Acoelomate Animals à organs are embedded in tissue, not in any body space (like us) several phyla including Platyhelminthes share the following characteristics: like cnidaria and ctenophora 1. have 3 true embryonic tissue layers à only 1 “internal space” =digestive cavity (=triploblastic): ectoderm 4. in terms of development these organisms are mesoderm protostomes endoderm between epidermis and digestive cavity is filled à mouth develops first in embryo during with a 3rd tissue layer = mesoderm gastrulation à mesoderm allows development of muscle 5. most have bilateral symmetry layers in body wall such design allows for a “front end” à mesoderm allows more elaborate organs = cephalization more specialization and greater division of labor than in Cnidaria head contains sense organs, simple brain 2. have true organs was a major new design each organ is a combination of several tissues à more efficient search for food, mates, etc specialized for a particular function most animals before this were sedentary filter feeders sponges have various specialized cells but no true tissues or organs jellyfish and corals have 2 true tissue layers and a few simple organs 3. acoelomate=without body cavity Animals - Animal Phyla: Phylum Platyhelminthes; Ziser Lecture Notes, 2015.10 1 Animals - Animal Phyla: Phylum Platyhelminthes; Ziser Lecture Notes, 2015.10 2 Phylum Platyhelminthes diverse array of parasitic species that parasitize (Flatworms) members of virtually every other animal phylum [helminth = worm] more specialization and division of labor among greater variety of tissues and organs simplest phylum at “organ level” of complexity acoelomate = no body cavity around digestive very diverse group but most are poorly known system includes flatworms, flukes, tapeworms have three true tissue layers (primary germ layers) = triploblastic 25,000 living species, few fossils à no hard parts embryonic adult tissues tissues poorly known in fossil record but possible trails have ectoderm à epidermis been found from 565MY mesoderm à parenchyma endoderm à gastrodermis may be first animal to have a head & tail may be first animal to have bilateral symmetry mesoderm makes more elaborate organs possible may be first animal to show directed movement à it differentiates into different kinds of wide variety of body forms all with bilateral symmetry muscle layers body is usually elongated & slender, leaf-like or organ systems are better developed long & ribbon-like only major phylum that is mostly parasitic species à flattened body allows them to still rely on of 4 classes, 3 are made up of entirely parasitic diffusion for exchange of gasses, nutrients species and wastes Body Wall range in size from few mm à 10 M long A. Epidermis free living in ocean and freshwater habitats, moist soil Animals - Animal Phyla: Phylum Platyhelminthes; Ziser Lecture Notes, 2015.10 3 Animals - Animal Phyla: Phylum Platyhelminthes; Ziser Lecture Notes, 2015.10 4 free living forms have single layer of ciliated cells eversible in some à can be extended to find food parasitic forms have syncytial layer that lacks cilia secretes enzymes to partially digest food before “eating” then suck in liquified food B. Muscle Layers once ingested enzymes are secreted into GVC two layers around body wall: mostly extracellular digestion circular muscle some intracellular after phagocytosis longitudinal muscle Respiration no rigid skeleton for muscles to act on no respiratory system thick muscle layers in pharynx (=feeding tube) make it “prehensile” flatworms have high surface/volume ratio in some primitive species these muscle cells gas exchange through flattened body wall resemble the epitheliomuscular cells of cnidarians Feeding & Digestion Nervous System free living forms are mainly carnivores beginnings of cephalization most species are endoparasites ie. at least some members have distinct head incomplete digestive tract in most flatworms were probably the first creatures to have a “brain” in some planarians digestive tract is highly branched to distribute food throughout the animal head with cephalic ganglia (~ simple brain) some parasites (eg. tapeworms) completely lack a digestive system have pair of ventral nerve cords pharynx = muscular “throatlike” tube connected by ladder like interconnections Animals - Animal Phyla: Phylum Platyhelminthes; Ziser Lecture Notes, 2015.10 5 Animals - Animal Phyla: Phylum Platyhelminthes; Ziser Lecture Notes, 2015.10 6 with true synapses between nerve cells some times produces a chain of zooids Excretion à superficial resemblance to segmentation they are the simplest major phylum with an excretory system regeneration some wastes like ammonia are eliminated by diffusion flatworms have considerable powers of through the body wall regeneration others have primitive excretory system replacement of lost parts = protonephridia (tube closed at one end and exiting body at other end) also to recover from long food shortage à in most takes the form of “flame cells” budding cupshaped area with tuft of flagella beat of flagella tapeworms bud off proglottids (reproductive resemble candle flame under microscope sacs) wastes and excess water diffuse into bulb polyembryony flagella create current to send wastes through tube which opens to outside of the body flukes Reproduction one egg can produce 100’s of larvae many reproduce both sexually and asexually increases chances finding a host Asexual Sexual fission almost all flatworms are monoecious (hermaphrodites) pinch in half Animals - Animal Phyla: Phylum Platyhelminthes; Ziser Lecture Notes, 2015.10 7 Animals - Animal Phyla: Phylum Platyhelminthes; Ziser Lecture Notes, 2015.10 8 cross fertilization not self fertilization Classification some with internal fertilization Class Turbellaria (planarians) free living ventral mouth locomotion by creeping on cilia and mucous Class Monogenea ectoparasites on skin or gills of fish simple life cycle – no intermediate host Class Trematoda (flukes) all are parasitic endoparasitic flukes parasites in blood or digestive system up to 5 developmental stages in 2 or more hosts Class Cestoda (tapeworms) all are parasitic endoparasites in intestine bud long chains of proglottids Animals - Animal Phyla: Phylum Platyhelminthes; Ziser Lecture Notes, 2015.10 9 Animals - Animal Phyla: Phylum Platyhelminthes; Ziser Lecture Notes, 2015.10 10 Class Turbellaria Feeding & Digestion (Planarians) incomplete digestive tract in most almost all are free living àmouth, no anus mostly bottom dwelling aquatic forms some have more than one mouth & more than one mostly freshwater pharynx some are marine a few are even terrestrial (6 sp in US) mainly carnivorous flattened, slender, ribbonlike or leaflike bodies feed on small crustacea, nematodes, rotifers, insects à still rely on diffusion for much exchange of gasses, nutrients and wastes can detect food at a distance by chemoreceptors often brightly colored entangle their prey in mucous some marine forms have warning coloration wraps its body around prey Body Covering some marine flatworms prey on molluscs using a neurotoxin produced by symbiotic bacteria epidermis is ciliated they engulf the whole animal or cover the opening of its secretes mucous trail and uses cilia to glide on it shell then produce the toxin to kill it land planarians can glide ~6’/hr pharynx = muscular “throatlike” tube contains rhabdites extend prehensile proboscis to get prey discharge into water swell and form protective mucous sheet around body secretes enzymes to help “predigest” prey may also release toxins to subdue prey and escape predators sucks up bits of prey Animals - Animal Phyla: Phylum Platyhelminthes; Ziser Lecture Notes, 2015.10 11 Animals - Animal Phyla: Phylum Platyhelminthes; Ziser Lecture Notes, 2015.10 12 in intestine secrete enzymes which further digest prey auricles also contain chemoreceptors phagocytic cells in gastrodermis take up bits of pieces some turbellaria have statocysts for reacting to of prey and complete digestion intracellularly gravity GVC extends to most parts of body Excretory System à also serves as distribution system protonephridia with “flame cells” undigested food is egested through mouth in freshwater forms this is mainly a way to get rid of Nervous System & Senses excess water distinct head with cephalic ganglia metabolic wastes still excreted through body wall pair of ventral nerve cords connected by ladder- reduced or absent in marine forms like interconnections Reproduction sense organs concentrated on head (vision, smell, touch, taste) Asexual Reproduction paired sense organs allow brain to discern the a. Regeneration direction of the stimulus turbellarians have considerable powers of 2 eyespots (=ocelli) regeneration can’t form images, only detect light àreplacement of lost parts auricles contain tactile cells àalso to recover from long food shortage tactile cells are also distributed over body some can survive for months by self surface digesting up to 90% of their body Animals - Animal Phyla: Phylum Platyhelminthes; Ziser Lecture Notes, 2015.10 13 Animals - Animal Phyla: Phylum Platyhelminthes; Ziser Lecture Notes, 2015.10 14 cross fertilization not self fertilization early researchers also reported learning by cannibalism some with internal fertilization taught planarian to run a maze cut in half and allowed to regenerate both new worms learned the maze quicker some with vaginas & penises - usually open through common genital pore à has never been repeated??? in some monoecious flatworms mating ritual resembles a fight: b.