Friday Fellow: Five-Slotted Sand Dollar

by Piter Kehoma Boll

If you ever walked along the beaches of the Atlantic Coast from the United States to Brazil, you probably found the skeletons of today’s fellow lying on the sand. Its scientific name is Mellita quinquiesperforata, known in English as the five-slotted sand dollar.

A washed ashore skeleton of the five-slotted sand dollar. Photo by Maria Fernanda Molina G.**

The five-slotted sand dollar is an echinoderm of the class Echinoidea and, therefore, closely related to sea urchins. Like all sand dollars, it has a flattened body with a secondary bilateral symmetry that evolved from the original radial symmetry of echinoderms (which itself is a secondary development of the original bilateral symmetry of bilaterian animals). Their body is flat, almost circular, but wider than long, reaching up to 12 cm in width. Live animals have a kind of velvet-like texture formed by the spines and hairs covering their skin. A star-like mark can be seen on their backs, which is formed by five rows of pores through which podia, responsible for gas exchange, come out. One of the arms of the star is directed to the front of the animal. The mouth is located at the center of the ventral side and the anus is at the posterior end of the body.

Five-slotted sand dollars are adorable. Photo by Andrea Caballero.*

The name of the five-slotted sand dollar comes from the fact that its body has five elongate perforations, four of which are continuous with the four lateral rows of pores and the fifth one is behind, between the two posterior rows. These openings help the sand dollar move more easily through the sand by allowing sand to pass through their bodies and they can also help drag food toward the mouth. At the same time, the perforations embed them better in the sand, reducing their chances of being swept away by the waves.

Ventral side of a live specimen. Photo by Andrew J. Crawford.

The five-slotted sand dollar likes substrates made of fine sand, being unable to burrow into gravel or coarse sand. Muddy substrate is aversive to them but they will burrow into it if there is no choice.

Dorsal side. Photo by iNaturalist user tropical_dragonfly.*

The five-slotted sand dollar is a deposit feeder, feeding on small organisms from the sand, especially bacteria and microscopic eukaryotes, which it removes from the small clay particles that it ingests. Its feeding behavior and general displacement through the sediment helps increase oxygenation of the substrate. Thus, its presence has a large impact on the community of organisms able to live on a beach.

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References:

Alexander, D. E., & Ghiold, J. (1980). The functional significance of the lunules in the sand dollar, Mellita quinquiesperforata. The Biological Bulletin, 159(3), 561-570. https://doi.org/10.2307/1540822

Bell, B. M., & Frey, R. W. (1969). Observations on ecology and the feeding and burrowing mechanisms of Mellita quinquiesperforata (Leske). Journal of Paleontology, 553-560. https://www.jstor.org/stable/1302333

Findlay, R. H., & White, D. C. (1983). The effects of feeding by the sand dollar Mellita quinquiesperforata (Leske) on the benthic microbial community. Journal of Experimental Marine Biology and Ecology, 72(1), 25-41. https://doi.org/10.1016/0022-0981(83)90017-5

Weihe, S. C., & Gray, I. E. (1968). Observations on the biology of the sand dollar Mellita quinquiesperforata (Leske). Journal of the Elisha Mitchell Scientific Society, 315-327. https://www.jstor.org/stable/24333312

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* This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.

** This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.

Friday Fellow: Pineapple Sea Cucumber

by Piter Kehoma Boll

Seafood is often a highly regarded food all around the world and include all sorts of marine organisms that humans found out that are edible. In Southeast Asia, one of these delicacies is a sea cucumber, Thelenota ananas, known as pineapple sea cucumber, tripang or prickly redfish.

A nice pineapple sea cucumber in the Maldivas. Photo by Albert Kang.*

The pineapple sea cucumber is an echinoderm, a group which also includes seastars, brittle stars, sea urchins, sand dollars and sea lilies. It is found in tropical and subtropical waters of the Indo-Pacific, occurring from the Red Sea southward along the east coast of Africa and eastward to Polynesia, being common in coral reefs, although in low densities.

Reaching up to 70 cm in length and 6 kg in weight, the pineapple sea cucumber is a relatively large sea cucumber. It has a reddish-orange and black color, usually brighter on the underside, and has many soft star-like projections (“teats”) all over the body.

A detail showing the star-shaped “teats”. Photo by Nick Hobgood.**

Like most sea cucumbers, the pineapple sea cucumber is a herbivore. As a larva it probably feeds on phytoplankton and, as an adult, on larger algae, including calcaerous green algae of the genus Halimeda. It grows slowly and has a long lifespan. In more subtropical areas, it reproduces in summer, from January to March, but in more tropical waters it is likely that it reproduces all year round. It can also involuntarily reproduce asexually if accidentally cut in half, with the anterior and posterior halves forming a new organism in a few weeks.

In the Northern Mariana Islands, with a human arm for comparison. Photo by John Starmer.*

As I said above, the pineapple sea cucumber is edible and is, in fact, a very healthy and promising food. As all sea cucumbers, it contains a fucoidan, a type of polysaccharide also found in brown algae and that has antioxidant and antiinflammatory properties. It is also rich in saponins, like other sea cucumbers and echinoderms, and these revealed to be good agents to reduce cholesterol levels and also have anticancer properties. More than that, the pineapple sea cucumber contains another compound, a glycosaminoglycan known as fucosylated chondroitin sulfate (FuCS-1), which revealed to have the ability to block HIV from entering cells and has, therefore, the potential to be explored for the development of new anti-HIV drugs, especially against some resistant variants.

A very red specimen in Malaysia. Photo by Tsu Soo Tan.*

Unfortunately, due to its slow development, the reproductive rate of the pineapple sea cucumber is unable to compensate its extraction from the ocean for human consumption. As a result, the natural populations have drastically decreased in the past decades, with a 60% reduction in New Caledonia and being almost extinct in some areas. As a result, it is listed as endangered in the IUCN’s red list. If we don’t start to respect this species by applying severe policies for harvesting it, we will end up losing a very precious fellow of our planet.

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References:

Conand C (1993) Reproductive biology of the holothurians from the major communities of the New Caledonian Lagoon. Marine Biology 116:439–450. https://doi.org/10.1007/BF00350061

Conand C, Gamboa R, Purcell S (2013) Thelenota ananas. The IUCN Red List of Threatened Species 2013: e.T180481A1636021. https://dx.doi.org/10.2305/IUCN.UK.2013-1.RLTS.T180481A1636021.en. Access on 30 July 2020.

Han Q, Li K, Dong X, Luo Y, Zhu B (2018) Function of Thelenota ananas saponin desulfated holothurin A in modulating cholesterol metabolism. Scientific Reports 8:9506. https://doi.org/10.1038/s41598-018-27932-x

Huang N, Wu M-Y, Zheng C-B, Zhu L, Zhao J-H, Zheng Y-T (2013) The depolymerized fucosylated chondroitin sulfate from sea cucumber potently inhibits HIV replication via interfering with virus entry. Carbohydrate Research 380:64–69. https://doi.org/10.1016/j.carres.2013.07.010

Reichenbach (1995) Potential for asexual propagation of several commercially important species of tropical sea cucumber (Echinodermata). Journal of the World Aquaculture Society 26(3):272–278. https://doi.org/10.1111/j.1749-7345.1995.tb00255.x

Wikipedia. Thelenota ananas. Available at < https://en.wikipedia.org/wiki/Thelenota_ananas >. Access on 30 July 2020.

Yu L, Xue C, Chang Y, Xu X, Ge L, Liu G, Wang Y (2014) Structure elucidation of fucoidan composed of a novel tetrafucose repeating unit from sea cucumber Thelenota ananas. Food Chemistry 146:113–119. https://doi.org/10.1016/j.foodchem.2013.09.033

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** This work is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported License.

Friday Fellow: Savigny’s Brittle Star

by Piter Kehoma Boll

It is time to present the second echinoderm here, and for that I have chosen a brittle star, actually the most widespread brittlestar in the world. Known scientifically as Ophiactis savigny and populary as Savigny’s brittle star or simply little brittle star, this species occurs in tropical and subtropical waters of all the world’s oceans.

One tiny specimen of Ophiactis savignyi. Photo by Ria Tan.*

The Savigny’s brittle star is very small, having a disc measuring between 0.5 and 11 mm in diameter and usually six long segmented arms. It can live from the intertidal zone to about 500 meters below the surface and is often found living inside sponges in a possible commensal association, sometimes occurring in very high densities.

The reproduction of the Savigny’s brittle star can be sexual or asexual. During sexual reproduction, both males and females release gametes into the water, where they are fertilized, while asexual reproduction occurs by fission of the discs, literally splitting the animal in half and then each half regenerates the missing parts. Males seem to be more prone to engage in asexual reproduction, which leads to a higher rate of males in the population in relation to females.

Hundreds of arms of many individuals of Ophiactis savignyi poking out from a spong Spheciospongia cf. vagabunda. Photo by Ria Tan.**

The diet of the Savigny’s brittle star is composed mainly of detrites or dead animals. Its association with sponges may be related to the fact that sponges pump water that carries particles that may also serve as food for the brittle stars. It is common to found the cavities of certain sponges completely filled by individuals of the brittle star, some of them already too large to be able to leave the sponge.

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References:

McGovern, T. M. (2002) Sex-ratio bias and clonal reproduction in the brittle star Ophiactis savigny. Evolution 56(3): 511-517. https://doi.org/10.1554/0014-3820(2002)056[0511:SRBACR]2.0.CO;2

Wikipedia. Ophiactis savigny. Available at < https://en.wikipedia.org/wiki/Ophiactis_savignyi >. Access on March 22, 2018.

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Friday Fellow: Royal sea star

by Piter Kehoma Boll

In order to celebrate the 5oth Friday Fellow, which was posted today, I decided to bring you an extra Friday Fellow! Afterall, there are plenty of interesting lifeforms to be shown.

As I have never presented you any echinoderm, I thought it would be interesting to start the second group of 50 FFs with one of them. So I’ve chosen the royal sea star (Astropecten articulatus).

Beautiful colors, don’t you think? Photo by Mark Walz.*

Found in waters from 0 to 200 m deep the West Atlantic coast from New Jersey to Uruguay, the royal sea star may reach around 20 cm in diameter and is easily identified by its color. Dorsally it has a series of dark blue to purple granulose papilae and is lined by orange marginal plates with supermarginal white spines that give it a comb-like appearence, hence the name “Astropecten“, meaning “star-comb”.

As most starfishes, the royal starfish is a predator. It feeds mainly on small and medium-sized mussels and ingests the prey intact, digesting it inside its mouth. As it is unable to digest food extraorally (outside its mouth) it cannot feed on anything that cannot be ingested whole.

Most of its activity occurs at dawn and dusk, which may be inversely related to the activity of predatory fish, as those are usually more active during the day.

Being a considerably common starfish, you may easily find one while walking on the beach, provided that the beach is at the right place.

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References:

Beddingfield, S., & McClintock, J. (1993). Feeding behavior of the sea star Astropecten articulatus (Echinodermata: Asteroidea): an evaluation of energy-efficient foraging in a soft-bottom predator Marine Biology, 115 (4), 669-676 DOI: 10.1007/BF00349375

Wikipedia. Astropecten articulatus. Availabe at: <https://en.wikipedia.org/wiki/Astropecten_articulatus >. Access on July 28, 2016.

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