1. Chapter 6
Sponges

3. Origin of Metazoa Evolution of the Metazoa
Evolution of eukaryotic cell followed by diversification
Modern descendants
Protozoa, plus multicellular plants, animals, and fungi
Multicellular animals
Referred to collectively as metazoans
Grade Parazoa

4. Phylum Porifera General Features Sessile sponges are filter feeders
Porifera means “pore‑bearing”
- bodies perforated by many pores
Skelton is composed of spicules
Sponges can regenerate
Body is efficient aquatic filter
Approximately 15,000 species of sponges
Most are marine
Few live in brackish water, 150 in fresh water

5. Phylum Porifera
Marine sponges found in all seas at all depths and vary greatly in size
Many species are brightly colored because of pigments in dermal cells
Some appear radially symmetrical but many are irregular in shape
Some stand erect, some are branched, and some are encrusting

7. Phylum Porifera
Fossil record of sponges dates back to the early Cambrian
Living sponges traditionally assigned to 3 classes: Calcarea, Hexactinellida, and Demospongiae
Members of Calcarea typically have calcium carbonate (calcareous) spicules with one, three, or four rays
Hexactinellids are glass sponges with six-rayed siliceous spicules
Members of Demospongiae have siliceous spicules, spongin fibers, or both
A fourth class, Sclerospongiae, was formed to contain sponges with massive calcareous skeleton and siliceous spicules

8. Figure 6_02

9. Phylum Porifera
Growth patterns often depend on characteristics of the environment-substrate, direction and speed of water current, space
Many animals live as commensals or parasites in or on sponges-crabs, nudibranch, fish
Sponges grow on a variety of other living organisms such as barnacles, coral, and molluscs
Few predators
Sponges may have an elaborate skeletal structure and often have a noxious odor

10. Sponge growing on coral

11. Phylum Porifera Form and Function
Body openings consist of small incurrent pores or dermal ostia and water outlets or osculum
Inside the body
Water is directed past the choanocytes where food particles are collected
Choanocytes (flagellated collar cells) line some of the canals
Keep the current flowing by beating of flagella
Trap and phagocytize food particles passing by

12. Phylum Porifera Types of Canal Systems
Asconoids: Flagellated Spongocoels
Simplest body form
Small and tube-shaped
Water enters a large cavity, the spongocoel
Lined with choanocytes
Choanocyte flagella pull water through
All Calcarea are asconoids
Leucosolenia and Clathrina are examples.

13. Figure 6_04

14. Class Calcarea

15. Phylum Porifera Syconoids: Flagellated Canals
Resemble asconoids but larger with a thicker body wall
Wall contains choanocyte-lined radial canals that fold back and forth to make canals then empty into spongocoel
Water enters radial canals through tiny openings called prosopyles, then to radial canals, then apopyle to spongocoel
Spongocoel is lined with epithelial cells rather than choanocytes
Food is digested by choanocytes

17. Phylum Porifera Leuconoids: Flagellated Chambers
Most complex and are larger with many oscula
Clusters of flagellated chambers are filled from incurrent canals, and discharge to excurrent canals- no spongocoel
Most sponges are leuconoid
The leuconoid system
Evolved independently many times in sponges
System increases flagellated surfaces compared to volume
More collar cells can meet food demands
Large sponges filter 1500 liters (400 gals) of water per day

18. Phylum Porifera Types of Cells
Sponge cells are arranged in a gelatinous extracellular matrix, mesohyl (filler)
Connective “tissue” of sponges
Absence of organs requires that all fundamental processes occur at the level of individual cells
Only visible activities of sponges are
Slight alterations in shape, local contraction, propagating contractions, and closing and opening of incurrent and excurrent pores
Movements occur very slowly

20. Phylum Porifera Pinacocytes Form pinacoderm Flat epithelial-like cells
Somewhat contractile
Some are myocytes that help regulate flow of water

21. Phylum Porifera Choanocytes
Oval cells with one end embedded in mesohyl
Exposed end has one flagellum surrounded by a collar
Collar consists of adjacent microvilli
Forms a fine filtering device to strain food
Particles too large to enter collar are trapped in mucous
Moved to the choanocyte and phagocytized
Food engulfed by choanocytes is passed to archaeocytes for digestion

24. Phylum Porifera Archaeocytes Move about in the mesohyl
Phagocytize particles in the external epithelium
Can differentiate into any other type of cell
Sclerocytes secrete spicules
Spongocytes secrete spongin
Collencytes secrete fibrillar collagen
Lophocytes secrete collagen

25. Phylum Porifera
Skeletal structure of a sponge can be fibrous and/or rigid
If present, rigid skeleton consists of calcareous or siliceous spicules
Fibrous portion
Collagen protein fibrils in intercellular matrix
Several types of one form of collagen, spongin, exists
Composition and shape the spicules
Forms the basis of sponge classification

26. Phylum Porifera Desmospongia-spongin, siliceous spicules or both
Calcarea-spicules 1,3 or 4 rays
Hexactinellida-spicules 6 rays
Sclerospongiae-spicules

29. Phylum Porifera Sponges consume detritus, plankton, and bacteria
Digestion is intracellular
No respiratory or excretory system-diffusion, Contractile vacuoles in freshwater sponges
No nervous system
Excellent filtering ability, some sponges can crawl

30. Phylum Porifera Sexual Reproduction
Most are monoecious-male and female sex cells in one individual
The free-swimming larva of sponges is a solid parenchymula

32. Phylum Porifera
Asexual reproduction can occur by bud formation or fragmentation
External buds-budding
Small individuals that break off after attaining a certain size
Internal buds or gemmules
Formed by archaeocytes that collect in mesohyl
Coated with tough spongin and spicules
Survive harsh environmental conditions
Sponges have a great ability to regenerate lost parts and repair injuries
Regeneration following fragmentation

33. Gemmule formation

34. Phylum Porifera Classification Class Calcarea-having spicules
Class Hexactinellida-glass sponge
Class Demospongiae-horn sponges like the bath sponges also freshwater sponges
Class Sclerospongiae-coralline or tropical reef sponges

35. Class Calcarea (Calcispongiae)
Phylum Porifera
Class Calcarea (Calcispongiae)
Calcareous sponges with spicules of calcium carbonate
Spicules are straight or have three or four rays
Most are small with tubular or vase shapes
Many are drab in color, but some are bright yellow, green, red, or lavender
Leucosolenia and Sycon are marine shallow-water
Asconoid, syconoid and leuconoid body forms

36. Class Hexactinellida (Hyalospongiae)
Phylum Porifera
Class Hexactinellida (Hyalospongiae)
Glass sponges with six-rayed spicules of silica
Nearly all are deep-sea forms
Most are radially symmetrical
Stalks of root spicules attach them to substrate

37. Phylum Porifera Class Demospongiae
Contains 80% of living sponge species
Spicules are siliceous but not six rayed
Absent or bound together by spongin
Leuconoid body form
All marine except for Spongillidae, the freshwater sponges
Freshwater sponges
Widely distributed in well-oxygenated ponds and springs
Flourish in summer and die in late autumn
Leave behind gemmules
Marine demosponges
Highly varied in color and shape
Bath sponges
Lacks siliceous spicules, have spongin skeletons

38. Figure 6_13a

39. Figure 6_13b

40. Figure 6_13c

41. Phylum Porifera Phylogeny and Adaptive Diversification
Sponges appeared before the Cambrian
Glass sponges expanded in the Devonian
One theory
Sponges arose from unicellular choanoflagellates
However, some corals and echinoderms also have collar cells, and sponges acquire them late in development
Molecular rRNA evidence suggests
Common ancestor for choanoflagellates and metazoans
Sponges and Eumetazoa are sister groups with Porifera splitting off before radiates and placozoans

42. Phylum Porifera Adaptive Diversification
Poriferans are a highly successful group
Diversification centers on their unique water-current system and its degree of complexity
New feeding mode has evolved for a family of sponges found in deepwater caves
Tiny hook-like spicules cover body
Spicule layer entangles crustaceans
Filaments of the sponge body grow over prey
Carnivores, not suspension feeders
Contain siliceous spicules, but lack choanocytes and internal canals
Illustrates the non-directional nature of evolution