EDITORIAL PUJ Towards a Unified Taxonomy

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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

2

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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