Kingdom Animalia (metazoans)

Grades

Mesozoa (a single phylum)

Parazoa (phylum Porifera and Placozoa)

Eumetazoa (all other phyla)

A. Syncytial ciliate hypothesis

B. Colonial flagellate hypothesis

C. Polyphyletic origin hypothesis

Phylum Mesozoa

Phylum Placozoa

Phylum Porifera - the sponges

General Characteristics

Mesohyl - gelatinous matrix

Spicules/Collagen

System of pores and canals

create system for filter feeding, gas exchange, and waste disposal.

Commensals/Parasites live in canals

Three Classes - Calcarea, Hexactinellida, and Demospongiae

Cell Types: (found in the mesohyl)

1. Pinacocytes -

2. Choanocytes -

3. Archaeocytes -

Skeleton:

1. Collagen fibers- tough fibrous protein

Spongin - special type of collagen

2. Spicules - Calcium carbonate or silica

Form and Function of Sponge Body:

Ostia -

Oscula/Osculum -

A. Asconoid

found only in Class Calcarea

B. Syconoid - similar to asconoids with tubular body and single large osculum BUT more complex

Water enters ostia -------> incurrent canals -------> prosopyle (small opening) ------> radial canals (food ingested) -------> apopyle (another opening) ---------> spongocoel ----> osculum

found in Classes Hexactinellida and Calcarea

C. Leuconoid - most complex sponges. Able to increase in size

over the other sponge types. Many oscula. Clusters of flagellated chambers.

Water enters ostia -------> incurrent cannals ------> chambers lined with choanocytes -----> excurrent canals -----> oscula

found in all Classes of sponges

Intracellular digestion (within archaeocytes) - feed on planktonic particles, detritus and bacteria.

No respiratory or excretory organs - use simple diffusion

Asexual reproduction - budding or regeneration

internal buds or gemmules form in some sponges to help survive hard times (freshwater)

Sexual reproduction (monoecious)

sperm and eggs arise from tranformation of choanocytes.

Viviparous - zygote receives nourishment from adult sponge;

forms ciliated larvae released into water. Cross fertilization.

Oviparous - eggs and sperm released into water.