Fish Shapes

Today in class we discussed fish mouth shape and body shape and what they mean about the fish.

Many fishes are identified by looking at or into the mouth. The number of mouth-types exhibited by different species is nothing short of astonishing. Three lakes in Africa contained about 900 species of cichlids, nearly all differentiated mainly by the way their mouths are shaped. (This number is rapidly dwindling, by the way, as the cichlids in these lakes are driven to extinction). Cichlid mouths are variously adapted to eat other cichlids' eggs, scales pulled from fishes' living bodies, algae from rocks, tiny invertebrates, and many other forms of food. The arrowana of South America has a mouth adapted for spitting water with precision at insects perched on overhead branches. Parrotfish mouths have evolved to look and act like beaks, which they use to grind at coral, making the sand that surrounds coral reefs. Seahorses and pipefish have tubular mouths for sucking in small prey in narrow places like a vacuum cleaner.  SOURCE

Fish with forward facing mouths eat what is in front of them - no surprise. Downward mouths eat algae, prey below them like crustaceans and molluscs, or they take in mouth fulls of gravel, eat the particles, and spit the gravel back out. Upward facing mouths indicate the fish eats prey above them - typical of benthic ambush predators. There are also bills and beaks. Bills are long and skinny used for poking in crevices and eating plankton one at a time. Beaks are used for chomping and can be seen on the parrotfish, a fish that chomps on the algae growing on the surface of dead coral. Fish can also have very large mouths common on filter feeders and fish that swallow large prey whole. Fish also have teeth - a surprise to many - and come in many shapes and size.

Body shape also tells you a bit about a fish. Com- pressed fish have flash and look skinny and can only be found in slow moving waters like coral reefs. Fusi-form fish are tapered like footballs and are very streamlined for constant fast swimming. Depressed fish are benthic and squashed looking. Eel shaped fish are poor swimmers and live on the benthos or in cracks and crevices.

Here is a website you can use to identify shapes - realize they are named a bit differently than how I do in class.

Jawless Fish

Today we discusses jawless fish. Jawless fish are primitive fish with a notochord instead of a backbone and a flat rasping mouth that cannot close like ours. As a result thes fish cannot bite... only scrape and hold on.

Pictured to the right, you can see five lamprey mouths and one lamprey head with blue eyes and seven gill holes.

Jawless fish include lampreys which are parasites and hagfish which are detritavores. Neither one will ever win a beauty contest.

Echinoderms

Echinoderm means spiny skin. Echinoderms include sea urchins, sea stars, sand dollars, sea cucumbers and some other odd organisms like feather stars and basket stars. All echinoderms have radial symmetry, spiny skin, and an endoskeleton called a test.

Most people are familiar with an orange sea star because on the east coast, that's all we've got. On the west coast and in other places around the world, it is easier to find a variety of sea stars in other colors and with different amounts of legs.

Sea stars have powerful tube feet that use water suction to open molluscs. When they eat molluscs, they actually stick their stomach into the shells of the mollusc, digest it, and then put their stomach.



Feather stars and basket stars both have crazy looking legs that they wave around to filter feed. Sea urchins and sand dollars are both covered with protective spines and eat with a scraping mouth called Aristotle's Lantern.

Sea cucumbers have lost most of their exoskeleton and are a bit squishier than other echinoderms. Sea cucumbers are important detritus eaters on the sea floor. When attacked by predators they will expel their guts as a meal for the predator as they make a get away. Sea cucumbers are able to regenerate these guts over time.

Crustacean Basics - A Review for Marine Ecology Class

Crustaceans have bilateral symmetry and a hard crunchy exoskeleton. Because the crustacean grows and the exoskeleton does not, crustaceans have to molt or shed their hard outercovering, exposing a new softer bigger covering that will harden in a few days.

LOBSTERS
There are two basic lobsters to be familiar with - the clawed lobster and the spiny lobster. Both are primarily scavengers. The clawed lobster has two different claws - a lighter faster shredder and a heavier more powerful crusher. The clawed lobster is more solitary because it is more aggressive. The spiny lobster does not have big claws, but can defend itself with its long whip like antennae. This lobster likes to congregate in groups and is not as aggressive. Both lobsters carry their eggs on the swimmerettes protecting them from potential predators.

Left: male ; Right: Female

CRABS - In general, you can tell the difference between boy crabs and girl crabs by looking at the shape of the plate on the abdomen. Boys have a thinner more pointy plate, girls have a wider more rounded plate because it is used to hold the egg mass. The mothers carry the eggs because not many predators will mess with them to get to the eggs.

• Blue Crabs are found in the Chesapeake Bay. They are very agressive, like to pinch, but are good to eat. They have a pointy-ended shell and swim fins. (you can kind of see the swim fins on the last leg of the crabs on the right)
• Spider Crabs have a rounder body shape, often a bumpy shell that will grow algae for camouflage, and longer more spindly legs. Spider Crabs include snow crabs and king crabs like the ones seen on Deadliest Catch. A decorator crab is a kind of spider crab that attaches stuff to its bumpy shell to blend in.
• Fiddler Crab males have one claw that is a lot bigger than the other. This is for impressing the ladies, and used to show dominance over other males. 
• Hermit Crabs have a weak exoskeleton and thus protect it with a stolen mollusc shell. They have adapted to this lifestyle and have modified back legs that hook on the inside to hold the shell on and one claw that is slightly larger to use as an operculum.

SHRIMP - miniature lobsters... use their swimmerettes to keep themselves moving - most Americans have never seen one with its head and legs still attached!

• Gulf shrimp are the ones people most people are familiar with because these are the ones we eat!
• Shore shrimp live in sea grasses, are fairly small and clear, and are not commercially harvested because no one would make any money.
• Snapping shrimp (or pistol shrimp) have slightly larger claws and can use them to make sonic waves to stun their prey with sound. 
• Mantis shrimp whack their prey with arms that can unfold and strike lightning quick. 
• Cleaner shrimp make their living eating parasites off of fish and other sea creatures. 

BARNACLES
If you look at a diagram, barnacles are like little shrimp glued on their backs with a white fence around them. They stick their feathery legs out to filter feed plankton. They are plankton for a while and once settled and glues onto a hard substrate never move again. This makes mating difficult, but the hermaphroditic barnacles have special talents. Gooseneck barnacles have a stalk that they attach to substrates with.

Nudibranchs - Sea Slugs

Nudibranch (naked-gills) are sea slugs that have lost the ability to make a shell over evolutionary history. They do however have some interesting adaptations to keep from getting eaten. Most nudibranch exhibit warning coloration because they are poisonous or have stingers - none that they make - they acquire them from the prey that they eat!

National Geographic did a great article a few years ago full of lovely photos. Both are linked here. Watch the video for a full-range spectrum of photos.

local bivalves

Most people do not know that there are freshwater clams and mussels in Lake Anna and that they can get as big as the palm of your hand. Nathan, a former student, did his Governor's School project about some of the habitat in the lake and I has asked him to bring in some of these beauties so we could get a good look at them. With the help of his brother, a current student, brought in three little clams for us to enjoy in class a few semesters back.

I found that taking pictures of them in the cup was not easy, but using the document camera, I was able to project an up close view of them onto the wall so that everyone could see the clams and their siphons in detail. Students were able to watch the clams in action while taking their practical. Now that may seem like an oxymoron - clams in action... but there was stuff to see.

You could clearly see the siphons and at times see particles being sucked into the siphons. I put some fish food in the cup and the suction power of the clams was enough to create a current that caused the fish flakes to swirl around in the top of the cup. In first period we were able to watch one of the clams use its foot to dig into the sand to sit upright with its siphons up.

So get to the Lake and have a look!

Cephalopods

Today students explored the wonders of cephalopods. Cephalopod means head-foot and includes octopi, squid, cuttlefish, and the chambered nautilus.

Cephalopods are characterized by their large well developed eyes, numerous tentacles, a parrot like beak in the center of the tentacles, and well developed chromatophores in their skin that allow them to change color.

We watched numerous videos today to see and understand how and why cephalopods make ink clouds, to see how an octopus can swim with jet propulsion or use its tentacles to crawl around, and we also saw how a octopus can eat a shark! Below is a video that I took at an aquarium that shows how an octopus uses its tentacles and suckers to move.


For more information about cephalopods, check out CephBase and the Australian Cephalopod Research page.
Students read a historical narrative about sea monsters and how those stories of the Kraken were based on squid sightings. We have known about the giant squid for several hundred years because of dead specimens and pieces found, but the first live one was not observed until 2005. Sailors used to think that the giant squid was much bigger because of a measurement error. Sucker marks on sperm whales were used to estimate size until they relaized that those marks and scars grew bigger as the whale grew.

Students then read a fictional account about a squid attacking the Jersey Shore (article pictured at left) and had to identify what parts of the stories were accurately portraying the squid and which parts were inaccurate.

Gastropods

Gastropod means "stomach foot" and includes all snails and anything else that makes one shell. Gastropods have one foot, one shell, and one siphon.

Some shells are spiral and have an operculum to act as a door for when they hide inside. The snail lives in the entire shell (all the way up into the top and retreats inside to hide when it feels threatened or exposed. The operculum blocks any would-be attackers and is made of a material similar to fingernails. These types of molluscs include whelks and moon snails.

Other shells are not spiral and the snail has good suction power so that predators have a difficult time pulling the snail off the rocks. These types of molluscs include slipper snails, abalones, and limpets.

Pearls

Pearls can be made by any mollusc that has a shell. I passed around my pearls and some shells that I have with pearls on the sides - not all pearls are free floating - they can be attached to the side of a shell. A mollusc makes a pearl to cover an irritating spot like a piece of sand that gets inside the shell. Pearls can be "glued" to the side of the shell or free to move inside the mollsucs shell. We prefer the "free" kind.

Any mollusk that produces a shell can produce a pearl. Nevertheless, naturally occurring pearls are rare, found in perhaps one of every 10,000 animals. The cultured pearl industry, which has flourished since the early 20th century, has developed techniques to greatly improve these odds. Indeed, more pearls are produced now than at any time in human history.( SOURCE This is a good website for lots of information on pearls)

Sally Sells Sea Shells

Students are in the midst of Unit 4 Molluscs busily learning about the different classes of Molluscs and trying to learn a variety of sea shells. Students lhave earned the basics about sea shells

• The shells found on the beach are from dead organisms.
• Any mollusc that has a shell, makes it shell.
• Sea shells are made of calcium carbonate.
• Shells are smooth on the inside because slimy molluscs don't want to rub their soft bodies on something rough. If they are smooth on the outside, then the mollusc also wears its body on the outside of its shell.

Today's cool mollusc was the chiton, an odd mollusc that has 8 overlapping plates held together by its soft squishy mantle, and the plates come apart when the animal dies. Chitons are built like armored cars and have great suction to stay on the rocky coast in waves and storms. They spend their days sliming around scraping algae. When pulled off a rock, it can roll into a ball to protect its squishy parts. More info can be found here.

Students also learned the four major classes of bivalves - clams, mussels, oysters, and scallops. Bivalves have 2 shells and 2 siphons, as well as adductor muscles to help keep their shells from opening for hungry predators. Bivalves include some of the more well know shellfish like scallops, clams, oysters, and scallops as well as a few like jingles, ark shells, and cockles. Pictured to the right are a clam (tan), oyster (grey), and mussel (black).

Mussels make byssal threads for attaching (so do ark shells and jingle shells) and scallops have eyespots to see predators. Oysters make cement to stick together and clams have a powerful foot for digging down and hiding.