Reef Ramblings

California Academy of Sciences 2012 new species list

Every year the California Academy of Sciences issues a press release detailing species newly described to science by academy scientists during the past 12 months.  The 2012 list comprises of 137 species new to science including 83 arthropods, 41 fishes, seven plants, four sea slugs, one reptile, and one amphibian; described by more than a dozen Academy scientists along with several dozen international collaborators.

“The ongoing discovery of new species is an important function of systematics-based institutions like the California Academy of Sciences,” said Dr. Terry Gosliner, Dean of Science and Research Collections at the Academy. “During these times, when we are facing the planet’s sixth mass extinction, species may be disappearing before we have a chance to find and describe them. How can we know what to protect, if we don’t know that it exists in the first place?”

Marine Highlights

Two of the marine highlights of the year were:

• A new species of deepwater Catshark from the Galapagos, the Jaguar Catshark, Bythaelurus giddingsi, collected via submersible from depths in the region of 428 –562 metres. The authors chose the common name partly because of its spotted pattern, and partly because it bears a striking resemblance to the fictional “Jaguar Shark” seen cruising the dark depths in the Wes Anderson film, ‘The Life Aquatic’.

Bythaelurus giddingsi – Jaguar Catshark.
Image: California Academy of Sciences

• The publication in June of, ‘Reef Fishes of the East Indies’, a three volume magnum opus, several decades in the making. Its geographic coverage spans the South China Sea, Andaman Sea, and the Coral Triangle—the region between the Philippines, Borneo, and New Guinea that is regarded as a global centre of biodiversity. Co-authored by Academy research associate Mark Erdmann, this three-volume book set provides descriptions and colour photographs of more than 2,500 reef fishes, including 25 new species.

Marine species

I’ve broken down the 41 species of fishes into their family groupings, 17 in all, and included size where possible, in order to make it easier to appreciate these new discoveries from a reef aquarium perspective.

Many of these new species seem to be small, cryptic, or of limited distribution, perhaps being found only at a single location or at a greater depth – all factors in their being previously undescribed – a reflection on the difficulty of fully exploring the underwater world. It’s likely that there are many more similar species awaiting discovery.

Snake Eels

Myrichthys paleracio, a new species of snake-eel from the Philippines.
Image: California Academy of Sciences

Anthias

A beautiful fairy basslet known only from a single deep reef off the southern Indonesian island of Lembata.
Image Credit: Gerald Allen, Conservation International

Coral Breams

A small coral bream with a blazing gold stripe known only from the Komodo islands in Indonesia.
Image Credit: Gerald Allen, Conservation International

Sandperches

A strikingly coloured, red spotted sand perch known only from southern Indonesia (Sumatra to Komodo) and west to the Andaman islands of India; in shallow depths of 2-8m.
Image Credit: Gerald Allen, Conservation International

Sand-divers

A deep reef species (below 60m depth) discovered in Cendrawasih Bay in West Papua; the name refers to the unusually long pelvic fins which this fish uses to rest on the bottom in tripod-like fashion.
Image Credit: Gerald Allen, Conservation International

Clingfishes

Aspasmichthys alorensis – a tiny clingfish known only from the Alor Strait in SE Indonesia – an area renowned for ferocious currents.
Image Credit: Gerald Allen, Conservation International

Lepidichthys akiko – a beautiful candy-striped clingfish known only from deep reefs of Cendrawasih Bay in West Papua.
Image Credit: Gerald Allen, Conservation International

Dragonets

Synchiropus tudorjonesi – Tudor Jones’ dragonet (male and female).
Image Credit: Gerald Allen, Conservation International

Gobies

As might be expected the most numerous of the new species are Gobies:

Acentrogobius cendrawasih – known only from a single silty gully off the Wandammen Peninsula in Cendrawasih Bay; unusual in that it lives at about 30m depth, other members of this genus are usually found above 10m.
Image Credit: Gerald Allen, Conservation International

Eviota atriventris Photo by J. E. Randall.

Eviota fallax
Image Credit: Gerald Allen

Grallenia baliensis – a miniscule sand goby found on the slopes of NE Bali during a 2011 survey.
Image Credit: Gerald Allen, Conservation International

Priolepis nocturna – a highly cryptic and rarely seen reef goby.
Image Credit: Gerald Allen, Conservation International

Tomiyamichthys gomezi – A beautiful shrimp goby that lives commensally with snapping shrimp.
Image Credit: Gerald Allen, Conservation International

Tryssogobius sarah – A delicate fairy goby with iridescent blue eyes known from deep (40-70m) reefs around Raja Ampat.
Image Credit: Gerald Allen, Conservation International

 Dartfishes

Ptereleotris rubristigma – a beautiful blue dart fish named for the prominent red spot on the gill cover; widespread throughout the East Indies region and found on soft bottoms exposed to currents.
Image Credit: Gerald Allen, Conservation International

List of Fishes

TL – Total length: term used by taxonomists to describe the length of a fish from its most forward part, e.g. its snout, to its rearmost part, e.g. the tip of the tail.

SL – Standard length: term used by taxonomists to describe the length of a fish from its most forward part, e.g. its snout, to the base of the tail. This measurement is used because long-preserved fish often lose the tips of the caudal fin rays through breakage after the desiccation effect of alcohol.

List of Sea Slugs

Notobryon thompsoni, a nudibranch found in South Africa.
Image: California Academy of Sciences

Four species of nudibranchs, in two families, were included in this year’s new species list. One species, Melibe coralophilia, is described as being found in association with two species of coral, the Blue Coral, Heliopora coerulea, and Porites species, although the nature of the association is currently unknown.

References

For references, see, ‘CalAcademy 2012 references‘

Adapted from materials provided by the California Academy of Sciences.

From my favourite new resource, Fishes of the East Indies, by Allen GR and Erdmann MV

Additional materials courtesy of FishBase

Tim Hayes

Reef Ramblings

©2012

Check out this fascinating, somewhat psychedelic, video of a night dive in the Red Sea shot under ultraviolet (UV) light, showing all manner of reef organisms exhibiting fluorescence. Animals including corals, fishes, echinoderms, and even the shell of a hermit crab show off a wide range of bizarre colouration.

Look out for the Scorpionfish and Pipefishes in particular.

In some of the sequences it’s particularly interesting to see the large quantity of zooplankton zipping around the reef, demonstrating how poorly our reef aquariums replicate the wild reef.

There’s a nice sequence of a family of clownfishes in their host anemone, which also shows large numbers of juvenile Dascyllus trimaculatus, Threespot Dascyllus or Domino damselfishes, sharing the safety of the anemone.

Also watch for the images showing Xenia species, Pulse Corals, happily pulsing away at night.

Fluorescence

Fluorescence is the result of a material absorbing one wavelength of light, re-emitting it as another, usually at a longer wavelength. The visible wavelength of light ranges from around 400 nm, blue light, to around 700 nm, red light. The UV light used in this video is UV-A and is in the range between 315 nm and visible light, probably around 380 nm. This makes the fluorescence produced even more remarkable as the UV light used is invisible to the human eye, yet we end up seeing these higher wavelength, visible colours.

You experience this phenomenon when you observe your aquarium under blue light alone, as most aquarium blue or ‘actinic’ lamps have a spectrum that reaches down to around 380 nm hence emitting UV-A.

UV light in this range is a useful tool for detecting newly settled juvenile corals in the reef aquarium; although newly settled corals are small and difficult to see, the fluorescence that they emit can make the easy to find.

See also, Coral magazine, Vol.5, No. 3, ‘Fluorescence’

Tim Hayes

Reef Ramblings

©2012-12-05

Coral Gobies are those Goby species that live in association with stony corals, often branching Acropora species, in a relationship that up until now has been described as commensal.

New research from the Georgia Institute of Technology reveals that the relationship between coral gobies and their coral hosts is more complex than previously believed. Coral gobies are small fishes, around 2.5 centimetres long, that spend their entire life living amongst the branches and crevices of their coral host, protected from predators.

This paper, published in the latest issue of the journal Science, ‘Corals Chemically Cue Mutualistic Fishes to Remove Competing Seaweeds’, seems to demonstrate that the relationship between the fish and the coral is a mutualistic one, benefiting both parties. The researchers found evidence that coral gobies respond to chemical signals from the coral, generated when the coral was under threat from toxic algae, stimulating the fish to remove the invasive seaweed.

The study revolved around Acropora nasuta, as with other Acroporids, an important reef building coral, and 2 species of coral goby, Gobiodon histrio – a popular aquarium species, and Paragobiodon echinocephalus. G. histrio was shown to consume the invasive seaweed whilst P. echinocephalus removed it.

Gobiodon histrio

Coral-dwelling gobies in the genus Gobiodon posses toxic skin secretions believed to act as a chemical defence against predation by larger fishes, this study also showed that the gobies eating the toxic seaweed increased the toxicity of their skin secretions.

Commensalism versus Mutualism

Commensalism is defined as a class of relationship between two organisms where one organism benefits without affecting the other. In view of this new research it would seem that this relationship should be redefined as one of mutualism, a relationship in which both organisms benefit. Given that this relationship has been described for two species of coral goby it seem likely that most, if not all, of the small fishes in this group are engaged in a mutualistic relationship with their coral hosts and hence should be provided with a suitable coral species in captivity.

Which Coral Host?

FishBase lists 20 species under Gobiodon ranging from 2.1 to 6.6 cms total length (TL) and 5 species under Paragobiodon ranging from 3.0 to 3.5 cms TL. I’ve done a quick cross reference between information from FishBase and the book Reef Fishes of the East Indies by Gerald Allen and Mark Erdmann, and come up with a list showing which fish species coexist with which coral.

(GA) source = Reef Fishes of the East Indies

In the Reef Aquarium

In light of the research revealing coral gobies to be in a mutualistic relationship with their coral host I would propose that, from an aquarium point of view, these coral goby species should be kept with a branching coral host to replicate their natural association. Although it would be next to impossible to define the exact species required for each individual fish imported, the provision of something close to their natural habitat may go a long way to reducing stress levels and improving their quality of life in captivity.

In many ways coral gobies are the perfect fish for the reef aquarium. They have little requirement for swimming room so their small size and sedentary lifestyle puts little load on the filtration system. Fed appropriate foods, these small fishes should be able live in captivity in a manner that mirrors their natural existence, noticing little difference from their life in the wild.

It is interesting to reflect that for very small fish, coral gobies can have an unusually long lifespan, living up to ten years in captivity. By contrast, the slightly smaller gobies in genus Trimma may have a lifespan measured in weeks.

See also, ‘An Introduction to Gobies for the Nano Reef: Genus Gobiodon and Paragobiodon – Coral or Clown Gobies.‘

Tim Hayes

Reef Ramblings

©2012

A new species of scleractinian or stony coral in the genus Leptoseris  has been described.

Dr. Bert W. Hoeksema of Naturalis Biodiversity Center in Leiden, the Netherlands, has published the description of a new species of Leptoseris that lives on the ceilings of caves in Indo-Pacific coral reefs. Unlike other members of the genus the new species, Leptoseris troglodyta, is azooxanthellate, having no symbiotic photosynthetic algae, and has a smaller size of polyp.

The genus Leptoseris is a member of the family Agariciidae. Up until now all the corals in this genus, although preferring lower light conditions, have proven to be zooxanthellate. Generally they are found on lower reef slopes, walls, or overhangs, exhibiting a wide range of forms such as encrusting, leafy, or vase-like with the morphology dependent on local environmental conditions.

Although Leptoseris species can occur deeper than 40 metres the new species has not so far been found deeper than 35 metres.

SeaLife Base lists 17 species under Leptoseris, other sources suggest 15 species.

The species description is published in the open access journal ZooKeys.

Tim Hayes

Reef Ramblings

©2012

I was intrigued by a recent Newquay Blue Reef Aquarium press release mentioning special events and activities to celebrate World Octopus Day this coming Monday.

Not having previously heard of World Octopus Day I decided to do a bit of research. It turns out that it is not one of those officially sanctioned ‘World Days’, indeed its true name turns out not to be World Octopus Day, but rather International Cephalopod Awareness Day.  It was established in 2007 by members of TONMO, The Octopus News Magazine Online forum, to bring attention to the diversity, conservation and biology of the world’s cephalopods. October 8 was chosen as an auspicious occasion for appreciating animals with a combination of 8 or 10 appendages – Octopus have eight arms while squid and cuttlefish have eight arms and two tentacles – the eighth day of the tenth month seeming an appropriate choice of date.

To increase the scope of the celebration four more days were added:

• October 8 – Octopus Day, for all the eight-armed species
• October 9 – Nautilus Night, a time for all the lesser-known extant cephalopods
• October 10 – Squid Day/Cuttlefish Day, or Squidturday, covering the tentacular species
• October 11 – Myths and Legends Day, for all the fantastical cephalopods of movies, literature and legend.
• October 12 – Fossil Day (to coincide with National Fossil Day), for all the incredible suckers that have gone extinct.

To find out more about this celebration of the world’s most intelligent invertebrates, go to the Cephalopod Awareness Day facebook page.

Tim Hayes

Reef Ramblings

8/10/2012

The Florida Fish and Wildlife Commission (FWC) made several changes and clarifications to marine life management, defined as tropical ornamental species, at its September Commission meeting in Tampa on Wednesday, including a three-year ban on the collection of the giant Caribbean Sea anemone, Condylactis gigantea.

Photo Robin Hayes ©2012

The prohibition of the collection the giant Caribbean Sea anemone was at the request of the Florida Marine Life Association (FMLA), the organisation of collectors that supply fish and invertebrates to the aquarium industry, and has the aim of letting their dwindling population recover and rebuild. The FMLA said that the anemone has suffered a sharp decline in the past few years, possibly from excessive collecting and partly from the cold weather that blanketed southern Florida in 2010.

The ban takes effect on 1^st November. Up until now commercial divers have been able to take up to 200 anemones per trip, and recreational divers could take up to five per day but it has taken more effort for divers to reach these quotas over recent years. In the early 2000s Commercial divers noticed a decline in the number of anemones in the Middle and Upper Keys. Landings of the giant anemones dropped from 227,238 in 1994 to 28,656 in 2011.

The FWC will return to the issue within three years with a proposal for future management of this species.

Management is important given the central role of Condylactis gigantea in the local ecosystem, where it provides shelter to a variety of commensal species including fishes and Periclemenes species cleaner shrimp, and serves as fish cleaning stations. The decline in numbers of this anemone might have a knock-on affect adversely influencing many other species.

The ban will prohibit collection in Florida waters, but Condylactis anemones should still be available from other locations, as it has a wide distribution in the Caribbean Sea and the Western Atlantic Sea, ranging from southern Florida through the Florida Keys to as far south as Brazil and east as Bermuda.

Other changes and clarifications by the FWC include:

• Removal of unicorn filefish, sand perch and dwarf sand perch from what is considered marine life, which will allow these species to be harvested with traditional fishing gear, such as hook and line and cast net, and without the requirement that they be kept in an aerated live well. The recreational bag limit of five of each species per day will no longer apply.
• Clarifying that size limits for angelfish extend to any hybrid forms of the species.
• Clarifying that commercial size limits for angelfish and butterfly fish apply to all harvesters, including recreational.
• Clarifying that the reefs built by Sabellarid tubeworms are live rock and, therefore, cannot be harvested.
• Prohibiting the harvest of black corals, which are already prohibited from harvest in federal waters.
• Expanding the definition of snapping shrimp to include all marine life snapping shrimp species.

Further information:

Concern has been raised as early as 2001 about the status of Condylactis gigantea and its collection for the aquarium trade. see:

Chiappone M, Miller SL, Swanson DW (2001) Condylactis gigantea – A giant comes under pressure from the aquarium trade in Florida. Reef Encounters 30: 29–31.

More recent information on collection for the aquarium trade can be found here:

Crawling to Collapse: Ecologically Unsound Ornamental Invertebrate Fisheries

Tim Hayes

Midland Reefs

©2012

”

Reef Fishes of the East Indies is a 3-volume set of books written and compiled by Gerald R Allen & Mark V. Erdmann.

Weighing in at just over 6.5 kg, Reef Fishes of the East Indies represents a mammoth undertaking. Comprising three hardbound volumes, packed together in a slipcase (10 cms in width!), this fantastic work covers the fishes of the ‘Coral Triangle’ in 1292 pages and 3,600 high quality colour photographs, many never before seen in print.

Embracing an area extending from the Andaman Sea to the Solomon Islands this is the only reference work to cover every known reef fish, making it the most comprehensive treatment of the region in a century. The East Indies encompasses a vast array of marine habitats and an unsurpassed marine biological diversity. Home to approximately 2,600 species of reef fishes occurring on coral reefs and nearby habitats the ‘Coral Triangle’ forms the basis of the reef aquarium hobby. The reef and related marine ecosystems of the region are the most bio diverse and economically valuable on the planet whilst, at the same time, amongst the most at risk with over 80% of its coral reefs being considered endangered.

The text provides up to date information on the classification, habitat, and distributional range of each species as well as an overall synopsis for each of the 120 families covered. Volume one includes descriptions of the regions that make up the East Indies along with a discussion of the zoogeography i.e. the geographic distribution of the species of the area. All useful information for the reef keeper aiming to put together a biotope aquarium.

Many of the featured species have not been previously recorded from the region, nor have their photographs appeared in print. Reef Fishes of the East Indies features the 2,631 known reef fishes of the ‘Coral Triangle’, including 25 species new to science.

To see samples of some of the photography, go to the Guardian, environment section.

Reef Fishes of the East Indies is an essential reference for advanced reef keepers, professional aquarists, biologists, naturalists, and scuba divers.   The book has been written to engender an appreciation of the region’s amazing biodiversity and the urgent need to conserve it for the benefit of future generations.

The book represents a milestone in the prolific careers of two dedicated marine biologists, Dr. Gerald R. Allen and Dr. Mark V. Erdmann, who have spent a combined total in excess of 60 years exploring and describing the fishes in the ‘heart’ of marine fish biodiversity.

Gerald R. Allen served as Senior Curator of Fishes at the Western Australian Museum in Perth and is an international authority on the classification of coral reef fishes. Since leaving the Museum in 1997, he has worked as a private consultant, primarily involved with coral reef fish surveys in Southeast Asia for Conservation International.

Mark V. Erdmann is senior advisor for Conservation International–Indonesia’s marine program, with a primary focus on managing CI’s marine conservation initiatives in the Bird’s Head Seascape in West Papua.

Published by Conservation International.

Available to special order from Midland Reefs (delivery 3 – 5 days). Price for the three-volume set is £ 204.99 including post and packing

For more about Gerald Allen, see Alert Diver Online, ‘A Magnum Opus of Tropical Reefs’

Tim Hayes

Midland Reefs

©2012

Family Fungiidae.

Commonly referred to as Plate or Mushroom corals (not to be confused with mushroom anemones), these are free-living corals that are found living directly on the bottom substrate. Do not place these corals on rockwork; it’s neither natural nor safe. These corals are capable of moving themselves around so if placed up on the rocks there is a very real danger of it trying to move to a new position and ending up falling on to some other coral below; usually with disastrous results to the coral it lands on, as these are strongly stinging corals. In some circumstances it may be necessary to corral these corals with small pieces of live rock to prevent them from moving into a position where they can sting other corals.

Genus Cycloseris

Genus Fungia

Common species: Plate corals, Mushroom corals.

There are a number of species of these two genera that are difficult to identify to species level. Circular, low-lying corals with a single mouth. Very hardy but should be placed on the bottom substrate of the aquarium. A naturalistic display can be achieved by placing a number of the corals together in a group on a sand substrate.

Excellent choice for those new to stony corals.

Genus Heliofungia

Common species: Long tentacled plate corals.

Similar to Fungia species these are circular in form but have long tentacles and may appear reminiscent of certain Anemone species. This is one coral that cannot be recommended as being suited to any other than advanced aquarists. The majority of these corals imported do not survive in captivity.

Genus Herpolitha

Genus Polyphyllia

Common species: Slipper corals.

Difficult to distinguish to species level these corals are very similar to Fungia except rather than being round they are elongated plates with rounded ends.

Fungiids – Mobile corals

Click for full image.

Unlike the majority of corals attached to the limestone substrate that makes up the reef, Fungiids can actively move around and find themselves better habitats. Compared to other species, they have a relatively thick layer of fleshy tissue covering the top of their calcium carbonate skeleton, expanding and contracting this tissue allows them to move around.

Corals on loose substrate, such as sand, are vulnerable to being covered by sediment if there is any shifting of the substrate owing to weather conditions or if foraging fish, digging for food, dump sand on them. Under these conditions corals can become smothered and suffocate, some species can dislodge sediment by expelling mucous but as a free-living corals Fungiids use the same technique as they do for movement to rid themselves of sedimentation.

To investigate how these corals coped with being buried in sediment Dr Pim Bongaerts, from the University of Queensland, brought specimens into the lab and put them in aquaria in order to film the process using time-lapse photography.

The corals were covered in a sediment made up of coarse sand (0.5 – 1.0 mm) and then over 20 hours were photographed every 10 seconds, the resulting footage shows the corals inflate and deflate their entire body in a series of rhythmic pulses shedding the sediment in a matter of hours.

Dr Bongaerts findings have been published in the journal Coral Reef:  Mushroom corals overcome live burial through pulsed inflation (P. Bongaerts, B. W. Hoeksema, K. B. Hay, & O. Hoegh-Guldberg)

For more information about Fungiids on Reef Ramblings, see also:

• Previously Unknown Feeding in a Large Polyped Stony Coral.
• 3 Aquarium Corals Feature in Top 10 List of Endangered  Coral Species.

Tim Hayes

Midland Reefs

©2012

I’ve just received my copy of the January 2012 issue of Aquarium Fish International featuring the first edition of my new regular column, ‘The Mariculturist’. The column looks at all aspects of breeding and propagation, covering fish, cnidarians and mobile invertebrates.

For this issue’s table of contents, see: AFI January 2012

You can read the Editor’s Note for this issue by going here.

Also there is some additional online content connected to my column, ‘Fish and Invertebrates Spawned in Captivity’ disappointingly this is an abbreviated version of my full (and ongoing) list, which you can see in full here: List of Ornamental Marine Fishes Bred in Captivity

If there are any areas of mariculture that you’d like to see covered in the column, please get in touch.

Similarly, if you know of any species of ornamental marine fish or invertebrate not included in my list  that has been spawned in captivity, please let me know by contacting me through Reef Ramblings.  Please include any supporting evidence you have, including photos or a reference from a scientific journal.

Update December 15th 2011

I’m happy to say that the list has now been updated on the AFI website.

Tim

Tim Hayes

Midland Reefs

©2011

Although not that common in the hobby Chitons do occasionally appear in our tanks, usually as hitchhikers. A recent paper, ‘A Chiton Uses Aragonite Lenses to Form Images’ by Daniel I. Speiser, Douglas J. Eernisse, Sönke Johnsen published in Current Biology, www.cell.com/current-biology/home, revealed some interesting information about chitons, including the fact that these are the first aragonite lenses ever discovered.

Lined chiton.  Photo by Kirt L. Onthank

For those of you unfamiliar with chitons, they are a marine molluscs of the Subclass Polyplacophora, which contains somewhere between 600 and 100 species of chitons. They are found from shallow waters to depths of about 400 m. As with gastropods such as the more familiar ‘turbo snails’, chitons have a muscular foot accommodating slow locomotion that can enable it to strongly attach to a substrate; it features a convex shell that distinguishes it from other molluscs by consisting of eight, overlapping, articulating plates held in place by a structure known as a girdle.  Most chitons are herbivorous grazers eating algae, bryozoans, diatoms and other bio films, scraping the substrate with well-developed radula and make a useful addition to the reef aquarium.

Not have looked closely into chitons, despite having had a number of them in my tanks over the years, I was surprised to learn about their sensory apparatus. The primary sense organs of chitons are the subradula organ, with which it tastes for food, and a large number of unique organs called aesthetes. The aesthetes consist of light sensitive cells just below the surface of the shell, although up until recently their capacity for vision was unknown. In some cases they are modified to form ocelli, with a cluster of individual photoreceptor cells lying beneath a small lens; an individual chiton may have thousands of such ocelli

The recent paper from Daniel Speiser, studying chiton vision at Duke University in Durham, North Carolina, has uncovered some information about how these animals see, including the unexpected make up of these lenses. X-ray analysis was used to determine the chemical composition and structure of the lenses and revealed that the chiton Acanthopleura granulata has the first aragonite lenses ever discovered. Aragonite is the same form of calcium carbonate with which corals build their skeletons and the mineral that makes up chiton shells.

In testing how well these eyes worked. They placed a small black disc into the animals’ field of view or dimmed the background from white to a uniform shade of grey that more diffusely blocked the same amount of light as the disc. The chitons clamped their shells tight when shown a 3-centimeter-diameter circle, roughly equivalent to a human seeing an object 20 times larger than the moon. They were unperturbed, however, when the researchers instead dimmed the light. The findings suggest that chitons can distinguish between approaching predators and the general dimming of light that might be caused by a passing cloud.

The researchers were surprised to find that chiton eyes worked equally well in air and in water, since light travels at different speeds through the two fluids, they suspect that chitons capitalize on aragonite’s unusual ability to transmit light at different speeds. The mineral bends the incoming rays in two directions and creates a double image. Chiton lenses may curve such that one image falls on the light-sensitive cells of the eye when the animal is in air, and the other image falls on these same cells when the animal is under water, Speiser says. The adaptation makes sense, as chitons live in intertidal zones and spend time above and below the water line. “I think this is a very clever and simple solution to the problem of making eyes that work in these two different settings,” he says.

Summary

Hundreds of ocelli are embedded in the dorsal shell plates of certain chitons. These ocelli each contain a pigment layer, retina, and lens, but it is unknown whether they provide chitons with spatial vision.  It is also unclear whether chiton lenses are made from proteins, like nearly all biological lenses, or from some other material. Behavioural trials further indicated that A. granulata‘s eyes provide the same angular resolution in both air and water.

Tim Hayes

Midland Reefs

©2011