Ashlan Cousteau

Elasmobranchii (pronounced ee-laz-mo-brank-ee-ee) are a familiar subclass of fish that includes some of the most misunderstood and maligned creatures in the world—sharks, skates, and rays. They’re characterized by a rigid dorsal fin (the top fin) and have four to seven pairs of gill slits to breathe.They’re all carnivorous, feeding on everything from large marine mammals to small crustaceans, and they lack a swim bladder, equipped instead with an oily liver to maintain buoyancy.

Osteichthyes (pronounced ah-stee-ick-thees) is a class of about 28,000 fish characterized (in most forms) by a bony skeleton, scales (some without), paired fins, a single pair of gill openings supported by bony gill arches each covered by an operculum, jaws, a mouth with many teeth, a swim bladder (air-filled sack) for buoyancy, paired nostrils, and external fertilization of eggs.

Bivalves are headless mollusks with a hinged, two-part shell, sort of like castanets. They’re very diverse, boasting a membership of more than 15,000 species divided into four main groups—clams, oysters, mussels, and scallops—generally based on where they live and the shape of their shells. Clams prefer an infaunal lifestyle, buried in the sand or silt, whereas mussels, oysters, and scallops live a more epifaunal lifestyle (on or above the seafloor).

While gastropod means stomach on a foot, cephalopod means head on a foot, but with these mollusks, the pod (foot) has evolved into many prehensile arms/tentacles, which may be equipped with suction cups, hooks, or gooey mucus to catch prey and perform other functions. Yes, we’re talking octopus and squid, and their close cousins, the nautilus and cuttlefish.

An ecosystem is a biological community of organisms interacting with their physical environment as a whole. Take a tour of three of the ocean’s varied ecosystems and some of the plants and animals that call them home. Swimming through Kelp Forests Imagine flying free through a giant forest surrounded by beautiful colors and bizarre, extraordinary animals.

The largest group in the mollusk family (accounting for about 80 percent of all mollusk species), is the class Gastropoda, which literally means a stomach with a foot on it. The name strikes us as more than a little demeaning, not to mention inaccurate—after all, snails and most slugs have easily recognizable heads and a complex anatomy, including a liver, lung, heart, kidney, a primitive brain, and, yes, a stomach.

Shoreline (littoral) ecosystems are those that follow the coastlines, where land and water meet. Think of them as the transition from land to sea. They’re generally wet or at least damp most of the time, and salty, but water and salt content vary based on how far inland you go and on the terrain and climate of the area.

The ocean’s water column (a conceptual pillar of water measured from the ocean’s surface to the seafloor) is often divided into five zones—the epipelagic, mesopelagic, bathypelagic, abyssopelagic, and hadalpelagic zones. The divisions generally correspond to differences in depth, amount of sunlight, temperature, pressure, nutrients, and organisms that live in those zones.

A reef is a ridge of rock, sand, or coral near the surface of the water, but because this article is about ecosystems, we’re going to focus on reefs that are teaming with life—coral reefs and oyster reefs. Coral and oysters, respectively, are responsible for building the foundation on which these living reefs grow.