Introduction to Sponges PDF

Introduction to Sponges fossil records of sponges date back to the early Cambrian (around 550 million years ago) and possibly Pre-Cambrian period Multicellularity has occurred in unicellular lineages at least 25 times → one such lineage included multicelled animals, such as phylum Pori...

Introduction to Sponges fossil records of sponges date back to the early Cambrian (around 550 million years ago) and possibly Pre-Cambrian period Multicellularity has occurred in unicellular lineages at least 25 times → one such lineage included multicelled animals, such as phylum Porifera, commonly known as sponges → most evidence points to choanoflagellates as the ancestors to animals Ecological Relationships there are approximately 5,000 species of sponges, mainly marine → there are about 150 species of freshwater sponges sponges grow on a variety of other living organisms, such as barnacles, coral, and mollusks → contrary to this, other animals can live as commensals or parasites both in and on sponges; including crabs, fish, etc. sponges have very few predators, due to their elaborate skeletal structures, aposematic coloration, and ability to produce a noxious odor the growth pattern of sponges is dependent on the shape of substrate, available space, and both the direction and speed of water currents General Features of Phylum Porifera Porifera means “pore-bearing,” which is a feature among sponges, since they have many pores and canals the skeleton of sponges are composed of spicules in size many species are brightly colored due to pigments in dermal cells some sponges appear radically symmetrical, but many are irregular in shape and have no symmetry the majority of sponges are filter feeders living sponges are assigned to 3 classes: 1) Calcarea 2) Hexactinellida 3) Demospongiae → a 4th class called, Homoscleromorpha, was a former subgroup of Demospongiae Sponge Structures and their Functions dermal ostia (ostium): small incurrent pores on the outside of a sponge that allows water to enter oscula: a large water outlet at the top of a sponge that allows water and waste to exit mesohyl: an extracellular matrix made up of a collagen-like gel, that provides structural support in sponges and transports nutrients Types of Sponge Cells choanocytes (collar cells): ovoid cells that line flagellated canals and chambers, that have various functions such as maintaining flows of water throughout the a sponge, digestion, and reproduction → one end is embedded in the mesohyl, while the exposed end contains the central flagellum and is surrounded by a collar of microvilli → flagella beat to pump water through the sponge, while the microvilli acts as a filter to strain food out from the water → particles too large to enter the collar of microvilli are trapped in mucus, then phagocytized by choanocytes; which later is moved to archaeocytes for digestion archaeocytes: ameboid cells that move within the mesohyl, and phagocytize particles in the external epithelium → archaeocytes are able to differentiate into other types of cells: 1) sclerocytes: cells that secrete spicules, which provide structure to the skeleton of sponges and some protection 2) spongocytes: cells that secrete spongin, which is a flexible protein that makes up the body wall and encases spicules to hold them together 3) collencytes: cells that secret fibrillar collagen to help form the mesohyl pinacocytes: flat epithelial-like cells that form a pinacoderm layer to cover exterior surfaces and some interior surfaces, which help provide minor protection against abrasions → some pinacocytes can transform into contractile myocytes to help regulate the flow of water porocytes: tubular cells that pierce the body wall, and remain contractile to control the water flow Types of Skeletons Fibrous Skeletons Rigid Skeletons all sponges with fibrous skeletons contain rigid skeletons are mostly comprised fibrils of collagen throughout the of spicules that can be made from extracellular matrix (ECM) either silica or calcium carbonate, which usually is a variation that → different varieties of collagen occur (eg: important to taxonomy Demospongiae species secret spongin, while → Demospongiae and glass sponges secrete Homoscleromorphs are the only sponges that make type IV collagen that is usually and in siliceous spicules, while calcareous sponges other animals) secrete calcium carbonate spicules Sponge Physiology sponges consume detritus, plankton, and bacteria → digestion is intracellular freshwater sponges have contractile vacuoles that have filtering capabilities → larger sponges can filter up to 1,500 liters of water per day some sponges can crawl up to 4 millimeters per day Adaptive Diversification diversification among sponges centers on their unique water-current system and its degree of complexity new methods of feeding have evolved for a family of carnivorous sponges that are found in deep water caves → some characteristics of these sponges include: tiny hook-like spicules that cover the body, that is used to entangle crustaceans and grows over them they lack choanocytes and internal canals Classes of Sponges Calcarea sponges in this class have spicules made of calcium carbonate, that are straight and tend to have 3 or 4 rays most sponges in this class are small with tubular or vase shapes many are lacking in color, but can sometimes be bright yellow, green red, and lavender sponges in this class can have any of the 3 canal systems, asconoid, syconoid, and leuconoid Hexactinellida (Hyalospongiae) sponges in this class are known as glass sponges, that have spicules made up of silica and have 6 rays most are radially symmetrical nearly all sponges in this class are deep-sea forms glass sponges have a unique tissue structure known as, syncytial tissue → the trabecular reticulum is the largest continuous syncytial tissue among animals, and is bilayered with choanoblasts and other cells → collar bodies of choanoblasts line chambers bet ween the bilayers of the trabecular reticulum to collect food Demospongiae sponges of this class have both siliceous spicules and/or spongin this class makes up 80% of all living sponge species, and have the leuconoid canal system almost all sponges in this class are marine, except for Spongillidae, which are freshwater sponges freshwater sponges inhabit well-oxygenated ponds and springs, and flourish in summer → when they die in late autumn, they leave behind gemmules freshwater sponges have siliceous spicules, and have spongin skeletons; making them more suitable for use as a bath sponge marine sponges can highly vary in colors and shapes Homoscleromorpha a subgroup of sponges that were formerly part of the Demospongiae class these marine sponges live in cryptic habitats and come in a range of colors a unique feature is that their pinacoderm have a basal lamina, which is not a true tissue, known as incipient epithelium → these sponges are the link bet ween having non-tissue and true tissue (eg: Collegen IV vs. incipient epithelium) Types of Canal Systems asconoid: the simplest body form of a sponge where they appear small and tube shaped, and are lined with choanocytes * refer to Sponge Structures and their Functions and Types of Sponge Cells, for how asconoid channel systems work → all ascanoid sponges are in the calcarea class syconoid: sponges that resemble asconoids, but are larger and have thicker body walls that are lined with epithelial cells instead of choanocytes → water enters through dermal ostia which lead to incurrent canals, then move to radial canals through prosopyles, which then exit through apopyles that lead to spongocoel leuconoids: channel systems that are larger and have many oscula; sponges with this channel system are the most complex, with spongocoel → like other channels, chambers are lined with choanocytes and water enters through incurrent canals, then are discharged to current canals that lead to oscula the leuconoid system evolved independently many times among sponges, where the system increased flagellated surfaces compared volume, since more collar cells can meet food demands → most sponges are leucanoids Reproduction and Development sponges are able to regenerate lost parts and repair injuries, along with reproducing asexually most sponges are monoecious, meaning they have both male and female sex cells → sperm arise from transformed choanocytes → oocytes develop from choanocytes or archaeocytes sperm released from one individual enters the canal system of another individual, where it gets taken in through choanocytes which become carrier cells, to carry sperm through mesohyl to oocytes → some sponges are oviparous, meaning they release both oocytes and sperm into water parenchymula: a free-swimming larvae of a sponge, that is an asexual reproductive bud → once larvae settle on a substrate, out wardly directed flagellated cells on the larval surface migrate inwards to become choanocytes in flagellated chambers all sponges form external buds that can remain or detach to form colonies, known as fragmentation sponges also have internal buds known as gemmules, that are dormant masses of encapsulated archaeocytes → gemmules can sur vive harsh environmental conditions such as drought, freezing, lack of oxygen, etc.