The Porifera (and friends)

Brought to you by the Metazoa.the Animal Phyla

Characteristics of Porifera

• Cellular Level of organization (multicellular)

• No organs or true tissues– One germ layer

• Body with pores• All aquatic• Flat epidermis

– Pinacocytes

• Gelatinous mesohyle– Amebocytes (archaeocytes)

• Collar cells (choanocytes)• Skeleton of collagen• Spicules often present

– CaCo3 or SiO2

• Absent nervous sys.• Sessile adults• Asexual or Sexual

reproduction

Phylum Mesozoa: Cilliated worm-like animals without a full metazoan organization..

(somatic cells surrounding reproductive cells)

• 1. Rhombozoa– Parasite– Cilliated– Lives in the kidneys

of cephalopods– .5 to 7mm– 20 to 30 cells in two

layers

• Orthonectida– Parasite– Cilliated– Lives in brittle stars,

bivalves, polychetes, & nemerteans

– .5 to 7mm– 20 to 30 cells in two

layers

Phylum Placozoa

• Trichoplax adhaerens– Click on the link to

see an image.

– About 3mm in length– No symmetry– No organs– No N.S.– Moves via cilia– Secretes digestive

enzymes and absorbs nutrients

– Possible relation to Cnidarians (mol.)

PoriferaThree Classes

1. Calcarea Spicules of crystaline calcium carbonate

Abundant in near-shore shallow water settings.

2. Hexactinellida Spicules of silica (glass sponges); some of their tissues are syncitial; possess a unique system for rapidly conducting electrical impulses across their bodies (pseudo nervous system?)

3. Demospongiae 90% of species; Spicules of silica, spongin, or both; Found from warm intertidal settings to cold abyssal depths, & all of the known freshwater poriferans are demosponges.

Origins of Porifera

• Colonial Ciliate Hypothesis– Volvox– Favored by DNA

evidence

• Syncytial Ciliate Hypothesis– Single cell w/ mult.

Nuclei– Present in some

Hexactinellida– Not likely based on

molecular evidence

Basic Structure• Spongocoel• Osculum: outcurrent pore

• Ostia: incurrent

pores

• Pinacoderm • Mesohyl

– Scleroblasts (spicules)– Archeocytes (undifferentiated)– Amoebocytes (digestion / transport)

• Choanocytes– Nutrient collection– Water current

3 Systems of Filtering

Asconoid Syconoid

Leuconoid

Sponge physiology• Mesohyl

– Gelatinous Matrix– Bordered by pinacocytes– Fibrils– Skeletal elements– Ameboid cells

• Pinacocytes– Exterior and interior

surface (epithelial cells)– Pinocytosis– Contractile myocytes

• pores

• Archaeocytes– Amoeboid– Phagocytosis more– Digestion – Plasticity can become…

• Sclerocytes (spicules)

• Spongocytes (spongin)

• Collencytes (collagen fibers)

• Lophocytes (collagen)

Sponge physiology contd.

• Choanocytes (collar cells)– Strainer (microvilli

connected by microfibrils)

– Phagocytosis– Pass food particles

to archeocytes

A feeding exception…

• Family Cladorhizidae– Carnivorous– Cave dwellers– Feed on crustaceans– Spicules act like Velcro!– Prey enveloped by

epithelial cells and filaments

– Example of adaptive radiation

QuickTime™ and a decompressor

are needed to see this picture.

Regeneration of Damage to Sponges

1. Easily repair wounds2. Somatic Embryogenesis

- Complete reorganization- Forms new organism from cell aggregates- Not well understood (adhesion)

3. Budding (New organism, identical DNA)4. Gemmules (internal buds) Fig. 12.13

- Archaeocyte rich mesohyl- Tough spongin coat- Survive tough times (cold or dry)- Common in freshwater sponges

Reproduction1. Budding - asexual2. Gemmules - asexual3. Sexual Reproduction

- Monoecious (protanderous)- In some, choanocytes transform into male

and female reproductive cells- In others, oocytes from transformed

archeocytes and sperm from choanocytes

Fertilization

1. Phagocytosis and passage of sperm to ova by choanocytes- Viviporous

2. Mixing of sperm and ova in water…spawning (more)- Oviporous

Life Cycle of a Sponge

This is for a Syconoid sponge. The cycle is slightly different for Demospongiae. See p. 249 of text.

Demospongiae• Develop from a free swimming parenchymula larva.• Flagelated cells that make the larvae mobile, migrate

to the interior and become choanocytes.

Remember, sponges can reproduce asexually by budding and gemmules (internal buds), or sexually by viviparity as well as oviparity.

In viviparity the embryo develops inside the body of the mother, as opposed to outside in an egg (oviparity)…also referred to as ovipary and vivipary