Invertebrate Zoology: The Phylum Porifera

-Porus, Ferre (L. pore to bear)
-unusual animals
-from Aristotle and Pliny to 1765, they were classified as plants
-not until recently was water flow observed (18th cent)
-primarily marine, mostly in shallower waters
-sessile, and attached to a substrate or objects, occasionally on other animals such as crabs

-Metazoan - cellular grade (multicellular)
-not a true tissue grade
-diploblastic, with Mesohyl
-Totipotent cells - retain capacity for development
-skeletal elements - mineral, protein (SiO2, CaCO3, spongin)
-Chanocytes ("Funnel cells")
-Adults, sessile, filter feeders
-Larvae - motile (2 larval types)
-Asymmetrical, a few radial

-Sponge Cell Types
-Spicules
-Spongin Fibers

- Pinacocytes - outer cells; equivalent to epidermis
- Chanocytes - similar to choanoflagellates
-collared cells with flagella - create water current and collect food matter
- Porocytes - specialized cells lining the ostia
- Amoebocytes - (=archeocytes) - amoeba-like cells
-store, digest, and transport food, excrete wastes, secrete skeleton
-give rise to buds in asexual reproduction
-Mesohyl (aka Mesenchyme) - beneath the pinacocytes - a gelatinous protein layer
-it contains the skeletal material (ie. spongin and spicules) and amoebocytes

4 Types
-Monaxon - needle-like or rod-like; straight or curved
-Tetraxon - has 4 prongs
-Triaxon or Hexaxon - 3 or 6 rayed
- Polyaxon - multiple short rods radiating from a common center ; burr shaped, star shaped

-give phylum its common name
-some species have no spicules, but have spongin
-spongin is a type of hardened secreted protein
-some species have both spongin and spicules
-Spicule and Spongin Formation - Amoebocytes

-Asconoid
-Syconoid
-Leuconoid
(increase in complexity of structure going down)

• most primitive and simplistic in structure
• have radial symmetry
• are tube shaped
two basic openings
• Ostia - incurrent pores that open into a central cavity called the spongocoel, lined with choanocytes or collar cells
• Osculum - the opening of the spongocoel to the outside, water leaves the sponge
-Asconoid Design
-imposes definite size limits to sponges due to the problem of water flow
-the spongocoel contains such a large volume of water that it is hard to push it out rapidly

-next level of complexity
-walls are invaginated allowing for greater surface area over which water can pass
-typically vase shaped like the asconoid sponges
-radial symmetry
-structure helps rectify some of the water movement problem
-increasing the surface area - so there are more choanocytes to water volume (allows for O2 exchange and slows water movement)
-decreasing the spongocoel volume
-these sponges are able to get bigger than asconoid

-highest level of complexity in sponges
-lost radial symmetry and are very irregular in shape and may attain large sizes
-invaginated and folded to form small flagellated chambers
-design further increases surface area, making these sponges highly efficient in moving and filtering water
-spongocoel is gone except for canals that lead to the osculum - or there may be a series of excurrent openings
-the largest sponges; mostly hydrologically efficient

-as surface area increases, flow velocity decreases

-sexual and asexual

Asexual
- budding - fragmentation of body wall, buds appear as outgrowth on sides of sponge - when they reach certain side they drop off and settle to the bottom to form a new sponge
- gemmules - occur only in freshwater sponges - groups of food laden amoebocytes that deposit a hard covering of spicules around them - formation is triggered by environmental conditions such as decreasing temperatures - they allow the sponge to pass the winter or periods of drought, after which the outer covering breaks open and a new sponge develops

Sexual
-gametes formed by amoebocytes
-there are both hermaphroditic and dioecious species
-most hermaphroditic species produce eggs and sperm at different times so they do not self fertilize
-sperm is released into environment via osculum and is brought in by another sponge via ostia
-fertilization takes place in parent sponge
-zygote is expelled - it drops to bottom and begins to develop

-Amphiblastula Larva
-hollow hemisphere
-cilia cover one half
-Parenchymula Larva
-solid sphere
-cilia cover entire cell

-no special organs
-main waste is ammonia -removed by water current with the sponge - is highly soluble in water

Class Calcarea
Class Demospongiae
Former Class Sclerospongiae
Class Hexactinellida

-spicules composed of CaCO3
-monaxon, tri or quadraxon spicules
-all 3 body types
-all less than 10cm high
eg. Leucosolenia and Grantia
-found in shallow coastal waters
-all are marine