Zoology

• Unikonts


  Eukaryotic organisms with a single flagellum
• Bikonts


  Eukaryotic organisms with two flagella
• Flagellar apparatus in eukaryotic cells

  • Centre of organization for the cytoskeleton
  • Usually a single 'kinetid' consisting of one or more basal bodies
  • May give rise to flagella or be non-flagellated
• Ancestral eukaryotes had a simple kinetid with one basal body anchoring one flagellum

  
• Unikonts retained this ancestral organization
• Bikonts descended from a common ancestor that had evolved a kinetid with two flagella, one anterior and one posterior
• Bikont


  Any of the eukaryotic organisms classified in the group Bikonta
• Shared traits of bikonts

  • Many single-celled members and the presumed ancestor have two flagella
  • Fusion of two genes (thymidylate synthase and dihydrofolate reductase) into a single unit
• Unikont was the ancestor of opisthokonts (Animals, Fungi, and related forms) and Amoebozoa
• Bikont was the ancestor of Archaeplastida (Plants and relatives), Excavata, Rhizaria, and Chromalveolata
• Alveolates


  Include ciliates, dinoflagellates, and apicomplexans, united by the presence of cortical alveoli underlying their plasma membranes
• Ciliates


  • Highly speciose aquatic unicells
  • Characterized by an abundance of flagella and dimorphic nuclei (micro- and macronuclei)
  • Micronucleus is transcriptionally inactive germ nucleus, macronuclei are for transcription
• Ciliates


  • Possess a cell mouth or cytostome
  • Covered with a pellicle
  • Have special organelles like trichocysts, toxicysts, and mucocysts
• Ciliates reproduce asexually through transverse binary fission
• Ciliates are a diverse group found almost everywhere there is water
• Ciliates


  • Paramecium
  • Vorticella
  • Balantidium
  • Stentor
  • Suctoria
• Apicomplexa


  • Characterized by an apical complex which functions in attachment and initial penetration of host cell
  • Includes secretory organelles like micronemes, rhoptries, and dense granules
  • Polar rings composed of microtubules, and in some species a conoid
• Nearly all apicomplexa are obligate intracellular parasites
• Life cycle of Plasmodium falciparum

  1. Infection of human with sporozoites

  2. Asexual reproduction (pre-erythrocytic and erythrocytic phases)

  3. Sexual reproduction (gametogenesis, fertilization, sporogony)
• Rhizaria


  • Species-rich supergroup of mostly unicellular eukaryotes
  • Vary considerably in form, no clear morphological distinctive characters
  • Most are biciliate amoeboflagellates, at least at some point in their life cycle

  
• Rhizaria


  • Produce shells or skeletons called tests
  • Nearly all have mitochondria with tubular cristae
• Actinopods


  • Amoeboid organisms with rigid and beautiful structure
  • Many have siliceous (glassy) shells and are planktonic
  • Capture small organisms with slender pseudopodia called axopodia
• Acantharia


  • Planktonic, free living, exclusively marine protozoa
  • Cell consists of central endoplasm and peripheral ectoplasm separated by central capsule
  • Skeleton of strontium sulfate, cell body covered with outer pellicle, have contractile myonemes
• Heliozoa


  • Spherical, predominantly freshwater, either floating or stalked
  • Body consists of outer cortex and inner medulla
  • Frequently enveloped by a shell (or test) composed of silica or organic material
  • Numerous radiating cytoplasmic masses (pseudopodia/axopodia) used for capturing food
• Periplasmic cortex


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• Myonemes


  • Contractile filaments grouped around the spicule
• Contractile vacuoles are absent
• Asexual reproduction


  Binary fission
• Amphilonche, Acanthochiasma


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• Heliozoans


  • Spherical and predominantly freshwater
  • Found either floating or stalked
  • Body consists of outer cortex containing food and contractile vacuoles, and inner medulla containing nuclei and axopods
  • Frequently enveloped by a shell (or test) composed of silica or organic material
  • Secretions exhibit a wide variety of shapes
  • Numerous radiating cytoplasmic masses (pseudopodia/axopodia) used for capturing food rather than locomotion
  • Ingest protozoans, algae, and other small organisms
  • Reproduce asexually by binary fission or budding, or sexually by autogamy
  • May have flagellated forms which may be gametes
• Actinophrys sol, Acanthocystis turfacea, Actinosphaerium


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• Radiolarians


  • Found in upper layers of all oceans
  • Mostly spherically symmetrical
  • Complex and beautifully sculptured, minute skeletons (tests)
  • Tests usually composed of silica, elaborately perforated in a variety of patterns
  • Pseudopodia extend through perforated skeleton
  • Chitinous central capsule encloses nuclei and divides cytoplasm into two zones
  • Outer cytoplasm contains vacuoles that control buoyancy
  • Reproduce asexually by budding, binary fission, or multiple fission
  • Skeletal remains settle to ocean floor and form radiolarian ooze
• Hexaconthium, Thalassicola


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• Foraminiferans (Forams)


  • Marine
  • Shells are chalky calcium carbonate, often shaped like microscopic snail shells
  • Tend to live attached to the bottom or to objects in the water
  • Shells have tiny holes (Foraminifera means "hole bearer") for projection of reticulopods
  • Shells may be unilocular or multilocular

  
• Globigerina, Elphidium


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• Excavata is a major supergroup of unicellular organisms belonging to the domain Eukaryota

  
• Excavates were formerly considered to be included in the now obsolete Protista kingdom
• Excavates


  • Classified based on their flagellar structures
  • Considered to be the oldest members (basal lineage) of flagellated organisms
  • Many lack 'classical' mitochondria, often referred to as 'amitochondriate'
  • Most retain a mitochondrial organelle in greatly modified form (e.g. hydrogenosome or mitosome)
  • Among those with mitochondria, the mitochondrial cristae may be tubular, discoidal, or laminar
  • Most have two, four, or more flagella and many have a conspicuous ventral feeding groove with a characteristic ultrastructure, supported by microtubules
• Groups within Excavata


  • Kinetoplastida
  • Metamonada
• Kinetoplastida


  • Flagellated protists characterized by the presence of a kinetoplast (an organelle with a large massed DNA)
  • Includes parasites responsible for serious diseases in humans and other animals, as well as various free-living forms
  • Kinetoplast is an unusual DNA-containing granule located within the single mitochondrion associated with the base of the cell's flagella
  • Kinetoplast contains many copies of the mitochondrial genome
  • Kinetoplast is auto-reproductive and transmitted only by the female individual in sexual reproduction
  • Classified into two monophyletic groups: biflagellate bodonids and uniflagellate trypanosomatids
  • Biflagellate forms have a leading and trailing flagellum, used for locomotion and attachment