Ponifera Flashcards
What are the three sponge classes?
Hexactinellidae Calcarea Demospongia
Describe ctenophores?
Rotational symmetry
Pair of tentacles
The gut is the only body cavity
Nerve net but no discrete gas exchange or secretory system
Hermaphroditic
Carnivorous
Sister group to all Metazoa
Describe the origin of sponges?
There is a similarity between sponges and choanoflagellates.
Hypothetical evolution from choanoflagellates to sponges.
- Somatic cell differentiation to attach to rock - new cell type
- The new cell (pinacocyte) is able to secrete an extracellular matrix
- Form a mesophyll skeleton between two layers of choanocytes
- Protosponge able to grow larger and feed more effectively
- Selection for a large embryo, sperm and eggs
What is the aquiferous system in sponges?
Underground layer of water bearing permeable rock from which groundwater can be extracted
Has two major advantages:
1. increasing food supply by pumping more water past the choanocytes
2. protecting the choanocytes from sediment and other things swept past the colony
Requires the controlled formation of ostia & specialisation of some pinacocytes to form muscle myocytes to control the opening of ostia
What is the structure of sponges?
Cell layers are called the pincoderm and the choanoderm with the mesophyll sandwiched between.
As well as the mesophyll (fibrillar collagen) sponges are also supported by many different types of spicules (calcium carbonate or silica)
The spicules are secreted by sclerocytes, which associate to make scleroblast. Nuclear division forms central and peripheral nuclei, the spicule is formed between each pair of nuclei. The cells disintegrate after spiracle formation
What diversity exists in the sponges?
Sponges can grow to very large sizes, and their structure can support a very large colony size.
The sponge with the biggest spicules live for 11,000 years.
11,000 species described.
Limited larva dispersal and asexual reproducion means that local or regional endemism is normal. A species is unique to a defined geographic location.
What are choanocytes?
Generate a flow of water through the sponges by cooperatively moving their flagella.
Provides both respiratory and digestive functions for the sponge, pulling in oxygen and nutrients, allowing a rapid expulsion of carbon dioxide and other waste products.
What else makes up sponge biomass?
The microbiome can make up to 40% of the sponge biomass.
Describe sponge nutrition?
Gain some of their nutrition from their microbiome.
Carnivorous sponges: sponges that live in nutrient poor environments that have evolved carnivorous traits. Spicules are modified to trap small crustaceans and other animals. Only evolved once.
Types of sponge reproduction?
-
Sexual
Normally more females. Normally simultaneous hermaphrodite. At least 8 different types of larval development.
Reproduction may be highly synchronous and occurs once or several times a year. -
Asexual
- Budding - cell masses that grow at the external surface of the colony. Dispersed by currents or waves
- Fragmentation - occurs through wave action, predation or death of part of a colony
- Gemmulation - generally occurs in freshwater species. Dormant resistant bodies form internally in sponges at the base, often to survive extreme environmental conditions. Only freed after extensive tissue damage. Some can even survive passage through an animal gut.
Ecological importance of sponges?
Bio-erosion: calcium carbonate into small chips using enzymes secreted. The chips are expelled and contribute to coral sands
Coral reef stabilisation: bind together coral rubble and other material as they grow
Associations of sponges with other species?
Primary producers through symbiosis
As prey for other organisms
Habitat provision
Ecosystem engineers
Agents of disturbance – grow over other organisms and suffocate them
Use as tools – e.g. by dolphins in Shark Bay
