General Zoology Chapter 12 - Sponges and placozoans

advantages of multicellularity

- Low surface area to volume ratio

- Allows individual cells to be more efficient

(instead of being a very large unicellular animal which is inefficient, become an organism with specialized cells)

note: specialized cells = more efficient

which organism was the first multicellular animal

sponge

what makes the organization of cells in sponges very distinct

Cells embedded in very tough extracellular matrix

sponges were not recognized as animals or plants until

19th century

in the tree, animals split off from ________________ which are ____________________

choanoflagellates, algae that are stocks of 2-12 cells that stick out and filter water

which animal (metazoans) was the first group to branch off of the group "other animals"

sponges

Describe choanocyte cells

- which organisms have them?

- structure and function of structure

- most organisms who have these cells are ___________ and ______________________

- choanoflagellates and sponges

- flagellum surrounded by collar of microvilli which collect particles for filter feeding, usually bacteria

- sessile (immobile or fixed to one place) and attach to hard surfaces

What is evidence for the common ancestors of metazoans being "colonial"

colonial makes sense as a "Prototype" multicellular organism

Similar cell communication mechanisms exist between

choanoflagellates and sponges

What is evidence against the common ancestors of metazoans being "colonial"

Choanocytes only in adult sponges, not in the larval form

Not seen in other phylogenetic groups, lost or suppressed (this is not surprising)

What has more evidence? for or against common ancestors of metazoans colonial

for

describe the latin name for sponge phylum

Porifera

porus (pore)

fera (bearing)

sponges ranges in size from _____ to ____

Range in size from a 2 mm across to 2 m across

Describe Sponge Structure

- Spicules imbedded in spongin for support

- Pinacoderm – incurrent pores on cells

- Dermal ostia – incurrent pores for the sponge

Phylum Porifera

Describe how sponges "eat"

- suspension feeders

- phagocytosis for small food particles

- pinocytosis for smaller proteins

Phylum Porifera

Organ System

- digestion is intracellular, no organs or true tissues

- nervous system absent or very primitive

Phylum Porifera

How do they live/where do they live

aquatic

stays in one spot

Phylum Porifera

Structure

- radial symmetry

- body with pores that facilitate water movement

- 3 types of body types

Phylum Porifera

Structure (body parts/symmetry)

- radial symmetry

Spongocoel - large central cavity

Ostia - tiny pores for water to enter

Osculum - a large aperture in a sponge through which water is expelled.n the surface of sponges that allow

Phylum Porifera myocytes

muscle cells arranged in circular bands around pores, regulate water flow through contraction

Phylum Porifera Describe Archaeocytes

(amoebocytes) ameboid cells that move in the mesohyl. they can specialize into sclerocytes, spongocytes, collencytes, and lophocytes

Phylum Porifera Describe Pinacocytes

flat cells that cover the outside of sponges

analagous to epithelial cells, closest thing a sponge has to true tissues

Phylum Porifera

What do each of these specialized Archaeocytes make:

Sclerocytes –

Spongocytes –

Collencytes –

Lophocytes –

Sclerocytes - make spicules

Spongocytes - make spongin

Collencytes - make collagen

Lophocytes - make collagen

Phylum Porifera: Sponges are made of...

- choanocytes

- mesohyl (gelatinous extracellular matrix in the center)

- archaeocytes (amoebocytes)

- pinococytes

- myocytes

Study this picture

Phylum Porifera What are the three types of sponge body forms?

Asconoid

Syconoid

Leuconoid

Phylum Porifera Asconoid

Smallest sponge with the simplest body plan

Phylum Porifera Syconoid

most efficient. has a lot of water

Phylum Porifera Leuconoid

most complex body form in sponges (best at filtering)

Phylum Porifera

Describe reproduction of sponges

Asexual

- create external or internal buds where buds detach and grow

- produce gemmules (internal buds) through somatic embryogenesis (process that creates embryos from vegetative cells without fertilization) Gemmules grow into sponges under more favorable conditions.

Sexual

- most sponges are monoecious (cross or self fertilize)

- produces parenchymula (free swimming larvae)

Phylum Porifera Which sponges develops blastula

Calcarea and a few Demospongiae

Phylum Porifera Describe blastula

made only by certain sponges, free swimming larvae from fertilized eggs that becomes inverted (leaving flagellated cells outside) to swim away to find a new place to grow

advantages of asexual reproduction

- No dilution of gene pool, offspring are all you (if you have good genes)

- clones favored in stable environments

- all of your population is reproductive

- offspring are often robust (strong/healthy) vs. individual gametes

disadvantage of asexual reproduction

• Offspring often do not disperse long distances

• Everyone is the same (Not favored in environments that change)

• Muller’s ratchet

– You accumulate negative mutations over time (easier to make mistakes then correct answer)

– Can lead to a less fit population

Advantages of sexual reproduction

- BIG ADVANTAGE: genetic variation for selection to act upon

- good at dispersing (and packaged well)

Disadvantages of sexual reproduction

- some population not reproductive

- fragile offspring

- diluted gene pool (good if bad genes, but bad if wasted good genes)

- most reproductive effort is wasted (finding partner/most gametes or offspring do not survive to reproduce)

Phylum Porifera

Taxonomy of sponges:

Class ____________________ - small calcareous sponges

Class ____________________ - siliceous

Class ____________________ - 95% of the species

Class Calcarea - small calcareous sponges

Class Hexactinellida - siliceous

Class Demospongiae - 95% of the species

Synctial cellular structure

many nuclei in a single cell (two ways)

- Fusion of many cells

- Cellular replication without cytokinesis

Phylum Porifera

Describe Calcarea (Calcispongidae) sponges

- spicules

- sponge shape

- sponge body form type

• Calcium carbonate spicules

• Any of the three sponge forms

• Typically small and vase shaped

Phylum Porifera

Describe hexactinellida sponges

Glass sponges

• Mostly deep sea

• Vase or funnel shaped

bodies

• Synctial cellular structure

Phylum Porifera

Describe Desmospongiae sponges

- sponge shape

- spicule

- which species?

• Siliceous, but not six rayed

• All leuconoid, all shapes

• Very diverse, most species (Contains all freshwater sponges)

Describe Phylum Placozoa

- what is unique about them

- how do they eat

- how do they reproduce

• ONE species – monotypic (having only one member) family and genus

• Scavengers (Glide over food, secrete digestive enzymes, absorb the products)

• Reproduce asexually by budding and fission (not sure if they're sexual since they produce eggs in captivity)

Describe Phylum Placozoa greek name

plakos (tablet) and zoon (animal)

what is the only species in Phylum Placozoa

Trichoplax adhaerens

Phylum Porifera

siliceous spicules (hexactinellida)

Phylum Porifera

siliceous spicules (demospongiae)

not six rayed

Phylum Porifera

calcareous spicules