This document summarizes key aspects of the phylum Porifera (sponges). It describes their multicellular origins, body structures, cell types, skeleton formation, water circulation, feeding, reproduction, development, and classification. The four classes of sponges - Hexactinellida, Calcarea, Demospongiae, and Sclerospongiae - are introduced along with examples.

1. Multicellular and Chapter 9 Tissue Levels of Organization

13. Spicules

14. Types of spicules

29. Feeding – filter feeding

36. Euplectella

39. Leucosolenia

42. Grass sponge

44. The End