This document summarizes key characteristics of poriferans (sponges) and placozoans. Sponges have choanocytes that capture food through phagocytosis and lack nerves and true musculature. They have an endoskeleton of mesohyl or spicules and spongin. Placozoans are simple multicellular organisms with two epithelial cell layers, glide using cilia or change shape, and digest food extracellularly. Both groups reproduce asexually through budding or fragmentation and sexually.

2. Poriferans (sponges)
• ‘pore bearing’
• Spongocoel
• Choanocytes or Collar cells
• Archeocytes
• Epidermal cells
• Has Mesophyl sandwiched between two thin layers
of cells.

3. Defining Characteristics
• Microvillar collars
surround flagella, with
units arising from
either single cells or
syncytia.
• Lack nerves and no
true musculature.

4. Skeleton
• Sponges are either radially symmetrical or
asymmetrical.
• Mesohyl=Endoskeleton
• Spicules=Sclerocytes
• Spongin=Spongocytes

5. Food Capture and Digestion
• detritus particles, plankton, bacteria
• Choanocytes
• Food items are taken into individual cells by
phagocytosis, and digestion occurs within individual
cells.

6. Excretion and Water Balance
• A sponge has carbon dioxide and other wastes
removed as the water moves in and out through the
pores.

7. Respiration and internal Transport
• Diffusion of gases through the help of water
• Archeocytes remove mineral particles that
threaten to block the ostia.

8. Nervous System
• A sponge has a very low level reaction to the world
around it and does not have a brain per se.

9. Reproductive system
• Asexual
+fragmentation
+buds
*external buds
*internal buds or gemmules
• Sexual (mesohyl)
+eggs and sperms
+hermaphroditic
*External and internal fertilization

10. Development
• Hollow blastula or Coeloblastula
• Amphiblastula-the hollow sponge larvae
• Some species, from coeloblastula to
stereoblastula
• Larvae are incapable to feeding and swim
for less than 24 hours before
metamorphosing.

11. Ecology and Evolution
• 98% in marine
• 2% in water and mostly with spongin fiber
• Many in tropics
• Sponges have strong structures that are able
to handle the high volume of water that
flows through them each day
• release toxic substances into the
environment

12. PLACOZOANS (Flat plate)
• They were discovered in the late 1880's
living on the glass walls of an aquarium in a
European laboratory.
• Single species

13. Defining Characteristic
• Multicellular
• Amorphous
• Mobile
• flagellated animals lacking a body cavity, digestive
system and nervous system
• composed of 2 layers of epithelial cells.

14. • 2 distinct layers of epithelial cells
+ventral- columnar cells w/ flagellum
- Glandular cells with enzymes
- Endodermal
+Dorsal- Flat, thinner and No gland cells.
-Ectodermal
+In between- fluid
-Contractile fibrous cells.

15. Movement
2 Ways;
• gliding on their cilia
• changing their shape like an amoeba.

16. Digestion
• Atops the food using the Ventral surface
• No sign of phagocytosis
• Extracellular digestion

17. Reproduction
• Sexual
+ generally, produces one oocyte.
+developed embryos
• Asexual
+Budding
+Fragmentation
+Binary fission