Scorpions: Hunters of the Night

Introduction

• Scorpions are arachnids thriving in diverse environments:
  • Mountains, plains, deserts, tropics, and subtropics.
• Anatomy is adapted for nocturnal hunting.
• Scorpions belong to class Arachnida, phylum Arthropoda.
• Estimated 1,750 to 2,500 species; ~25 species potentially lethal to humans.
• Size diversity: from 9mm Typhlochactas mitchelli to 21cm emperor scorpion.
• Known for evolutionary resilience and adaptability.

Anatomy

Body Structure

• Two main parts: prosoma (cephalothorax) and opisthosoma (abdomen).
• Prosoma:
  • Comprises five fused segments.
  • Contains chelicerae, pedipalps, and four pairs of walking legs.
  • Eyes include one pair of median eyes and 2-5 pairs of lateral eyes.
• Opisthosoma:
  • Divided into mesosoma (pre-abdomen, 7 segments) and metasoma (post-abdomen, 5 segments).
  • Mesosoma includes genital opercula and pectines (comb-like sensory organs).
  • Metasoma ends in a venomous sting (telson and aculeus).
  • Venom: neurotoxic peptides for prey paralysis and defense.
  • Adaptable venom composition.

Vulnerability and Reproduction

• Predators: owls, bats, snakes, lizards, and more.
• Sexual cannibalism in some species (Buthidae family).
• Males consumed by females post-mating.

Digestive System

• Begins in preoral cavity (front end of cephalothorax).
• Prey grasped and crushed by chelicerae and pedipalps.
• Food transformed into liquid broth by enzymes.
• Pathway: preoral cavity ,\rightarrow mouth ,\rightarrow pharynx ,\rightarrow oesophagus.
• Midgut includes small stomach and narrow intestine (anterior mesosomal and posterior metasomal parts).
• Hepatopancreas functions like liver/pancreas, stores nutrients, regulates water balance.
• Excretory organs: Malpighian tubules and coxal glands.

Respiratory System

• Lungs with four pairs, open through stigmata.
• Structure: compressed sacs with folded inner membranes (book lungs).
• Gas exchange through rhythmic abdomen movement.
• Heart: extends over several segments with ostia regulating blood flow.

Nervous System

• Consists of central, peripheral, and visceral nervous systems.
• Central: brain, suboesophageal ganglia, double ventral ganglionic nerve cord.
• Peripheral: sends impulses to sensory organs and extremities.
• Visceral: autonomously controls heart rate, respiration, digestion.

Sensory Organs

• Eyes, pectines, sensory hairs distributed over the body.
• Two median eyes, up to ten lateral eyes.
• Light-sensitive metasomal sensor.
• Median eyes: high vision and spatial resolution.
• Lateral eyes: sensitive light sensors.
• Pectines: detect chemical signals, surface structures, ground vibrations.

Reproductive System

• Asexual reproduction.
• Males: testicles, vas deferens, other structures.
• Females: ovary, oviducts, common genital chamber.
• Internal fertilization; most scorpions are viviparous.
• Mating involves a dance (promenade à deux).
• Males attract females with visual, mechanical, chemical signals.
• Parthenogenesis (asexual reproduction) in some species.
• Prenatal development types: apoicogenic and catoicogenic.
• Post-birth: young cling to mother's back.
• Up to nine moults; lifespan 15-25 years or longer.

Fluorescence

• Scorpions fluoresce green-blue under UV light.
• Cause: special chemical compounds in the cuticle.
• Function remains unclear; may help in UV detection.

Conclusion

• Scorpions help maintain ecological balance as hunters.
• Encourage appreciation of biodiversity and ecosystem roles.
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