Sponges and Cnidarians

By: Elina Shapiro and Gilbert Hernandez

Phylum Porifera (Sponges)

Porifera or sponges are the simplest animal in the animal kingdom. They have no tissues, muscles, nerves, or internal organs. Instead their cells perform actions that organs are supposed to. There are 5,000 species known to man including the vase sponge (Ircinia campana), the yellow sponge (Cleona celata), and the sea squirt (Didemnum molle).

Common Sea Squirt

Vase Sponge Yellow Sponge

Evolution

Sponges are undoubtedly the first fossils recovered. They date all the way back to the Precambrian era.

Symmetry and Body Cavity

Sponges are asymmetrical and acoelomate.

Body Structure

Sponges have three body types: asconoid, syconoid, and leuconoid

Asconoid- Are tube-shaped and have a central shaft called the spongocoel.

Syconoid- Similar to asconoids they have a tubular body but are more complex. These have collar-cell-lined radial canals that empty into the spongocoel. Water enters through canals and then filters through tiny holes called prosopyles into the radial canals. Food is there ingested by the collar cells. Syconoids usually don’t form colonies like asconoids do. However, during their development syconoid sponges do pass through the asconoid stage.

Body Structure Cont.

Leuconoid- These don’t have a spongocoel and instead have chambers that contain collar cells. The only way in or out is through canals.

Skeleton

A sponge skeleton is made up of calcium carbonate or silicon dioxide that are in the for of spicules (stiffened rods or spikes which are also used for defense). Some don’t even have a skeleton.

Nutrition and Digestion

They feed by filtering food particles (sometimes bacteria) out of the water using choanocytes (collar cells). Choanocytes create the water currents by beating their flagella. Sponges don’t have a real digestive system but they do use choanocytes to digest the food particles.

Transportation and Circulation

While in the larvae stage sponges float along by means of water currents. As adults they don’t move at all (they’re sessil). A sponge has water flow in through its pores.

Respiration

Sponges don’t have a respiratory system. They pump water all through their canals and extract oxygen from the water.

Water Balance and Excretion

Sponges beat the flagella of certain cells to pump water in or out. And they don’t have excretory organs so wastes leaves with water.

Reproduction

Sponges can reproduce sexually and asexually.

Asexually- They reproduce by budding internally or externally. The new sponges are exactly like their parent.

Reproduction Cont.

Sexually- Even though sponges are hermaphroditic they don’t fertilize their eggs with their own sperm (which would be asexual reproduction). Instead all the sponges of the same species release sperm on one night (usually the full moon) and fertilize each other in the water. The new sponges are different from either parent.

Nervous System

Sponges don’t have a nervous system. They don’t have nerve or sensory cells.

Classes

The three classes of sponges are:

Calcarea

Hexactinellida

Demospongiae

Phylum Cnidaria

The Phylum Cnidaria has thousands of living species worldwide, which include hydroids, jellyfish [ like the Physalia physalis (the Portuguese Man of War)], anemones, and corals.

The Portuguese man of war

Evolution

Cnidarians were one of the first recognized animal fossils. They can be dated back 550 million years ago.

The first Cnidarians that were made of soft tissue only remain today in exceptional cases.

The first coral reefs date back 500 million years and structurally differ from the ones today.

Body Structure

Cnidarians can have one of two basic body types: polypoid or medusoid

Polypoids- have tentacles and a mouths generally facing up and the other side connected to a colony of other creatures of the same species.They also have sturdy skeletons. A couple of examples of cnidarians with polypoid body structures would be corals and sea anemones.

Body Structure Cont.

Medusoids- this organism is basically upside-down, with the mouth and tentacles usually pointed down. These types of Cnidarians are generally free-swimmers like jellyfish.

Skeleton

Their endoskeleton is the mesoglea and their exoskeleton is made up of calcium carbonate and chitin.

Symmetry and Body Cavity

Cnidarians are radially symmetrical and they are acoelomate

Nutrition

Most Cnidarians feed on prey that come into contact with their tentacles. These usually include large protists, crabs, worms, fish, and even other cnidarians.

Others like coral live symbiotically with algae (dinoflagellates and even sometimes chlorophyta). They absorb the carbon dioxide produced by the Cnidarians, sunlight via photosynthesis and release oxygen, the algae produce carbohydrates which the Cnidarians use as a main food source.

Digestion and Excretion

Since Cnidarians don’t have any organs the gastrovascular cavity serves as their stomach and anus. It ingests food and then secretes digestive enzymes which break the food down into small particles that are digested into the cells lining gut. And the waste is secreted out of where it came in.

Transportation and Circulation

The nerve net and nerves control the movement throughout their body. And Cnidarians have not true circulatory system.

Respiration

Cnidarians don’t have a real respiratory system. Instead respiration takes place through diffusion of oxygen directly through their tissues without specialized organs like the trachea, lungs or even gills.

Water Balance

Cnidarians diffuse water through their tissue.

ReproductionThey can reproduce both sexually and asexually.

Asexual- Asexual larvae bud laterally from adult polypoid and develop into polypoids themselves. Budding is usually incomplete so colonies of identical polypoids tend to form.

Sexually- A key characteristic here is the alteration of generations. Which is when a asexually reproducing organism reproduces and has an organism that can reproduce sexually.

Reproduction Cont.

These grow to full maturity and then release the male and female gametes. Those then unite to form a zygote. This forms a spherical structure (the blastula) through cell division. The larvae then forms from the blastula. The larvae then swims until it finds a surface to attach to. Then it passes through metamorphasis to the polypoid stage.

Nervous System

Is a nerve net that has a network of nerve fibers that can communicate when they overlap.

Classes

The four classes of cnidarians are

Cubozoa (Medusoid)

Scythozoa (Medusoid)

Hydrozoa (Medusoid and Polypoid)

Anthozoa (Polypoid)