So, there is a pressing need to develop a consensus on the taxonomic ... assigned for post-graduate students in all Egyptian. Medical ... the sphere of interest of protozoology because nobody is better to study ... Apicomplexa ... Chromalveolata.
Vol. 6, No. 1, 2013
ISSN: 1687-7942
E D I TO R I A L
PUJ
Towards a Unified Taxonomy Hala S. Elwakil1, Sherif M. Abaza2 Departments of Medical Parasitology, Faculty of Medicine, Ain Shams1 and Suez Canal2 Universities Received: March, 2013 An interactive session entitled “Towards a Unified Taxonomy” was presented and settled in the 3rd Annual Conference of the Egyptian Parasitologists United EPU (Ain Shams Guest House; 10-11 October, 2012). Taxonomy and the evolutionary interrelationships of parasites infective to human, remains a topic of debate. So, there is a pressing need to develop a consensus on the taxonomic classification scheme used in the curricula assigned for post-graduate students in all Egyptian Medical Parasitology Departments, with special emphasis on the protozoa. Protozoa The different classification schemes concerning parasitic protozoa were discussed and a voting among the attendees of the conference was done on three main classification schemes: Traditional classification, Utilitarian classification and Super-groups classification. The Super-groups classification was agreed upon by 60% of the attendees. As early as the year 1880 Gold fuss(1) established the concept of 3 great groups of protozoa (amoebae, flagellates and ciliates) on the basis of their mode of locomotion and this number was increased to four by the addition of the sporozoans by Butschli(2). By the beginning of the 1960s, there was an improvement in light microscopy with the related fixation and staining techniques, and the use of electron microscopy which led to exploration of previously unknown sub cellular structures that became of immense value in the comparative taxonomy. This improvement paved the way to publish a revised classification by the Society of Protozoologists in 1964(3). It was widely accepted and appeared in standard textbooks(4). They classified the phylum protozoa into four subphyla; Sarcomastigophra, Sarcodina, Ciliophora and Cnidospora. In 1980, the Society of Protozoologists published its classification(5), which was outlined by Orihel and Ash(6) in their Traditional Classification (Table 1). More recently, studies at biochemical and molecular levels led to expansion in the total number of high-level taxonomic groups and the discovery of new and unique differentiating characteristics. The Utilitarian classification by Corliss(7,8) depends on evolutionary relationships as only one of several factors that will determine groupings of organisms. Familiar names have been retained as far as possible, so as to permit every reference to information retrieval systems. Two kingdoms under the Empire Eukaryota were created: Archezoa and Protozoa (Table 2). Archezoa are defined as eukaryotes that are primitively without mitochondria and peroxisomes. Cavalier-Smith and Chao(9) defined them as remnants of early premitochondriate eukaryote lineages.
Accepted: March, 2013 Studies on rRNA regard Giardia as well as other genera placed in the kingdom Archezoa as very primitive and consider them as representing an early stage of eukaryote evolution(10). In Utilitarian classification the refined kingdom Protozoa is more discriminating and more restricted in its boundaries than was the ‘old’ phylum Protozoa. It contains many conventional groups of old phylum protozoa and is purged of many other major taxa as Opalinids and Microsporidia. Adl et al(11) utilized results from both ultrastructural research since 1980 and molecular phylogenetic studies and transformed the four eukaryotic groups: plants, animals, fungi, and protistsinto six supergroups (Figure 1). They proposed the Super groups classification scheme that is based on nameless ranked systematic subordinate groups. They adopted this system in order to avoid the problem of a single change causing a cascade of changes to the system so it is more flexible and easier to modify. Schmidt and Roberts(12) retained phylum and subordinate taxon names -which are all virtually consistent with the rankings of Adl et al(11) in a published classification(13) as they believed that taxonomic names that are proper nouns are most easily remembered (Table 3). The removal of Archezoa and phagotrophic Chromists from the kingdom Protozoa should not exclude them from the sphere of interest of protozoology because nobody is better to study those groups than protozoologists. Helminthology Kingdom Animalia has a subkingdom Metazoa which includes 2 phyla: Platyhelminthes with 2 classes (Trematodes and Cestodes) and Nematodes. Phylum Platyhelminthes as found in older literature was classified into 4 classes namely Turbellaria, Monogenea; Trematoda and Cestoidea. Class Trematoda was classified into 3 subclasses according mainly to intermediate hosts (Digenea, Aspidogastrea and Didymozoidea). In 1993, Brooks and McLennan(14) utilized more levels than typically encountered in old literature such as superclasses, subsuperclasses, infraclasses, cohorts and subcohorts in addition to familiar classes and orders. Rohde’s(15-17) phylogeny was based both on 18S ribosomal DNA and on reassessment of structural features. On the other hand, Littlewood(18-20) phylogeny was a consensus one using all available data, both morphological and molecular. Classification of Phylum Nematoda is based on analysis of small subunit ribosomal RNA genes from more than 300 species(21-22). After reviewing several taxonomic studies(23-25), the following taxonomic classification was adopted (Figure 2 and Tables 4-6).
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PUJ; 2013, 6(1): 1-5
Editorial
Table (1): Outline of traditional classification(6). Phylum
Kingdom Protista Subkingdom Protozoa
Subphylum
Sarcomastigophora
Apicomplexa (The sporozoans)
Genera Giardia
Chilomastix
Trichomonas
Trypanosoma
Leishmania
Dientamoeba
Sarcodina
Entamoeba
Iodamoeba
Endolimax
Acanthamoeba
Naegleria
Balamuthia
Class
Subclass
Mastigophora
Order
Coccidia
Sporozoa
Suborder
Genera Isospora
Eimeriina
Eucoccidiida
Haemosporina
Babesia
Piroplasmea
Enterocytozoon
Ciliophora (The ciliates)
Balantidium
Table (2): Outline of utilitarian classification(7). Kingdom Archezoa
Eukaryota Protozoa
Phylum
Class
Order
Retortamonadea
Diplomonadida Enteromonadida Retordamonadida
Microspora
Microsporea
Microsporida
Percolozoa Parabasala Euglenozoa Ciliophora
Heterolobosea Trichomonadea Kinetoplastidea Litostomatea
Schizopyrineda Trichomonadida Trypanosomatida Vestibuliferida
Coccidea
Eimeriida
Metamonada
Cyclospora Cryptosporidium
Plasmodium
Microspora
Empire
Sarcocystis
Toxoplasma
Trepomonada
Apicomplexa
Rhizopoda
Lobosea
Haemosporida Piroplasmida Acanthopodida
Entamoebia
Entamoebea
Entamoebida
Haematozoea
Encephalitozoon
Septata
Genera
Giardia Enteromonas Chilomastix Retortamonas Encephalitozoon Nozema Entercytozoon Septata Naegleria Dientamoeba Trichomonas Leishmania Trypanosoma Balantidium Toxoplasama Cyclospora Isospora Sarcocystis Cryptosporidium Plasmodium Babesia Acanthamoeba Entamoeba Iodamoeba Endolimax
Table (3): Outline of super-groups classification(12). Supergroup Amitochondriate (core) Excavates Excavata Mitochondriate Excavates
Phylum Retortamonada
Class
Order
Retortamonadea
Retortominadida
Diplomonadea
Diplomonadida
Family Hexamitidae
Trichomonada
Trichomonadida
Euglenozoa
Kinetoplasta
Trypanosomatida
Percolozoa
Heterolobosea
Schizopyrinida
Trichomonadidae
Trichomonas
Monocercomonidae
Dientamoeba Leishmania Trypanosoma
Vahlkampfiidae Eimeriidae
Conoidasida Chromalveolata
Eucoccidiorida
Apicomplexa
Ciliophora
Sarcocystidae Cryptosporidiidae
Aconoidasida Litostomatea
Giardia Enteromonas
Enteromonadida
Parabasalia
Genera Chilomastix
Naegleria Eimeria Sarcocystis Cryptosporidium Plasmodium
Haemosporida Piroplasmorida
Babesia
Vestibuliferida
Balantidium Encephalitozoon
Opisthokonta
Entercytozoon
Microsporidia
Septata
Amebozoa
Conosa Discosea
Stramenopiles
Archamoebae Longamoebia
Entamoeba
Entamoebida
Entamoebidae
Mastigamoebida
Mastigamoebidae
Endolimax
Centramoebida
Acanthamoebidae
Acanthamoeba
Iodamoeba
Blastocystis
Opalinata
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Elwakil and Abaza
Figure (1): A consensus phylogeny of the major groups of eukaryotes based on published molecular phylogenetic and ultrastructural data (adapted from Baldauf)(13).
Figure (2): Taxonomic classification of Trematodes(14). 3
Editorial
Table (4): Outline of taxonomic classification of Trematodes(14). Class Trematoda Subclass Digenea Superorder Order Superfamily Anepitheliocystida Thin walled bladder cercaria
Strigeida Forked tail cercaria Echinostomata Operculated eggs Cercaria encyst on grass
Diplostomoidea
Diplostomoidae
Gymnophallioidea
Gymnophallioidae
Gymnophalloides
Echinostomatidae Fasciolidae Gastrodiscoidae Heterophyidae Opisthorchiidae Dicrocoeliidae Paragonimidae Plagiorchiidae Troglotrematidae
Echinostoma Fasciola & Fasciolopsis Gastrodiscoides & Watsonius Heterophyes & Metagonimus Opistherchis & Clonorchis Dicrocoelium & Eurytrema Paragonimus Plagiorchis Nanophyetus
Licinthodendriidae
Phaneropsolus
Echinostomatoidea Paramphistomoidea
Dicrocoeliidea
Plagiorchiata Operculated eggs
Genera Schistosoma
Schistosomatidae
Opisthorchiodea Epitheliocystida Thick walled bladder cercaria
Family
Schistosomatoidea
Plagiorchioidea
Alaria & Diplostomum
Table (5): Outline of taxonomic classification of Cestodes(14). Class Cestoda Order Pseudophyllidea
Family
Genera
Diphyllobothridae
Diphyllobothrium
Hymenolepididae
Hymenolepis
Taeniidae
Taenia & Echinococcus
Dilepididae
Dipylidium
Davaineidae
Raillietina celebensis
Anoplocephalidae
Bertiella studeii, Inermicapsifer madagascariensis
Mesocestoididae
Mesocestoides lineatus, M. variabilis
Cyclophyllidea
Table (6): Outline of taxonomic classification of Nematodes(22).
Class Enoplea (Aphasmidea)
Subclass Enoplia
Order
Kingdom Animalia Subkingdom Metazoa Phylum Nematoda Suborder Superfamily
Family
Trichurida
Trichenelloidea
Dioctphymatidae Rhabditida
Dioctophymatoidea Rhabdiasoidea
Trichuridae Capillaridae Trichinellidae Dioctophymatidae Rhabdiasoidea
Ancylostomatoidea
Ancylostomidae
Trichostrongyloidea
Trichstrongylidae
Metastrongyloidea
Angiostrongylidae
Strongylida
Ascarididae Ascridida Rhabditea (Phasmidea)
Ascaridoidea Anisakidae
Rhabditia
Oxyurida
Oxyuroidea Dracunculoidea Gnathostomatoidea Physalopteroidea Sipruroidea Thalazoidea
Camallanina
Spirurida
Oxyuridae Dracunculoidae Gnathostomatoidae Physalopteroidae Gongylonematidae Thelaziidae
Spirurina Filarioidea
Acanthocephala: Moniliformis moniliformis & Macranthorhynchus hirudinaceus. Nematomorpha: Gordius aquaticus & Parachordodes alpestris.
4
Filarioidae
Onchoceridae
Genera
Trichocephalus Capillaria Trichinella Dioctophyma Strongyloides Ancylostoma Nectaor Ternidens Oesophagostomum Mammomonogamus Trichstrongylidae Haemonchus Angiostrongylus Ascaris Toxocara Anisaks Beudoterranova Enterobius Dracunculus Gnathostoma Physaloptera Gongylonema Thelazia Wucheraria Brugia Loa Mansonella Meningonema Dirofilaria Onchocerca
Elwakil and Abaza
Acknowledgment:The authors are grateful to Prof. Dr. Heba E. Abdel Aaty and all members of the Medical Parasitology Department, Faculty of Medicine, Ain Shams University for providing their version of the taxonomic classification of helminthes taught to underand post-graduate students.
13. Baldauf SL. The deep roots of eukaryotes. Science; 2003, 300:1703–6. 14. Brooks, DR, McLennan DA. Parascript: Parasites and the language of evolution. Washington, DC: Smithsonian Institution Press; 1993. 15. Rohde K, Hefford C, Ellis JT et al. Contributions to the phylogeny of the Platyhelminthes based on partial sequencing of 18s ribosomal DNA. Int J Parasitol; 1993, 23:705-24.
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