The 18 species of Histioteuthid squids, the biggest no larger than a football, are often strawberry colored, with dark photophores resembling black seeds adding to the sweet fruit-like appearance.   All the species live in the mesopelagic, that region in the ocean between 200 and 1000 meters that goes from dimly lit to a full on dark habitat.  Light comes from above in the form of attenuated sunlight and below in the form of bioluminescence.  Given the drastic changes in light with depth, the mesopelagic is filled with a cornea-copia of truly amazing, dare I say monstrous, visual adaptations.  The Histioteuthid squids are no expectation.  The left eye can be twice the diameter of the right eye, a trait only acquired with adulthood.  The left eye can gain such proportions it actually pushes the head out of alignment with the squid’s body in some species.

New work by Kate Thomas and colleagues reveals why these strawberry squid’s different eyes have made such a spectacle of themselves.  The group found that the squids oriented the enlarged left eye upward and the smaller right eye slightly downward.   The squids often held a slanted angle with their body so the eye looking upward was near 45˚ and the downward near 120˚.  Given the field of view of the eyes, the large eye would receive light from directly above to 90˚ horizontal on the left side.  The small eye from 43-198˚ or from directly below to horizontally on the right side.

To keep these eyes aimed in the right area, the strawberry squids also demonstrate a peculiar behavior.  Squids would ratchet themselves, turning the body while the head maintain the same orientation.  The head would, at a precise stopping point, suddenly snap around to match the body orientation. “This may allow histioteuthids to compensate for the unbalanced fields of view created by [different sized] eyes and rapidly change which direction each eye is facing, or to scan their environment.”

But why two different eyes?  Thomas explains, “Eyes are metabolically expensive to grow, maintain, and use, so while larger eyes can improve both sensitivity and resolution, selection probably favors an eye just large enough to perform a necessary visual task but no larger.”  It is actually cheaper, in the total calories needed sense, to have the eyes perform to unique functions and allow one of them to be itty bitty.

And with that, my friends, eye take my leave.

The post The Little Strawberry Squid with the Big Eye first appeared on Deep Sea News.

Reader Jonathan W. wrote into DSN with this

You guys are some of the most accessible in marine science, so I thought I pose this incredibly specific question that’s nagged at me for years: We all know a nauplius has a compound eye, but I’ve run across passing mention of *adult* barnacles retaining an eye or eye spot somewhere that can sense light and dark…Does a mature barnacle possess an “eye?” If so, where is it?

Well Jonathan W. adult barnacles do have an eyespot. It is a third eye that occurs in the middle of their crustacean foreheads and aligns their arthropods selves with a cosmic energy.

Seriously though, the adult barnacle eyespot is much cooler than a cosmic eye. The larva crawls around until it finds a favorable spot to set up shop.  Usually next to adults already hanging about, because no barnacle wants to be alone.  At this point larva attaches their head to the rock or other hard surface using cement secreted by the first antennae.  This triggers a metamorphosis that turns them into tiny adults. Basically a barnacle spends its entire life doing a keg stand, well without the beer or circle of frat boy cheering it one.

During this metamorphosis the compound eye is lost, shed with the larval exoskeleton.  It is replaced with a group, called ocelli, of 3 large photoreceptors.  These receptors have only an “on” or “off” response and can detect the presence or absence of light.  As experiment try this: barnacles in shallow water will generally withdraw and close up when suddenly placed in a shadow.

The post The all seeing, all knowing, eye of upside down barnacles first appeared on Deep Sea News.

The largest measured giant squid eye is 27 centimeters (10.63 inches), roughly the size of a large dinner plate. Whereas all giant squids don’t have goliath fine china size eyeballs, most are between 5-15 centimeters (~2-6 inches), their peepers are huge. The swordfish has roughly the same body size as a giant squid, yet its eye is just a third of the diameter.

Why?

Why are giant squid eyes giant?

Why are the eyes bigger than fish?

Last year scientists proposed that the gigantism of giant squid eyes was a novel adaptation to spot their main predator, the sperm whale [1].  Bigger eyes can take in more light and in general animals living in perpetual darkness, like those in caves and in the deep oceans, possess very large eyes.  However, as Ed Yong describe

“Using a mathematical model, they found that in the deep ocean, eyes suffer from a law of diminishing returns. Small eyes can see dramatically further if they grow a bit bigger. But once the pupil passes 2.5 centimetres, these improvements become tinier and tinier. Once the pupil reaches 3.5 centimetres, and the eye itself reaches 9 centimetres, there’s very little point in making it any bigger. And that’s exactly where fish have stopped. Even though the swordfish’s head is capable of holding a much larger eye, it doesn’t.”

From mathematical modeling, the reason for the giant squid’s large eye is that in the dark a pupil can easily pick up a large and dimly lit object…like your mom (sorry I couldn’t resist).  More seriously, a sperm whale disturbing bioluminescent organisms as it moves through the water would be an easy optical target for the giant squid.

But new work cast doubts on this idea.

First, let’s go back to the beginning.  How large is a giant squid’s eye? If you scale a smaller squid up to giant squid size proportions, would the eye be the same size as a giant squid?

This is key.

Think of it this way.  If you scaled a Chihuahua up to Great Dane size would its tongue be the same size as Great Dane?  When you make organisms larger all the individual parts must get larger too.

But does this account for all of the ocular size differences? If yes, then we need no special reason to account for the behemoth ocular awesomeness of giant squids.  The giant squid simply has a squid eye as big as it’s supposed to be for a squid.

Lars Schmitz and his team took measurements of body size and eye size for 87 squids. What they found was the eyes of giants and colossal squids were not out of proportion compared to other squids. For giant squids 98.8% and for colossal squid 100% fell within predictions based on other squids. In other words, these massive squids do no have unusually large eyes for their body size.  The authors of this recent study do note that other squids, particularly the bobtail squids, have much larger eyes than you would expect, mainly because their bodies are shortened relative to other squids.

Compared to fish, all squids have very large eyes.  This holds even if the fish and squid are the same size.  On average, Schmitz and his team found that squid have ~1.7 times the eye diameter of fish for any given body size.

The authors go a step further and reexamine the original eye model proposed last year.  Schmitz and colleagues used more accurate parameter estimates including a range of eye sizes of giant squids. They found that over similar distances that point and diffuse light sources could be detected equally well.  To restate, a giant squid can just as easily detect the diffuse light of large object like a sperm whale triggering tons of bioluminescent plankton as a small fish using bioluminescence.  It’s just as likely a squid uses its large eyes to hunt others as it is to prevent be hunted itself. At an eye diameter of 15 centimeters this distance is 80 meters (262 feet) and at 4 centimeters the distance is 50 meters (160 feet), roughly 2/3 and 1/2 the length of football field. So larger pupils are equally great at detecting small point flashes, large form illumination, and even large dark objects.

[1] Nilsson et al. A unique advantage for giant eyes in giant squid. Current Biology 2012, 22:1–6. doi:10.1016/j.cub.2012.02.031.

[2] Schmitz et al. Allometry indicates giant eyes of giant squid are not exceptional. BMC Evolutionary Biology 2013 13:45 doi. 10.1186/1471-2148-13-45

The post Why the giant squid eye? first appeared on Deep Sea News.

I’m fairly sure it’s just the eye of a large [Xiphiidae or Istiophoridae], likely a swordfish or marlin. They get seriously big, but people don’t realize it because most of the eye is inside the head.

He then went a step further and then emailed a few of his colleagues

talked with some colleagues — definitely a swordfish eye

There you have it.  New reports on the eye also mention the presence of bones which obviously rules out the giant squid!

So does this mean I win the internet?

The post Solved! Where did the Big Eye In The Sea come from? first appeared on Deep Sea News.

Crazy doesn’t even come close to how freakin’ wierd this fish is.  At my old stomping grounds, MBARI, Bruce Robison and Kim Reisenbichler now know why. Desribed in 1939, Macropinna microstoma, the barreleye fish, isn’t exactly new to science.  All the species in the Opisthoproctidae family are known for having ultra-sensitive tubular eyes that face upward, well adapted for collecting light.  Slight problem.  If the eyes constantly face upward, looking forward to capture prey with their wee little mouths is impossible.

Using MBARI’s remote operate vehicles Robison and Reisenbichler were able to view the barreleyes in the ocean between 600 and 800m.  The found that the eyes of Macropinna can rotate within transparent shield that covers the fish’s head, allowing it to look at whatever it wants.  This transparent, fluid-filled shield that covers the top of the fish’s head was unknown to science, i.e. existing descriptions and illustrations do no show it.  Likely, when previous specimens were caught in deep-sea trawls there were damaged or lost.

But the craziness of this fish doesn’t stop with the clear skull or pivoting eyeballs…

In addition to their amazing “headgear,” barreleyes have a variety of other interesting adaptations to deep-sea life. Their large, flat fins allow them to remain nearly motionless in the water, and to maneuver very precisely (much like MBARI’s ROVs). Their small mouths suggest that they can be very precise and selective in capturing small prey. On the other hand, their digestive systems are very large, which suggests that they can eat a variety of small drifting animals as well as jellies. In fact, the stomachs of the two net-caught fish contained fragments of jellies.

And now for the video…

Bruce H. Robison, Kim R. Reisenbichler (2008). Macropinna microstoma and the Paradox of Its Tubular Eyes Copeia, 2008 (4), 780-784 DOI: 10.1643/CG-07-082

The post Scientists Solve The Mystery Of Why This Fish Is So Freakin’ Crazy first appeared on Deep Sea News.

Bathynomus giganteus (Arthropoda: Crustacea: Isopoda: Cirolanidae)

You know those cute little roly-poly bugs you found under rocks as a kid? You poke at them and they curl up into a little ball? Well, magnify that times 1000, take away the functional role of the eyes, head to the deep-sea and you’ve got the Giant Isopod, Bathynomus giganteus!

Description Bathynomus giganteus was first discovered in fishermen’s nets in the Gulf of Mexico and was described as the type species of the genus by Alphonse Milne Edwards in 1879 (12). It is the largest known isopod, reaching lengths up to 50cm. That is about the length of small dog or cat! Most isopods only reach lengths between 1-5cm. They have a strong and thick exoskeleton and take on the general shape of your typical “flattened” isopod. B. giganteus has 7 pairs of pereopods, or legs, which are uniramous (meaning only one pair of legs per segment). The first pair of pereopods is modified into maxillipeds (literally “mouth feets”) that help move food to its 4 sets of jaws modified for cutting and tearing.

Physiology

Interestingly, they have a compound eye with over 3,500 facets (4). The eyes are overgrown by the exoskeleton and exposure to natural daylight causes irreversible damage to their photoreceptors (4). It isn’t clear whether these eyes have any function or just evolutionary remnants from a relatively young diversification (8), but they do not respond to the visible spectrum and have only low sensitivity to the ultraviolet spectrum at the 360nm wavelength (4). It is suggested that they rely mainly on chemoreception (4) and possibly mechanoreception (7) or to find prey items.

Isopods have hemocyanin for transport of oxygen, but in B. giganteus it also acts a major phenoloxidase (13). The hemocyanin protein of B. giganteus also has amino acid substitutions at the N-terminus that are more similar to primitive arthropods such as the chelicerates (sea spiders, horsesheoe crabs) and myriapods (centipedes & millpedes) (13).

Nutrition

Gut content analysis of B. giganteus show mostly fish fragments, as well cephalopod, caridean shrimp and galatheid crab remains (3). In smaller quantities, sponge fragments, other isopods, echinoderms, nematodes and tunicates have been found (1, 3). Unfortunately, large quantities of plastic were discovered in the guts of 3 specimens from north of the Yucatan Peninsula in the southern Gulf of Mexico (3). Most authors agree that B. giganteus is a scavenger (3, 5, 6), but some suggest it is also a facultative predator (3, 6). Specimens in aquaria have survived 8 weeks between feedings (5) and it speculated that this may be an adaptation for carrying its brood, which would be severely impacted by a full stomach (3). Further support for this hypothesis are the large quantities of lipid reserves in the hepatopancreas (14) and fat bodies (2) of this isopod. B. giganteus has also been collected from baited traps outside of methane seeps in the northern Gulf of Mexico (11). Stable carbon, nitrogen and sulfur isotope analyses confirm a detrital source of nutrition with some input from chemosynthetic sources, ranging from 0-45% (11).

Reproduction

Eggs of the giant isopod are also giant, up to 13mm diameter (6) and are brooded in a brood pouch above the stomach and internal organs (10). Females do not feed when brooding and seem to bury themselves in the sediment to reduce energy expenditure during brooding, which would insulate them and protect the brood and adults from predators. This unfortunately appears to make them more susceptible to trawls since brooding females have only been caught in trawls and not baited traps (1, 3). Juveniles of Bathynomus giganteus are called mancas and reach length up to 6cm. Mancas are characterized by the lack of the seventh pair of pereopods. The smallest sexual mature males and females reported are around 21cm (3) and 16.6cm (5), respectively. Individuals from the Gulf of Mexico show patterns of seasonal reproduction (3) and appear to release their brood between August and February (3), with low reproductive activity in the summer (1).

Ecology

Isopods apparently make good taxis as well! Several epibionts have been documented on the carapaces of B. giganteus including the barnacle Octolasmis aymonini, the gastropod Mitrella amphisella, serpulid polychaetes and hydrozoans (1, 3). Interestingly, Mitrella amphisella, from a family of carnivorous snails (Columbellidae), is found mainly on females and in the brood pouch (3). Not much is known about what types of organisms eat Bathynomus giganteus, but one paper reports a specimen in the gut contents of a tiger shark (3).

Biogeography

B. giganteus occurs at depths between 310-2140m (6), although in one rare case a single specimen was reported from 80m off the coast of Brazil (9). The giant isopod has a more or less global distribution. No one has studied to my knowledge the genetic connectivity between these isolated populations, but there is no doubt that further sampling should turn up more specimens from other areas of the world

Further Reading:

1.    Barradas-Ortiz, C., P. Briones-Fourzan, and E. Lozano-Alvarez. 2003. Seasonal reproduction and feeding ecology of giant isopods Bathynomus giganteus from the continental slope of the Yucatan peninsula. Deep Sea Research Part I: Oceanographic Research Papers 50:495-513.

2.    Biesiot, P. M., S. Y. Wang, H. M. Perry, and C. Trigg. 1999. Organic reserves in the midgut gland and fat body of the giant deep-sea isopod Bathynomus giganteus. Journal of Crustacean Biology 19:450-458.

3.    Briones-Fourzán, P., and E. Lozano-Alvarez. 1991. Aspects of the biology of the giant isopod Bathynomus giganteus A. Milne Edwards, 1879 )Flabellifera: Cirolanidae), off the Yucatan Peninsula. Journal of Crustacean Biology 11:375-385.

4.    Chamberlain, S. C., V. B. Meyer-Rochow, and W. P. Dossert. 1986. Morphology of the compound eye of the giant deep-sea isopod <I>Bathynomus giganteus</I>. Journal of Morphology 189:145-156.

5.    Cocke, B. T. 1986. Deep-sea isopods in aquaria. Tropical Fish Hobbyist 35:48-52.

6.    Holthuis, L. B., and W. R. Mikulka. 1972. Notes on the deep-sea isopods of the genus Bathynomus A. Milne Edwards, 1879. Bulletin of Marine Science 22:575-591.

7.    Klages, M., S. Muyakshin, T. Soltwedel, and W. E. Arntz. 2002. Mechanoreception, a possible mechanism for food fall detection in deep-sea scavengers. Deep Sea Research Part I: Oceanographic Research Papers 49:143-155.

8.    Kussakin, O. G. 1973. Peculiarities of the geographical and vertical distribution of marine isopods and the problem of deep-sea fauna origin. Marine Biology 23:19-23.

9.    Lemos de Castro, A. 1978. Descricao de uma especie nova gigante do genero Bathynomus Milne-Edwards

do litoral brasileiro (Isopoda, Cirolanidae). Revista Brasileira de Biologia 38:37-44.

10.    Lloyd, R. E. 1908. The internal anatomy of bathynomus giganteus, with a description of the sexually mature forms. Memoirs of the Indian Museum 1:81-102.

11.    MacAvoy, S. E., R. S. Carney, C. R. Fisher, and S. A. Macko. 2002. Use of chemosynthetic biomass by large, mobile, benthic predators in the Gulf of Mexico. Marine Ecology Progress Series 225:65-78.

12.    Milne-Edwards, A. 1879. On a gigantic isopod from the great depths of the sea. Annals and Magazine of Natural History 5:241-243.

13.    Pless, D. D., M. B. Aguilar, A. Falcon, E. Lozano-Alvarez, and E. P. Heimer de la Cotera. 2003. Latent phenoloxidase activity and N-terminal amino acid sequence of hemocyanin from Bathynomus giganteus, a primitive crustacean. Archives of Biochemistry and Biophysics 409:402-410.

14.    Steeves, H. R. I. 1969. Lipid contents of the hepatopancreas of the isopod Bathynomus giganteus A. Milne Edwards, 1879. Crustaceana 16:135-138.

The post From The Desk of Zelnio: Bathynomus giganteus first appeared on Deep Sea News.