Lesson Outline I. Protozoans II. Porifera III. Cnidarians IV. Ctenophores V. Worm Phyla VI. Mollusks VII. Bryzoans VIII. Arthropods IX. Echinoderms X. Chordates Taxonomic Hierarchy The animal kingdom is divided into major groups called phyla .
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V. Worm Phyla
Each phylum is divided into smaller groups called classes, and so on down to the smallest groupings called genus and species:
The protozoa (“first animals”) are single-celled animal plankton called zooplankton.
Two important marine protozoa are
For example, a foraminiferan is a single celled animal that feeds on diatoms and dinoflagellates in the plankton.
The term zooplankton is also used to describe its niche. A zooplankton organism lives in the plankton and consumes other plankton, both plant and animal.
Photo: Reef Indicators Lab, USFForaminifera
Foraminifera are single-celled animals that feed on phytoplankton.
Forams have porous shells of calcium carbonate called tests.
Spines and cytoplasmic extensions from the test trap small particles of food.
Upon death, the tests fall to the ocean floor where they may comprise an important fraction of the sediments that accumulate on the deep sea bottom.
Photo: Paul HargravesRadiolaria
Radiolaria form porous, symmetrical, glass-like shells made of silica.
Like forams, radiolarians have spines to ensnare food. They also have pseudopods for capturing prey.
They are most abundant in warm equatorial waters. The bottom sediments in these regions are dominated by radiolarian “ooze”.
Photo: Columbia University DEESPorifera
The Porifera are the sponges, or the “pore-bearing” animals.
Approximately 5000 species of sponges are known, of which more than 95% are marine.
Sponges are benthic animals, found in nearly all marine regions from the intertidal to the deep-sea.
Generally, sponges are sessile, though it has been shown that some are able to move slowly (up to 4 mm per day) within aquaria.
Sponges are benthic filter feeders.
Water is drawn in through small pores in the outer walls by the beating of internal, flagellated cells.
These cells filter particles from the water as the water is pumped through the internal canals and chambers, then out other larger openings.
The flow of water through the sponge is unidirectional, driven by the beating of the flagella of the internal cells.
The name Cnidaria comes from the Greek word “cnidos”, which means stinging nettle.
The cnidarians include jellyfish, anemones, corals, and hydras.
The members of this phylum are characterized by a gelatinous bodies, tentacles, and stinging cells called cnidoblasts.
The stinging cells, cnidoblasts, contain small, sometimes toxic darts coiled up in a capsule. When the trigger is touched, the stinging cell releases the coiled, barbed thread, which wraps around or injects a paralyzing toxin into the prey.
There are three major classes within the phylum Cnidaria:
Photo: Thomas Gibson, FKNMSClass Hydrozoa
Many hydrozoans are colonial, existing as large colonies of individual members. The most well-known hydrozoans are the fire-coral and the Portuguese Man-O’War.
Fire corals often cover other structures including corals, but they are not a true coral. They are usually tan-colored with whitish tips.
Fire coral is a sessile benthic predator that kills its prey with a powerful sting.
The Portuguese Man O’War is also a colonial form of hydrozoa.
The float is a gas-filled member of the colony. Other members hang downward from the lower surface of the float; some of these have stinging cells.
These organisms are able to kill sizable fish with their tentacles.
Scyphozoans include most of the jellyfish familiar to beach-goers and divers.
Some jellyfish are pelagic, free-swimming forms of the open ocean.
Most species are planktonic, and one order, the Stauromedusae, are sessile on the ocean floor.
Jellyfish range in size 12 mm to more than 2 m across.
Their life cycle involves an alternation between sessile polyp stage and a free-swimming medusa stage, though the medusa stage, shown here, usually predominates.
This class consists of the true corals, the sea fans, and the sea anenomes.
Anthozoans live exclusively as polyps.
While they retain their stinging cells and may feed on prey or particulate food, some anthozoans supplement their diet by growing symbiotic algae in their tissues.
Most hermatypic (reef-building) corals of the tropics have symbiotic algae, called zooxanthellae, living inside their tissues.
For this reason, reef-building corals are exclusively shallow-water dwellers; without light they cannot survive (although solitary corals and anemones may inhabit much cooler and deeper waters).
Sea anemones are soft-bodied anthozoans that usually attach to rocks or coral.
They have a central mouth surrounded by tentacles with stinging cells.
Anemones are found in coastal areas all over the world, especially in warmer waters.
These are about the size of a fist, and have a jelly-like body. Comb jellies are not jellyfish, and they lack stinging cells.
Ctenophores entrap plankton and detritus with a single pair of tentacles out the back of the animal. Their niche is that of a plankton predator.
The marine species in these groups are primarily benthic detritus feeders, an important niche at the base of the detritus food chain.
Among the more than 50,000 mollusks are some of the most familiar invertebrate marine species, such as clams, snails, and the octopus.
Most species of mollusks are benthic, but there are a few pelagic forms, like the nautilus and squid.
There are seven classes of mollusks, five of which contain the predominant marine species:
Members of the subclass Polyplacophora (“many plates”) are more commonly called the chitons.
Chitons are benthic algae feeders that move slowly along hard surfaces.
Chitons have an eight part shell with overlapping plates.
Often found in the intertidal zone and on sea walls, a chiton uses its muscular foot to attach itself tightly to surfaces.
The scaphopods, or tusk shells, are a small group of benthic detritus feeders.
They are sedentary animals with a slender, tubular shell open at both ends.
Scaphopods have a well-developed foot, used for burrowing, located at the large end of the shell.
The bivalves (“two shells”) are perhaps the most well known mollusks because they are a source of food for humans.
Clams, mussels, oysters and scallops are all bivalves. There are about 15,000 known species of bivalves, about 80% of them marine.
Most species of bivalves are benthic filter feeders.
A few species are very motile, like scallops that can swim quickly by opening and shutting their shells. Others, like the clams, can move slowly through the mud on a muscular foot. Still other bivalves, like oysters and mussels, are sessile.
While most bivalves are benthic as adults, they have a planktonic larval stage to allow for them to populate new areas of sea floor.
The gastropods (“stomach-foot”) make up about 70% of Molluscan species (around 35,000).
Most gastropodshave spiral shells, like the conchs, snails, and whelks. A few species do not have any shell.
Many have a radula that is used to bore through the shell of a clam or snail to eat the animal inside.
Conchs snails are an important source of protein in many tropical island areas of the Caribbean.
There are a few cone shells in the central Pacific Ocean that can shoot a poison dart up to a few inches that is lethal to humans.
While cephalopods (“head-footed”) look different from the other mollusks, they are similar in internal construction.
The most obvious difference between most cephalopods and other mollusks is the apparent lack of a shell. The octopods do not have shells at all; the squid have a small internal shell. Nautiluses are the only cephalopods with an external shell.
Squids have a streamlined tube shape, with 10 tentacles, two being longer and having “suction cups” on the end.
Squids swim normally with a pair of fleshy fins on each side, and can go in either direction, or just “hover” in one place.
However, they can escape swiftly with a “jet propulsion” by blasting water out of their mantle cavity through their siphon, even adding ink to confuse a predator.
The octopus is a benthic predator, feeding mainly on crabs.
The Bryozoa (“moss animals”) are benthic filter feeders, consuming bits of detritus and plankton as the water passes by .
Bryozoans form colonies attached to rocks and other hard surfaces, and are often among the first organisms to grow on hard substrate (natural or artificial).
Arthropods (“joint-foot”) have jointed appendages. This class includes crabs, lobsters, shrimp, barnacles.
Arthropods have rigid exoskeletons made of chitin, a type of carbohydrate with nitrogen. Aquatic species often have calcium carbonate in it for extra strength. The skeleton provides protection for the animals, and gives support for the internal attachment of the arthropod’s muscles.
Although arthropods grow, their exoskeletons do not grow with them. So they must periodically shed, or “molt” their exoskeletons in favor of a new one. Lost limbs can gradually be regenerated after successive moltings.
1. Copepoda: Copepods
2. Euphausiacea: Krill
3. Ostracoda: Ostracods
4. Brachiopoda: Brine shrimp
5. Cirripedia: Barnacles
6. Decopoda: Shrimp, lobster, crabs
7. Xiphosura: Horseshoe crabs
8. Stomatopoda: Mantis shrimp
Copepods are small crustaceans that are the most important zooplankton. They are found almost everywhere where water is available and they constitute the biggest source of protein in the oceans. Most of the economically important fisheries depend on copepods.
After copepods, Euphausiidsare the second most important zooplankton group in the world oceans.
Most are herbivorous, but some are omnivorous feeders.
Commonly known as “krill”, they are a major food source for adult fish, seals, whales and birds.
Larval and immature fish feed on the smaller juvenile euphausiids.
Krill live in the dark, at 100 meters or more by day. Many adults migrate to the surface at night to feed on the phytoplankton.
A feature that distinguishes an ostracod from other crustaceans is the carapace that encloses the body.
Within the carapace are several pairs of short limbs which enable the animal to scramble around and feed on the floor of the sea.
Commonly referred to as “brine shrimp”.
Despite a superficially similar appearance to clams, they are actually completely different in their anatomy.
They use a fringe of tentacles known as the lophophore to sweep food particles into their mouths.
Barnacles attach themselves upside down on a rock with their feet in the water.
Inside the “shell” of a barnacle is a segmented body with six pairs of segmented legs used for filter-feeding from the water.
More than 8,000 species of crustaceans that include shrimp, lobsters, crayfish, hermit crabs, and crabs. Decapods are arthropods with ten main legs. One or more of the five pair may be modified as claws. The walking legs are associated with a skeletal structure called the carapace, which covers both the head and the thorax.
Horseshoe crabs, common in Tampa Bay, have evolved little in the last 250 million years. They have survived because of their hard, curved shell, which makes it difficult for predators to overturn them and expose their soft, vulnerable undersides. The horseshoe crab can go a year without eating and endure extreme temperatures and salinity.
Stomatopods are predatory crustaceans that live in the shallow waters of tropical and subtropical seas. They are not closely related to shrimps or the other decapod crustaceans, although they are commonly known as “mantis shrimp” due to the raptorial appendages that they use to efficiently capture and subdue prey.
These animals range in size from 1-2 cm to more than 30 cm, and are one of the most aggressive and pugnacious of all creatures.
Up to 4 cm in length, arrow worms, which are not actually worms, have elongated transparent bodies with fin-like appendages that give the appearance of an arrow.
They remain almost motionless in the water, but are capable of swift darting motions when pursuing prey.
Arrow worms feed voraciously on smaller zooplankton, which they capture with a cluster of small chitinous hooks located near the mouth.
There are about 6000 species of this phylum, whose name literally means “spiny skin.” Starfish and sea urchins are several well known members of this group.
Echinoderms live in the sea only, none inhabit land or fresh water. All echinoderms exhibit radial symmetry, that is, the creatures have appendages (or body construction) which point outward from the center of the body like the spokes on a bicycle wheel. These appendages usually occur in multiples of five, although there are a few exceptions.
1. Crinodea: Sea Lilly
2. Asteroidea: Starfish
3. Holothuroidea: Sea cucumber
4. Echinoidea: Sea urchin & sand dollar
5. Ophiuroidea: Brittle star & Basket star
Sea lilies and feather stars. All crinoids are passive suspension feeders. They produce no feeding/respiratory current but rely on ambient water movement.
Asteroids, or sea stars, have arms which seem to connect together in such a way as to make it difficult to discern where the arms end and the central disk begins. Sea stars are capable of regenerating limbs in the event that one or more is severed or damaged.
This class is composed of animals known as sea cucumbers. The sea cucumber feeds by positioning itself in a spot on the sea floor where a current will bring a steady supply of food (plankton and other organic particles) its way. The tentacles are opened to collect the food. Then, the cucumber sticks each tentacle in its mouth, one at a time, and ‘licks’ them off.
Sea urchins, heart urchins, cake urchins and familiar sand dollars. Most sea urchins have a large number of sharp spines pointing out in all directions. These spines offer protection from many would-be predators.
Brittle stars and basket stars. Ophiuroids have a distinct central body part (called a central disk) with arms radiating out from the body. Adjacent arms do not connect with each other.
rod-like, semi-rigid supporting structure
2. Dorsal Hollow Nerve Tube
the top of the nerve tube is often enlarged to form the brain
3. Gill Slits
always present in embryonic stages, fish retain them as adults while mammals develop lungs
Tunicates that are common in local waters are benthic filter feeders.
They are named for their outer coating, or “tunic” that is indigestible to predators.
These species are only two to four inches long and live in grass bottom communities filter feeding with a very efficient pharynx.
There are seven classes of vertebrates, only six have marine species.
While the first agnathans were detritus feeders, modern ones are parasites or scavengers.
The lamprey is an “eel like” fish that attaches to the sides of host fish and sucks its body fluids until it is near dead, then moves on to another fish.
The hagfish are “eel like” scavengers that burrow into the body cavity of dead fish and eat from the inside out.
Sharks and rays are both pelagic and benthic predators or scavengers, feeding on everything from mollusks to large fish.
These fish have flexible skeletons made of cartilage instead of bone. Only their teeth (and in some cases the vertebrae or scales) have calcium.
Many shark species have a lateral line, a line of sensory organs running down the side of the body, that detects minute changes in water pressure caused by a fish swimming nearby.
Photo: The Florida AquariumSkates and Rays
Most rays are benthic predators, feeding on crabs and other shellfish.
They are generally not a threat to humans, but the stingray can deliver a very painful sting if stepped on.
This class includes most of what we typically call fish, for example trout, grouper, goldfish, and sea horses.
They occupy a wide variety of niches from herbivores to top predators.
There are eight species of sea turtles, five are found in Florida waters.
All sea turtles come ashore to deposit eggs on the beach.
All eight species of sea turtles are endangered and protected by state and federal laws.
Another member of marine reptiles are the sea snakes.
All sea snakes are deadly poisonous, much like a cobra and a coral snake, but fortunately for humans, they are fairly docile.
Some sea snakes bear their young live; some come ashore to lay their eggs.
Sea snakes are found only in the Pacific and Indian Oceans.
The crocodile is also a marine reptile, living in both fresh water and in estuaries.
The type in Florida is not considered dangerous to humans, but the type found in Africa and Australia is very dangerous and even attacks a few humans every year.
There is also a marine lizard that lives in parts of the Pacific that feeds on benthic algae but spends much of its time on rocks along the shore.
The penguin has given up flight and now uses its wings as swimming flippers and feeds on fish and krill.
Other birds spend much of their time at sea feeding on fish, but must come ashore to build their nests and lay their eggs.
Even though these mammals do not live on land now, they still must breathe air through lungs.
The seals, sea lions, and sea otters are also mammals that spend much of their life at sea but also can live on land, if necessary.
All marine mammals are protected by both state and federal Laws.