Why were sponges mistaken for plants?
Sponges were reclasssified as animals in mid the 18th century, but were not widely accepted as animals until the late 19thC.
They are a side branch of k. Animalia, primitive animals.
The are sessile and relatively insensitive.
Describe sponges' two major "sensitivities" to the environment
They alter how they reproduce in response to environmental conditions. Reproduce by budding during good conditions and by production of reduction bodies during environmental hardship conditions.
They have the ability to shut down the water flow through them if conditions (turbidity) warrant it.
Describe the process of filter-feeding and the role of choanocytes in sponges.
A process by which they circulate water and collect tiny, particle-size food from the water. Water enters through ostia (pores) and is moved through by choanocyte cells which stimulate a water current. The ring of pseudopodia of the choanocytes traps passing food.
How do choanocytes give credibility to the idea that animals originated from flagellates?
Choanocytes are very similar to a type of protozoan known as choanoflagellate. Both have a ring of pseudopodia and flagella. These choanoflagellates were also known to exist in colonies (though not spherical colonies).
Describe the morphology of the sponge
There are three cell types that form layers, but these layers are not well-defined. The three cell types are choanocytes, pinacocytes, and amoebocytes. The Mesohyl separates the coanocytes and the pinacocytes and contains the amoebocytes
Describe the role of amoebocytes in the sponge
There are different types of amoebocytes, but they all appear to be totipotent. They are able to change into other types of amoebocytes or into pinacocytes or choanocytes. Amoebocytes participate in reproduction and the produce spicules.
Sponges have a great ability to regenerate due to the totipotency of amoebocytes. Regeneration is the process by which an orgaism can "grow back" a missing piece of itself. The cells can reorganize to reform the individual, or can give rise to completely separate individuals.
What are the two categories of skeleton components produced by amoebocytes?
spicules, spongin fibers.
Rigid structures that form a framework to support the body of the sponge. Sponoges either have calcareous (calcium carbonate) or siliceous (silicon) spicules but not both
Describe spongin fibers
Very strong fibers made of the protein spongin. They are a specialized form of collagen and are found in the mesohyl of sponges. They help hold the sponge together and provide strength to the overall sponge structure.
Describe the level of specialization among amoebocytes
There is some level of specialization among the amoebocytes. Some are specialized to produce spicules (calcareous or siliceous) and some are specialized to produce spongin fibers. Even though they are somewhat differentiated, they still have totipotent capabilities and can undifferentiate to become another type of cell.
Describe the body plans of sponges
There is a trend toward more complex body plans. This allows more surface area to interact with the water that is flowing through the sponge. The more complex body plans also slow the rate of flow of the water. This means that there is more time to get nutrients, get rid of waste, and perform gas exchange. The pseudopodia of the choanocyte are the primary sites for these processes
What is the difference between excretion and secretion?
excretion is getting rid of waste while secretion is the production of a chemical for use by the body
Identify the main types of reproduction in the sponges
Sponges reproduce asexually and sexually.
The three forms of asexual reproduction are budding, production of reduction bodies, and gemmule production.
In sexual reproduction, sponges are monoecious with nonsynchronous hermaphroditism and are protandrous.
Describe reproduction by budding in sponges
A form of asexual reproduction in which a small sponge grows out the side of the parent sponge during good conditions. Each bud starts out as a cluster of amoebocytes. The buds break free and develop into solitary individuals. In colonial forms, the buds don't break free and remain attached.
Describe reproduction by production of reduction bodies in sponges.
A form of asexual reproduction that occurs during environmental hardship conditions. In lower forms of invertebrates, it is common for harmful conditions or seasonal change (extreme temperatures, lack of water, lack of oxygen) to control means of reproduction.
A reduction body is a cluster of amoebocytes also known as "internal buds" because they develop inside the body of the sponge. When the adult is killed by harsh conditions, it disintegrates and the reduction bodies are carried off where they can later develop into adult sponges when conditions are favorable.
A type of regeneration in which each parent sponge may form dozens of reduction bodies. This is not just a survival mechanism.
Describe reproduction by production of gemmules.
This process is primarily in freshwater sponges and is similar to the production of reduction bodies.
A gemmule is a cluster of amoebocytes that have a strong, protective covering and are covered with spicules on the outside and contain nutrients inside. The protective covering is chitinous (composed of chitin). Chitin is similar in structure to cellulose which strengthens and provides structural support.
Describe gametogenesis during sexual reproduction
Gametogenesis is the production of gametes (eggs and spermatozoa). Since sponges exist at the cellular level, cells produce gametes (not structures or organs).
The eggs are produced by amoebocytes in the mesohyl and are usually kept in the mesohyl. The spermatozoa are produced by amoebocytes or choanocytes. If produced by amoebocytes, the spermatozoa must be transported to choanocytes to be released into the water current.
Describe how fertilization occurs in sponges
For fertilization to occur, the spermatozoa is released from one individual and enters a conspecific functioning as a female. Fertilization occurs in the mesohyl. The pseudopodia of choanocytes help to take in the entering spermatozoa. In some species, the choanocytes give the entering spermatozoa to the amoebocytes who will take them to the eggs. In other species, the choanocytes themselves will revert to amoebocytes to travel into the mesohyl and transport the spermatozoa.
Describe the blastula stage of development of the embryo
In most sponges, the embryo develops in the mesohyl. During the blastula stage, some cells on one particular side develop flagella pointing towards the blastocoel. This is the anterior end. The flagelatted cells will become choanocytes while the other cells become amoebocytes or pinacocytes. At some point during this stage, the blastula everts (turns inside out) leading to the amphiblastula form
Describe the amphiblastula stage of development of the embryo
The amphiblastula is the proper name for the blastula that results from eversion. The flagella are pointed towards the outside. This allows for locomotion and movement away from the parent sponge. This may be a dispersal mechanism that spreads the offspring so they are not in competition with each other. This is a free-swimming stage until the amphiblastula attaches by the posterior end and continues through gastrulation.