Phylum Placozo— all marine, asymmetrical adults, low level or organization (no nervous system, no muscles, no digestive system) Possibly diploblatic, small ind. Swim, large ind. Crawl or cilary gliding. Do phagocytotic feeding (endocytosis)
No anterior or posterior but does have dorsal and ventral
Double layer plate that has several thousand cells
Placozoa Dorsal cells:
Flattened
Shiny spheres (lipid droplets that help arrange themselves)
Extracellular and positive toxins
Monociliate
Singe cilium per cell
Placozoa ventral cells-
Columnar cells
Most monociliate
No shiny spheres
May be vaginated for feeding
Mesenchyme in Placozoa
Between dorsal and ventral
Non-living gel
Ameboid cells
Use Pseudopodia to move
Placozoa Reproduction:
Asexual:
Binary fission and budding (flagellated buds)
Sexual:
Not understood
eggs in mesenchyme
fertilization never observed
No survival past 64 cells in lab
Phylum Porifera: multicellular, sessile, and filter feeders (FLAGELLATED CHOANOCYTES)
Have an Aquiferous system
Totipotents cells (cells that change form and function)
3 classes of Porifera:
Calcarea
Hexactinellida (glass sponges)
Demospongiae: most sponges
Porifera body plan- simple tissues, aquiferous system, and totipotent cells
Are like a rigid perforated bag
Have a spongocoel: cavity inside bag that is lined with choanoderm (collar cells for water flow)
Choanoderm: generate water currents and circulation
Used for food capture (filter feeding)
Sperm capture
Gas exchange
Waste removal
Pinacoderm- outside of sponge that is lined with pinacocytes
Internal cavities of the aquiferous system are called endopinacocytes and lead into the spongocoel
Ostia are small holes in the pinacoderm that are entrances to the aquiferous system
Holes on outside that allow water in
Osculum- opening where water leaves aquiferous system
Choanoderm and pinacoderm are both a single cell in thickness
Mesohyl: between the pinacoderm and choanoderm
Acellular, non-living, and gelatenous
Contains living cells and spicules (made of silicon and provide structural support)
Functions of the mesohyl: found in Porifera
Digestion
Gamete production
Skeletal formation
Transport of waste and nutrients
Choanoderm increases folding and therefore increases surface area to volume ratio
Helps with absorption of materials and things the cells need
Asconoid condition:
Unfolded Choanoderm
Synconoid condition:
Folded Choanoderm
Leuconoid condition:
Multiple independent chambers of Choanoderm (more contact with water)
Porocytes (porifera): make up the pores and form the ostia
Contractile: can squeeze water to help it move through the aquiferous system
Choanocytes are not coordinated
Flagella move independently
Distinct morphology
Do phago and Pinocytosis
Sclerocytes: provide structure and produce spicules
Are found in mesohyl
Archaeocytes: ameboid cells that can differentiate into different types
Are motile
Functions:
Digestion
Transportation
Reproduction
Organic poriferan support:
Collagen - linked to spongin
Calcium- Calcarean sponges
Silicon- in spicules
Inorganic poriferan support: spicules
Some lack spicules and are softer
Spicules come in a variety of sizes and shapes (# of axes or rays)
Nutrition in porifera:
Intracellular digestion
Use archaeocytes for larger particles as it is the lining of intake tubes
Choanocytes used for smaller particles and microvilli (partial digestion)
Excretion and Gas exchange in Porifera:
Simple diffusion
Choanoderm: helps get rid of metabolic waste from intracellular digestion
Release from choanocytes and minimize contact between good and bad
Freshwater sponges use contractile vacuoles
Do osmoregulation (controls water in and out)
Poriferan reproduction: both asexual and sexual
Asexual: fragmentation, pieces fall off and spread to new areas
Gemmules
Sexual: gametes
Gemmule formation: archaeocytes in mesohyl that are doing rapid mitosis
Nurse cells (can change what they are to overcome environmental struggles)
Are engulfed by archaeocytes and act as food stores
Archaeocytes are surrounded by spongin
Spicules are integrated and gemmule’s form
Sexual reproduction in Porifera (broadcast spawning)
Most are hermaphroditic (totipotent cells)
Won’t self fertilize because cross fertilization is better
Choanocytes
Look like sperm in a skirt
Sperm enter aquiferous system
If cross choanoderm, will fertilize mesohyl
If captured by choanocytes: lose collar and flagellum and carry sperm to mesohyl
Poriferan larvae are released into the environment
Must go through metamorphosis
Class Calcarea: calcium based spicules (synapomorphy)
Asconoid, synconoid, and leuconoid
All Marine
Class Hexactinellida: glass sponges that have 6-rayed silicon-based spicules
Lacks pinacoderm
Single plasma membrane and multiple nuclei
1 big cell and lots of nuclei (cyncytial)
Class Demospongia: 80% of all species
Most of these are leuconoid (type of complex sponge)
Spongin and silica for support
Some without spicules
Phylum Cnidaria: corals, jellyfish, sea anemonies
Dimorphic life cycle
Polypoid are sessile and do asexual reproduction
Medusoid form (jellyfish): sexual reproduction
Body plan of Cnidarians:
Diploblastic (no mesoderm)
Cnidae (stinging cells)
Tentacles
Gastrovascular cavity
Incomplete gut and no anus
Mesenchyme and mesoglea are derived from the ectoderm