A day at the Aquarium

December 29, 2015 • 2:00 pm

by Greg Mayer

My Okinawa correspondents spent Boxing Day at the Okinawa Churaumi Aquarium, and sent me a bunch of pictures. The aquarium is a sprawling complex on the coast in northwestern Okinawa, and includes large areas of gardens and park land, and a recreation of traditional Okinawan homes and buildings, as well as the aquarium proper.

Okinawa Charaumi Aquarium
Okinawa Churaumi Aquarium

It reminded me, as I’m sure it did many of you, of the Sausalito Cetacean Institute. That’s Ie Shima island in the background.

Okinawa Churaumi Aquarium
Okinawa Churaumi Aquarium

One of the main attractions at the Aquarium is the Kuroshio Sea Tank. It’s enormous.

Kuroshio Sea Tank
Kuroshio Sea Tank

When my correspondents told me they were going to the Aquarium, they mentioned something about “whale sharks”, but I didn’t query them further. It turns out the Aquarium actually has whale sharks (Rhincodon typus), the world’s largest species of fish!

A whale shark
A whale shark

And not just one!

Two whale sharks
Two whale sharks

Although whale sharks are, for sharks, specialized feeders– they feed on plankton– they are “typical shark” shaped.

Sharks are cartilaginous fishes (Chondrichthyes), which are of two main types: the Holocephali, comprising the ratfishes and chimaeras (we’ve mentioned them here before at WEIT), and the Elasmobranchi, comprising sharks and rays. Most people have a good idea of what sharks and rays look like. Here are some more typical sharks (I don’t know what species– any shark people out there?) Note that the gill slits are on the side of the head; the fellow in the middle is male, as you can tell by the large claspers medial to the pelvic fins.

Typical sharks
Typical sharks

And here’s a typical ray (again, no ID). Note the flattened shape, and the spiracles (whitish bits) behind the eyes– these are the vestigial first pair of gill slits. The flat body of the ray is mostly the greatly enlarged pectoral fins.

A ray

Most people also know the manta ray (Manta birostris). It’s a little unusual for a ray, being pelagic and filter feeding, so the mouth is at the front tip of the body– and, it’s got those crazy cephalic fins or “horns”, from whence it gets the alternative vernacular name “devil fish”. Do note that the gills are on the bottom of the head.

A manta ray
A manta ray

There is more diversity among sharks and rays than most people realize. Sawfish, which look a lot like sharks with a saw strapped to their snout, are actually rays, but shouldn’t be confused with the similar looking saw shark, which is a shark. There are also angel sharks, which look a lot like rays, and guitarfish, which are rays that look a lot like sharks– in fact, more shark-looking than angel sharks.

I’ve never seen either angel sharks or guitarfish in any aquarium, and thus was delighted to find that Okinawa Churaumi has guitarfish (which, remember, are rays). Here’s a guitarfish surrounded by three sharks, with a typical ray off to the right (and a shadowy form below and to the right). If you look carefully, you can see the spiracle (again, whitish looking) on top of the head, behind the eye.

A guitarfish with three sharks (one only a tail), a typical ray, and a menacing black hulk).
A guitarfish with three sharks (one only a tail), a typical ray, and a shadowy form below and to the right.

In the following picture, we get a really good view of why it’s a ray. Note that the gill slits are on the bottom of the head, as is the mouth (the latter is typical, but not diagnostic, of rays). And, the pectoral fin is joined seamlessly to the head– at a point above, in fact, of the gill slits (which is why the slits are on the bottom of the head). The spiracle, already spatially distant from the other gill slits in sharks, is thus, in rays, separated from the other slits by the interposition of the enlarged pectoral fin.

The underside of a guitarfish's head
The underside of a guitarfish’s head

In the next (and last) picture, note that the dorsal, caudal, and pelvic fins all are at least passably shark-like, but that the enlarged pectoral fin is being flapped for locomotion in the manner of a ray. (Also, it’s a male– you can see the free distal ends of the claspers below the second dorsal.)

A guitarfish swimming along the bottom.
A guitarfish swimming along the bottom.

More on the Okinawa Churaumi Aquarium tomorrow.

Shark jaws

October 23, 2010 • 5:50 am

Here are two more photos from my immensely edifying visit to Jim Krupa’s lab at The University of Kentucky.  They show the extreme diversity of morphology that evolution can produce in a single group.

The first shows the jaw of what I remember as a tiger shark, Galeocerdo cuvier.  National Geographic notes that “They have sharp, highly serrated teeth and powerful jaws that allow them to crack the shells of sea turtles and clams. The stomach contents of captured tiger sharks have included stingrays, sea snakes, seals, birds, squids, and even license plates and old tires.”

The rows of teeth are lined up, waiting in the wings, to be replaced after one on duty is lost. The teeth aren’t embedded in the jaw, but merely in the gum tissue.  Wikipedia has a good article on them.

Sharks are in the class Chondrichthyes:  they have cartilage rather than bone.  The subclass Elasmobranchii includes sharks, skates and rays.  And the tiger shark is in the largest order of elasmobranchs, the Carcharhiniformes.

And here’s one of the weirdest elasmobranchs—the jaw of the Port Jackson shark (Heterodontus portusjacksoni), endemic to Australian waters.  It’s in the order Heterodontiformes (“bull sharks”), distinguished, among other things, by having the mouth completely in front of the eyes. The “Heterodontus” part of the genus name means “different teeth,” and that’s indeed what you see, spectacularly, in the jaw.  Having differentiated teeth in the jaw is very rare in sharks:

The small teeth in front are for grabbing and piercing, the ones at the rear for grinding up stuff, especially molluscs.  The Florida Museum of Natural History site notes:

This species feeds primarily on echinoderms, crustaceans, molluscs, and some small fish. Sea urchins and large gastropod molluscs are noted in almost every study on the diets of Port Jackson sharks. Stomach contents are typically ground up too small for full identification, thus leading researchers to believe Port Jackson sharks grind their food thoroughly before swallowing. This is also supported with juvenile diets, since it has been noted that juveniles eat more soft-bodied animals, and contain less molar-like teeth.

Here’s what the jaws look like in situ:

For $750 you can actually buy a Port Jackson shark for your aquarium, but I’m not sure why anyone would do that, as they grow over five feet long.

You can see the variety of sharks’ teeth here, and if you’re into buying recent or fossil teeth, here’s a place to start,

Sharks with head claspers (sort of)

September 30, 2009 • 9:00 am

by Greg Mayer

In my post on the genitalia of ratfish (which are shark relatives), I noted that although no extant sharks had similar structures, some fossil ones did, so here are what two species of these sharks looked like. Both are members of the family Stethacanthidae, known for its sexual dimorphism.Falcatus falcatus, by Smokeybjb, from WikipediaFig. 1. Female (above) and male Falcatus falcatus (Carboniferous of North America). Note the pelvic claspers on the male, and the roughened denticles atop the head, as well as on the head clasper

How exactly the male ratfish uses his head clasper during mating is obscure (at least to me), and the use of the head clasper (the spine of the first dorsal fin) in the shark Falcatus would also be obscure, except that a pair has been found fossilized in flagrante delicto, the female grasping the head clasper in her mouth, her body parallel to and above the male’s.  There would have to be more to their mating than this to bring the male’s pelvic claspers in to position, but it does provide at least a partial picture of mating and courtship in this fossil species. A nice photo of the fossil pair is at the fine website on Fossil Fishes of Bear Gulch maintained by Richard Lund and Eileen Grogan. They also have a photo of the rather similar Damocles serratus (presumably so named because its own sword [clasper] was always hanging over its head).

Equally bizarre is Stethacanthus, with a brush-like set of denticles atop the first dorsal fin, a large first dorsal fin spine, and roughened denticles atop the head. It’s not clear exactly how, or for what, this structure was used, but the fact that it occurs only in males, and that the related Falcatus (and almost certainly Damocles as well) used a similar structure in mating, suggests some sort of sexual behavior function.

Stethacanthus by Dmitry Bogdanov, from Wikipedia

Fig. 2. Male (to left) and female Stethacanthus altonensis (Carboniferous of North America).

Lund and Grogan provide further discussion and illustration at their website, and one of Lund’s papers is in the American Museum of Natural History’s digital library of its scientific publications. Matt Celeskey at the Hairy Museum of Natural History has reconstructions of both Falcatus and Stethacanthus.

Filling a demand that I didn’t know existed, in the mid 1990’s two excellent and well-illustrated popular accounts of the history of fishes were published, both emphasizing the fossil record. WEIT readers should enjoy both; Long has more on these odd sharks and ratfish.

Long, J.A. 1995. The Rise of Fishes: 500 Million Years of Evolution. Johns Hopkins University Press, Baltimore.

Maisey, J.G. 1996. Discovering Fossil Fishes. Henry Holt, New York.