Jellyfish range in size from as tiny as a pinhead to larger than a human with diets that vary accordingly. Jellyfish feed on phytoplankton, copepods, fish eggs, larvae and even other jellyfish. They form large swarms known as blooms that eat almost everything in the water around them. Most jellyfish species passively hunt and eat whatever tangles in their tentacles, but some swim and chase their prey.
Found in both fresh and saltwater and in every ocean at various temperatures and depths, jellyfish have evolved a highly sensitive nervous system designed to help them hunt. They have a simple digestive system with a gastrovascular cavity and an opening that functions as the mouth. Jellyfish are largely carnivorous, their tentacles lined with stinging capsules or venom that stuns their prey. The arms around the opening catch and bring their prey to the jellyfish's mouth, and the digestive process begins almost immediately. Jellyfish excrete waste through this opening as well. Some species are aggressive and have potent venom in their tentacles that paralyzes or kills their prey. The box jellyfish in particular is an excellent and swift swimmer. Other species are filter feeders, consuming seawater and whatever edible items it contains, including zooplankton, eggs and larvae.Learn More
According to the St. Lawrence Global Observatory, lobsters prefer rocky ocean bottoms covered with algae. They can hide in the rocks, and the algae makes it easier for them to blend in. The algae also attracts food for the lobsters. When lobsters cannot find rocks, they will burrow into pebbles, sand, or clay. Lobsters stay at the entrance of their shelters, claws out so they can defend themselves.Full Answer >
Krill live in all the oceans of the world, the most abundant of which is Antarctic krill. This species, found in the Southern Ocean, has an accumulated weight of between 125 million to 6 billion tons.Full Answer >
The ambulacral groove is a deep linear depression located in the ambulacrum in some echinoderms such as starfish. The ambulacrum is an area in echinoderms that is marked by calcitic plates and located over the radial canals of the internal water-vascular system.Full Answer >
Sharks and whales are enormous ocean creatures that have large, torpedo-shaped bodies and dorsal fins. Both species swim well in the water, use their senses to catch prey and, as meat eaters, rely on carnivorous food to survive. Both the shark and whale have large teeth and huge jaws, and neither seem to show mercy when they kill.Full Answer >