MARINE Invertebrates BIOL 505 Understanding Marine Invertebrates, Their Environments and Processes

Poriferans Poriferan General Features Phylum Porifera Defining characteristic: collar cells (choanocytes) with microvilli surrounding a flagella. Arise from single cells or syncytia. Most spp. (98%) are marine. No terrestrial. 5,000 – 10,000 extant spp. Lack nervous system, musculature, locomotion, specialized reproductive, digestive, respiratory, sensory, or excretory systems. No organs at all! No oral, anterior, or posterior regions.

Poriferans Poriferan General Features Only few cell types within individual, but cells function independently. When dissociated, cells dedifferentiate into amoeboid cells, reaggregate, then redifferentiate to form sponge. Amazingly, sponge cells can recognize other spp., as well as self cells within same spp. Demonstrated in >25 spp. Multicelluar? Or organized colonial living by individual cells?

Poriferans Poriferan General Features Typically fairly rigid, perforated bag with inner surface lined with flagellated cells (choanocytes or collar cells). Empty space inside sponge – spongocoel. Choanocytes: 1.Generate current for ventilation of water through sponge. 2.Capture food particles 3.Capture incoming sperm for reproduction.

Poriferans Poriferan General Features Next to choanocyte layer is layer of gelatinous, non- living material – mesohyl (“middle stuff”). Although non-living and acellular, it contains amoeboid cells – archeocytes that wander through mesohyl by cytoplasmic streaming.

Poriferans Poriferan General Features Archeocytes: 1.Digest food material captured by choanocytes. Digestion completely intracellular. 2.Store digested food 3.Can differentiate into sperm (flagellated) or eggs (although gametes can develop through changes to choanocytes, too!). 4.Likely participate in non-self recognition in contact with other sponge spp. 5.Act to eliminate waste material.

Poriferans Poriferan General Features Archeocytes: 6.Can become specialized to secrete structural elements in the mesohyl – spicules made of either Si, or CaCO 3, or fibers made of spongin protein. Cells secreting spicules – “sclerocytes” Cells secreting spongin – “spongocytes” Both derived from archeocytes.

Poriferans Poriferan General Features

Poriferans Poriferan General Features Archeocytes: Spicules and fibers from spongocytes and sclerocytes are: 1.used for spp identification (systematics) 2.used by sponge for support, shape, and discouraging predation.

Poriferans Poriferan General Features Archeocytes: Gemmule formation. At certain times, sponges produce dormant structures – gemmules. 1.Archeocytes gather nutrients by phagocytosis. 2.Archeocytes aggregate and cells around the cluster form a thick capsule around the cluster. 3.When conditions are right, living cells leave the gemmule and differentiate to form a functional sponge.

Poriferans Poriferan General Features Archeocytes: Gemmule formation. Gemmules are more resistant to freezing, desiccation, anoxia than the sponge that produces it. They provide mechanism for withstanding unfavorable conditions by entering period of dormancy. Gemmule formation can be a form of asexual reproduction, resulting in many offspring genetically alike.

Poriferans Poriferan General Anatomy Pinacocytes - outer epithelial layer of most sponges, composed of flattened, contractile cells. Lack a basal lamina. Form an outer layer – pinacoderm. Also form inner layer lining incurrent canals and spongocoel where there are no choanocytes. As pinacocytes contract, causes slight shape changes in sponge and may also help regulate water flow through incurrent openings.

Poriferans Poriferan General Features

Poriferans Poriferan General Anatomy Ventilation Because sponges don’t really move and have no muscles or nerves, they rely on water flow for removing waste, bringing food, gas exchange, movement of sperm. Partly due to action of choanocytes, and partly due to architecture of the sponge (Bernouli’s principle), water flow is efficiently utilized by the sponge. Water flows into the sponge and into the spongocoeld through ostia (small openings around the sponge), and out of the sponge through the osculum (large opening of the spongocoel.

Poriferans Poriferan General Anatomy Ventilation Ostia are always plentiful, but depending on the structure of sponge, may only be one osculum. Large sized sponges must filter large volumes of water per day to obtain sufficient food material. But water moving too fast will not allow food extraction. Instead, water flow is slowed in the choanocytes and speeds up again after entering spongocoel.

Poriferans Poriferan Diversity 3 basic levels of sponge shape: 1.Asconoid – simple, basic tube structure with one osculum. 2.Syconoid – increased degree of evagination with one osculum. 3.Leuconoid – most complex evagination, with multiple oscula. Increased evagination away from spongocoel increases extent of flagellated surface area enclosed by sponge. Most sponges are of leuconoid structure.

Poriferans Poriferan Diversity

Spongia sp ?

Poriferans Poriferan Diversity All sponges are placed in 3 classes based mainly on the chemical structure and morphology of the support structures (spicules). 1.Class Calcarea 2.Class Demospongiae 3.Class Hexactinellida

Poriferans Poriferan Diversity 1.Class Calcarea Have spicules made only of CaCO 3. Class is represented by all 3 types of construction. All living asconoids are in this class.

Poriferans Poriferan Diversity 2.Class Demospongiae Largest class (>80% of all sponge spp.) Have spicules made of spongin and/or silica, but never CaCO 3. Some spp. Have no spicules or fibers. All freshwater sponges (~300 spp.) in this class, and possess contractile vacuoles! Contains a group of deep water, carnivorous sponges (with no ostia, no oscula, nocanal system and no choanocytes) feed by entrapping small crustaceans.

Poriferans Poriferan Diversity 2.Class Demospongiae

Liosina sp?

Xestospongia sp

Poriferans Poriferan Diversity 3.Class Hexactinellida. Sponges with six-rayed, silica spicules. “Glass sponges” Structurally complex and symmetrical. May be either syconoid or leuconoid. Different than other classes because outer layer is syncytial (have several nuclei in single cytoplasmic membrane) rather than cellular, and no pinacoderm layer.

Poriferans Poriferan Diversity 3.Class Hexactinellida. Inner layer also syncytial. Long, thing (~50 um d) silica fibers produced at base of Hexactinellida sponges convey light better than synthetic fiber optics and are structurally superior.

Poriferans Poriferan Reproduction Sponges reproduce both asexually (fragmentation, buds and gemmules), or sexually (eggs and sperm). Many spp. Hermaphroditic. Fertilization and early development usually internal. In some spp. Choanocytes capture incoming sperm, dedifferentiate to become amoeboid cells, then transport sperm to mesohyl where egg is fertilized.

Poriferans Poriferan Reproduction Steps. 1.In some spp. Choanocytes capture incoming sperm, 2.dedifferentiate to become amoeboid cells, 3.transport sperm to mesohyl where egg is fertilized. 4.Retain developing embryo for some time. 5.Release of swimming larvae through oscula. A few spp. are oviparous; fertilized eggs shed into water and embryonic development external.

Psuedospongioformus bobulous larvae

Poriferans Poriferan Reproduction Embryonic Development. In Calcareous sponges. 1.Embryo develops into hollow coeloblastula. 2.In some spp. fast dividing cells at one end become flagellated toward blastocoel. 3.Along slower cell division region, blastula breaks open. 4.Flagellated cells now outside. 5.Flagella propels larva (amphiblastula) through water flagellated end first.

Poriferans Poriferan Reproduction Embryonic Development. In Calcareous sponges. 6.In some spp. the initially hollow coeloblastula fills with cells that detach from blastula wall. 7.Fill the blastocoel. 8.Termed stereoblastula.

Poriferans Poriferan Reproduction Embryonic Development. In Demosponges. 1.Most embryos develop directly into stereoblastula. 2.Differentiate to highly flagellated parechymella (or parenchymulla) larvae, where each cell has its own flagellum. 3.Some parenchymella larvae posses spicules, choanocytes, and basic canal systems.

Poriferans Poriferan Reproduction Embryonic Development. In Hexactnella. 1.Most embryos develop directly into stereoblastula. 2.Differentiate highly and posses siliceous spicules, choanocytes, and basic canal systems. 3.Only cells in the larval midsection flagellated. 4.Each cell has several flagella.

Poriferans Poriferan Reproduction Embryonic Development. Sponge larvae cannot feed. Usually swim for <24 hrs before settling. Once attached to substrate, cells from different parts of the larva migrate and differentiate and begin to form the adult sponge.