These animals have well-developed neuronal and digestive systems. A mouth opening that is ventral to the rhynchocoel leads into the foregut, followed by the intestine. The mantle cavity develops independently of the coelomic cavity. It is estimated that 23 percent of all known marine species are mollusks; there are over 75,000 described species, making them the second most diverse phylum of animals. Most mollusks are dioecious animals and fertilization occurs externally, although this is not the case in terrestrial mollusks, such as snails and slugs, or in cephalopods. It is a cladistic definition (a node-based name), so the affiliation to Lophotrochozoa of spiralian groups not mentioned directly in the definition depends on the topology of the spiraliantree of life, and in some phylogenetic hypotheses, Lophotrochozoa may even be synonymou… The morphology of the shell and the underlying animal can vary from circular to ovate. Parasitic forms feed on the tissues of their hosts. The number of fossil species is estimated between 60,000 and 100,000 additional species. Phylum Annelida includes vermiform, segmented animals. Many flatworms are parasitic, including important parasites of humans. Earthworms are the most abundant members of the class Oligochaeta, distinguished by the presence of the clitellum as well as few, reduced chaetae (“oligo- = “few”; -chaetae = “hairs”). The parasite infects various organs in the body and feeds on red blood cells before reproducing. The name of the phylum is derived from the Latin word annellus, which means a small ring. (b) Polyarthra, from the class Monogononta, has a smaller corona than Bdelloid rotifers, and a single gonad, which give the class its name. In the shell-bearing Nautilus spp., the spiral shell is multi-chambered. Class Aplacophora (“bearing no plates”) includes worm-like animals primarily found in benthic marine habitats. Mollusks are predominantly a marine group of animals; however, they are known to inhabit freshwater as well as terrestrial habitats. Captaculae serve to catch and manipulate prey. This necessarily limits the thickness of the body in these organisms, constraining them to be “flat” worms. QUESTIONS Use the phylogenetic trees at the end of this pdf to answer the following questions. Which node in the 3-domain tree represents the common ancestor of all Eukaryotes? Tapeworm (Taenia spp.) They lack circulatory and respiratory systems, and have a rudimentary excretory system. The Lophotrochozoa- which includes the segmented worms, molluscs, lophophorates and several smaller phyla. Start studying lophotrochozoa: Phylum Mollusca. As the name suggests, bivalves are enclosed in a pair of shells (valves are commonly called “shells”) that are hinged at the dorsal end by shell ligaments as well as shell teeth (Figure 10). The proportion of undescribed species is very high. Nemerteans have almost no predators and two species are sold as fish bait. The rotifers are a microscopic (about 100 µm to 30 mm) group of mostly aquatic organisms that get their name from the corona, a rotating, wheel-like structure that is covered with cilia at their anterior end (Figure 4). Scaphopods are usually buried in sand with the anterior opening exposed to water. Lophotrochozoa: pictures (320) Lophotrochozoa: specimens (126) Lophotrochozoa: maps (42) Related Taxa. Platyhelminthes are traditionally divided into four classes: Turbellaria, Monogenea, Trematoda, and Cestoda (Figure 2). These chambers are filled with gas or water to regulate buoyancy. The flatworms are acoelomate organisms that include many free-living and parasitic forms. Watch the video below to see a nemertean attack a polychaete with its proboscis. The lophophores include groups that are united by the presence of the lophophore, a set of ciliated tentacles surrounding the mouth. Flatworms have an excretory system with a network of tubules throughout the body with openings to the environment and nearby flame cells, whose cilia beat to direct waste fluids concentrated in the tubules out of the body. All have a trochophore larva (from the … Which of the following statements about the anatomy of a mollusk is false? The Lophotrochozoa comprise one of the major groups within the animal kingdom, In turn, the Lophotrochozoa belongs to a larger group within the Animalia called the Bilateria, because they are bilaterally symmetrical with a left and a right side to their bodies. The Platyhelminthes consist of two lineages: the Catenulida and the Rhabditophora. Tapeworms live in the intestinal tract of the primary host and remain fixed using a sucker on the anterior end, or scolex, of the tapeworm body. The remaining body of the tapeworm is made up of a long series of units called proglottids, each of which may contain an excretory system with flame cells, but contain reproductive structures, both male and female. Annelids have a segmented body plan wherein the internal and external morphological features are repeated in each body segment. Lophotrochozoa vs Ecdysozoa Difference between lophotrochozoa and ecdysozoa, the two major bilaterian, is discussed in this article.Based on the recent studies using nuclear and mitochondrial DNA sequences, scientists revised the taxonomy of Animal Kingdom. Additionally, a tongue-like organ called a radula, which bears chitinous tooth-like ornamentation, is present in many species, and serves to shred or scrape food. The mantle (also known as the pallium) is the dorsal epidermis in mollusks; shelled mollusks are specialized to secrete a chitinous and hard calcareous shell. A ring of four nerve masses called “ganglia” composes the brain in these animals. Dactylogyrus, commonly called a gill fluke, is about 0.2 mm in length and has two anchors, indicated by arrows, that it uses to latch onto the gills of host fish. Lophotrochozoa is one of the three major clades that comprise bilateral animals, or Bilateria. These phyla are also bilaterally symmetrical, meaning that a longitudinal section will divide them into right and left sides that are symmetrical. This includes digestive, nervous, excretory, reproductive, and respiratory systems. The flow of fluid in these vessels is facilitated by the contraction of muscles in the body wall. خبـــيـــر الإدارات القانونية وأعمال المحاماة المعتمد, خبـــيـــر العلاقات الدبلوماسية و القنصلية المعتمد, خبـــيـــر الإدارات القانونية وأعمال المحاماة المعتمد – Online, مدير التسويق الإليكتروني المعتمد – Online, يؤسس فريق خدمات الاستشارات الإدارية في المجلس العربي للتنمية الإدارية أعماله على الفهم الكامل للشركات والهيئات، والعمليات التنافسية الفعالة، وبيئة العمل، والأهداف المقررة والتحديات التي …, ورشة عمل ” إستراتيجيات إدارة المعرفة في المؤسسات الحكومية”, ورشة عمل “الإتجاهات الحديثة في بناء السمعة والهوية للشركات”. Most gastropods bear a head with tentacles, eyes, and a style. Eyes may be absent in some gastropods species. The epidermis is protected by an acellular, external cuticle, but this is much thinner than the cuticle found in the ecdysozoans and does not require periodic shedding for growth. Ribosomal RNA sequences show these various phyla to be related. The foot is a retractable as well as an extendable organ. Although their taxonomy is currently in flux, one treatment places the rotifers in three classes: Bdelloidea, Monogononta, and Seisonidea. 1. Tapeworms do not possess a digestive system; instead, they absorb nutrients from the food matter passing them in the host’s intestine. The lophotrochozoans are triploblastic and possess an embryonic mesoderm sandwiched between the ectoderm and endoderm found in the diploblastic cnidarians. Phylum Platyhelminthes is divided into four classes. Can Snail Venom Be Used as a Pharmacological Painkiller?Marine snails of the genus Conus (Figure 13) attack prey with a venomous sting. (credit: Mark A. Wilson). All animals in this class are carnivorous predators and have beak-like jaws at the anterior end. The trematodes, or flukes, are internal parasites of mollusks and many other groups, including humans. The class Turbellaria includes mainly free-living, marine species, although some species live in freshwater or moist terrestrial environments. The tissue beneath the shell is called the mantle. Eyespots and statocysts may be absent in some species. Trematodes have complex lifecycles involving a molluscan secondary host and a primary host in which sexual reproduction takes place. Excretion is facilitated by a pair of metanephridia (a type of primitive “kidney” that consists of a convoluted tubule and an open, ciliated funnel) that is present in every segment towards the ventral side. The mantle is always withdrawn at the rear to form a mantle cavity, which contains anus and gills. سجل بياناتك الآن وسوف يتم إبلاغكم عند فتح باب التسجيل. Cephalopods such as squids and octopi also produce sepia or a dark ink, which is squirted upon a predator to assist in a quick getaway. The epidermal tissue is a single layer cells or a layer of fused cells (syncytium) that covers a layer of circular muscle above a layer of longitudinal muscle. This combination video and animation provides a closeup look at annelid anatomy. Sexual dimorphism is the predominant sexual strategy in this phylum. The name “mollusca” signifies a soft body, since the earliest descriptions of mollusks came from observations of unshelled cuttlefish. Figure 12. Figure 2. These animals possess a radula that is modified for scraping. Phylum Annelida includes segmented worms. Figure 13. A unique characteristic of this phylum is the presence of a proboscis enclosed in a rhynchocoel. Trematodes are responsible for serious human diseases including schistosomiasis, a blood fluke. Cestodes, or tapeworms, infect the digestive systems of primary vertebrate hosts. Rotifers are typically free-swimming and truly planktonic organisms, but the toes or extensions of the foot can secrete a sticky material forming a holdfast to help them adhere to surfaces. These animals lack a well-developed respiratory system, and gas exchange occurs across the moist body surface. A circulatory system consists of a closed loop of a pair of lateral blood vessels. In many dioecious species, males are short-lived and smaller with no digestive system and a single testis. Lophotrochozoa is a monophyletic group of animals that includes annelids, molluscs, bryozoans, brachiopods, platyhelminthes, and other animals that descended from the common ancestor of these organisms. (a) Species from the class Bdelloidea are characterized by a large corona, shown separately from the whole animals in the center of this scanning electron micrograph. Examples are shown in Figure 14. This is called protostomy or “first mouth.” In protostomy, solid groups of cells split from the endoderm or inner germ layer to form a central mesodermal layer of cells. In some nemertine species, a pilidium larva may develop inside the young worm, from a series of imaginal discs. T. saginata, which infects both cattle and humans, can reach 4–10 meters in length; the specimen shown here is about 4 meters. The blood vessels are connected to the rhynchocoel. Members of class Monoplacophora (“bearing one plate”) posses a single, cap-like shell that encloses the body. Some species bear a specialized band of segments known as a clitellum. Reproduction in cephalopods is different from other mollusks in that the egg hatches to produce a juvenile adult without undergoing the trochophore and veliger larval stages. Phylum Mollusca is a very diverse (85,000 species) group of mostly marine species. Phylum Annelida contains the class Polychaeta (the polychaetes) and the class Oligochaeta (the earthworms, leeches and their relatives). The overall body can be divided into head, body, and pygidium (or tail). Digestive and excretory wastes are collected in a cloacal bladder before being released out the anus. The proboscis may be extended or retracted by the retractor muscle attached to the wall of the rhynchocoel. Alimentary, nervous, and excretory systems are more developed in the nemertini than in less advanced phyla. These animals are found in marine, terrestrial, and freshwater habitats, but a presence of water or humidity is a critical factor for their survival, especially in terrestrial habitats. These clades are upheld when RNA sequences are compared. Some animals may also have cross-connecting vessels in addition to lateral ones. Gastropoda includes shell-bearing species as well as species with a reduced shell. Trematodes have complex lifecycles that involve a primary host in which sexual reproduction occurs, and one or more secondary hosts in which asexual reproduction occurs. However, cross-fertilization is preferred in hermaphroditic animals. Mollusks have a radula for grinding food. University of California Museum of Paleontology -- Introduction to the Brachiopoda Brachio-Philes - a good up to date intro to the Brachiopods. The Platyhelminthes consist of two lineages: the Catenulida and the Rhabditophora. A pair of protonephridia, or primitive kidneys, is present in these animals to facilitate osmoregulation. Gonads are interspersed with the intestinal diverticular pouches and open outwards via genital pores. This property has been commercially exploited to produce pearls. Members of this class are found in marine as well as freshwater habitats. The many chetae of polychaetes are also arranged within fleshy, flat, paired appendages that protrude from each segment called parapodia, which may be specialized for different functions in the polychates. Links. Figure 4. The (a) nautilus, (b) giant cuttlefish, (c) reef squid, and (d) blue-ring octopus are all members of the class Cephalopoda. These worms typically reproduce asexually by budding. Several phyla within the Lophotrochozoa have trochophore larvae (Nemertea, Mollusca, Sipuncula, Echiura, Pogonophora, Annelida), and several have a lophophore, a ring of tentacles encircling the mouth (Bryozoa, Entoprocta, Phoronida, Brachiopoda).. 1. Some bivalves like oysters and mussels possess the unique ability to secrete and deposit a calcareous nacre or “mother of pearl” around foreign particles that may enter the mantle cavity. Phylum Mollusca is a large, marine group of invertebrates. (c) The Trematoda class includes Fascioloides magna (right) and Fasciaola hepatica (two specimens of left, also known as the common liver fluke). Phylum Cnidaria includes animals that show radial or biradial symmetry and are diploblastic, that is, they develop from two embryonic layers. Paired longitudinal nerve cords emerge from the brain ganglia and extend to the posterior end. Figure 18. Annelida: information (1) Annelida: pictures (33) Class Aplacophora. Most of the flatworms are classified in the superphylum Lophotrochozoa, which also includes the mollusks and annelids. The planarian is a flatworm that has a gastrovascular cavity with one opening that serves as both mouth and anus. Members of a species mate, and the female then lays the eggs in a secluded and protected niche. The (a) earthworm, (b) leech, and (c) featherduster are all annelids. (credit a: modification of work by S. Shepherd; credit b: modification of work by “Sarah G…”/Flickr; credit c: modification of work by Chris Gotschalk, NOAA). These animals bear a single conical shell, which has both ends open. These animals are asymmetrical and usually present a coiled shell (Figure 11). These findings have led researchers to study conotoxins for possible medical applications. The rotifers are filter feeders that will eat dead material, algae, and other microscopic living organisms, and are therefore very important components of aquatic food webs. The visceral mass is present above the foot, in the visceral hump. Nearly all (about 99 percent) cnidarians are marine species. Torsion is an independent process from coiling of the shell. This is called “jet” propulsion. This cavity is quite distinct from the coelomic cavity, which in the adult animal surrounds the heart. CLADE LOPHOTROCHOZOA Phylum Platyhelminthes Hickman Chapter 14 Getting Ahead Figure 14.1 (page 290) Clades within Protostomia Phylum Platyhelminthes Characteristics of Phylum Platyhelminthes (page 295) Form and Function Figure 14.7 (page 294) Epidermis, Muscles Figure 14.9 (page 295) Nutrition and Digestion Excretion and Osmoregulation The flatworms are acoelomates, so their bodies are solid between the outer surface and the cavity of the digestive system. – A free PowerPoint PPT presentation (displayed as a Flash slide show) on PowerShow.com - id: 45b91f-NmY1Z These animals may also show simultaneous hermaphroditism and participate in simultaneous sperm exchange when they are aligned for copulation. (credit: David Burdick, NOAA). The Catenulida, or "chain worms" is a small clade of just over 100 species. However, the offspring do not fully attach from the parents and, resemble a chain in appearance. Most of the flatworms are classified in the superphylum Lophotrochozoa, which also includes the mollusks and annelids. The worms may produce enzymes that digest the host tissues or simply graze on surface mucus and skin particles. Bivalves often possess a large mantle cavity. Nemertea are soft and unsegmented animals (Figure 6). Many of the eggs are released in feces and find their way into a waterway, where they are able to reinfect the primary snail host. Figure 5. These worms typically reproduce asexually by budding. Some conotoxins have been shown to block neuronal ion channels. The system is responsible for the regulation of dissolved salts and the excretion of nitrogenous wastes. Females of some species care for the eggs for an extended period of time and may end up dying during that time period. The group is characterized by the rotating, ciliated, wheel-like structure, the corona, on their head. These animals lack a calcareous shell but possess aragonite spicules on their epidermis. A looped digestive system, multiple pairs of excretory organs, many gills, and a pair of gonads are present in these animals. The mantle cavity encloses the ctenidia as well as a pair of nephridia. (a) Class Turbellaria includes the Bedford’s flatworm (Pseudobiceros bedfordi), which is about 8–10 cm in length. Ocelli or eyespots are present in pairs, in multiples of two in the anterior portion of the body. The anatomy of a Nemertean is shown. Phylum Platyhelminthes. Figure 14. Annelids show the presence numerous chitinous projections termed chaetae, and polychaetes possess parapodia. This phylum can be segregated into seven classes: Aplacophora, Monoplacophora, Polyplacophora, Bivalvia, Gastropoda, Cephalopoda, and Scaphopoda. Some of the phyla classified as Lophotrochozoa may be missing one or both of these defining structures. The head contains sensory organs in the form of a bi-lobed brain and small eyespots near the corona. A chitinous-toothed tongue called the radula is present in most mollusks. All of the remaining flatworms discussed here are part of the Rhabditophora. Aplacophora: information (1) Aplacophora: pictures (5) ... Phylum Bryozoa moss animals. (d) Class Cestoda includes tapeworms such as this Taenia saginata. The clitellum, seen here as a protruding segment with different coloration than the rest of the body, is a structure that aids in annelid reproduction. Shown are examples from two of the three classes of rotifer. Mollusks have a muscular foot, which is used for locomotion and anchorage, and varies in shape and function, depending on the type of mollusk under study. A digestive gland is connected to the stomach. The number and size of chaetae are greatly diminished in Oligochaeta compared to the polychaetes (poly=many, chaetae = hairs). Mollusks have a dramatic variety of form, ranging from large predatory squids and octopus, some of which show a high degree of intelligence, to grazing forms with elaborately sculpted and colored shells. The cladogram above shows the major groups in the Lophotrochozoa. Since the entire spectrum of conotoxins, as well as their mechanisms of action, are not completely known, the study of their potential applications is still in its infancy. The foot is the ventral-most organ, whereas the mantle is the limiting dorsal organ. 2. Mollusks are eucoelomate, but the coelomic cavity is restricted to a cavity around the heart in adult animals. It also means the beginning of cephalization, the evolution of a concentration of nervous tissues and sensory organs in the head of the organism, which is where it first encounters its environment. Annelids are protostomes. Mollusks are protostomes. Mollusks display a wide range of morphologies in each class and subclass, but share a few key characteristics, including a muscular foot, a visceral mass containing internal organs, and a mantle that may or may not secrete a shell of calcium carbonate (Figure 8). Figure 10. One of the functions of the mantle is to secrete the shell. Most monogeneans are hermaphroditic, but the male gametes develop first and so cross-fertilization is quite common. Annelids display bilateral symmetry and are worm-like in overall morphology. Respiration is facilitated by gills known as ctenidia. Animals in class Gastropoda (“stomach foot”) include well-known mollusks like snails, slugs, conchs, sea hares, and sea butterflies. Phylum Mollusca is the predominant phylum in marine environments. This schematic drawing shows the basic anatomy of annelids in a cross-sectional view. Mollusks can be divided into seven classes, each with distinct morphological characteristics. Animals belonging to superphylum Lophotrochozoa are triploblastic (have three germ layers) and unlike the cnidarians, they possess an embryonic mesoderm sandwiched between the ectoderm and endoderm. The juvenile worm infects the intermediate host and takes up residence, usually in muscle tissue. In addition, these vessels are connected by transverse loops in every segment. The mastax or jawed pharynx is another structure unique to this group of organisms. The eggs are eaten by an intermediate host. Most flatworm species are monoecious, and fertilization is typically internal. http://cnx.org/contents/185cbf87-c72e-48f5-b51e-f14f21b5eabd@9.44:1/Biology, Describe the unique anatomical and morphological features of flatworms, rotifers, Nemertea, mollusks, and annelids, Describe the development of an extracoelomic cavity, Discuss the advantages of true body segmentation, Explain the key features of Platyhelminthes and their importance as parasites, Describe the features of animals classified in phylum Annelida. There are four traditional classes of flatworms, the largely free-living turbellarians, the ectoparasitic monogeneans, and the endoparasitic trematodes and cestodes. Trochophore larvae are characterized by two bands of cilia around the body. These mussels, found in the intertidal zone in Cornwall, England, are bivalves. The Lophotrochozoaare a diverse group of phyla. Mollusk species that are exclusively aquatic have gills for respiration, whereas some terrestrial species have lungs for respiration. A well-developed and complete digestive system is present in earthworms (oligochaetes) with a mouth, muscular pharynx, esophagus, crop, and gizzard being present. They are also more “typical” lophotrochozoans, since both groups include aquatic species with trochophore larvae, which unite both taxa in common ancestry. Figure 9. Figure 7. Some species bear hemoglobin as well as other yellow or green pigments. Clicking on the lineages on the phylogenetic trees will take you to the Wikipedia entry for that group. Most of the flatworms are classified in the superphylum Lophotrochozoa, which also includes the mollusks and annelids. The species is a member of the phylum Nemertea. This chiton from the class Polyplacaphora has the eight-plated shell that is indicative of its class. Figure 11. The subclass Brachiobdella includes species like Branchiobdella balcanica sketi and Branchiobdella astaci, worms that show similarity with leeches as well as oligochaetes. The nemertini show a very well-developed digestive system. Describe the features of animals classified in phylum Annelida The annelids and the mollusks are the most familiar of the lophotrochozoan protostomes. In this lab we will examine one acoelomate lophotrochozoan phylum and several smaller pseudocoelomate and eucoelomate lophotrochozoan phyla. Describe the features of animals classified in phylum Annelida The annelids and the mollusks are the most familiar of the lophotrochozoan protostomes. Nevertheless their placement with the Lophotrochozoa is upheld when ribosomal RNA and other gene sequences are compared. Figure 5 shows the anatomy of a rotifer belonging to class Bdelloidea. Flatworms have three embryonic tissue layers that give rise to surfaces that cover tissues (from ectoderm), internal tissues (from mesoderm), and line the digestive system (from endoderm). Members of class Scaphopoda (“boat feet”) are known colloquially as “tusk shells” or “tooth shells,” as evident when examining Dentalium, one of the few remaining scaphopod genera (Figure 15). Ctenidia are enclosed in a large mantle cavity and are serviced by large blood vessels, each with its own heart associated with it; the mantle has siphonophores that facilitate exchange of water. Describe the features of animals classified in phylum Annelida The annelids and the mollusks are the most familiar of the lophotrochozoan protostomes.
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