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Eight-armed Sea Star

Luidia maculata Müller and Troschel, 1842


Luidia maculata sighted on Changi Beach, Singapore, 2009. (Photo by Wang Luan Keng, used with permission)


Overview


Luidia maculata, is an active, carnivorous sea star found commonly in the Indo-Pacific region, including Singapore, where it is commonly found inhabiting lower reef slopes and adjacent sea beds1 . It is one of the largest species of sea star in Singapore, as it can grow up to 60cm (approx. 2 feet) across in diameter 2 , where most sea stars on our shores do not grow any larger than 30cm in diameter. This species is typically observed to have eight arms, instead of the usual five arms seen in most sea stars. It also moves rapidly when completely submerged, and is usually more active at night3 .

Luidia maculata can be found mainly in the Indo-West Pacific region, including Singapore. The species is uncommon in Singapore and was initially thought to be restricted to Pulau Ubin and Pulau Tekong, but has recently been recorded in areas such as Changi Beach, Chek Jawa, East Coast Park, Pulau Semakau, and Tuas4 . Besides Singapore, it is also distributed in the Persian Gulf, Maldive area, Bay of Bengal, north Australia, the Philippines, China and south Japan5 .


Current distribution map of recorded Luidia maculata occurrences worldwide. (Image adapted from Ocean Biogeographic Information System (OBIS))


Seven-armed Luidia maculata sighted at Ras Sedr, Egypt, 2012. (Photo by Walaa, used under Creative Commons Attribution-Share Alike 3.0 Unported Generic License)


Habitat


Luidia maculata is typically a reef-associated benthic dweller that lives in subtidal waters on soft or loose sediment, or near areas with seagrass or coral rubble on Singapore's Northern shores. It can be found at a depth range of 0-134 m6 7 . Sea stars of this genus can use their arms and spines to burrow into the sediment, which would explain why they are sometimes seen washed up onshore after storms or any large disturbances8 .



Luidia hardwicki burying itself in sand (Photo by Ria Tan, 2013, used under Creative Commons Attribution 2.0 Generic License)


What are sea stars?

Sea stars (class Asteroidea), known more commonly as starfish, are star-shaped marine, benthic invertebrates. More specifically, they are under the phylum Echinodermata (see Taxonavigation), which are known for their five-point radial symmetry. This means that sea stars are also related to other echinoderms like brittle stars (class Ophiurodea), sea urchins (class Holothuroidea), and sea lilies (class Crinoidea)9 . Although brittle stars are also star-shaped echinoderms, they should not be confused with sea stars, which have arms that blend into one another before joining to form the central disk, whereas the longer and slender arms of brittle stars appear more disjointed from the central disk10 .

The general anatomy of a typical sea star can be seen in the figures below. However, not all the features labeled in the diagrams are present in all sea stars. Some sea stars - including Luidia maculata - do not possess an anus, or a pyloric stomach. The arms of sea stars have tiny tube feet on the oral surface, which are able to sense physical and chemical stimuli11


Diagram of oral and aboral view of a typical sea star. (Image by BIODIDAC, used under the Creative Commons Attribution-NonCommercial 4.0 Generic License)


Detailed diagram of the internal anatomy of a sea star, including the pyloric and cardiac stomachs, gonads, tube feet and water vascular system which are shown. (Image by BIODIDAC, used under the Creative Commons Attribution-NonCommercial 4.0 Generic License)


Identification


The genus Luidia Forbes, 1839 is the only one in the family Luidiidae and can generally be distinguished by their long arms that are tapered to a pointed end and tiny sharp spines along the side of their arms, which end in large tube feet with pointed tips.1 . The species is usually observed having eight arms, but can also have six to nine arms12 . It can grow up to 60cm in diameter (including its arms) 2 . The upper surface which is the aboral surface of the sea star, may vary in colour from greyish-blue to brown and beige, but is typically darker towards the centre and is covered in dark blotches along the arms, as well as being covered in umbrella-like structures called paxillae. Unlike typical sea stars like in the figures above, it lacks an eversible stomach and an anus, and possesses only a mouth, oesophagus, and cardiac stomach for feeding11


Sharp spines along the arms of Luidia maculata (Photo by Ria Tan, 2008, used under Creative Commons Attribution 2.0 Generic License)


Numerous tiny "umbrella-like" paxillae lining the upper surface of Luidia maculata. (Photo by Ria Tan, 2009, used under Creative Commons Attribution 2.0 Generic License)

How can we distinguish them from other species of starfish in Singapore?

Distinguishing them from Archaster typicus Muller & Troschel, 1840

Due to their similar appearance, the species can be mistaken for the species Archaster typicus Müller & Troschel, 1840 (also known as the Common Sea Star or Sand-sifting Sea Star), which is also found in the Indo-West Pacific region, and on the shores of Singapore such as Chek Jawa13 . The two similar-looking species are most easily differentiated by the number of arms: Archaster typicus usually has five arms (though it can also have six arms), while Luidia maculata usually has seven or eight arms. The Common Sea Star also has tube feet with pointed suckers, whereas the tube feet of the Eight-armed Sea Star do not end in suckers, but pointed tips14 .


Archaster typicus found on the shores of Singapore. (Photo by Wang Luan Keng, used with permission)


Pointed tips on tube feet of Luidia maculata (Photo by Ria Tan, 2008, used under Creative Commons Attribution 2.0 Generic License)

Distinguishing them from Astropecten spp.

Luidia maculata may also look rather similar to sea stars of the genus Astropecten as both have tapered arms with spines along them. In addition to Astropecten species typically possessing five arms, one can look at the marginal plates on the aboral surface to distinguish the two families. Marginal plates on the top surface of the latter are broad and conspicuous, whereas those of Luidia cannot be distinguished from the paxillae12 15 .

Large and conspicuous marginal plates as highlighted on the top aboral surface of the Painted Sand Star (Astropecten sp.). (Image adapted from Ria Tan, 2005, under the Creative Commons Attribution 2.0 Generic License)


Luidia maculataArchaster typicusAstropecten sp.

Side-by-side comparison of three similar-looking sea stars found in Singpaore: Luidia maculata, Archaster typicus, and an Astropecten species. (Photos 1 & 3 by Ria Tan, used under the Creative Commons Attribution 2.0 Generic License; Photo 2 by Wang Luan Keng, used with permission)


Biology & Behaviour


Feeding

Luidia maculata is an active carnivorous sea star that hunt and feed on small creatures such as crustaceans, molluscs and even other smaller echinoderms buried in the sediment. They do not evert their stomachs out to digest their prey like other sea stars, but like others they swallow their prey whole instead 1 . As is seen in other Luidia species, their oral side is the one facing the substratum, while its aboral side is the one viewed from above. This allows them to efficiently move across the substrate rapidly and efficiently feed on prey on the substratum8 .

Life History

Sea stars (class Asteroideatypically go through a life cycle from an embryo to bipinnarian larvae, followed by a brachiolarian larval stage, before metamorphosing into pentaradially symmetrical, free-living juveniles which then develop into adult sea stars. However, sea stars under the order Paxillosida do not go through a brachiolarian larval stage, but undergo metamorphosis from a bipinnarian larva to juvenile starfish16

Reproduction

Luidia maculata and closely related relatives from the same genus can undergo asexual reproduction through both regeneration of body parts, as well as larval cloning, as shown in studies that analysed sequences of mitochondrial tRNA to identify the taxa of starfish larvae9 17 .

DID YOU KNOW? 

Sea stars (class Asteroidea) are often observed to adopt an unusual position during spawning, as though standing on its “tip-toes”, with the disc protruding upwards. However, it has not yet been studied why they do so or how the position affects spawning, though it is suspected that the posture might aid in releasing gametes8


Luidia maculata possibly in spawning position, at East Coast Park. (Photo by Ria Tan, 2008, used under Creative Commons Attribution 2.0 Generic License)


Relationships with other organisms


It has been observed to associate with other marine invertebrates, such as polychaete worms, in commensalistic relationships8 . For instance, the Portunid swimming crab Lissocarcinus polybioides Adams & White, 1849 is known to closely associate with the species Luidia maculata in sub-tidal waters at a similar depth range. In a study by Rajan et al., 2012, it was observed that the crabs would remain closely attached to the sea star at all times, even when burrowed into the sand or when detached from it18 . We can even watch as two commensal crabs "accompany" the sea star while it moves across the seabed in Lembeh Strait, Indonesia, in the video below! Unfortunately, this aspect of the sea star's ecology is not very well-studied or known, especially whether such relationships could possibly bring it any benefit or harm.


Video of Luidia maculata with commensal crabs, Lembeh Strait, Indonesia, 2008. (Video by Youtube user: blennywatcher)


Conservation


Status

The species was classified Endangered (EN) in the Singapore Red Data Book in both 1994 and 20084 7 , and it was described as an "important component of Singapore's marine invertebrate 'megafaunal' biodiversity"4

Its global status has not yet been assessed as there is no information on the species or members of the same genus by the International Union for Conservation of Nature's Red List of Threatened Species (IUCN) Red List, the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) or the Convention on the Conservation of Migratory Species of Wild Animals (CMS) 19 .

Threats

As with many other species in Singapore, one of the reasons for the species' loss of habitat is land reclamation around the areas where it is typically found, such as Changi, Ubin, and Tekong areas20 . Furthermore, Davison et al., (2008) have predicted that populations have likely diminished further since the first publication in 1994, due to large-scale reclamation of seabed habitat at Pulau Tekong. As a result, while it could previously be found near the mainland, after reclamation it can only be found now in the Pulau Ubin and Tekong area, and in low abundance4 .


Taxonomy


Nomenclature

Binomial: Luidia maculata

    • The genus Luidia was named after the Welsh naturalist Edward Lhuyd, who was often referred to by his Latin name Eduardus Luidius. 21 8

    • The specific name maculata is derived from the Latin word 'maculosus' which translates to “spotted”, referring to the spotted appearance of the sea star21 .

Vernacular/Common Name: Eight-armed Sea Star, Seven-armed Sea Star

    • So named because the species is typically observed to have eight (or seven) arms. Unfortunately, not very appropriate because the name can be used to describe several other species of Luidia with similar number of arms as well21 .

Taxonavigation

Taxonomic hierarchy of Luidia maculata:

Taxon

Name

Kingdom

Animalia

Phylum

Echinodermata

SubphylumAsterozoa

Class

Asteroidea

SuperorderValvatacea

Order

Paxillosida

Family

Luidiidae

Genus

Luidia

Species

Luidia maculata

Type Information

There are 2 syntype specimens (RMNH 539) for this species from Japan, and they can be found at the Japan Museum SieboldHuis in Leiden, Netherlands.

Below is the original description of the species by Muller and Troschel (1842)22 , from System der Asteriden, describing the type specimens' locality and current location. 


Original description of species Luidia maculata by Muller and Troschel (1842) in System der Asteriden (1842). (Image adapted from Biodiversity Heritage Library under Creative Commons Attribution 2.0 Generic License)

Synonyms

  • Luidia varia (Mortensen, 1925) accepted as Luidia maculata Müller & Troschel, 1842
  • Luidia maculata var. ceylonica (Döderlein, 1920) accepted as Luidia maculata Müller & Troschel, 1842

  • Luidia maculata f. herdmani (A.M. Clark, 1953), later accepted as Luidia herdmani A.M. Clark, 1953 (raised to species by A.M. Clark5 )

  • Luidia maculata var. quinaria (von Martens, 1865), later accepted as Luidia quinaria von Martens, 1865 (raised to species by Ives (1891)

Phylogeny


Cytochrome Oxidase I is a gene often used in DNA barcoding of many animal species, specifically Metazoa. Although it is not a gene directly involved in speciation, it can be used to predict the time since speciation (divergence between two species). This is termed as COI distance and is computed using magnitude of sequence divergence between species. While the gene's mutation rate is fast enough to distinguish between closely related species, it is also slow enough to be conserved between conspecifics23 . The COI distance between two distinct species is typically between 2-3%. 

Phylogenetic analysis of the Luidia genus was conducted using Cytochrome Oxidase Subunit I (COI) sequences of Luidia species from China, in a study by Xiao et al. (2013)24 . The study revealed 100% bootstrap values for Luidia maculata in the consensus trees obtained and hence, strong support for three main clades, and particularly for L. maculata as a distinct species. Of the three clades, the first clade consisted of Luidia quinaria from the Sea of Japan, the second included seven species (L. quinaria, L. yesoensis, L. changi, L. orientalis, L. avicularia, L. longispina, and L. hardwicki), while the last clade included only L. maculata. The consensus tree for genus Luidia obtained by Xiao et al. (2013) through Maximum Parsimony is shown below. 

Boostrap values and probability of 100% for Clade C was also obtained through Maximum Likelihood and Bayesian Analysis, respectively, thus providing strong support for Luidia maculata as a distinct species24 .

Maximum Parsimony Tree obtained based on COI sequences. Bootstrap value for each node is indicated above the node. The highlighted box at the bottom of the tree shows a high bootstrap value of 100% for Clade C which includes only Luidia maculata, indicating strong support for Luidia maculata as a distinct species. (Figure adapted from Xiao et al., 2013).


One of the ongoing phylogenetic classification debates within the class Asteroidea is regarding the phylogenetic status of the order Paxillosida. Common traits that evolved in sea stars within this order such as families Astropectinidae and Luidiidae - in which the only genus is Luidia - include the lack of an anus and eversible stomach, as well as the lack of a brachiolarian larval stage in their development. However, not all Paxillosidan species lack these traits25 .

In their study, Matsubara et al. (2005) performed molecular phylogenetic analyses based on the amino acid sequences of all protein coding genes in five asteroid species, and using the two species Paracentrotus lividus (Cantatore et al., 1989) and Cucumaria miniata (Arndt and Smith, 1998; Scouras et al., 2003) as outgroups. The five species included three Paxillosidan species: Astropecten polyacanthus, Luidia quinaria and Asterias amurensis. By obtaining the following Maximum Likelihood Tree and two other trees, the results of the study provided supporting evidence for the relationships between the above asteroid species, and the monophyly of the clade including the paxillosidan species. This suggests that the paxillosidans may not have been the first to diverge amongst asteroids25 .

Furthermore, Matsubara et al. (2005) concluded that when "these paxillosidan characters (the absence of anus, the lack of extra-oral feeding, the absence of suckered tube feet, and the lack of a brachiolaria) are mapped parsimoniously on the phylogenetic framework obtained in the present study, it is suggested that these characters have derived within the paxillosidan lineage; they are therefore unlikely to represent the primitive state of asteroids". Therefore, their results supported the hypothesis that these traits were not ancestral to the order but instead, paxillosidans had lost these characters while adapting to their habitats25 .

Maximum Likelihood Tree of five asteroid species, including three Paxillosidan species, and two other trees that were not rejected, providing evidence for monophyly of the clade. (Figure adapted from Matsubara et al., 2005)


Future Research


Areas for future research, for both the species Luidia maculata and its genus, that have yet to be addressed include:

  1. Unusual spawning position during reproduction and its benefits
    • Possible a platform for better release of gametes

  2. Relationships with other organisms
    • As of now, few studies have been conducted on the ecological role of Luidia maculata specifically in its habitats, and how it interacts with other organisms.
    • Any studies that do exist are very recent.

  3. Global Status and Threats of Luidia maculata
    • Insufficient data and recorded occurrences may explain why the species has not yet been assessed by any organisation

Glossary


Benthic: The benthic zone is the ecological region at the lowest part of a water body which typically the sediment surface. 

Eversible: An eversible stomach is one that can be turned inside out

Bipinnarian larva: The first stage in the larval development of most starfish, where the larva is free-living and covered in cilia. This is followed by a brachiolarian stage.

Brachiolarian larva: Second stage in the larval development of most starfish, where the larva has bilateral symmetry. This stage is not present in starfish of the order Paxillosida.

Commensalistic: Commensalism or a commensalistic relationship is one which benefits one party, but neither has no effect (neither benefit nor harm) on the other party.


References


Footnotes
Ref Notes
1 Schoppe, S., 2000. A guide to common shallow water sea stars, brittle stars, sea urchins, sea cucumbers and feather stars (echinoderms) of the Philippines. Times Media Private Limited, Singapore, pp. 144. [ a b c ]
2 Wang, L. K. & K. H., Yeo, 2011. Sea stars. In: Ng, P. K. L., R. T. Corlett & H. T. W. Tan (eds.). Singapore Biodiversity: An Encyclopedia of the Natural Environment and Sustainable Development. Editions Didier Millet, Singapore, p. 552. [ a b ]
3 "Sea stars," by Tan, R. WildSingapore, Oct 2016. URL: http://www.wildsingapore.com/wildfacts/echinodermata/asteroidea/asteroidea.htm (accessed on 2 Dec 2018)
4 Davison, G.W. H., P. K. L., Ng & H. H., Chew, 2008. The Singapore Red Data Book: Threatened plants and animals of Singapore. Nature Society (Singapore), Singapore, p. 285. [ a b c d ]
5 Clark, A.M. & F. W. E., Rowe, 1971. Monograph of shallow-water Indo-West Pacific echinoderms: i-vii. Trustees of the British Museum (Natural History), London, p. 110. [ a b ]
6 Rowe, F. W. E. & J. Gates, 1995. Echinodermata. In: A. Wells (ed.). Zoological Catalogue of AustraliaVol 33. CSIRO, Melbourne, p. 510.
7 Ng, P. K. L. & Y. C., Wee, 1994. The Singapore Red Data Book: Threatened plants and animals of Singapore. Nature Society (Singapore), Singapore, p. 90. [ a b ]
8 "Learning about Luidia! 5 Things about The OTHER Sand Star!" by C. Mah. The Echinoblog, 22 Apr 2014. URL: http://echinoblog.blogspot.com/2014/04/learning-about-luidia-5-things-about.html (accessed on 15 Nov 2018) [ a b c d e ]
9 Ruppert, E. E., R. S., Fox & R. D., Barnes, 2004. Invertebrate Zoology: A Functional Approach, 6th Edition. Cengage Learning, Boston, pp. 990-1004. [ a b ]
10 "Sea stars," by Tan, R. WildSingapore, Oct 2016. URL: http://www.wildsingapore.com/wildfacts/echinodermata/asteroidea/asteroidea.htm (accessed on 2 Dec 2018)
11 Ruppert, E. E., R. S., Fox & R. D., Barnes, 2004. Invertebrate Zoology: A Functional Approach, 6th Edition. Cengage Learning, Boston, pp. 928-940. [ a b ]
12 Clark, H. L., 1946. The Echinoderm Fauna of Australia: Its Composition and Its Origin. Carnegie Institution of Washington, Washington, p. 70-72. [ a b ]
13 "Sand sea stars," by Tan, R. WildSingapore, Oct 2016. URL: http://www.wildsingapore.com/wildfacts/echinodermata/asteroidea/astropecten.htm (accessed on 2 Dec 2018)
14 "Eight-armed Luidia sea star," by Tan, R. WildSingapore, Oct 2016. URL: http://www.wildsingapore.com/wildfacts/echinodermata/asteroidea/luimaculata.htm (accessed on 13 Nov 2018)
15 "Painted sand stars," by Tan, R. WildSingapore, Oct 2016. URL: http://www.wildsingapore.com/wildfacts/echinodermata/asteroidea/sandpainted.htm (accessed on 2 Dec 2018)
16 Mercier, A. & J. Hamel, 2013. Reproduction in Asteroidea. In: Lawrence, M (ed.). Starfish: Biology and Ecology of the Asteroidea. John Hopkins University Press, Baltimore, pp. 37-50.
17 Knott, K. E., E. J., Balser, W. B., Jaeckle & G. A., Wray, 2003. Identification of Asteroid Genera with Species Capable of Larval Cloning. Biological Bulletin, 204(3): 246-255.
18 Rajan, R., C. Venkatraman, G. Sivaleela, D. P., Aranthaman, P. Padmanaban & K. Venkataraman, 2012. Notes on the association of Lissocarcinus polybiodes Adams and White, 1848 (Portunidae, Caphyrinae), with sea star Luidia maculate Muller and Troschel, 1842. Rec. zool. Surv. India, 112(Part-2) : 23-26.
19 "Luidia maculata Müller & Troschel, 1842," by Palomares, M. L. D. & D. Pauly. SeaLifeBase, 2018. URL: https://www.sealifebase.ca/summary/Luidia-maculata.html# (accessed on 2 Dec 2018)
20 Ng, P. K. L. & Y. C., Wee, 1994. The Singapore Red Data Book: Threatened plants and animals of Singapore. Nature Society (Singapore), Singapore, p. 90.
21 "Luidia maculata Müller & Troschel, 1842," by Mitel, C. & F. Ziemski. DORIS, 05 Feb 2017. URL: http://doris.ffessm.fr/ref/specie/1653 (accessed on 13 Nov 2018) [ a b c ]
22 Original description: Müller, J. & F. H. Troschel, 1842. System der Asteriden. 1. Asteriae. 2. Ophiuridae. Vieweg: Braunschweig, Germany, p. 77. Available online at http://www.biodiversitylibrary.org/item/44159.
23 Hebert, P. D., S. Ratnasingham & J. R. deWaard, 2003. Barcoding animal life: cytochrome c oxidase subunit 1 divergences among closely related species. Proceedings: Biological Sciences270(Suppl 1): S96-S99.
24 Xiao, N., R. Liu, S. Yuan & Z. Sha, 2013. A Preliminary Phylogenetic Analysis of Luidia (Paxillosida: Luidiidae) from Chinese Waters with Cytochrome Oxidase Subunit I (COI) Sequences. J. Ocean Univ. China (Oceanic and Coastal Sea Research), 12(3): 459-468. [ a b ]
25 Matsubara, M., M. Komatsu, T. Araki, S. Asakawa, S. Yokobori, K. Watanabe & H. Wada, 2005. The phylogenetic status of Paxillosida (Asteroidea) based on complete mitochondrial DNA sequences. Molecular Phylogenetics and Evolution, 36(2005): 598–605. [ a b c ]


This page was authored by Tashfia Raquib (tashfia.raquib@hotmail.com) 

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