Poriferans and Placozoans (Sponges) PDF

PORIFERANS AND PLACOZOANS Chapter 3 (SPONGES)  Sponges and placozoans constitute the simplest of the multicellular animals (metazoans). Considering the lack of organs and systems in sponges, one can wonder whether sponges are truly multicellular animals or whet...

PORIFERANS AND PLACOZOANS Chapter 3 (SPONGES)  Sponges and placozoans constitute the simplest of the multicellular animals (metazoans). Considering the lack of organs and systems in sponges, one can wonder whether sponges are truly multicellular animals or whether they represent a highly evolved form of colonial living by individual cells.  Long considered an “evolutionary dead end,” it now seems from molecular analyses that while demosponges and glass sponges may well have given rise to no further lineages, the calcareous sponges along with those in another group, the Homoscleromorpha, may in fact be the ancestors of other multicellular animals, making the phylum Porifera paraphyletic.  In addition, Placozoans are thought to have evolved during the Ediacaran eon (635–542 Ma) or Cryogenian era (720–635 Ma) and by some authors are considered to be the most primitive metazoans, older than sponges, and hence their study may be crucial for understanding early stages of metazoan evolution. Objectives 1. Understand the general characteristics, morphology and anatomy, biology, and diversity of poriferans and placozoans; 2. Distinguish poriferans and placozoans from other metazoans; and 3. Determine the importance of poriferans and placozoans on modern invertebrate research. General Characteristics General Characteristics Taxonomy Kingdom – Animalia Subkingdom – Parazoa Phylum – Porifera General Characteristics Latin, “porus” which means “pores”; “ferre” which means “to bear” pore-bearing Animal with pores sessile with porous bodies and choanocytes General Characteristics Inhalent appertures (Ostia) Osculum Spongocoel 2 cell layers Outer ectoderm Inner endoderm Mesohyl General Characteristics Asymmetrical Adults: Sessile Larval Stage: Free- swimming Reproduce by FRAGMENTATION Morphology and Anatomy General Characteristics Choanocytes Flagellum Collar General Characteristics Pinacocytes contractile, flattened, nucleate cells constituting the epidermis and lining internal cavities General Characteristics Porocytes are tubular cells that make up the pores into the sponge body through the mesohyl. General Characteristics Spicules are stiffened rods or spikes made of calcium carbonate or silica which are used for structure and defense. Morphology and Anatomy Morphology and Anatomy Morphology and Anatomy Morphology and Anatomy Asconoid Water in – ostia Spongocoel Water out - osculumç Morphology and Anatomy Syconoid Water in – ostium Incurrent canal Prosopyle Radial canal Apopyle Spongocoel Water out - osculumç Morphology and Anatomy Syconoid Water in – ostium Incurrent canal Prosopyle Radial canal Apopyle Spongocoel Water out - osculum Morphology and Anatomy Leuconoid Water in – ostium Incurrent canal Flagellated chamber Excurrent canal Spongocoel Water out - osculum  Spongin skeleton made of network of protein Morphology and fibers Anatomy Spicules hard spear or star- shaped structures CaCO3 (limestone) or silica (glass) LOCOMOTION Reproduction  Reproduction Sponges can regenerate (regrow) lost body parts through mitotic cell division (asexual) Sponges also reproduce asexually by budding Sponges are hermaphrodites (produce both eggs & sperm) Sponges reproduce Sexually by releasing eggs & sperm into the water from the Osculum Cross-fertilize each other’s eggs  Adaptations Gemmules are specialized buds made to survive harsh weather (hot or cold) Contain food, amoebocytes, and a protective covering of spicules Released when a sponge dies Resist dessication (drying out) Become adult sponge conditions become favorable Diversity and Classifications Diversity and Classifications Class Calcarea have calcareous spicules as in Astaeospongia or more commonly, non- spicular porous chambers. When spicules are present, they are not fused and are typically monaxons and/or tetraxons. Diversity and Classifications Diversity and Classifications Class Demospongea with skeletons of spongin and siliceous spicules, or a skeleton of fused opaline silica. When present, spicules are commonly monaxon, tetraxon, or polyaxon, but never triaxon. Diversity and Classifications Diversity and Classifications Class Hexactinellida (Hyalospongae) with siliceous spicules that are usually triaxons and commonly fused to form a net or box-like pattern. They are often called glass sponges. Grantia Diversity and Classifications Diversity and Classifications Class Homoscleromorpha Recent molecular data that incorporate 18S and 28S ribosomal DNA (rDNA) sequences, along with mitochondrial genome information, support moving these sponges (fewer than 100 species) from the Demospongiae into this separate class, Homoscleromorpha. Although most homoscleromorph species lack spicules, when the spicules are present, they are entirely siliceous, as in hexactinellid sponges, but they have a distinctly different morphology. Diversity and Classifications Class Homoscleromorpha Moreoever, the members of this class are unique among sponges in that they have a clear, distinct basal membrane underlying the epithelium, as well as in the fact that all their epithelial cells bear cilia. Diversity and Classifications Class Sclerospongiae smallest class, which have skeletons that contain all three kinds of material: calcium carbonate, silica, and spongin known as "coralline sponges“