab monitoring site. Retrieved 26 June 2018.
  15. ^
    doi:10.3389/fmars.2018.00164
    .
  16. ^ a b Tan, Ria (November 2019). "Coastal horseshoe crab". Wild Singapore. Retrieved 17 January 2023.
  17. ISBN 978-0-674-01159-5
    .
  18. JSTOR 2408025
    .
  19. ISBN 978-0-387-89959-6
    .
  20. JSTOR 1541959
    .
  21. doi:10.1007/BF00005621
    .
  22. ISBN 978-1-58829-046-5
    .
  23. PMID 12116485
    .
  24. ISBN 978-0-674-01159-5
    .
Retrieved from "https://en.wikipedia.org/w/index.php?title=Tachypleus_gigas&oldid=1167760793"