Biological Sciences
Nematoda Characteristics
Nematodes, or roundworms, are characterized by their unsegmented, cylindrical bodies and a protective cuticle. They are found in diverse habitats, including soil, freshwater, and marine environments. Nematodes play important roles in nutrient cycling and can be both beneficial and harmful to plants and animals, making them a significant focus of study in ecology and agriculture.
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10 Key excerpts on "Nematoda Characteristics"
eBook - PDF- Gregory A. Lewbart(Author)
- 2021(Publication Date)
- Wiley-Blackwell(Publisher)
537 Invertebrate Medicine, Third Edition. Edited by Gregory A. Lewbart. © 2022 John Wiley & Sons, Inc. Published 2022 by John Wiley & Sons, Inc. Natural History and Taxonomy The most numerous of the multicellular organisms, 23 000 spe- cies have been described, but over 1 000 000 species of nematodes are estimated worldwide (Platt et al. 1984; Giblin‐Davis 2000; Lambshead and Boucher 2003; Blaxter 2011; Seesao et al. 2017). Some estimates are even larger with the possibility of up to 100 million species (Dorris et al. 1999). The bulk of information about the phylum Nematoda is concerned with the thousands of parasitic species, particularly those of medical, veterinary, and entomopathogenic significance, and the free‐living Caenorhabditis elegans. It is believed that nematodes originated in freshwater and migrated to and colonized saltwater and terrestrial habitats. The free‐living species occur in widely differing habitats, including pools of polar ice, hot springs, marine waters, and the bottoms of beer‐fermenting vats, as well as soils and detritus of all types. They are the most highly ecologically and physiologically adapt- able metazoans. Recent molecular taxonomic work has placed the nematodes, along with other molting protostomes, including all arthropods, into a clade called the ecdysozoans (Giribet and Edgecombe 2017; Giribet and Edgecombe 2019). The typical nematode is bilaterally symmetrical, elongated, and tapered at both ends, although the head is somewhat bluntly rounded or truncate and has a terminal mouth (Figures 21.1– 21.3). A slitlike anus is subterminal at the posterior tip, which generally tapers to a point. Nematodes are more or less circular in cross section. Coloration may range from colorless to black- ish, with most species translucent, their color imparted by the gut contents and intestinal cell inclusions. The cuticle is vari- ously marked, sculptured, or scaly, usually in a transverse pat- tern that may be difficult to detect.
eBook - ePub- Dennis Jacobs, Mark Fox, Lynda Gibbons, Carlos Hermosilla(Authors)
- 2015(Publication Date)
- Wiley-Blackwell(Publisher)
CHAPTER 6 Nematoda (‘roundworms’) part 1: concepts and bursate nematodes- 6.1 Introduction
- 6.2 Key concepts
- 6.2.1 Recognition features
- Surface structures
- Accessory sexual structures
- Head, mouth and associated structures
- Appearance in histological sections
- 6.2.2 General biology
- Feeding mechanisms
- Life-cycle
- 6.2.1 Recognition features
- 6.3 Bursate nematodes
- 6.3.1 Bursate superfamilies
- The ‘strongyles’
- General strongyle life-cycle
- General strongyle epidemiology
- 6.3.2 Trichostrongyloidea
- Important trichostrongyloids
- Ostertagia and Teladorsagia
- Haemonchus
- Trichostrongylus
- Nematodirus
- 6.3.3 Strongyloidea
- Important strongyloids
- Strongylus
- The cyathostomins
- Syngamus and Stephanurus
- 6.3.4 Ancylostomatoidea (hookworms)
- Important hookworms
- Ancylostoma
- Uncinaria
- 6.3.5 Metastrongyloidea (lungworms)
- General life-cycle
- Important lungworms
- Angiostrongylus
- Oslerus (Filaroides)
- Dictyocaulus
- Metastrongylus
- 6.3.1 Bursate superfamilies
6.1 Introduction
As most nematode roundworms are tiny and unpretentious, they escape public attention and are generally ignored by wild-life filmmakers. Nevertheless, they are one of the most numerous and diverse metazoan life-forms on this planet. The great majority are free-living, with species adapted to virtually every habitable aquatic or terrestrial ecological niche. A small minority are parasitic on plants and an even smaller proportion exploit animals for part or all of their life-cycle. Even so, the number of animal parasitic nematodes can be daunting for the student. Luckily, a detailed knowledge of every pathogenic species is unnecessary. This is because closely related nematodes tend to have similar life-cycles, epidemiology, pathogenesis and drug susceptibilities. An appreciation of group characteristics therefore saves a lot of repetitive learning. In this context, the best taxonomic level for our consideration is the superfamily (with names ending in –oidea; see Section 1.2.2). This chapter and the next provide an overview of these shared traits and outline the biology of an illustrative selection of important nematode parasites within each category.
eBook - ePubParasitology
An Integrated Approach
- Alan Gunn, Sarah J. Pitt(Authors)
- 2022(Publication Date)
- Wiley(Publisher)
Nematodes are very uniform in their appearance, and their thin, elongate, and cylindrical shape explains why they are commonly known as ‘roundworms’. They lack a well‐defined head and have a worm‐like (vermiform) body that tapers at the anterior and posterior ends. The body is covered by a complex layered cuticle that is secreted by the underlying epidermis and is periodically shed during the juvenile stages to enable growth. The cuticle is proteinaceous but, unlike that of insects, it is not chitinous. Nematodes do, however, contain chitin, and it occurs in their eggshells, their pharynx, and in the sheath of microfilarial nematodes. In common with other higher invertebrates, nematodes are triploblastic and bilaterally symmetrical. That is, they have three primary germ layers during embryonic development, and the left side of their body is arranged the same as the right side. Although some nematodes have annulations (ridges around the body) on the surface of their cuticle there are no body segments and unlike the trematodes and cestodes they do not have suckers. Their body cavity takes the form of a pseudocoelom that contains fluid (haemolymph) at exceptionally high pressure and serves to maintain the hydrostatic skeleton. For example, the pressure within A. suum is 6.6–37.6 kN m −2, which is considerably higher than that of other invertebrates with hydrostatic skeletons: in earthworms the pressure is only 0.28–2.8 kN m −2. The high internal pressure necessitates the cuticle to be extremely strong and affects other aspects of nematode biology. For a more familiar comparison, typical values for human blood pressure would be 16 kN m −2 systolic and 11 kN m −2 diastolic. The mouth of nematodes is usually surrounded by lips/mouthparts that are arranged symmetrically, and there is a muscular pharynx that pumps food into the body. The gut is tube‐like and terminates in an anus close to the posterior of the worm
eBook - PDFNematology
Concepts, Diagnosis and Control
- Mohammad Manjur Shah, Mohammad Mahamood, Mohammad Manjur Shah, Mohammad Mahamood(Authors)
- 2017(Publication Date)
- IntechOpen(Publisher)
Section 1 Recent Nematode Diagnostic Methods and Tools Chapter 1 Introductory Chapter: Nematodes - A Lesser Known Group of Organisms Mohammad Manjur Shah and Mohammad Mahamood Additional information is available at the end of the chapter http://dx.doi.org/10.5772/intechopen.68589 1. Introduction Nematodes are a group of lesser-known but the most abundant group of multicellular organ-isms on earth. They can be defined as a group of thread/worm-like, transparent, bilaterally symmetrical, pseudocoelomate and multicellular organisms that are free-living or parasitic to plants or animals. Numerically, they form the most abundant phylum within the meio- and mesofauna. However, for many of us, nematodes are something unseen and unheard. It is assumed to be due to their small size as well as their habit of remaining hidden in soil, water, plant and animal tissues. Nematodes, being ubiquitous, are associated with plants, insects, other invertebrate and vertebrate animals including domestic animals and even human beings. They exhibit different modes of life—parasitic (plant and animal), free-living, preda -tory, insect associates, entomopathogenic, terrestrial, aquatic (marine and freshwater) etc. The plant parasites may be migratory ectoparasites (feeding at different places but the body remaining outside of plant tissue) or migratory endoparasites (feeding at different places at the same time migrates inside the plant tissue) and some of them may be sedentary (in the forms with obese females like Meloidogyne sp.). Some are semiendoparasites (half of the body embedded in plant tissues while half remains outside), for example, Tylenchulus semipenetrans . 2. Brief history Our knowledge of animal parasitic nematodes is much more ancient than that of plant-parasitic and free-living forms. Animal parasitic forms were known to us as early as 1500 BC. Large round worm like Ascaris lumbricoides and the dreaded Guinea worm, Dracunculus medinensis , etc., were known at that time [1].
eBook - PDF- A.J. Nappi(Author)
- 2002(Publication Date)
- CRC Press(Publisher)
C hapter 7 General Morphology of Parasitic Nematodes Nematodes are unsegmented worms that typically are elongate and cylindrical in shape with tapered ends. Roundworms vary considerably in size from microscopic to over a meter in length. They possess a fluid-filled cavity or pseudocoel, and a complete digestive system comprised of an anterior mouth, a muscular esophagus (pharynx), an intestine, and a rectum that terminates posteriorly at the anus. The mouth may be surrounded by lips and a buccal cavity with cutting plates or teeth. Parasitic nematodes commonly feed on the semi-liquid contents of the host’s alimentary canal, intestinal mucosa, blood or other body fluids, and various lysed tissues. In some forms, the muscular esophagus is cylindrical and virtually of a uniform diameter throughout, and the parasite is termed filariform. This type of esophagus generally characterizes infective stage larvae. In certain other nematodes, the esophagus is expanded posteriorly into a valved bulb, and the parasite is termed rhabditiform (Fig. 1). The latter type frequently characterizes the free-living larval stages. Some nematodes have both filariform and rhabditiform stages in their life cycles. The body is covered by a non-cellular cuticle, which may exhibit longitudinal ridges, striations, wart-like structures, lateral expansions anteriorly and posteriorly, and spines. Before reaching sexual maturity, all nematode larvae undergo a series of four molts or ecdyses. Cuticular structures of some importance are amphids and phasmids. Amphids are a pair of minute sensory organs, considered to be chemoreceptors that open on each side of the head. Phasmids are a pair of caudal (post-anal) organs similar in structure to amphids. Some phasmids are glandular and serve an excretory function, while others are sensory and believed to be involved in chemoreception.
- Prasad, D(Authors)
- 2021(Publication Date)
- Biotech(Publisher)
Chapter 32 Biology and Life-Cycle of Economically Important Plant Parasitic Nematodes Kabindra Singh Rathour * and D. Prasad Division of Nematology, I.A.R.I., New Delhi – 110 012 The word ‘Nematode’ is derived from the Greek words- ‘nema’ meaning thread, and ‘oides’ meaning resembling or form ( i.e. threadworms). They are also known as roundworms being tubular in shape and rounded in cross section. In USA they are often nick-named nemas and Britishers call them eelworms. Nematodes may be defined as triploblastic, bilaterally symmetrical, unsegmented, pseudocoelomate, vermiform metazoans with well developed reproductive, digestive, excretory, nervous and musculature systems and with lacking specialized organs for respiration and circulation. They have tubular gonads which open separately in females but join elementary canal in males to open through a cloacal aperture. Life-Cycle The life-cycle of plant parasitic nematodes start with eggs, the embryonic and post-embryonic stages. Generally, there are six stages in the life cycle– the egg, four larval or juvenile stages, and the adult male or female. The life cycle is simple and direct ( Figures 32.1A and 1B ). This ebook is exclusively for this university only. Cannot be resold/distributed. After a series of cell divisions (transverse and longitudinal), the 1 st stage larva (lacking of stylet) is formed. However, in the dorylaims ( Longidorus spp.; Trichodorus spp. and Xiphinema spp. etc.), a weak stylet is discernible. In majority of plant parasitic nematodes except the dorylaims, after embryogenesis the 1 st stage larva (J1) is formed and still enclosed within the egg-shell and it is the only second stage larva (J2) which normally emerges as the infective stage. In the dorylaim nematodes, the first stage larva itself emerges from egg followed by a quick moult in to second-stage larva.
eBook - PDF- Andreas Schmidt-Rhaesa(Author)
- 2013(Publication Date)
- De Gruyter(Publisher)
Wilfrida Decraemer, August Coomans and James Baldwin 1 Morphology of Nematoda Nematode morphology forms the basis for understanding nematode development, function, behavior, evolution and relationships. Nematodes are apparently simple orga-nisms, but their similar appearance is deceiving as these animals possess amazing plasticity to adapt to a wide range of conditions and habitats. In the last decade, mor-phological studies have developed toward a more integra-ted approach, combining classical and modern tools and techniques, such as electron, confocal and 4D microscopy (Bumbarger et al. 2007, Ragsdale & Baldwin 2010), with information from molecular analyses and gene studies (Bert et al. 2008). Nematodes are generally described as small, non-segmented animals with typical thread-like bodies ( nema = thread in Greek). They are mostly translucent, allowing observation of their internal anatomy by light microscopy without dissection or sectioning. Nematodes possess an apparently simple and relatively conserved basic body plan that consists of an external cylinder (the body wall) and an internal cylinder (the digestive system), which are separated by a pseudocoelomic body cavity filled with fluid under pressure and containing a number of cells and other organs, such as the reproduc-tive tract. 1.1 General and external morphology 1.1.1 Size Free-living and plant-parasitic nematodes are usually smaller than 1 mm. The smallest free-living marine nematode species so far recorded was a female of Hapa-lomus minutus (Desmoscolecida), 82 μm long, that was described from a sandy beach in Togo, whereas the longest species is Cylicolaimus magnus (Leptosomati-dae, Enoplida), 21 – 34 mm long, first recorded from the English Channel. The shortest plant-parasitic nemato-des are less than 300 μm long ( Neopsilenchus minor , Tylenchidae), and the longest may grow up to 12 mm ( Paralongidorus epimikis , Longidoridae).
- Hazem Shawky Fouda(Author)
- 2019(Publication Date)
- Delve Publishing(Publisher)
2.2 CLASSIFICATION It is evident that recent studies showed that the nematodes can be placed in the phylum Nematoda. The present-day classification shows that the nematodes can survive in diverse habitats and due to this they possess diverse habits. The Adenophorea members can survive in fresh water and they are free living. This specific class can comprise of 3 plant- parasitic genera. These species generally come under Dorylaimina. Most of the parasites harboring the animals come under Enoplida. We can observe a lot of diversity in class Secernentia. The members of this class have diverse behavior and their habitats are diverse. Some of the members of Tylenchida order and can attack leeches. The members of Spirurida, Ascaridida can attack vertebrates. Petersen has described the fecundity of Reesimermis nielseni . Otieno has explained the parasitic development stages of this organism. 2.3 IDENTIFICATION There is a key to identify the nematodes which can be linked with the insects. Some of these members can be linked with the bio control work and some were proved as effective candidates. There are some nematodes which can use the insects as the hosts and they even inflict disease and sometimes it may lead to the death of the insect. These nematodes need a vertebrate host. If we observe the heteroxenous parasites, they are capable of utilizing the insects and they use them mainly as hosts. These nematodes can be encircled by the host cells and they are rarely seen in the intestinal tract. The pharynx Biological Control with Nematodes 31 and the stylet can be rarely present and they do not have any valves. Mostly we can observe juvenile stages only. If we observe the monoxenous parasites, they use a specific host. We can see both adult and juvenile stages. These nematodes can survive freely in the body cavity. Mostly there wil be no host tissue surrounding them. The stylet is absent whereas valved pharynx is present.
eBook - PDF- Jack Chernin(Author)
- 2000(Publication Date)
- CRC Press(Publisher)
What are the characteristic features of digenean eggs? Outline the basic life-cycle of both a monogean and a digenean trematode. Describe the larval stages that can occur during a digenean life-cycle. What are the necessary requirements of a trematode habitat? What are the general characteristics of nematodes? Give a general description of a typical nematode. What are the distinguishing features of the internal anatomy of a nematode? How does a nematode maintain its body shape and what type of ‘skeleton’ does it have? Describe the mouth parts of a nematode in relation to its type of feeding. 41 P A R A S I T O L O G Y Question 3.6 What types of musculature do nematodes have? Question 3.7 Describe the nervous system and sense organs associated with nematodes. Question 3.8 Outline the nematode reproductive system. Question 3.9 Describe a typical nematode life-cycle. Question 3.10 Name the different orders of nematodes. 42
eBook - PDF- Bert Zuckerman(Author)
- 2012(Publication Date)
- Academic Press(Publisher)
Behavior of Free-Living Nematodes DAVID B. DUSENBERY School of Biology Georgia institute of Technology Atlanta, Georgia 30332 I. Introduction 127 II. Locomotion 128 A. General 128 B. Methods of Analysis 129 C. Repertoire 131 D. Mechanism of Accumulation 132 E. Influence of Environmental Factors on Movement 136 III. Sensory Behavior 137 A. Stimuli 137 B. Genetics 144 C. Adaptive Value 148 IV. Stage-Specific Behavior 152 A. Larvae 152 B. Dauer Larvae 153 C. Males 153 D. Senescent Nematodes 155 V. Summary 155 References 156 I. INTRODUCTION The nematodes form a very important group of animals that have received much less study than deserved. They appear to be nearly as important in human health and agriculture as insects, and yet there are ten times as many entries in Biological Abstracts for the latter. Even from a less ethnocentric point of view, nematodes are significant. Hyman (1951) estimates 500,000 nematode species, 127 NEMATODES AS BIOLOGICAL MODELS Copyright © 1980 by Academic Press, Inc. VOLUME i All rights of reproduction in any form reserved. ISBN 0-12-782401-4 3 128 David B. Dusenbery which is of the same order as is the number of insect species. In soil, where comparisons have been made, the biomass of the two groups is roughly equal (Kühnelt et al., 1976). The great disparity in research effort is simply because nematodes are much less visible to the casual observer. As a consequence of this situation, there is a great need for basic biological research on nematodes. Much of the required work could be done on any typical nematode species, and since the free-living microphagous forms are most convenient to work with, they are of great interest. One of the areas in which basic knowledge is lacking for this group is that of behavior. This void is particularly surprising in view of the fact that behavior is presumably one of the more important aspects of parasitic lifestyles, It is also unfortunate from the point of view of basic behavioral biology.
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