Lecture 1

• Life is divided into two super-kingdoms: the Prokaryaand Eukarya – these are sub-divided into six kingdoms
• Each kingdom has a hierarchy of taxa: Phylum, Class,Subclass, Order, Family, Genus and Species
• Animal species are given unique binomial namesbased on their genus and species – e.g, Mytilus edulisNB: always in italics or underlined, no capital letter onspecies name
• Modern phylogenies (Trees of Life) suggest multiple origins for contemporary animal taxa
• PORIFERA -> Calcarea, demosponhgiae, hexactinellida, homoscleromorph
• The key features of Porifera are:

  Most primitive of multicellular animals.No organs or organised tissues.Cells perform various functions.Always sessile, but some capable of moving.Body plan built round a series of canals– rely on maintaining constant water flow to obtain oxygen and food, and to remove waste.5000 marine species.Mainly shallow water, but one group common in deep sea.Variable size and shape, often brightly coloured (e.g., Cliona spp.
• Mesophyl sandwiched between two main layers of cells.Body consists or cells held in a matrix of spongin and calacareous/siliceous spicules.• Filter feed using choanocytes.
• Water leaves through the osculum
• It absorbs the food particles through phagocytosis
• Choanocytes = flagellated cell which line internal chambers of sponges.
• The collar allows the O2 in

  Beating the flagellum -> way of feeding for oxygenation and moving sperm and eggs around.

  
• Spicules = structural elements found in most sponges (calcareous orsiliceous)

  Megascleres: large spicules

  Microscleres: small spicules

  A leuconid calcareous sponge with the spicules in natural position
• Triradiate spicules formed by 3 sclerocytes coming together, eachforming 1/3rd of the spicule.

  A hexactinellid sponge with spicules in natural position
• Asexual or sexual reproduction – fertilization external or internal.
• Sequential hermaphrodites (one before the other) – release gametes into water for external fertilisation (“smoking sponges”)
• Smoking sponges releases it's gametes into the ocean -> they will all mix which is external fertilisation
• Some Demospongids are viviparous – choanocytes of adjacent individual recognise and capture sperm without digesting them and transfer them to oocytes. (so fertilisation becomes internal in that organism)
• Larva enables the spread of gametes
• upright -> have a good water flow through the osculum so it will have good food availability

  
• Pleating means larger surface area so it can pump a lot more water through its body.

  
• Archeocytes: large, phagocytic, used in digestion, can transform into other cell types, can produce eggs but not sperm.
• Collencytes: secrete collagen
• Sclereocytes: secrete spicules
• Spongocytes: secrete spongin (thick fibrous material which stiffens mesophyll)
• Choanocytes: flagellated cells that create currents of waterin the sponge, produces sperm and can produce eggs.
• FeedingPORIFERA

  Basic, but highly efficient• Feed on very fine plankton including bacteria and dinoflagellates• Specialized, flagellated cells = choanocytes – move flagella to draw in water through pores• No gut – direct cellular ingestion of captured food
• Sponges can feed:

  filter tiny plankton from the water covered with small pores -> Ostia which lead to a system of internal canals. Eventually out to one/ more larger holes (Ascalon)

  Within canals of the sponge, chambers are lined with specialised cells

  Flagella pushes water (brings in nutrients and oxygen while it carries out waste such as CO2 )

  Sticky collars of the collar cells pick up tiny bits of platonic food brought in with the water
• Carnivorous deep-sea sponges, increased SA helps to capture prey and release eggs into passing ocean currents. Packets of sperm are also produced and released.

  
• Calcareous sponges”.• CaCO3 spicules – mainly shallow, for ease of calcification, and strictly marine.• Typically, <10cm, drab colour.
• DEMOSPONGIAE

  • 75% of sponge species.• All leuconoid – soft body covers hard, massive skeleton.• Silica spicules.• Shallow to great depth (widest range of habitats).• Brilliant colours.• Long-lived (<1000yrs!).• Commercially important as bath sponges.
• HEXACTINELLIDA• The “glass sponges”-> allows more water to flow through it• Variation from basic sponge plan – silicaspicules form framework between which livingtissue is suspended like a cobweb, withmesophyll absent/minimal, no pinacoderm, andno choanocytes.• Skeleton made of 4- and 6-pointed siliceous spicules.• Mainly pale and deep sea.• Long-lived (< 15,000 years!). 10cm Euplectella aspergillum (Venus’ flower basket)
• Pheronema sp. at 1200m depth in the Porcupine Seabight, NE AtlanticPheronema is so productive at these depths that the sediment at the seabed is composed of siliceous spicules!
• Pheronema sp. at 1200m depth in the Porcupine Seabight, NE AtlanticPheronema is so productive at these depths that the sediment at the seabed is composed of siliceous spicules!
• Darwin’s Paradox (1842): How can such high production flourish in such nutrient poor conditions?2013: Dutch scientists showed that the immense filtering capacity of reef sponges effectively recycled nearly all the nutrients and organic matter produced by other reef organisms by capturing it and turning it into sponge tissue that was then grazed on by molluscs, crustaceans and fish!
• Comb jellies key features - • 2 classes: Tentaculata and Nuda.• Cilia (combs) used for swimming.• Colloblasts – sticky and adhere to prey.