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Diversity of Protists I01:15

Diversity of Protists I

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Excavata is a diverse group of protists that includes both chemoorganotrophic and phototrophic species, with some thriving in anaerobic environments. Among the key groups within Excavata are diplomonads and parabasalids, which are flagellated protists that lack mitochondria and chloroplasts. These microorganisms typically inhabit anoxic environments, such as the intestines of animals, where they exist either symbiotically or as parasites, relying on fermentation for energy production. Some...
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Rhizaria are a diverse group of unicellular protists characterized by their threadlike cytoplasmic extensions known as pseudopodia. These structures aid in both locomotion and feeding, giving Rhizaria an amoeboid appearance. Their amoeboid morphology once led to taxonomic confusion, but molecular phylogenetics has clarified their evolutionary placement and emphasized their shared use of pseudopodia despite divergent lineages.This clade comprises diverse lineages such as Chlorarachniophyta,...
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Bacterial Phylum Spirochaetes01:30

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Spirochetes, unique bacteria in the phylum Spirochaetes, are gram-negative, motile, tightly coiled, slender, and flexible. They inhabit aquatic sediments and animals, with some causing diseases like syphilis. Spirochetes are classified into eight genera based on habitat, pathogenicity, phylogeny, and characteristics.Their distinctive motility arises from endoflagella, located within the cell’s periplasm. These endoflagella anchor at the cell poles and extend along the cell length, encased...
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Diversity of Protists II01:27

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Alveolates are a group of organisms recognized by the presence of alveoli, which are cytoplasmic sacs located beneath the cell membrane. While their function remains uncertain, alveoli may help regulate water balance by controlling how much water enters and leaves the cell. In dinoflagellates, these structures may serve as armor plates. There are three major types of alveolates: ciliates, which move using cilia; dinoflagellates, which use flagella for movement; and apicomplexans, which are...
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Amoebozoa represent a diverse group of terrestrial and aquatic protists that utilize lobe-shaped pseudopodia for locomotion and feeding. This characteristic differentiates them from the Rhizaria, which possess threadlike pseudopodia. The primary classifications within Amoebozoa include gymnamoebas, entamoebas, and the plasmodial and cellular slime molds. Phylogenetic evidence indicates that Amoebozoa diverged from a lineage that ultimately gave rise to fungi and animals.Gymnamoebas and...
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Protists are diverse eukaryotic microorganisms that lack the specialized tissues of plants and animals and the chitinous cell walls of fungi. Their early divergence within Eukarya resulted in structural, functional, and ecological diversity. They are classified into supergroups such as Archaeplastida, Excavata, Amoebozoa, Rhizaria, Alveolata, and Stramenopiles, determined through genetic analysis and structural similarities.Structural and Functional AdaptationsProtists have various adaptations...
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Protaspid larvae are unique to trilobites.

Rudy Lerosey-Aubril1, Lukáš Laibl2

  • 1Department of Organismic and Evolutionary Biology and Museum of Comparative Zoology, Harvard University, 26 Oxford Street, Cambridge, MA, 02138, USA.

Arthropod Structure & Development
|May 24, 2021
PubMed
Summary

A recently discovered fossil, initially thought to be an early aglaspidid relative, is reclassified as an asaphid trilobite protaspis. This finding confirms that trilobite-specific larval exoskeletons are unique to the Trilobita subphylum.

Keywords:
AglaspididaEuarthropodaLarval ecologyOrdovicianProtaspisTrilobita

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Area of Science:

  • Paleontology
  • Developmental Biology
  • Evolutionary Biology

Background:

  • Trilobites exhibit a unique developmental trait: early biomineralization of their dorsal exoskeleton, forming protaspides.
  • Fossilized protaspides are crucial for understanding early euarthropod development and evolution.
  • A recent discovery of a protaspid-like fossil with aglaspidids suggested this trait extended beyond trilobites.

Purpose of the Study:

  • To re-evaluate the taxonomic assignment of a protaspid-like fossil found in Siberian strata.
  • To determine if protaspides are unique to trilobites or present in related fossil groups.

Main Methods:

  • Comparative morphological analysis of the fossil specimen.
  • Stratigraphic and paleoecological context assessment.
  • Phylogenetic inference based on morphological characteristics.

Main Results:

  • The Siberian protaspis-like fossil is identified as belonging to the asaphid trilobite genus Isotelus or a closely related taxon.
  • The fossil was found in association with other asaphid trilobites, supporting its reclassification.
  • The presence of protaspides is confirmed as a trait exclusive to trilobites.

Conclusions:

  • The developmental trait of protaspis formation is unique to the extinct subphylum Trilobita.
  • The initial interpretation of the Siberian fossil as evidence for non-trilobite protaspides is incorrect.
  • Trilobite larval development remains a key model for studying euarthropod evolution and development.