Rev 11/06/2021
Kingdom Animalia
Sub-kingdom Parazoa |
Phyum Porifera: sponges, colonies of cells without apparent specialization of function
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Sub-kingdom Metazoa Acoelomata |
multicellular animals not possessing a true coelom |
Phylum |
Characteristics |
Coelenterata
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(lower
Metazoa, unsegmented,
diploblastic -ectoderm and endoderm) Classes:
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Platyhelminthes
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flatworms,
unsegmented, triploblastic (ectoderm, endoderm
and mesoderm) Classes:
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Nemertea | also flattened worms, but have circulatory system and anus; unsegmented, triploblastic |
Nematoda Diesing, 1861 | roundworms; unsegmented, triploblastic |
Nematomorpha | e.g., Gordius, horsehair worms - like nematodes, but no excretory or lateral chords; unsegmented, triploblastic |
Acanthocephala | like nematodes but hooked proboscis; unsegmented, triploblastic |
Rotifera | have ciliated disks wafting food particles; may anchor at posterior end; have features of platyhelminthes and nematodes. Among the smallest of the metazoa; unsegmented, triploblastic |
Gastrotricha | small, ciliated; have features of Rotifera and Nematoda; unsegmented, triploblastic |
Kinorhynchia | bristles on cuticle, no cilia; have similarities with Rotifera and Gastrotricha; unsegmented, triploblastic |
Priapulida | marine, mud dwellers; have posterior appendages; unsegmented, triploblastic |
Endoprocta | simple, archaic; have tentacles; unsegmented, triploblastic |
Note: in the older literature all these phyla were included as classes of the Aschelminthes, e.g., L.H. Hyman (1930s) | |
All the above phyla are unsegmented and have no coelom. Other invertebrates (Annelida, Arthropoda, etc.) are coelomate, and segmented. |
Nematoda and Nemata are variously used. Both Cobb and Chitwood supported the contraction "nema", and the shorter phylum name. Current argument is for standard use of Nematoda.
(i) unsegmented worms, basic elongate body shape often have cuticular markings - annulation, striation ratio of axes may change with stage and sex, loss of mobility
(ii) bilateral symmetry, radial symmetry superimposed anterior
(iii) Triploblastic - 3-cell layers - ectoderm is a cellular hypodermis (see Bird and Bird, 1991 - prefer epidermis). Endodermal central portion of alimentary canal, ectoderm in anterior and posterior region. Mesoderm cells (e.g., muscles) do not completely surround a body cavity - pseudocoelomate. (Pseudocoelom is vaguely defined as a body cavity not completely surrounded by mesoderm).
(iv) Cuticle - proteinaceous (not chitin) with outer lipid layers; extends into body cavities. Secreted by hypodermis; Usually molted 4 times.
(v) Hypodermis (epidermis) thickened into chords, thicker laterally than dorso-ventrally. Excretory tubules in lateral chords, nerve cells associated with dorso-ventral chords. Muscle groups between chords in four quadrants.
(vi) Movement - generally dorso-ventral undulation, but 3-dimensions (flexibility) - internal hydrostatic pressure counters muscle contraction.
(vii) Excretory system is simple and tubular or epidermal glands, no cilia or flame cells
(viii) No respiratory system - surface-to-volume ratio is important for gaseous diffusion - consider relative to activity. Note: surface of a cylinder: s=2.pi.r.l volume of a cylinder: v=pi.r.r.l s/v ratio for a vermiform nematode = 2/r - as r increases, s/v decreases, independent of length. surface of a sphere: s=4.pi.r.r volume of a sphere: v=(4/3).pi.r.r.r s/v ratio for a spherical organism = 3/r - as r increases, s/v decreases, but is greater than for a vermiform nematode of the same radius. However, movement is compromised.
(ix) No circulatory system - note reversible effects of nemastatic cholinesterase inhibitors (e.g., carbamates Aldicarb)
(x) Sexes usually separate; sexual dimorphism - females with separate
anus and gonopore, male with common
cloaca for intestine and
gonad. Sexual dimorphism may also be exhibited in differences
in size and shape of males and females. Gonads tubular, single or double; Amoeboid sperm. Parthenogenesis common - useful adaptation to parasitism, but no genetic recombination. Males often few, or reduced and do not feed.
(xi) Development by total cleavage of egg - no yolk. Direct develop- ment, no metamorphosis.
(xii) Size range 0.2 mm to 9 meters. Most terrestrial forms <2 mm. Paralongidorus maximus longest plant parasite, 12 mm.
(xiii) Trophic levels - primary consumers, secondary consumers, decomposition food chains (biodegradation, env markers) C:N ratios vs bacteria - mineralization.
Letters to the Editor Nematology Newsletter (June 2000)
Phylum Nematoda or Nemata
I enjoyed reading the articles in Nematology Newsletter 45 (4), especially the article on "The English word "Nema" Revised." Since this article draws again the attention to the existence of two names for the phylum, I would like to make some comments and suggestions.
Maggenti (1981) in his book on General Nematology stated, "I will hold to the concept that nematodes belong in a phylum of their own, Nemata, as first proposed by Cobb, 1919, and reinstated by Chitwood in 1958." Later, Maggenti et al (1987) in their article "A reappraisal of Tylenchina (Nemata). 2. Classification of the suborder Tylenchina (Nemata: Diplogastria)." Revue de Nématologie 10(2) drew our attention to the fact that nematodes, being widely accepted as a phylum, have two different phylum names in use: Nemata (Cobb, 1919) and Nematoda (Potts, 1932).
At the NATO Advanced Research Workshop on Morphological Identification of Plant Parasitic Nematode Genera, Raleigh, June 1988, Maggenti again raised the problem of correct nomenclature and spelling upon phylum status recognition (see Maggenti, 1988, Teaching Nematology: to read is to learn, pp. 313-322 in R. Fortuner, ed. in Nematode Identification and Expert System Technology) and convinced the attendants to use Nemata in the future and, so several of us did. From that period on, you will notice an increase in the use of Nemata compared to a level use of Nematoda (see for example Fundamental and Applied Nematology 15(1) 1992).
However, there are no rules for higher taxa nomenclature. According to Article 1 of the Code of Zoological Nomenclature, the code excludes taxa above the family group. Further , Nemata appeared confusing for my non -nematologist colleagues and also for other nematologists working in other fields, for example on free-living marine nematodes. All textbooks on general zoology use Nematoda as well as do most non-nematologists (for example in recent articles on classification based on molecular data). Both terms for the phylum remained in use in Fundamental and Applied Nematology for example, until volume 20, 1997 in which only Nematoda appears upon action of the chief -editors who systematically changed Nemata into Nematoda.
By writing the article on the English word nema in the newsletter showing a preference for the word nema to nematoid or nematode, I believe it is time that nematologists decide on the use of the phylum name. Since Nematoda is the most commonly used name, although not the oldest one, I propose to indicate it as THE NAME of the phylum to use. A statement could be given by editors of important journals.
Looking forward to comments, I send you my best regards.
Sincerely yours,
Wilfrida Decraemer
Koninklijk Belgisch Instituut voor Natuurwetenschappen
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