Plankton are autotrophic, prokaryotic or eukaryotic algae that live near the water surface where there is sufficient light to support. They inhabit oceans, seas, lakes, and ponds. All plankton ecosystems are driven by the input of solar energy. Zooplankton provides carbon to the planktic food web, either respiring metabolic energy, or upon death as biomass or detritus. They are the initial prey for almost all fish larvae as they switch from their yolk sacs to external feeding. They provide a crucial source of food to larger, more familiar aquatic organisms such as fish and whales.

The common jellyfish feeds by collecting medusa, plankton and mollusks with its mucus bell nematocyst-laden tentacles and bringing the prey into its body for digestion. They are found throughout most of the world’s oceans. They do not have respiratory parts such as gills, lungs, or trachea. It is a small organism, so it respires by diffusing oxygen from water though the thin membrane covering its body. It is probably rare for these to live more than about six months in the wild.

The hermit crab species have long, spirally curved abdomens, which are soft. The abdomen is protected from predators by a salvaged empty seashell carries by the hermit crab, into which its whole body can retract. As the crab grows in size, it has to find a larger shell and abandon the previous one. If the hermit crab cannot find a well-fitting shell, it will most likely be eaten.

Sea cucumbers are echinoderms from the class Holothuroidea. They are marine animals with leathery skin and an elongated body containing a single, branched gonad. Sea cucumbers are scavengers found on the sea floor worldwide. They all have an endoskeleton just below the skin. They catch collagen that forms their body wall. This can be loosed and tightened at will, and if the animal wants to squeeze through a small gap, it can liquefy its body and pour it into the space. To keep itself safe, the sea cucumber will hook up all the fibres to make its body firm again.

Brittle stars are echinoderms in the class Ophiuroidea and are closely related to starfish. They crawl across the seafloor using their flexible arms for locomotion. The ophiuroids generally have five long slender, whip-like. This species can readily regenerate lost arms or arm segments unless all arms are lost. They use this ability to escape predators. They move fairly rapidly by wriggling their arms which are highly flexible and enable the animals to make snake-like movements. They live in areas from the low-tide level downwards.

Sea Vases are widely distributed in Northern European waters, but they have also spread to other parts of the world. The soft, smooth, translucent tunic is pale yellow or green in color with orange body parts visible through the translucent tunic. Since Darwin’s time, they have been recognized as being possibly the closest invertebrate relative of humans.

Oysters are filter feeders, drawing water in over their gills through the beating of cilia. Suspended plankton and particles are trapped in the mucus of the gill, and from there are transported to the mouth, where they are eaten, digested and expelled. Oysters provide habitat for many marine species. The hard surfaces of oyster shells and the nooks between the shells provide places where a host of small animals can live. Oysters consume nitrogen and remove them from the water.
Clamworms have been recorded throughout Europe and the North West Atlantic, as well as in the Gulf of Maine and South Africa. It is a scavenger on the bottom of shallow marine waters and feeds on other worms and algae. To feed, it uses a proboscis, which has two hooks at the end, to grasp prey and draw it into its mouth. They can protect themselves by secreting a mucus substance that hardens to form a sheath around them.
Metridium are sea anemones found mostly in the cooler waters of the northern Pacific and Atlantic oceans. They are characterized by their numerous threadlike tentacles. In larger specimens, the oral disk becomes densely curved and frilly.
Barnacles are typed of anthropods. They tend to live in shallow and tidal waters and are sessile. They are encrusters so they attach themselves permanently to a hard substrate. They are well adapted against water loss and their calcite shells are impermeable.

Oyster drills can be found to the Atlantic coast of North America, from Nova Scotia to Florida. They live in low tide down to a depth of 25 feet. They are a species of predatory sea snail and their species is a serious problem in commercial oyster beds, and it has been accidentally introduced well outside of its natural range.

Bugula are a very common found from Maine to North Carolina. Bugula neritina is of current interest as a source of cytotoxic chemicals, and are under investigation as anti-cancer agents.

Chitons have a dorsal shell which is composed of eight separate shell plates or valves. They live worldwide, in cold water and in the tropics. Most of them inhabit intertidal or sub tidal zones and do not extend beyond the photic zone. They live on hard surfaces, such as on or under rocks, or in rock crevices. They creep along slowly on a muscular foot and have a considerable power of adhesion.

Ribbed mussels are found on the New Zealand and South American coasts, as well as from Namibia to Port Alfred, South Africa. This animal grows up to 9 mm in length and usually lives in crowded intertidal beds. They are filter feeders so they eat floating scraps of algae and phytoplankton.
Spirorbis is a genus of very small worms that usually live with a white coiled shell. They live in rocky shores and they are usually attached to seaweeds, but some live directly on rocks, shells, or other hard substitutes.