Marine Biology Lecture (2) PDF

 Types of Cells  Absence of tissues and organs means that fundamental processes occur on the cellular level.  Respiration and excretion occur by diffusion in each cell.  Types of Cells  Pinacocytes are thin, flat, epithelial- type cells that cover...

 Types of Cells  Absence of tissues and organs means that fundamental processes occur on the cellular level.  Respiration and excretion occur by diffusion in each cell.  Types of Cells  Pinacocytes are thin, flat, epithelial- type cells that cover the exterior and some interior surfaces of the sponge.  Mesohyl is the gelatinous matrix containing skeletal elements and amoeboid cells.  Other cell types secrete skeletal elements  1- spicules (sclerocytes),  2- spongin (spongocytes) and  3- collegen (collenocytes).  Choanocytes, flagellated collar cells, generate a water current through the sponge and ingest suspended food.  The choanocytes pass food particles to archaeocyte cells (amoeboid cells) for digestion.  Digestion occurs entirely within cells, there is no gut.  Suspension Feeders  Sponges are suspension feeders capturing food particles suspended in the water that passes through their body. archaeocyte cells (amoeboid cells)  Suspension Feeders  Water flows in through incurrent pores called dermal ostia.  It flows past the choanocytes where food particles are collected on the choanocyte collar.  Choanocytes take in:-  small particles by phagocytosis. Protein molecules by pinocytosis.  Sponges can also absorb nutrients dissolved in the water.  Sexual reproduction  Most sponges are hermaphrodites meaning that each individual functions as both male and female. Monoecious  Gametes are derived from archaeocytes.  Most sponges are (viviparous): after fertilization, the zygote is retained and is nourished by the parent. Ciliated larvae are later released.  Some are (oviparous) releasing gametes into the water.  Asexual reproduction  Sponges have remarkable regeneration capabilities.  Regeneration following fragmentation is a form of asexual reproduction.  External buds can break off to form new sponges.  Internal buds (gemmules) in freshwater sponges can remain dormant in times of drought.  Radiate Animals  Phylum Cnidaria & Phylum Ctenophora  Radial Symmetry  Diploblastic – 2 embryonic tissue layers  Phylum Cnidaria  All animals except sponges belong to the clade Eumetazoa (the animals with true tissues).  Phylum Cnidaria is one of the oldest groups in this clade.  Habitat A. Aquatic 1. Most Marine 2. Few fresh-water Cnidarians: Animals with Stinging Cells ORGANIZATION OF THE CNIDARIAN BODY 1. Radial symmetry  2- CNIDARIAN BODY PLANS Cnidarians often exhibit two different body plans in their life cycles 1. Polyp (cylindrical body) 2. Medusa (Umbrella shape)  Polyp  Sessile  cylindrical body that has an opening at one end, the mouth, which is usually surrounded by a ring of tentacles Hydra sea anemone Coral  Medusa  Umbrella shape  Tentacles around mouth  Motile, Free-floating Body Wall 1- an outer tissue layer, the epidermis, derived from ectoderm 2- Inside the body is a large cavity (gastrovascular cavity) that is lined by a layer of cells called the gastrodermis, derived from endoderm 3- Between these two layers is a gelatinous material called mesoglea.  Body Wall  Level of organization is tissues not organs  The epidermal layer contains several types of cells organized into tissues. In colonial forms, polyps may be specialized for feeding, reproduction, or defense.  STINGING CELLS Stinging cells help jellyfish catch prey because they contain organelles called nematocysts. a specialized cell containing a barbed or venomous coiled thread that can be projected in self-defence or to capture prey.  TYPES OF CNIDARIANS Representative cnidarians include hydrozoans, jellyfish, sea anemones, and corals. These marine predators include colonial and solitary benthic organisms, as well as some of the largest members of the marine plankton: Hydrozoans Scyphozoans Anthozoans  1- Class Hydrozoa  Hydrozoans are Mostly marine.  Usually colonial, sometimes solitary.  Class Hydrozoa - Polyps  Colonial forms of hydrozoans usually contain two types of polyp: The feeding polyp (gastrozooid) and the reproductive polyp (gonozooid) Class Hydrozoa – Typical Life Cycle  Class Hydrozoa Green Hydra Brown Hydra with buds Brown Hydra eating Hydra eating Daphnia  Class Hydrozoa - Medusae  Hydroid medusae are usually smaller than those in the class Scyphozoa.  Around the inside of the opening is a muscular ring of tissue called the velum. The velum can contract and relax, changing the diameter of the opening, and playing an important role in swimming  Specialized organs:  Statocysts – equilibrium allow them to detect gravity and their orientation.  Ocelli – light sensitive  Class Hydrozoa Order: Siphonophora  E.X: Portuguese man-of-war  Are actually colonies of polyp individuals.  One polyp may be gas filled and used as a float.  Feeding polyps each with one long tentacle  Reproductive polyps Portuguese Man 0f War (a Hydrozoan), NOT a true jelly fish  Portuguese Man 0f War Tentacles of Physalia physalis Class Hydrozoa  Hydrocorals resemble true corals.  Calcareous skeleton  Fire coral  2-Class Scyphozoa  In the class Scyphozoa, medusae are the prevalent form of the life cycle.  No velum present.  Rhopalium : sense organ containing statocysts and sometimes ocelli.  Class Scyphozoa  Tentacles contain nematocysts used to paralyze prey animals.  In the center are four frilly oral arms used to capture and ingest prey.  Jellyfish Purple lion’s mane Lion’s mane Sea Nettle Upside down Jelly fish Giant Jelly off Coast of Japan