Lower Invertebrates

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Ingestion

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key attribute of being an animal.

Obtaining food is one is the only life processes that requires a specific type of activity. Capturing food for eating requires though, responses to environemental stimuli, specific behaviors and techniques.

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Phylogenic tree

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Diagram arranging the 9 phyla of animals in increasing order of specialization, type of symmetry and body cavity.

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Symmetry

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having corresponding parts or proportions. The most advanced animals are bilaterally symmetrical as opposed to radially symmetrical

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Bilateral symmetry

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Plane of symmetry dividing them into relatively equal halves (a left and a right). Most advanced animals are bilaterally symmetrical. Snakes are bilaterally symmetrical. ex: humans

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Radial Symmetry

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Animals with more than one plane of symmetry.

ex: starfish

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Lateral

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refers to the sides of an animal. Only bilaterally symmetrical animals have lateral surfaces. Used to describe bilaterally symmetrical animals.

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Dorsal

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refers to "back" or the surface not dedicated to the delicate organ systems and opening into the body. More exposed surface. Used to describe bilaterally symmetrical animals.

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Ventral

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Surface facing the ground. Opposite of Dorsal. Used to describe bilaterally symmetrical animals.

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Anterior

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refers to the head end, where the nerve tissue aggregates to form a brain. Used to describe bilaterally symmetrical animals.

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Posterior

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opposite of anterior. where the anus and often tail are located. Used to describe bilaterally symmetrical animals.

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Oral surface

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surface where the openings to the body are located. It is kept more protected and less exposed. Used to describe radially symmetrical animals.

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Aboral Surface

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opposite of oral surface. Used to describe radially symmetrical animals.

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Cephalization

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organization of tissues to form a head. Lack of cephalization disallows terms like anterior and posterior for being used to describe radially symmetrical animals.

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Sac - like system

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Digestive system of simplest animals. Single opening is used to obtain food and get ride of undigested food.

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One - way system

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More advanced digestive system. Has a separate mouth and anus. Often specialized into organs to make it much more efficient.

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Sessile

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non mobile, passive feeders

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Motile

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Search for food, or better feeding areas, relocate due to environmental conditions, hide from predators. Motile animals tend to have bilateral symmetry.

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Gametes

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Sperm (male) and Ova (female). Gametes are haploid and their union forms a zygote (diploid), which marks the beginning of a new individual capable of producing its own type of gamete.

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Polymorphic

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animals capable of having more than one distinct body form. To complete their life cycle requires an alternation of these forms. Offspring of an individual bear little resemblance to the parent type (seemingly). More common in less specialized and parasitic organisms. One advantage is polymorphic animals put much less strain on a singular food source and they become widely distributed.

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Metamorphosis

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Young undergo metamorphosis after feeding and dispersing themselves in the polymorphic cycle and develop into adults.

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broadcasters

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Many simple aquatic animals are broadcasters. They shed their gametes into the water, much like pollen into the air in the anticipation that fertilization will occur. Promoted by factors such as location and timing for fertilization to successfully occur.

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Hermaphroditic

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Specialized animals with male and female gametes. They produced both sperm and ova but do not engage in self - fertilization. Cross - fertilization is ensured through the timing of the release of the different gametes. Occurs mostly in less motile animals.

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Sponges

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-simplest organisms

- sac - like body plan, radically symmetrical, sessile, hermaphroditic and lacking cephalization.

-Phylum Porifera

_live attached to a surface

- have pores

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Incurrent Openings

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pores through which water travels into an internal cavity of a sponge. Passages through Pore cells (porocytes) which can regulate the size of the opening to control the amount of water that is passing through the body cavity.

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Excurrent Opening or Siphon

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Water exits sponge through this opening

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Collar cells

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-specialized cells that line the internal cavity of a sponge and create water currents by the movement of their flagella. As "new water" enters the cells lining the cavity extract food and oxygen from it and dispose of cellular wastes.

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Gemmules

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when water conditions become inclement sponges are known to produce gemmules, asexually produced spore - like structures that leave the parent organisms along with spent water.

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Amoebocytes

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another type of cell found in a sponge.

-specialized in their ability to create salts, like calcium carbonate or silicon dioxide to produce spicules.

-also specialized to produce sperm which is released through the osculum.

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Spicules

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hardened crystalline deposit made by amoebocytes in sponges. Provide support and are often referred to as the skeleton of a sponge.

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Spongeon Fibers

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supportive cell network in sponges.

-remain flexible.

-do not get hard and brittle.

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Regeneration

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re- grow lost body parts. Sponges are capable of this.

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Cnidaria

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animals such as jelly fish, hydra, Portuguese man of war, sea anemones and tiny creatures that make coral reefs are members of the phylum Cnidaria.

-all have a sac - like body forms, some are sessile some are not.

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Nematocysts or Cnidoblasts

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Cnidaria are united by the presence of nematocysts or cnidoblasts. These are stinging cells that work on a system of water pressure. When something in the environment triggers the barb extending from the surface of the nematocyst, the cell collapses and shoots out a protein filament designed to harpoon its prey. This filament bears a chemical anaescthetic which paralyzes the food so it can be ingested.

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Polyp

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Sessile form of cnidaria. Generally have an elongated body ending in a mouth surrounded by feeding tentacles.

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Tentacles

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Tentacles in cnidaria are specialized with nematocysts.

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Medusa

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Motile form of cnidaria, which appears to be a modified, inverted polyp with a bell shaped digestive cavity. This simple animal is capable of changing the shape of its bell to propel itself through the water.

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Mesoglea

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third, gel like layer in cnidaria that holds the other two layers apart

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Endoderm

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inner layer in cnidaria. specialized to secrete digestive enzymes to digest prey that has been captured and ingested.

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Gastrovascular cavity

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The products of digestion in cnidaria diffuse through the chamber and are either absorbed by the cells of the endoderm to be used by the cell or are released through the mouth.

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ectoderm

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Outer body wall in cnidaria, provides some protection from the environment and is equipped with tentacles and nematocysts.

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Nerve Net

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Some cells in the mesoglea of cnidaria are nerve like in that they can conduct electrical messages. This arrangement with its lack of any concentration of nerves forming a centralized nervous system has been given the term nerve net.

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Hydrozoans

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sessile creature where the primary body form is a polyp. Genus hydra is a well known fresh water example. broadcaster and reproduce asexually through budding. They are generally lead solitary life styles but some are colonial such as Genus Obelia and the Portugese Man of War.

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Schyphozoans

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motile with a medusa body form for the majority of their life cycle. Solitary individuals commonly called jellyfish. Clustered together because of their polymorphic life cycles. Adult medusas are typically male or female. Their gametes are released into the water where fertilization occurs. The resulting zygotes develop into larvae which attatch to surfaces and develop as polyps which reproduce vegetatively to produce medusas once again.

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Anthrozoans

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primarily sessile polyps with more complex tissue structures. There are many colonial and solitary examples including anemones and coral -forming anthozoans.

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Flatworms

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Phylum contains 3 classes of distinct animals planaria, flukes and tapeworms.

phylum platyhelminthes.

Dorso- ventrally flattened, have 3 tissue layers, some degree of cephalization and usually a sac - like body cavity.

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Tubellaria

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members of the class Tubellaria.

-free living and aquatic, can also be found in damp soils and mud.

most studied tubellarian is planaria

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Planaria

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can be found in cool, slow moving streams.

- hermaphroditic; produce both sperm and ova. They shed their sperms into the water surrounding them through openings in their ventral surface.

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pHARYNX

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Planaria have a ventral pharynx which is a muscular tube through which they ingest their food. Pharynx conducts food into the gastrovasuclar cavity where enzymes are secreted to digest it.

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Intestines

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Intestine or gastrovacular cavity of planaria, extends and branches in both the anterior and posterior direction to conduct nutrients throughout the body. The movement of the nutrients is dependent upon diffusion as well as the movement of the entire body

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Cilia

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the ectodermal wall of planaria are equipped with cilia, allowing these worms to slide through the water a process called ciliated gilding.

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Mesoderm

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planaria are capable of sliding and twsiting and turning their bodies and contracting and extending themselves. This is possible because of the development of muscles in the middle tissue called the mesoderm

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eyespots

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one distinct feature of planaria is their eyespots.

- these are light detectors only and not capable of vision.

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Ganglion

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the multicellular eyeposts of planaria are specializations of a small mass of nerve cells normally called a ganglion. because of the location and specialization of this ganglion it is sometimes referred to as a primitive brain.

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ladder like nervous system

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present in planaria.

-extending in a posterior direction from the eyespots is a pair of nerves with cross branches into the lateral tissue of the worm. The arrangement is called a ladder - like one because of the arrangement of the nerves. It is a significant system because the nerve cords that extend the length of the worm are located in the mesoderm on the ventral side and are paired.

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metabolic wastes

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animals produce metabolic wastes carbon dioxide, and ammonia which readily diffuse out of the cells that make them.

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flame cells

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located at the ends of nephridiophores, these cells collect body fluids containing the wastes and conduct it along the tubes to the outside through pores call nephridiopores because of the action of the cilia.

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NEPHRIDIOPORES

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Wastes exits through these pores.

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Flukes and tapeworms

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-class trematoda = flukes

-class cestoda =tapeworms

- members of both are flat and display a corresponding level of tissue and organ development as planaria

- parasitic

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parasitism

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results in two characteristics.

1. diminishes the need for specializations to obtain and digest nutrients

2. it increases the degree of specialization required ensuring the survival of their offspring. Parasites typically serve in partnership with their host, taking in their bodily fluids or juices and robbing their hosts of their intended benefits. They rarely kill their hosts, but may make the host weak and more susceptible to other infections and diseases that may be life threatening.

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Liver and blood flukes

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source of many human impact stories.

- liver flukes cause much sickness in undeveloped countries where the need for sanitation was poorly understood. the same was true for blood flukes in the southern united states and for the same reasons.

-larvae would gain entrance to the into humans by burrowing through skin from the water of soil where they could be found. Once in humans, they would migrate to favorable tissues and develop into the adult version of worms. This could led to a single person becoming infected by hundreds of parasitic worms.

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Scolex

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Tapeworms have unique body plans. They lack any real concentration of nerve tissue or ganglia in their anterior end so they don't have a head. Instead they have a scolex.

-Scolex: specialized with hooks and suckers for attachment to the inner walls of mammalian intestines.

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Proglottids

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extending from the scolex are reproductive packages called proglottids. Each proglottid contains a male and female sex organ. Scolex continuously reproduce immature proglottids which absorb nutients from and release wastes into their environement. These nutrients allow the development and maturation of sex organs.

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Nematodes

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Phylum: Nematoda

-commonly called roundworms

- display huge advancement in body plan over porifera, cnidaria and platyhelminthes.

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Tube - like intestine

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Nematodes have a tube - like intestines which have both a seperate mouth and anus (as opposed to a sac - like system with only one opening). This is possible by the internal seperation of the endoderm from the mesoderm.

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Pseudocoelom

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Speration from the endoderm from the mesoderm internally in Nematodes create a pseudocoelem, which is the beginning marker of a true coelom.

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(True) Coelom

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A true coelom is a characteristic of all higher, more developed animals. Nematodes are the first of the lower invertebrates (Porifera, cnidaria, platyhelminthes and nematodes to posses one).

- A true coelom differs from a Pseudocoelom by the presence of the mesodermal tissue on both sides of the body cavity.

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Nematodes' internal organ systems

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-Many nematodes are parasitic and display a reduction in the development and specialization despite having a coelom.

-nematodes have little need of a nervous system that helps them respond to their environment as they live inside organisms.

-Similarily their digestive systems only need to be able to digest bodily fluids, so they are less complex

-they are lacking in skeletal and circulatory systems.

-excretory systems are not significant as diffusion plays a large role.

-reproductive system and life cycles are advanced so that the secondary hosts can promote the distribution of offspring into different primary hosts.