Poriferans Flashcards
What does poriferan mean
Pore bearing
Poriferan general overview/ history
- simplest animal group among multicellular/metazoans
- possess unique body forms from other animals but show genetic similarity
- paraphyletic: members evolved from 2 or more ancestors
- fossils exist since 580M years ago
Poriferans feeding
Pelagic feeders
-feed in floating/ drifting microorganisms
Poriferan habitat
98% marine, 2% fresh water, no terrestrial species
- sessile: most are attached, few are mobile like protoplasmic Amoeboid movement
- fork aquatic community among sedentary organisms
- provide shelter for other aquatic organisms including Cyanobacteria and bacteria
Poriferan shape
Mostly shapeless and asymmetrical with few exemptions
-anterior, posterior or oral regions not clearly differentiated
Poriferan organs systems
Lack specialized organ system for reproduction, digestion, sensory, respiration and excretion
Poriferans possess redufferentiation capacity meaning:
Ability to reaggregate to reform when split
Poriferan general body Plan
-Body is rigid, perforated bag (porocyte), with flagella (known as choanocyte or collar cells) lining the interior.
Body divided into
- Spongicoel (internal space of a sponge)
- choancyte: used in capture of food and sperm for fertilization and generate current of seawater through and within the organism.
- mesohyl: gelatinous, no living layer containing live and mobile Amoeboid cells called archaeocytes
- epidermis: pinacocyte and nucleus
Archaeocytes move within the mesohyl by cytoplasmic streaming and perform important functions like:
- differentiate into specialized cells when necessary
- food digestion
- stored digested food material
- may give rise to flagellated sperm and eggs
- non-self recognition when in contact with other sponges
- become specialized into secreting supporting elements
Secreting supporting elements
- may be calcareous or siliceous spicules or may be fibrous collagenous protein called spongin within the mesohyl layer
- cells secreting spicules are called sclerocytes and those secreting spongin are spongicytes
Function of spicyles and spongin fibers
Maintain shape, scaring predators and classifying sponges
Gemmules
Seasonal dormant cells produced by freshwater and some marine poriferans to avoid harsh environmental conditions.
-hatch under favourable conditions releasing cells which differentiation into functional sponges
-also a means of asexual reproduction, releasing many identical offspring
How are gemmules formed
Formed by phagocytizing other cells and surrounding them with thick cells making them resistant to harsh environmental conditions (freezing, drying up and anoxia)
Tissue regression
Fresh water and some marine species in unfavourable conditions can reduce drastically into tiny mass with a protective coat
Pinacocyte
Outer covering arranged in layers called a pinacoderm
Ostia
Narrow opening/ channels allowing water into the sponge which are released by a single osculum
-some members are large (1m) and can filter several litres of water per day through Ostia for food captured by internal flagella
Diversity of the poriferans
- differentiated into 3 levels of complexity of the choanocyte in the relation to the spongocoel
- simplest to most complex = asconoid sponge, syconoid sponge, leuconoid sponge (largest group)
Asconoid sponge
-vase-like-radially symmetrical, tubular, small (usually <4cm tall), with single osculum or opening from internal atrium
Syconoid sponge
First stage of body wall folding
- Invaginations (incurrent canals), and Evaginations (radial canals) but each of these are blind and do not meet, but are linked by prosopyles
- produced by folding of pinacoderm and choanoderm: increase thickened of mesohyl-outer part=cortex
- choanocytes now in chambers, not directly in atrium
- connected to atrium and to outside with system of canals, but connection to outside may be via Ostia openings in thickens pinacoderm
Leuconoid sponges
- produced by further folding and thickening of mesohyl, flagellated canals become flagellated chambers: openings to these called prosopyles, water exits chambers via apopyle , excurrent canals lined by pinacocytes
- increase complexity and increase surface area
- regulation of water flow through sponge-it is not uniform
- water speed function of cross sectional diameter of channels
- permits choanocytes to move water through a small volume: achieve adequate exchange
Classification of poriferans based on chemical composition and morphology of the support elements:
- calcarea
- desmospongiae
- hexactinellida
- homoscleromorpha (previously part of desmospongiae)
Class Calcarea-calcareous sponges
- spicules composed of calcium carbonate only!!!!!, no spongin
- all spicules are of the same general size and shape, Monaxons with 3 (triactinate) or 4 (quadractinate) points
- all 3 body types found in this class-asconoid, syconoid and leuconoid (this class only)
- many have little colour but there are some brilliantly coloured totes found at shallow depths
Class Hexactinellida (Glass Sponges)
- Silica spicules (some have chitinous fibers as well) - Triaxon with 6 points (hexactinellid)
- some species inhabit soft bottom sediment, supported by turf of spicules, others attach to substrate
- complex in structure and symmetry
- body canal may be leuconoid or syconoid
- body layers have unique multinuclei within a cell cytoplasm
- lack pinacoderm
- basal long-thin silica fibers emits light through my to be for direction
- osculum covered by a sieve plate of silica spicules
- marine and usually grow in deep water
- may provide protection and habitual for commensal shrimp.
Differences of calcarea and Hexactinellida
Hexactinellida are
- larger than calcarea (30-40cm)
- less tendency to grow in clusters than calcarea
