56. Phylum Arthropoda: important evolutionary changes. Class Arachnida. Order Scorpiones and order Araneae.
Covers the general features of Phylum Arthropoda, including the exoskeleton, jointed appendages, segmentation and open circulatory system, then contrasts Class Crustacea with Class Arachnida. It goes on to describe scorpions and spiders, noting tail structure, pedipalps, silk production and reproduction, and closes with arachnid body plan, eyes, venom and the black widow as an example species.
Inside: 5 sections · 3 min
Topic 56 of 64 in the MU Sofia syllabus for Biology (Dental Medicine, Year 1). The free AceMed note covers it in 5 sections, about 342 words (3 min of reading).
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Phylum Arthropoda
Class Crustacea
Class Arachnida
Order Scorpiones (Scorpions)
Order Araneae (Spiders)
Phylum Arthropoda
Characteristics
Exoskeleton: Composed of chitin, providing protection and serving as attachment points for muscles.
Jointed Appendages: Includes legs, antennae, and mouthparts that facilitate movement and feeding.
Segmented Body: Divided into multiple segments, each potentially carrying a pair of appendages.
Bilateral Symmetry: The body is symmetrical along a central line.
Open Circulatory System: Features a dorsal heart and hemolymph that bathes organs directly.
Developed Nervous System: Includes well-developed ganglia for nerve signal processing and control.
Class Crustacea
Characteristics
Species Inclusion: Comprises lobsters, crayfish, and copepods.
Habitat: Primarily aquatic; predominantly marine with some freshwater species.
Morphology:
Two pairs of antennae, one pair of mandibles, and two pairs of maxillae.
Compound eyes and specialized walking legs, including chelipeds (claws) used for capturing prey.
Class Arachnida
General Traits
Legs: Characterized by eight legs, with the front pair often serving sensory functions.
Habitat: Predominantly terrestrial, though some species inhabit freshwater and marine environments.
Diverse Groups: Includes spiders, ticks, mites, and scorpions.
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