Virtual Museum

Phylum Porifera Phylum Porifera can best be represented as sponges, which are the

simplest animals that lack tissue organization but they do have specialized cells. Sponges are built up from relatively few cell types, the main ones being choanocytes, pinacocytes, and amoebocytes. Choanocytes are vase shaped cells with a collar. Extending from the centre of this collar is the single flagellum whose beating drives the water currents that keep the sponge alive and healthy. Pinacocytes, form much of the epidermis of sponges and are as close as a sponge gets to having tissue. Generally they cover the exterior and some interior surfaces. They can change their size and can therefore change the size of the openings of the ostia thus controlling the flow of water through the sponge. Amoebocytes come in several forms, they are alike in that they are mobile and move around within the sponge body.

Sponges are generally hermaphroditic; however they are only one gender at a time, being either male or female. Sperm is released into the canals and is then pumped out of the sponge through the osculum where it is likely to be drawn into the canal system of another sponge that is female at the time. Then this sponge transfers the sperm to the ova. Sponges also reproduce asexually by releasing fragments of themselves, or special groups of cells called gemmules. These gemmules have protective coats of spongin and have particular environmental conditions they need to have met before they germinate.

Sponges are important to the environment because when they are photosynthesizing endosymbionts produce up to three times more oxygen than they consume, as well as more organic matter than they consume. Sponges also are important because they eat bacteria for where they live.

Phylum Cnidaria The phylum Cnidaria have many different mechanisms to survive, the most important are how they feed and reproduce. Cnidarians feed in several ways: predation, absorbing dissolved organic chemicals, filtering food particles out of the water, and obtaining nutrients from symbiotic algae within their cells. Most obtain the majority of their food from predation but some; depend almost completely on absorbing dissolved nutrients. Reproduction is asexual or sexual. In the Cnidaria, sexual reproduction often involves a complex life cycle with both polyp and medusa stages. Some have no polyp stages and some have no medusae which shorten the reproduction cycle. All known cnidaria can reproduce asexually in many ways. This phylum is ecologically important for a number of reasons. Cnidaria’s are the builders of some of the richest and most complex ecosystems on the planet, coral reefs. Other cnidarians are important as predators in the open ocean. Cnidaria also give their symbiotic algae carbon dioxide, some nutrients to other species. The cnidaria and the porifera have some similarities, they are both invertebrates and both live in the oceans, but for the most part the two are very dissimilar. The cnidaria is far more advanced than the porifera because it is able to move around and is more functional. The porifera is unable to move more than 4mm per day where as the cnidarian can move around a vast area of the ocean. The Cnidarian are also more complex in their structure than the simple Porifera.

Phylum Platyhelminthes The Phylum Platyhelminthes have various

adaptions’ that enable it to survive in different environments. Some allow this phylum to be free-living and parasitic. The adaption’s that allow it to survive while its free living, are that they are mostly predators or scavengers, and terrestrial species are mostly nocturnal and live in shaded humid locations such as leaf litter or rotting wood. Parasitic species normally move between different habitats as they change life cycle stages and hosts. The parasitic species have complex life cycles specialized for parasitism in animal tissues. Reproduction in this phylum can best be described through flatworms because they are a good example of this phylum. Flatworms are hermaphroditic and capable of sexual and asexual reproduction. Asexual reproduction occurs through fragmentation or fission. Since the flat worms are hermaphrodites, sexual reproduction occurs through the exchange of sperm.

Phylum Nematoda

The Nematoda is one of the most advanced systems, compared to the platyhelminthes. The Playhelminthes lacks a complex life cycle, a full digestive track and many organs. The Nematoda does not lack these things and is a very complex system compared to the playhelminthes. The Nematoda has eye spots and sensory systems where as the playhelminthes lacks this. In general the Nematoda is more advanced in many ways.

Phylum Annelida The phylum Annelida has three main different classes, Class

Oligochaeta, Class Polychaeta, and Class Huridina. The Oligochaeta class is the second most numerous group of annelids with around 3,100 species. Oligochaeta live in marine, freshwater and terrestrial habitats. Generally they have a more rounded cross-section, a less distinct head and are less diverse in form than the Polychaetes. This class’s reproduction may be asexual through fission. A few species are parasitic but most species are free living. The Polychaeta class are the most diverse and most speciose group of the Annelida containing over 5,500 species. They are predominantly marine animals and are divided ecologically into the Errantia and the Sedentaria depending on whether or not they live sedentary lives in holes or live more active lives. Most polychaetes are gonochoristic which means they are either male or female at one time. However some are sequential hermaphrodite, which means that they are one sex first and then change to being the other sex. Reproduction is often accompanied by the production of special modified reproductive segments which may, or may not, become independent of the parent worm before mating. The Huridina class contains the 500 or so species of animals commonly known as leeches. Leaches are well known for their blood sucking habits and their head to tail looping mode of locomotion.

The Annelids are very similar to the Nematods in many ways. The Annelids have a variety of functions that allow it to be very successful in many different environments; they feed on a wide range of material, and have a true closed circulatory system. The Nematods are only able to be successful in most environments.

Phylum Mollusca The Phylum Mullusca has many biological mechanisms to survive in its environment,

some being respiration, circulation, excretion, reproduction and nervous system. In this phylum most molluscs have only one pair of gills, or even only one gill, each gill has an incoming blood vessel connected to the hemocoel and an outgoing one to the heart. In this system there are three kinds of cilia, one of which drives the water current through the mantle cavity, while the other two help to keep the gills clean. Molluscs' circulatory systems are mainly open. The atria of the heart also function as part of the excretory system by filtering waste products out of the blood and dumping it into the coleom as urine. A pair of kidneys to the rear of and connected to the coelom extracts any re-usable materials from the urine and dumps additional waste products into it, and then ejects it via tubes that discharge into the mantle cavity. Molluscs have two pairs of main nerve cords, the visceral cords serving the internal organs and the pedal ones serving the foot. Both pairs run below the level of the gut, and include ganglia as local control centers in important parts of the body. One handles messages from and to the eyes and the other controls the foot. Molluscs have a head with eyes, and all have a pair of sensor-containing tentacles, also on the head, that detect chemicals, vibrations and touch. The simplest molluscan reproductive system relies on external fertilization, but there are more complex variations. All produce egg. Some molluscs use internal fertilization and/or are hermaphrodites, functioning as both sexes; both of these methods require more complex reproductive systems.

The three main characteristics that all Mullusca’s must have are the dorsal part of the body wall is a mantle which secretes calcareous spicules, plates or shells. It overlaps the body with enough spare room to form a mantle cavity. The anus and genitals open into the mantle cavity and two pairs of main nerve cords. The two most universal features of the body structure of molluscs are a mantle with a significant cavity used for breathing and excretion, and the organization of the nervous

Phylum Arthropoda The Phylum Arthropoda has many different mechanisms that allow it to survive, some

being respiration, circulation, excretion, nervous system and reproduction. Arthropods have a wide variety of respiratory systems but most possess a respiratory system in the form of tracheae and spiracles. Arthropods have open circulatory systems, although most have a few short, open-ended arteries, they also possess an open or lacunnar circulatory system with a simple heart, one or more arteries, and no veins. There are two different types of arthropod excretory systems, but the main one is the end-product of biochemical reactions that metabolise nitrogen is ammonia, which is so toxic that it needs to be diluted as much as possible with water. Nervous system includes a brain and ganglia and living arthropods have paired main nerve cords. Reproduction normally sexual and gonochoristic, but can be parthenogenetic.

There are many characteristics of this phylum. For the most part they are bilaterally symmetrical. Body has more than two cell layers, tissues and organs and the body cavity has a true coelom. Most have a through straight gut with an anus and an external skeleton. In this phylum they can feed on almost anything and live everywhere.

There are many groups of Arthropoda and I am only going to be looking at two, trilobites and chelicerates. Trilobites are a group of formerly numerous marine animals that disappeared in the Permian-Triassic extinction event, though they were in decline prior to this killing blow, having been reduced to one order in the Late Devonian extinction.

Chelicerates include spiders, mites, scorpions and related organisms. They are characterized by the presence of chelicerae, appendages just above / in front of the mouth. Chelicerae appear in scorpions as tiny claws that they use in feeding, but those of spiders have developed as fangs that inject venom.

Phylum Echinodermata The phylum Echinodermata has many different

mechanisms that enable it to survive in a variety of places. They have a circulation, excretion, nervous systems and a reproduction system. They have a poorly defined open circulatory system. Although echinoderms possess a complete digestive gut, it is very simple, often simply leading directly from mouth to anus. It can generally be divided into a pharynx, stomach, intestine and anus or cloaca. This phylum is also without excretory organs. They have a simple radial nervous system that consists of interconnected neurons with no central brain. Nerves radiate from central rings around the mouth into each arm or along the body; the branches of these nerves coordinate the movements of the organism. The nervous system also includes a circum-oesophageal ring. Reproduction can be both sexual or asexual but in this phylum they normally reproduce sexually. Sexual reproduction depends on the species and the environmental conditions. The eggs and sperm cells are released into open water, where fertilization takes place. The release of sperm and eggs is coordinated temporally in some species, and spatially in others. Asexual reproduction consists of the shedding of arms for long periods of time.