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The Lophotrochozoa Protostomes Characteristics • Protostome groups consisting of two large clades the Lophotrochozoans and the Ecdysozoans. • Lophotrochozoans include 10 smaller protostome phyla. • Acoelomate, Pseudocoelomate or Eucoelomate bodies. Protostome Characteristics Protostome Development is characterized by: • blastopore becomes the mouth • Spiral / determinate cleavage • Schizocoely Mouth Formation Blastopore becomes the mouth and the anus forms secondarily Future anus blastopore archenteron (primitive gut) mouth Cleavage • Cleavage is the initial process of development after fertilization of the egg. Radial Cleavage planes are symmetrical to the polar axis Produces regulative development Spiral Cleavage: cleavage planes are oblique to the polar axis Produces mosaic development Schizocoely blastocoel Mesodermal cells Split in mesoderm ectoderm endoderm Developing coelom mesoderm Lophotrochozoans Characteristics The name Lophotorochozoa comes from the names of the larval type of the two major animal groups including the Lophophorata and the Torchozoa. Trochophore Larva Lophotrochozoans Characteristics Organ level of organization Tissues are organized to form organs which are used to accomplish physiological functions. Triploblastic 3 Germ Layers 3 Tissue Layers endoderm gastrodermis mesoderm mesoderm ectoderm epidermis Lophotrochozoans Characteristics Bilateral Symmetry • with anterior and posterior ends Cephalization • concentration of sensory organs in the head of the animal Lophotrochozoans Characteristics Digestive System • complete (they have an anus!) • some regional specialization Circulation System • no system (or organs) • performed by the pseudocoelom fluid Gnathiferans and Smaller Lophotrochozoans The Lophotrochozoa Gnathifera There are 4 different phyla that are classified as Gnathifera. Rotifera Acanthocephala Gnathostomulid Micrognathozoa Gnathifera Characteristics • Other than the Acanthocephalans all phyla posses small, cuticular jaws with a homologous microstructure. Gnathifera Characteristics Eutely • each individual of a species has the same number of cells • growth occurs by cells getting bigger rather than dividing P: Gnathostomulida : gnatho, “jaw”; stoma, “mouth” • • • • • • Benthic, interstitial Monociliated epidermal cells Jaws and muscular pharynx Often vermiform Hermaphroditic About 80 species have been described jaws and basal plate Gnathostomulid P: Micrognathozoa Limnognathia maerski Phylum Rotifera the rotifers Phylum Rotifera: rota, “wheel”; fera, “to bear” • Includes about 1,800 described species. • Tiny metazoans (up to 3 mm), that are predominantly freshwater although some are marine and terrestrial (live in mosses). The “wheel” animals { Head Trunk Foot { { Corona – have a “crown” of cilia called a corona – the corona creates a current to bring food into the mouth Corona of Foscularia species Body Wall and Support • Most rotifers possess a gelatinous cuticle outside the syncytial epidermis. • They possess a skeletal lamina which produces the lorica and other surface structures. Rotifers of the genus Keratella donot possess a foot. They are fast swimmers. Their lorica (shell) looks like a jigsaw puzzle and is covered with small spikes. There are long spines on each corner. The photograph shows how the cilia are grouped in tufts. Kellicottia is a rotifer that lives in open waters of lakes. The long spines might prevent them from being eaten by predators. Well developed and complex muscle bands Body appears to be composed of segments, they are superficial segments. Feeding – have a specialized feeding structure called the: mastax-trophi complex modified jaws within the mastax a modified muscular pharynx Looking down into the corona…. Mastax-trophi complex Some of the trophi (jaws): Ramate mastax These are crushing/grinding forms. Malleate mastax Some of the trophi (jaws): Forcipate mastax These are grasping, predatory forms. Incudate mastax Nervous and sensory system - cephalization, cerebral ganglia - dorsal and ventral nerve cords - eyes Circulatory system – no system (no organs) – performed by fluid in pseudocoelom Excretion – protonephridia and flame cells – cloacal bladder (collects wastes) Reproduction Sexual - complex life cycle with different types of eggs - usually dioecious but in some groups, males are absent (parthenogenesis) - Parthenogenesis: unisexual reproduction where females produce offspring from unfertilized eggs (virgin birth) Reproduction • 2 types of eggs: amictic & mictic Amictic eggs – Asexual Reproduction • diploid (mitotically produced) • can’t be fertilized • develop into diploid, amictic females Reproduction Mictic eggs- Sexual and Asexual Reproduction • • haploid (meiotically produced) produced after some sort of environmental stimulus (eg. high density, change in temperature) if unfertilized, develop into haploid males if fertilized, secrete a thick, protective shell until the environment is favorable again, after which they develop into diploid, amictic females Brachionus is a very common genus. They carry their eggs on their foot. The various species can be identified by the spines on their lorica (shell). Asplanchna is a large bag-shaped rotifer. This individual carries an almost fully developed embryo inside. Eggs maintained in maternal tube Resting eggs of monogonont rotifers Reproduction • Because of the reduced role of males in reproduction, most males are incapable of feeding and do not even have a digestive tract (they are just there for sperm delivery!). • Males have never been recorded in Bdelloid rotifers. This means they haven’t had sex in millions of years!