Category Archives: mollusks

Friday Fellow: Common Sea Angel

by Piter Kehoma Boll

Last week I presented a beautiful sea snail, the common sea butterfly, with wing-like parapodia that allows it to swim. The sea butterflies belong to a group of marine gastropods known as Pteropoda due to this foot modified into fins. There are two main groups of pteropods, Thecosomata, that have a shell, and Gymnosomata, that don’t have a shell. While the shelled ones are called sea butterflies, the naked ones are called sea angels or naked sea butterflies.

The most popular sea angel is Clione limacina, the common sea angel. Its body is mostly transparent and, like all pteropods, has two parapodia that look like wings which, together with its elongate and shell-less body makes it look like an angel indeed. Despite its angelic appearance, the common sea angel is a fearsome creature.

Despite the serene appearance, meeting this beautiful gastropod can be a frightening experience. Foto by Kevin Raskoff, Hidden Ocean 2005 Expedition: NOAA Office of Ocean Exploration.

Being a predator, the common sea angel is specialized in eating the common sea butterfly. Both species share the same environment in arctic waters and their association is known for centuries. The way that the common sea angel captures and eats the common sea butterfly is impressive and kind of scary.

A specimen, that was washed ashore, on a human hand for comparison. Photo by iNaturalist user nbenson.*

When the sea angel detects a sea butterfly nearby, it starts a pursue and everts six adhesive buccal cones from its mouth, forming a basket-like structure. This structure is used to capture the sea butterfly and, once the poor shelled snail is traped, the sea angel rotates the sea butterfly’s shell until its opening is directed to the predator’s mouth.

After that, the terror begins. The poor sea butterfly has withdrawn into its shell by this time, but the sea angel uses a group of chitinous hooks in its mouth to perforate the sea butterfly’s body and, helped by the radula, pulls the whole body of the prey from inside the shell, swallowing it entirely at once. It is likely a horrible death for the poor sea butterfly. After finishing swallowing one sea butterfly, the common sea angel can go after another one in about 2 minutes.

Drawing of a common sea angel feeding on a common sea butterfly. BC = buccal cones, HK = chitinous hooks, S = the shell of the sea butterfly. Extracted from Lalli (1970).

While the life cycle of the common sea butterfly is short, lasting only a year, that of the common sea angel is much longer. As a result, there are no adult sea butterflies to serve as food for the common sea angel from later autumn to early spring. For a long time it was thought that the common sea angel would spend this whole time without eating, and indeed it was found that it can survive long periods in starvation. However, analyses of the stomach content of the common sea angel revealed the presence of amphipods and eventually calanoid copepods, suggesting that it can rely on some alternative food sources in cases of extreme necessity. Their main food, however, is the common sea butterfly with no doubt. They start to feed on them when they are still larvae, always capturing and ingesting sea butterflies that have a size similar to theirs.

Will the common sea angel be able to survive on these other prey types if the populations of the common sea butterfly decline due to climate change? If find it unlikely and I hope we don’t need reach a point in which this becomes an option.

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References:

Böer M, Graeve M, Kattner G (2006) Exceptional long-term starvation ability and sites of lipid storage of the Arctic pteropod Clione limacina. Polar Biology 30:571–580. doi: 10.1007/s00300-006-0214-6

Conover RJ, Lalli CM (1972) Feeding and growth in Clione limacina (Phipps), a pteropod mollusc. Journal of Experimental Marine Biology and Ecology 9(3):279–302. doi: 10.1016/0022-0981(72)90038-X

Kallevik IHF (2013) Alternative prey choice in the pteropod Clione limacina (Gastropoda) studied by DNA-based methods. Master thesis in Biology, The Arctic University of Norway.

Lalli CM (1970) Structure and function of the buccal apparatus of Clione limacina (Phipps) with a review of feeding in gymnosomatous pteropods. Journal of Experimental Marine Biology and Ecology 4(2):101–118. doi: 10.1016/0022-0981(70)90018-3

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

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Friday Fellow: Common Sea Butterfly

by Piter Kehoma Boll

People love to name sea creatures by making analogies with things found on land. Today’s species is one more of this type, being the best known species of the so-called sea butterflies and, therefore, known as the common sea butterfly. It has nothing to do with butterflies, though, and its scientific name, Limacina helicina, is better to describe it.

The common sea butterfly is a mollusk, more precisely a gastropod, and, as it has a shell, it is a “snail”. It does not crawl through the floor as most snails though. With a spiral shell measuring only about 10 mm in diameter, it lives in the water column and is sometimes described as a planctonic species. It can swim by itself, though, because its fleshy foot is changed into two expansions called parapodia that act as two large fins. Its shell is mostly transparent and the soft parts are mainly purple, although the parapodia are almost transparent as well.

The common sea butterfly is truly a beautiful creature, isn’t it? Photo by Russ Hopcroft, University of Alaska, Fairbanks.

The habitat of the common sea butterfly includes the cold waters of the Arctic region, including the Arctic Ocean and neighboring areas of the Atlantic and Pacific oceans. In the Pacific, it can occur southward to Japan and the northern parts of the United States. Larger specimens tend to inhabit deeper waters, up to 150 m deep, while smaller ones live closer to the surface, up to 50 m down. Until very recently, the common sea butterfly was thought to inhabit Antarctic waters as well but molecular studies revealed that the populations around Antarctica belong to a different species, Limacina antarctica.

See how fast they can beat their wings.

The diet of the common sea butterfly includes several smaller planktonic creatures, especially small crustaceans, such as nauplii (larvae) of copepods, as well as dinoflagellates, ciliates and diatoms. Juveniles of their own species are also very common, sometines making up the second most common item in their diet. In order to capture food, they produce a spherical web of mucus that floats above them in the water. This web traps other organisms in the water column and is later sucked and eaten by the sea butterfly together with the entrapped creatures. This web is very difficult to observe during the day because of diffuse refraction but appears clearly at night. When disturbed by light, however, the common sea butterfly tends to quickly swallow its web and sink to escape from danger.

A commo sea butterfly with its spherical mucous web seen as an oval concentration of finer particles right above the snail. Extracted from Gilmer & Harbinson (1986).

The thin shell of the common sea butterfly consists of aragonite, which is highly soluble and sensitive to changes in temperature and acidification of the water. Studies have shown that the expected increase in ocean acidification due to human-induced climate changes will probably have a negative impact on populations of the common sea butterfly and related species. This is particularly worrisome regarding the common sea butterfly because it is the a key species in Arctic ecosystems, being an important food source for many marine animals, such as fish, whales, birds and even other mollusks.

The little snail will not give up the fight so easily, though. Studies have shown that the periostracum (the outer organic layer of the shell) can prevent the aragonite to dissolve and an physical trauma that breaks the periostracum, allowing the direct contact of the aragonite with the water, is necessary to cause dissolution. And even when this happens, the common sea butterfly can compensate by building new aragonite layers on the inner surface of the shell and it is able to extract aragonite from water for this purpose even when the levels in water are very low.

The common sea butterfly is small but it is also tough.

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References:

Corneau S, Alliouane S, Gattuso JP (2012) Effects of ocean acidification on overwintering juvenile Arctic pteropods Limacina helicina. Marine Ecology Progress Series 456:279–284. doi: 10.3354/meps09696

Comeau S, Jeffree R, Teyssié JL, Gattuso JP (2010) Response of the Arctic pteropod Limacina helicina to projected future environmental conditions. PLoS One 5(6):e11362. doi: 10.1371/journal.pone.0011362

Gilmer RW, Harbinson GR (1986) Morphology and field behavior of pteropod molluscs: feeding methods in the families Cavoliniidae, Limacinidae and Peraclididae (Gastropoda: Thecosomata). Marine Biology 91:47–57. doi: 10.1007/BF00397570

Gilmer RW, Harbinson GR (1991) Diet of Limacina helicina (Gastropoda: Thecosomata) in Arctic waters in midsummer. Marine Ecology Progress Series 77:125–134.

Lischka S, Büdenbender J, Boxhammer T, Riebesell U (2011) Impact of ocean acidification and elevated temperatures on early juveniles of the polar shelled pteropod Limacina helicina: mortality, shell degradation, and shell growth.  Biogeosciences 8:919–932. doi: 10.5194/bg-8-919-2011

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From headache to migraine: is Xenacoelomorpha a basal bilaterian clade or a group of weird deuterostomes?

by Piter Kehoma Boll

Seven years ago I discussed the phylogenetic position of Acoelomorpha and their close relative, Xenoturbella, which together form the clade Xenacoelomorpha. Being very simple bilaterian animals, lacking almost every major structure common to most other bilaterians, their exact position is usually considered to be basal inside Bilateria but the idea that they are deuterostomes was raised after some molecular studies grouped them with the clade Ambulacraria, which includes echinoderms and hemichordates.

Being deuterostomes would mean that Xenacoelomorpha suffered a huge simplification of their anatomy. Back in 2013, when I wrote the other article, this was causing a lot of controversy but, a time after that, new molecular studies confirmed the basal position of Xenacoelomorpha and it became kind of well accepted that they are, indeed, the basalmost clade in Bilateria.

A simplified version of the animal tree of life showing the uncertain position of Xenacoelomorpha. The position of Placozoa and Ctenophora is not very clear too.

But once a trouble, always a trouble.

By 2019, a new study that tried to anticipate effects of systematic errors during molecular phylogeny studies, such as long-branch attraction, concluded that the basal position of Xenacoelomorpha is an artifact and that, when one tries to minimize the errors, their position as sister-group of Ambulacraria becomes clear. However, their tree also suggests that Deuterostomia is not monophyletic, as Chordates appear as sister-group to Protostomia and Xenacoelomorpha+Ambulacraria is the basalmost group, i.e., the sister group of the rest of the Bilateria. However, the idea of Deuterostomia not being monophyletic is very unexpected.

As I mentioned in my old post, the main problem in Xenacoelomorpha appearing inside Deuterostomia is related to their oversimplification. They lack almost everything that any typical bilaterian has. What would have forced them to become that simple?

Xenoturbella japonica, a xenacoelomorph. Credits to Nakano et al. (2017).*

Another recent study suggested that, in the case of Xenoturbella at least, this may be the result of their soft-substrate burrowing habits. They compare Xenoturbella to nudibranchs, among which some species have similar lifestyles. One of these nudibranchs, Xenocratena, was actually discovered at about the same time as Xenoturbella living in the same environment. They have a paedomorphic (more simplified, “baby-like”) anatomy compared to other nudibranchs. However, it is not at all as simple as Xenoturbella.

The burrowing nudibranch Xenocratena suecica. Credits to Martynov et al. (2020).*

On the other hand, there is another genus of nudibranchs that is indeed oversimplified, Pseudovermis, and it lives burrowed in soft substrate as well. Molecular analyses revealed that Pseudovermis is not closely related to Xenocratena but to Cumanotus, another burrowing nudibranch, which suggests that this simplification occurred twice among nudibranchs.

Phylogenetic relationships among nudibranchs. See Pseudovermis and Cumanotus at about 2 o’clock and Xenocratena at about 7 o’clock. Credits to Martynov et al. (2020).*

This is not an evidence that Xenoturbella is a simplified deuterostome, but it is a good argument. But what about the simplifications of Acoelomorpha? I think that if Xenoturbella was not closely related to Acoelomorpha I would be more willing to accept this hypothesis. My heart leans toward the hypothesis of basal Xenacoelomorpha, though. However, as any cientist should do, I will accept Xenacoelomorpha as deuterostomes if enough evidence is presented.

Xenoturbella is always the main problem in this equation, The nervous system of Acoelomorpha, for example, although simplified, has kind of the basic pattern found in all bilaterians and could have evolved from the oral ring in a cnidarian-like ancestor according to some hypotheses. In Xenoturbella, though, the nervous system is much weirder, being formed by a simple network of difuse neurons below their skin. I guess addressing the organization of the nervous system in all these groups is a good topic for another post.

If there is one thing, in my opinion, that makes the position of Xenacoelomorpha within Deuterostomia somewhat convincing is the fact that many features of Deuterostomia seem to be more primitive inside Bilateria when compared to those in Protostomia, so the position of Xenacoelomorpha among Deuterostomia is more plausible than their position among Protostomia(although this is not even considered possible anymore) for sure. We tend to think that deuterostomes are more “derived” simply because humans are deuterostomes. But this discussion is also a subject for another post.

What do you think? Are you team basal or team deuterostome?

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You may also like:

Hagfish: another phylogenetic headache

Xenoturbella: a growing group of weirdoes

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References:

Cannon JT, Vellutini BC, Smith J, Ronquist F, Jonfelius U, Hejnol A (2016) Xenacoelomorpha is the sister group to Nephrozoa. Nature 530: 89–93. doi: 10.1038/nature16520

Jondelius U, Raikova OI, Martinez P (2019) Xenacoelomorpha, a Key Group to Understand Bilaterian Evolution: Morphological and Molecular Perspectives. In: Pontarotti P (ed) Evolution, Origin of Life, Concepts and Methods. Cham: Springer International Publishing, . pp. 287–315. doi: 10.1007/978-3-030-30363-1_14

Martynov A, Lundin K, Picton B, Fletcher K, Malmberg K, Korshunova T (2020) Multiple paedomorphic lineages of soft-substrate burrowing invertebrates: parallels in the origin of Xenocratena and Xenoturbella. PLoS ONE 15(1): e0227173. doi: 10.1371/journal.pone.0227173

Philippe H, Poustka AJ, Chiodin M, et al. (2019) Mitigating Anticipated Effects of Systematic Errors Supports Sister-Group Relationship between Xenacoelomorpha and Ambulacraria. Current Biology 29(11):1818–1826. doi: 10.1016/j.cub.2019.04.009

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Friday Fellow: Asian Clam

by Piter Kehoma Boll

Since humans appeared on Earth and started to migrate, they carried other species with them to new localities. This made humans not the only species to become invasive and, in the past centuries, with human movement throughout the planet becoming more and more intense, invasive species became more and more common.

Among bivalvian mollusks, two very popular invasive species are the golden mussel and the zebra mussel, but they are not the only ones. There is one small bivalvian that is not that often a nuisance in human activities but is certainly a problem for native species, the so-called Asian clam, Corbicula fluminea.

An Asian clam in Hong Kong. Photo by Tommy Hui.*

The Asian clam is native from Eastern Asia where it lives burried in the sediment of rivers, prefering sandy sediments in oxygen-rich waters. Their small bivalvian shell measures up to 5 cm although most adult specimens are about 3 cm long. They have a brown to golden color, sometimes combined, but the colored layers sometimes flake off, causing white blotches.

The food of the Asian clam consists mainly of phytoplankton that it filters from the sediment. Human populations from Eastern Asia, such as the Chinese and Koreans, often use the Asian clam as a food source. During the 20th century, when many East Asian people migrated to other countries, the Asian clam was carried with them to be raised as food. As a result, this mollusk was introduced in North and South American river basins and started to spread quickly

The Asian clam is not as tolerant to environmental changes as other invasive bivalvians but its advantage is its rapid reproduction. Although there are both dioic and hermaphrodite lineages in this species, the invasive populations are all hermaphrodites. Fertilization occurs inside the body of the mother clam and the larvae develop inside, being released already as tiny shelled individuals.

The first records of this species in North America are from areas in the west coast of the United States in the 1920s. One century later the species is found throughout the whole country, having reached the east coast in less than four decades, and going north to Canada and south to Mexico and Central America.

Asian clam in Massachusetts, USA. Photo by iNaturalist user jfflyfisher.*

In South America, the species was introduced simultaneously in the La Plata River between Argentina and Uruguay and in the Jacuí river in southern Brazil in the 1970s. Currently, less than 50 years later, it is found as far north as Colombia as southward into Patagonia. The species was also introuced in Europe, Africa and Australia.

Shells collected in the La Plata River in Buenos Aires, Argentina. Photo by Diego Gutierrez Gregoric.*

The main impact caused by the invasion of the Asian clam is that it competes with native bivalvians, frequently leading to local extinctions, which is a major threat especially to many rare species that may disappear in a few decades. Although impacts on human activities are not that common, there are cases of large numbers of individuals clogging pipes and other structures.

A shell in Colombia. Credits to iNaturalist user gerardochs.*

Since there are fossil records of species of the genus Corbicula in North America, a hypothesis was raised suggesting that, instead of an invasion, the spread of the Asian clam in this continent is actually a recolonization following the last glaciation and that these individuals may be the result of small populations that remained hidden somewhere. However, it is very unlikely that the species would have remained hidden in very small populations for thousands of years to suddenly start to spread like hell in a few decades. Humans are to be blamed, as always.

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References:

Araujo R, Moreno D, Ramos MA (1993) The Asiatic clam Corbicula fluminea (Müller, 1774) (Bivalvia: Corbiculidae) in Europe. American Malacological Bulletin 10(1): 39–49.

Planeta Invertebrados. Corbícula. Available at < http://www.planetainvertebrados.com.br/index.asp?pagina=especies_ver&id_categoria=27&id_subcategoria=0&com=1&id=143 >. Access on 13 February 2020.

Sousa R, Antunes C, Guilhermino L (2008) Ecology of the invasive Asian clam Corbicula fluminea (Müller, 1774) in aquatic ecosystems: an overview. Annales de Limnologie 44(2): 85–94. doi: 10.1051/limn:2008017

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Friday Fellow: Hawaiian Black Nerite

by Piter Kehoma Boll

The sea is so full of different lifeforms that it is hard to leave it once we are there. Thus, we will continue in the sea this week, but moving to the middle of the Pacific Ocean, more precisely to the Hawaiian islands. There, on the shore, we can find today’s fellow.

An aggregate of Nerita picea in Kauai. Photo by Phil Liff-Grieff.*

Named Nerita picea, it is a small snail found on the rocky shores across most of Hawaii, often in aggregates. It is commonly called the Hawaiian black nerite in English but the native Hawaiians call it pipipi.

Empty shells of the Hawaiian black nerite. Photo by Donna Pomeroy.**

The Hawaiian black nerite measures about 1 cm in length and its shell is externally black with spiral ribs, sometimes with a thin lighter line running between them, and often with a whitish tone on the tip of the spiral. Its ribs are relatively little marked when compared to most nerite species. Internally, the shell is white. The soft parts of the body are also mostly dark in color and so is the operculum, the lid that closes the opening of the shell when the snail retracts. The foot, however, is lighter. When a live animal is picked, it quickly retracts into the shell, covering the opening with the operculum and letting a white margin around it.

A live specimen in Oahu with the soft parts visible. Photo by Isaac Lord.**

Like most intertidal snails, the Hawaiian black nerite is a herbivore and grazes on algae growing on the rocks. It prefers to live at the splash zone and slightly above it, differing from its closest relative, Nerita plicata, which lives in the upper zone, avoiding the splashes.

Due to its tropical distribution, the Hawaiian black nerite reproduces continuously throughout the year. There is no sexual dimorphism between males and females, which is, I guess, “the rule” for snails.

The Hawaiian black nerite was traditionally used as food by the native Hawaiians and its shells can be found in large numbers in archaeological sites of the archipelago dating back more than a thousand years. Empty shells of the Hawaiian black nerite are also commonly used by small hermit crabs of the genus Calcinus.

Calcinus hermit crabs using the shells of dead Hawaiian black nerites. Photo by CA Clark.***

Despite being a common species in Hawaii and having a historical importance as food, little seems to be known about the life history of the Hawaiian black nerite.

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References:

Dye T (1994) Apparent ages of marine shells: implications for archaeological dating in Hawai’i. Radiocarbon 36(1):51–57.

Frey MA (2010) The relative importance of geography and ecology in species diversification: evidence from a tropical marine intertidal snail (Nerita). Journal of Biogeography 37:1515–1528. doi: 10.1111/j.1365-2699.2010.02283.x

Pfeiffer CJ (1992) Intestinal Ultrastructure of Nerita picea (Mollusca: Gastropoda), an Intertidal Marine Snail of Hawaii. Acta Zoologic 73(1):39–47. doi: 10.1111/j.1463-6395.1992.tb00947.x 

Reese ES (1969) Behavioral adaptations of intertidal hermit crabs. American Zoologist 9(2):343–355. doi: 10.1093/icb/9.2.343

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Friday Fellow: Strawberry Top Snail

by Piter Kehoma Boll

Look at this thing:

It is so beautifully red like a strawberry that I feel my mouth salivating and an urge to bite it. But instead of a juicy sweet fruit like a strawberry, this is a hard salty seashell belonging to the species Clanculus puniceus that has the appropriate common name of strawberry top shell.

This species is found in the Indian Ocean along the eastern coast of Africa, from the Red Sea to Cape Agulhas, including nearby islands such as Madagascar and the Mascarenes. It belongs to the family Trochidae, commonly known as top shells or top snails because their shell resembles a spinning top.

Strawberry top shell in South Africa. Photo by iNaturalist user jaheymans.*

The shell of the strawberry top snail measures, in the adult, at least 15 mm in diameter, reaching up to 23 mm, and has a beautiful red color, caused by uroporphyrins, that can vary from orange-red to crimson. The spiral of the shell, when seen from above, has a line formed by black dots, caused by melanin, intercalated by two or three white dots. When seen from below, there are two additional lines with this pattern that run side by side near the shell opening.

The shell seen from several angles. Photo by H. Zell.**

As usual among top snails, the strawberry top snail lives in intertidal and subtidal zones and feeds on algae that it scrapes from rocks using its toothed tongue (the radula). They are dioecious, i.e., there are male and female individuals, as in most sea snails, but there is no sexual dimorphism.

Due to its beauty, the shell of the strawberry top snail is highly desired by shell collectors. However, little is known about the natural history of this particular species. I wasn’t even able to find a photograph in which the snail itself is visible.

This was the only photograph I found in which the soft part of the body of a snail in the genus Clanculus is visible. The species, from Taiwan, was not identified. Photograph by Cheng Te Hsu.***

If you work with this species or at least has a photograph of a living specimen showing the snail inside the shell, please share it! We need more available information on the wonderful creatures that share this planet with us.

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More marine snails:

Friday Fellow: Ornate Limpet (on 3 May 2019)

Friday Fellow: Tulip Cone (on 29 December 2017)

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References:

Herbert DG (1993) Revision of the Trochinae, tribe Trochini (Gastropoda: Trochidae) of southern Africa. Annals of the Natal Museum 34(2): 239–308.

Wikipedia. Trochidae. Available at < https://en.wikipedia.org/wiki/Trochidae >. Access on 29 July 2019.

Williams ST, Ito S, Wakamatsu K, Goral T, Edwards NP, Wogelius RA, Henkel T, Oliveira LFC, Maia LF, Strekopytov S, Jeffries T, Speiser DI, Marsden JT (2016) Identification of Shell Colour Pigments in Marine Snails Clanculus pharaonius and Cmargaritarius (Trochoidea; Gastropoda). PLoS ONE 11(7): e0156664. doi: 10.1371/journal.pone.0156664

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Friday Fellow: Ornate Limpet

by Piter Kehoma Boll

Gastropods are the most species-rich class of animals on Earth after insects but it’s been a long time since I presented one here. So, today I’m bringing you one from the coasts of New Zealand, the ornate limpet Cellana ornata.

Two ornate limpets on the coast of Northland, New Zealand. Photo by iNaturalist user pedromalpha.*

Its cone-shaped shell, like in most limpets, has a characteristic pattern that can be used to recognize it. There is a series of elevated ridges running from the dark center toward the margins of the shell. They are usually eleven in number and have an orange tinge, sometimes very strong, almost red or brown, and sometimes very weak, almost white. The region between the ridges is darker, usually black, and has a row of white nodes running parallel to the ridges, sometimes with an additional row of smaller nodes on each side. The pattern may be obscured by other organisms growing on the shell, especially algae and barnacles.

An ornate limpet covered by barnacles. Photo by iNaturalist user pedromalpha.*

As common among limpets, the ornate limpet lives in the intertidal zone on the surface of rocks. It feeds on algae growing on the substrate, scraping them from the rock using their radula, the toothed tongue of gastropods. When the waves are striking the rock or the rock is exposed to the sun and drying, the ornate limpet lowers its shell against the substrate and remains firmly attached using its powerful foot. Only when the conditions are ideal, i.e., when the rock is wet and without strong waves, does the ornate limpet move around.

A beautiful specimen of the ornate limpet in Stewart Island. Photo by iNaturalist user naturewatchwidow.**

The ornate limpet lives about two years and its reproduction happens during summer, around February, which means that each individual reproduces a maximum of two times before dying. Environmental conditions probably affect longevity, because specimens living in less exposed rocks have a higher metabolism than those inhabiting a substrate that is constantly subject to desiccation and that forces them to remain inactive for long periods.

Compared to other closely related species, the ornate limpet has a short life and few reproductive events. Nevertheless, it is still a common species around New Zealand, having developed an increased fecundity that allows it to flourish.

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References:

Dunmore RA, Schiel DR (2000) Reproduction of the intertidal limpet Cellana ornata in southern New Zealand. New Zealand Journal of Marine and Freshwater Research 34(4): 653–660. doi: 10.1080/00288330.2000.9516966

Smith SL (1975) Physiological ecology of the limpet Cellana ornata (Dillwyn). New Zealand Journal of Marine and Freshwater Research 9(3): 395–402. doi: 10.1080/00288330.1975.9515575

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Friday Fellow: Giant Clam

by Piter Kehoma Boll

One more giant is coming to our team, again from the sea, but this time from the bilvavian molluscs. Its name is Tridachna gigas, commonly known as the giant clam.

Found in shallow coral reefs of the Indian and Pacific Oceans, especially around Indonesia, the giant clam can grow up to about 1.2 m, weigh more than 200 kg and live more than 100 years, being the largest living bivalve mollusk.

400px-giant_clam_282323115150429

The giant clam is seen in coral reefs as a giant lump of molluscan material. Watch out, Dory! Photo by flickr user incidencematrix.*

One interesting aspect of the giant clam and its close relatives is that they live in a symbiotic association with some dinoflagellates (the so-called zoxanthellae, also found in corals), having even a special structure, the zooxanthellal tubular system, to house them. During the day, the giant clam exposes its mantle to the light in order to allow the algae to photosynthesize. Part of the nutrients produced by the algae are given to the clam. This allows the giant clam to survive in otherwise nutrient-poor environments, where its standard bivalvian feeding stile, by filtering partiles from the water, would not be enought to allow it to grow properly.

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A half-closed shell. Photo by The Central Intelligence Agency.

The giant clam is used as food in many Asian countries, especially Japan and countries from Southeast Asia and Pacific Islands. Additionally, the giant shell is considered a valuable decorative item and can be sold for large amounts of money. Due to such exploitations, the giant clam populations are starting to decline and the species is considered vulnerable by the IUCN.

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An empty shell exposed in Aquarium Finisterrae, Galicia, Spain. Photo by Wikimedia user Drow male.**

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References:

Klumpp, D. W., Bayne, B. L., & Hawkins, A. J. S. (1992). Nutrition of the giant clam Tridacna gigas (L.) I. Contribution of filter feeding and photosynthates to respiration and growth. Journal of Experimental Marine Biology and Ecology, 155(1), 105–122. doi:10.1016/0022-0981(92)90030-e

Norton, J. H., Shepherd, M. A., Long, H. M., & Fitt, W. K. (1992). The Zooxanthellal Tubular System in the Giant Clam. The Biological Bulletin, 183(3), 503–506. doi:10.2307/1542028

Wells, S. (1996). Tridacna gigas. The IUCN Red List of Threatened Species doi:10.2305/IUCN.UK.1996.RLTS.T22137A9362283.en. Access on September 1, 2018.

Wikipedia. Giant clam. Available at < https://en.wikipedia.org/wiki/Giant_clam >. Access on September 1, 2018.

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Friday Fellow: Greater Blue-Ringed Octopus

by Piter Kehoma Boll

Tropical waters are always thriving with diversity, therefore it is hard to keep away from them. Today’s Friday Fellow is one more creature from the tropical oceanic waters, more precisely from the Indo-Pacific waters. Being found from Sri Lanka to the Phillipines, Japan and Australia, our fellow is called Hapalochlaena lunulata and popularly known as the greater blue-ringed octopus.

This adorable octopus is very small, measuring only about 10 cm, arms included. It is, however, easy to caught attention because its whitish to dark-yellow body is covered by about 60 rings that show a beautiful electric-blue color with a black outline. As with most octopuses, the color may change according to the animal’s needs in order to make him more or less visible.

A specimen of the greater blue-ringed octopus in Indonesia. Photo by Jens Petersen.*

This adorable color pattern, which may look attractive to us, humans, is nevertheless a warning sign. The grater blue-ringed octopus is a venomous creature and may even kill a human being if threatened. As other octopuses, it is a predator and feeds mainly on crustaceans and bivalves and immobilizes them with a toxin before consumption. This is a mild toxin, though. The real danger is on its defensive behavior.

When threatened, the greater blue-ringed octopus usually begins a warning display by flashing its rings in strong colors. If this is not enough to make the threatening creature retreat, it will atack and bite its harasser. The bite is usually painless but deadly. The venom injected is nothing more nothing less than the infamous tetrodoxin, the same thing that makes a pufferfish a dangerous meal. As you may know, tetrodoxin is a potent neurotoxin that kills within a few minutes to a few hours by blocking the action potential in cells, leading to paralysis and death by asphyxia. In the greater blue-ringed octopus, tetrodotoxin is produced by bacteria that live inside their salivary glands.

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A greater blue-ringed octopus swimming. Photo by Elias Levy.**

A study analyzing the sexual behavior of the greater blue-ringed octopus showed that mating occurs during encounters of both male-female and male-male pairs. The mating ritual of octopuses consists of the male introducing the hectocotylus, a modified arm specialized in delivering sperm, into the female mantle. In male-male pairings, one of the males always put its hectocotylus into the other male’s mantle and there was no attempt from the receptive male to avoid the act. The only difference between males mating with females or with other males was that they only delivered sperm to females and never to males. What can we conclude? Have octopuses found an efficient way to be bisexual creatures by having fun with other males while still able to keep their sperm to give it to females?

The diversity of life always fascinates us!

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References:

Cheng, M. W.; Caldwell, R. L. (2000) Sex identification and mating in the blue-ringed octopus, Hapalochlaena lunulataAnimal Behavior 60: 27-33. DOI: 10.1006/anbe.2000.1447

Mäthger, L. M.; Bell, G. R. R.; Kuzirian, A. M.; Allen, J. J.; Hanlon, R. T. (2012) How does the blue-ringed octopus (Hapalochlaena lunulata) flash its blue rings? Journal of Experimental Biology 215: 3752-3757. DOI: 10.1242/jeb.076869

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Friday Fellow: Tulip Cone

by Piter Kehoma Boll

The year has almost ended, but if you would touch today’s Friday Fellow, it would end for you right now, and without a new year coming.

Living along the coasts of the Indian Ocean, including East Africa, Madagascar,  India, West Australia and several archipelagos such as Mascarene Islands and the Philippines, our fellow, Conus tulipa, is popularly known as tulip cone. Despite its beautiful name, however, it is not a nice species to have nearby.

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A live Conus tulipa in La Réunion, Mascarene Islands. Photo by Philippe Bourjon.*

The tulip cone is a species of the genus Conus, predatory sea snails that feed on a variety of animals, such as fish, worms and other mollusks. They capture prey by stinging them with a venomous harpoon that is made of a modified tooth of their radula (tongue). The harpoons are stored in a sack and shot on a nearby prey. Because many species feed on fast moving prey, such as fish, they have a very powerful venom able to kill the target in a few seconds. In some species, including the tulip cone, this powerful venom is strong enough to kill an adult human being.

As with all other venomous species, though, not everything is bad. Several different toxins and other components have been recently isolated from the venom of the tulip cone, many of which may eventually be used to develop new medicines.

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References:

Alonso, D.; Khalil, Z.; Satkunanthan, N.; Livett, B. G. (2003) Drugs From the Sea: Conotoxins as Drug Leads for Neuropathic Pain and Other Neurological Conditions. Mini Reviews in Medicinal Chemistry3: 785–787.

Dutertre, S.; Croker, D.; Daly, N. L., Anderson, Å,.; Muttenhaler, M.; Lumsden, N. G.; Craik, D. J.; Alewood, P. F.; Guillon, G.; Lewis, R. J. (2008) Conopressin-T from Conus tulipa reveals an anatagonist switch in vasopressin-like peptides. Journal of Biological Chemistry283, 7100–7108.

Hill, J. M.; Alewood, P. F.; Craik, D. J. (2000) Conotoxin TVIIA, a novel peptide from the venom of Conus tulipa. The FEBS Journal, 267 (15): 4649–4657.

Wikipedia. Conus tulipa. Available at < https://en.wikipedia.org/wiki/Conus_tulipa >. Access on December 28, 2017.

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