Phylum Porifera

Halichondria panicea, Breadcrumb sponge Belonging to the phylum Porifera, and

really not much of an animal, is the bread crumb sponge, so called because it crumbles easily when pried off the rocks. Sponges are really a loose collection of cells, which carry out the basic functions of animal life almost independently of one another. They are the only animals to correspond to the cell aggregate plan.

Phylum Porifera

Halichondria panicea, Breadcrumb sponge

Bread crumb sponge is often camouflaged by green algae, which provides the sponge with nutrients in return for protection. For a long time, nobody even knew if the sponge was an animal. Then it was discovered that water 7was entering through tiny pores, oxygen and food was being removed, and waste was being expelled through much larger pores, which on the bread crumb sponge resemble volcanoes.

Phylum Porifera

Haliclona oculata

This sponge reaching up from the ocean floor is appropriately named deadman’s fingers. Sponges, because they are filter feeders, live in water. Many phyla are totally aquatic, and many are largely marine, that is most members are found in salt water. Sponges are permanently attached to the bottom and do not draw away when touched, as they have no nervous system nor distinct tissues or organs.

Phylum Coelenterata (Cnidaria)

Tealia felina, Dahlia anemone

Again, it is hard to believe that this is an animal. Sea anemones are commonly called the flowers of the sea. Their tentacles resemble petals. Sea anemones, jellyfish and hydroids all belong to the phylum Coelenterata. They are more complex animals than the sponge, and their design conforms to that of the blind sac plan. These animals have a single opening to take in food and expel waste.

Phylum Coelenterata (Cnidaria)

Tealia felina

Small animals that come within range of the tentacles are quickly enveloped, and the captured prey drawn into the sac where it is digested. While digesting, the anemone resembles a stewed tomato. Can you think of any disadvantages in having a single opening serving as both a mouth and an anus?

Phylum Coelenterata (Cnidaria)

Tubularia sp.

Hydroids also belong to the phylum Coelenterata, but are relatively small and inconspicuous. Like most coelenterates, hydroids have special stinging cells called cnidocytes at the tip of their tentacles. Prey brushed against the tentacles is impaled by a barb ejected from the cnidocyte.

Phylum Coelenterata (Cnidaria)

Solitary hydroid

Hydroids usually form delicate bush-like colonies, but solitary forms do exist. Reproductive structures resemble clusters of grapes.

Phylum Coelenterata (Cnidaria)

Cyanea capillata

The lion’s mane is the world’s largest jellyfish. Unlike the hydroids, some jellyfish deliver a powerful sting. With the sac opening located in the center and encircled by tentacles, jellyfish can be considered upside down sea anemones.

Phylum Coelenterata (Cnidaria)

Aurelia aurita

The moon jelly, a jellyfish, it is almost transparent as it drifts along with the currents. It’s four circular gonads, the reproductive structures, are the most visible parts of the jellyfish. All coelenterates are radially symmetrical, that is their parts are arranged around the center, like spokes on a wheel.

Phylum Nemertina (Rhynchocoela)

Amphiporus angulatus

A ribbon worm, belonging to the phylum Nemertina, moving over the bottom using hair-like cilia. Though relatively primitive, these animals are not radially, but bilaterally symmetrical, an important development.

Phylum Nemertina (Rhynchocoela)

Ph. Nemertina

Like most animals that are longer than they are wide, these worms have a head and a tail. Bilateral symmetry implies that if a line were drawn straight down the middle of this worm, it would be divided into two mirrored portions. How is this an advantage over radial symmetry?

Phylum Nemertina (Rhynchocoela)

Ph. Nemertina

These worms are remarkably elastic, and this contorted position shows the underside of this worm. With bilateral symmetry come the beginnings of features more developed in higher phyla.

Phylum Mollusca

Lunatia heros

The moon snail outdoes itself exhibiting one of the characteristics of the phylum Mollusca, the strong muscular foot used for locomotion. When foraging, the foot and the head extend out from the shell. The shell provides protection for the soft-bodied mollusk inside. And believe it or not, the moon snail is able to completely withdraw its head and large foot when threatened.

Phylum Mollusca

Littorina littorea

A party of periwinkles feed on the slimy algae covering the rocks. Mollusca is a large phylum and an important one. It is the first phylum to fully exhibit the tube within a tube body plan.

Phylum Mollusca

Aeolida sp.?

This is a nudibranch, commonly called a sea slug. Think of it as a snail removed from the shell and untwisted. With a nudibranch, the bilateral symmetry is evident; there is a definite head with tentacles, where the mouth is located, and at the tail end, an anus.

Phylum Mollusca

Coryphella rufibranchialis

Nudibranchs are beautiful animals, despite their close relation to the common garden slugs. Internally, they exhibit the tube within a tube body plan, common to the majority of bilaterally symmetrical animals. The inside tube is a digestive system; the outside tube is a fluid filled body cavity called the coelem. The coelem is of great significance in animal evolution.

Phylum Mollusca

Mytilus edulis

Within the phylum mollusca, is a class of animals called the bivalves, that is, having two shells compared to the one shell carried by the snails. In certain areas, these blue mussels completely cover the bottom.

Phylum Mollusca

Placopecten magellanicus

A large bivalve, the scallop, a large circular muscle that holds the two halves of the shell together, and it is this muscle that is the edible part of the scallop.

Phylum Mollusca

Bathypolypus arcticus, Little octupus

The octopus is a most unlikely mollusc, but it along with the squid, nautilus and cuttlefish, are grouped within the phylum Mollusca. With the squid and cuttlefish, the shell remains, but is internalized. The octopus has lost its shell entirely.

Phylum Annelida

Nereis virens

The clam worm, a worm with a difference. Its body is divided into similar rings or segments, which places it in the phylum Annelida, the segmented worms. Segmentation has improved the annelid’s ability to burrow and swim. When swimming, the clam worm is continually rewriting the letter “S”.

Phylum Annelida

Tomopteris sp.

Some annelids are very effective swimmers, and spend their whole life in the open water. Segmentation has obviously not affected the digestive tube of these worms, but the encircling tube, the fluid-filled coelem, is segmented.

Phylum Annelida

Amphitrite johnstoni

Other annelids build tubes for themselves. This annelid is normally obscured by its tube, which it constructs with the use of its long, orange tentacles. The red tentacles are for respiration.

Phylum Annelida

Pectinaria gouldii

The delicate trumpet worm – another tubeworm. It uses quartz sand grains to construct its tube. The segmented body is only visible when the worm is removed. Like many tube-dwelling annelids, it feeds by ingesting sand, extracting food particles and excreting the dirt, hence the coiled castings.

Phylum Arthropoda

Pandalus borealis

This shrimp is a member of the largest and most diverse phylum – Arthropoda. Three quarters of all animal species are arthropods. A distinguishing feature of all members is a jointed or segmented outer skeleton, known as an exoskeleton. Segmentation of the shrimp’s muscular abdomen allows for quick backward movement as well as being a delicacy for seafood fans.

Phylum Arthropoda

Gammarus oceanicus

The amphipod’s body is completely segmented. If seaweed is pulled aside or a rock lifted up at low tide, these animals demonstrate their flexibility as they hop into the air or scoot across the rocks to escape.

Classification

Carcinus maenas

The green crab exhibits the jointed legs from which the phylum derives its name, and all members share. “Arthron” for jointed as in arthritis, “pod” for leg as in tripod.

Phylum Arthropoda

Caprella sp.

A caprellid, a delicate crustacean, on a sponge. Phylum Arthropoda is also extremely diverse. Along with the largely aquatic crustaceans, it includes the largely terrestrial insects, scorpions and spiders. All arthropods exhibit the tube within a tube body plan, along with bilateral symmetry, segmentation, and a well-developed head.

Phylum Arthropoda

Pagurus acadianus

The hermit crab has taken to inhabiting the vacated homes of molluscs, the shell of the moon snail.

Phylum Arthropoda

Pagurus acadianus

The hermit crabs soft abdomen is well adapted for wrapping around the spiral interior of the snail’s shell.

Phylum Arthropoda

Balanus balanoides

At first glance, an unlikely member of the phylum arthropoda, the barnacle, can be easily mistaken for a mollusc. However, when submerged, these top plates move apart and the animal begins to feed.

Phylum Arthropoda

Balanus sp.

Barnacles extend from 3 to 6 pairs of segmented feathery legs, which trap minute food particles and then are withdrawn. A 19th century biologist described the barnacle as nothing more than a little shrimp-like animal standing on its head in a limestone house and kicking food into its mouth.

Phylum Echinodermata

Strongylocentrotus droebachiensis These are the needle-like spines of the sea urchin, which belongs to the phylum Echinodermata. Echinodermata is translated as hedgehog or spiny skin. Another common feature of this phylum, are tube feet, seen here extending between the spines.

Phylum Echinodermata

Strongylocentrotus droebachiensis

The tube feet are primarily used for locomotion, but may be used for feeding and respiration. The tube feet of the sea urchin are arranged in five rows running from the mouth on the underside to the anus on top. Sea urchins are closely related to sand dollars and sea buns.

Phylum Echinodermata

Asterias forbesii

A common seastar moving slowing using tube feet on the underside of each arm. The echinoderms are a confusing bunch, are well developed structurally, thought to extend from a bilateral ancestor, and the larvae are bilaterally symmetrical, but the adults are radially symmetrical, with no head or brain.

Phylum Echinodermata

Ophiopholis aculeata

The brittle stars are another group of echinoderms. As the name implies, their arms break off easily. The arms of the brittle star are sharply set off from the central disc.

Phylum Echinodermata

Gorgonocephalus arcticus

Another brittle star – the basket star. Though beautiful, the arms signify death for many small prey. Sometimes these animals form entangled masses and the net is spread even wider.

Phylum Echinodermata

Cucumaria frondosa

One group of echinoderms not sought after by shell collectors, the sea cucumbers. Although bearing no obvious resemblance to the seastars, sea urchins or brittle stars, the 5 rows of longitudinally arranged tube feet provide the necessary clue to indicate their relationship to other echinoderms.

Phylum Echinodermata

Psolus fabricii

When undisturbed, the crown of tentacles surrounds the mouth. Food particles are collected by the tentacles, which are then placed in the mouth and wiped off, as they are withdrawn. The anus is located at the opposite end of the animal.

Phylum Chordata

Halocynthia pyriformis

This is a sea peach, a tunicate. The name tunicate is suggested by the tough leathery tunic that covers these animals. Tunicates are filter feeders, and have an incurrent and excurrent siphon. Internally, they have a well-developed circulatory and digestive system, and therefore possess the tube within a tube body plan.

Phylum Chordata

Boltenia ovifera

Not a fruit, but a vegetable, the sea potato. Like a sea peach, but on a stalk. Tunicates are one of the most unlikely animals to bridge the gap between invertebrates and the vertebrates. But zoologists have placed the tunicates in the phylum Chordata that is, with those animals possessing a backbone. Among other similarities, tunicates in their larval stages develop the beginnings of a backbone, which later disappears.

 

Phylum Chordata

Sculpin

The fish is no borderline invertebrate, possessing a well-developed vertebral column. There is much debate as to which invertebrate phylum, the invertebrates evolved from. The phyla Annelida, Echinodermata and even Nemertina have been suggested. Whatever their origin, the invertebrates, those spineless, are an immensely fascinating and diversified group.