Fall 2012 Keen Lecture 26. Phylum Porifera (sponges) (19 Nov 2012 ) •Choanoflagellates •major lineages of animals •sponges Students should be able to: •describe the most important cell type in choanoflagellates and sponges •explain how this cell functions •explain the principle of continuity •use the principle of continuity to predict water velocity within a sponge •analyze the efficiency of three sponge body plans •predict the most common body type in modern sponges
Transcript
Fall 2012 Keen
Lecture 26. Phylum Porifera (sponges) (19 Nov 2012 ) •!Choanoflagellates •!major lineages of animals •!sponges
Students should be able to: •!describe the most important cell type in choanoflagellates and sponges •!explain how this cell functions •!explain the principle of continuity •!use the principle of continuity to predict water velocity within a sponge •!analyze the efficiency of three sponge body plans •!predict the most common body type in modern sponges
Choanoflagellates •! cell ovoid, with a collar of microvilli (tentacles) surrounding the single flagellum •! movement of flagellum ! (1) locomotion and (2) feeding (bacteria trapped on collar) •!Watch a video at home
Sponge choanocyte
Evidence that choanoflagellates are the sister group of Metazoa 1.! Collar cells (shared between choanoflagellates, sponges, and a few other metazoans) 2.! DNA sequence data 3.! Choanoflagellates have homologues of metazoan cell signaling and adhesion genes
E.g., the Hedgehog gene (involved in cell signaling) is known in metazoans and choanoflagellates, but not other non-metazoan taxa (Ruiz-Trillo et al., 2008)
Major lineages of metazoans
see also Table 31. 1 8th & 9th eds
Sponge features: biology •! All aquatic, mostly marine •! ~8000 species (7000 species of demosponges) •! Adults sessile, larvae motile •! Mostly filter feeders on microscopic particles (bacteria, organic detritus, etc.), captured on microvilli, digested intracellularly
Quan
Sticky Note
digested intracellularly: digest in side your cell --> no gut or digestive tract
Video clip on sponges
Phylum Porifera (sponges) are sometimes called
vacuum cleaners of the sea
=
Phylum Porifera (sponges)
How can an animal without muscles, nerves, organs, or other complex structures filter 1500 liters of water every day?
Sponge morphology example
•! Sponges have only •! a few types of cells.
ECM called mesohyl
•! choanocytes
Simple body plan
•! Sponge sizes = 2 meters in diameter max.
•! Exit speeds of water = 8.5 cm/second
•! How can a flagellum on a tiny cell be strong enough to push that much water out of the body?
Sponges use the Principle of Continuity
Reducing the cross-sectional area of an outflow results in increased velocity.
Cross-sectional area
•! Principle of Continuity: •! X-area in . velocity in = X-area out . velocity out
Given a rigid pipe and an incompressible fluid
Many small inputs and fewer outputs
Sum of all X-sectional areas in >>> x-sectional area out
so, water exits very quickly
Think—pair—share:
What is the problem with this body design?
Why are these sponges always small (< 3 cm)?
Quan
Sticky Note
Surface Area vs Volume
asconoid sponge leuconoid sponge syconoid sponge
Sponge features Aquiferous system: varies in complexity among different kinds of sponges
Images from Biomedia Museum
Quan
Sticky Note
black area: food collecting choanocyte
Two other designs:
in syconoid sponges choanocyte lie in canals
in leuconoid sponges choanocytes lie in chambers like clusters of grapes
How many choanocytes in a sponge?
•! in a leuconoid sponge 10,000 flagellated chambers per cubic cm.
•! each chamber has 50-100 choanocytes •! approx. half to one million choanocytes
per cubic cm.
Sponge features •! Some demosponges have spongin (complex network of collagen) but no spicules: these have long been harvested for use as bath sponges
Largely replaced by synthetic sponges and luffa.
Sponges features Glass sponges and demosponges: siliceous spicules Calcareous sponges: spicules of calcium carbonate
