Biology of Lophotrochozoa and Cephalopods

Cephalopods and Pain Perception

• Recent research indicates that cephalopods can experience pain.
• Reference: Crook R. J. (2021). Behavioral and neurophysiological evidence suggests affective pain experience in octopus.
  • Source: iScience, 24(3), 102229.
  • DOI: https://doi.org/10.1016/j.isci.2021.102229
• Implications for policy: Should the NIH revise animal welfare rules to categorize cephalopods similarly to mammals?

Learning Objectives

• Understand the classification and characteristics of Lophotrochozoa.
• Analyze structure, nutrition, reproduction, and movement in:
  • Platyhelminthes (flatworms)
  • Annelids (segmented worms)
  • Molluscs (soft-bodied animals)
• Identify different types of Platyhelminthes and their roles in disease.
• Examine the body structure of Molluscs and their classification.
• Investigate the connection between the cephalopod nervous system and pain perception.

Classification of Lophotrochozoa

• Members possess:
  • Lophophore: a feeding apparatus with ciliated tentacles.
  • Trochophore: a free-swimming larval stage.
• Phyla include:
  • Mollusca
  • Annelida
• Molecular evidence for their classification also involves:
  • Platyhelminthes, some with trochophore-like larvae.

Metazoa Hierarchy

• Metazoa (Animals)
• Eumetazoa (with specialized tissues)
• Bilateria (bilateral symmetry, triploblastic)
  • Divided into:
  • Protostomia (mouth first)
    • Ecdysozoa (e.g., Nematoda)
    • Lophotrochozoa (e.g., Annelida, Mollusca)
  • Deuterostomia (anus first, e.g., Chordata)

Platyhelminthes (Flatworms)

• General Characteristics:
  • Most are parasitic.
  • Organ-level organization without specialized circulatory or respiratory systems.
  • Exhibit cephalization and bilateral symmetry.
  • Acoelomates, lacking a body cavity.

Types of Platyhelminthes

• Turbellarians: Free-living flatworms.
• Trematodes: Flukes that are mostly parasitic.
• Cestodes: Tapeworms that inhabit intestines.

Trematodes (Flukes)

• Well-developed reproductive systems, typically hermaphroditic.
• Complex life cycles, significant disease impact (e.g., Schistosomiasis affecting 300 million people).

Common Trematodes in Humans

• Schistosoma species: Causes blood flukes, high infection rates across continents.
• Chlonorchis sinensis: Chinese liver fluke; risk from raw fish consumption.
• Fasciolopsis buski: Intestinal fluke from aquatic vegetation.

Cestodes (Tapeworms)

• Adaptations for attachment include a scolex at the anterior region.
• Body consists of a series of proglottids, each containing full reproductive systems.
• Notable for self-fertilization and complex life cycles (documented cases in pork tapeworms).

Annelida (Segmented Worms)

• Distinct feature: Metamerism (true segmentation).
• Segmentation aids in fluid-filled coelomic movements, functioning as a hydrostatic skeleton.
• Systematic Circulatory Structure: Closed circulatory system with ventral nerve cords.

Classes of Annelida

• Polychaetes: Diverse; characterized by many bristles (chaetae), external fertilization, and metamorphosis.
• Oligochaetes: Few bristles, hermaphroditic with primarily direct development (e.g., earthworms, leeches).

Leeches

• Characteristics include producing hirudin (anticoagulant), freshwater habitat, lacking chaetae.

Mollusca

• Phylum includes:
  • Gastropoda: Snails and slugs.
  • Bivalvia: Clams, oysters, and mussels.
  • Cephalopoda: Squid, octopuses, and nautilus.

General Mollusca Anatomy

• Body Plan: Three-part structure consisting of:
  • Visceral mass: Housing internal organs.
  • Mantle: Covers organs, may produce a shell or gills.
  • Head-Foot: Involved in movement and sensory perception.
• Radula: Unique structure for feeding, scrapes food particles.

Bivalvia

• Function by filtering water, no radula, closed circulatory system.
• Structure features include two hinged shells and separate sexes.

Gastropoda

• Characterized by a distinct head, elongated foot, and respiratory adaptations (gills in aquatic species).

Cephalopoda Adaptations

• Notable for an advanced nervous system, closed circulatory system, and prominent eye structure.
• Jet propulsion mechanism allows rapid movement.
• Specialized reproductive structures (spermatophore and hectocotylus) aid in reproduction.