PHYLUM PORIFERACHAPTER 4
ORIGINS OF MULTICELLULAR
ANIMAL ORIGINS
OTHER
EUKARYOTES
Choanoflagellates
Sponges
Other animals
Anim
als
Individual
Collar cell
(choanocyte)
▸ origins? ▸ syncytial ciliate hypothesis ▸ colonial flagellate hypothesis ▸ polyphyletic origin ▸ molecular evidence? ▸ colonial flagellate hypothesis...
BASAL PHYLOGENY
THE ROOT OF THE ANIMAL TREE▸ METAZOA (EUMETAZOA?) ▸ which group diverged first? ▸ Porifera ▸ Cnidaria ▸ Ctenophora ▸ Placozoa
Telford et al. Evolution: A sisterly dispute. Nature (2016) vol. 529 (7586) pp. 286-287
SIMION ET AL., 2017
MYSTERY PHYLUM?
PLACOZOA▸ Phylum Placozoa ▸ only one species ▸ Trichoplax adhaerens
▸ poorly understood ▸ asexual reproduction ▸ fragmentation/budding
▸ sexual?
0.5 mm
placozoan
SPONGES
PORIFERA▸ Phylum Porifera— ▸ porus-pore, fera-bearing ▸ Sessile, aquatic ▸ Simple cellular level of organization
BASIC FEATURES
ANATOMY▸ general body form ▸ Spongocoel ▸ Ostia ▸ Osculum
choanocyte
pinacocyte
archaeocyte
spicule
ostium (porocyte)
osculum
▸ Pinacocytes ▸ protective, sometimes contractile
▸ Mesohyl ▸ Spongin, Spicules ▸ Archaeocytes—ameboid cells (amoebocytes)
▸ Choanocytes— “collar” cells
Spongocoel
Osculum
Pore
Epidermis Water
flow
Mesohyl
Choanocyte
Spicules
Amoebocytes
Flagellum
Collar
Food particles
in mucusChoanocyte
Amoebocyte
Phagocytosis of
food particles
BODY FORMS
ANATOMY▸ Body form— ▸ Asconoid ▸ Syconoid ▸ Leuconoid
Syconoid sponge
BODY FORMS
ANATOMY▸ syconoid anatomy
EXTE
RIOR
SPON
GOCO
EL
INCURRENT CANAL
RADIAL CANAL
prosopyle
apopyle
ostium
PORIFERA
REPRODUCTION▸ Asexual ▸ external or internal buds ▸ Gemmules ▸ somatic embryogenesis
▸ Sexual ▸ mostly monoecious sponges ▸ cross- or self-fertilize ▸ archaeocytes
▸ development ▸ blastula (coeloblastula) ▸ inversion - amphiblastula ▸ some develop into stereoblastula
PORIFERA
TAXONOMY▸ Class Calcarea— ▸ small calcareous sponges
▸ Class Hexactinellida— ▸ silicious, interconnected spicules ▸ syncytial body
▸ Class Demospongiae— ▸ 95% of species
▸ Class Homoscleromorpha?
