6.3 Marine worms: flatworms, roundworms, and annelids

Marine worms are fascinating creatures with diverse adaptations. From flat and round to segmented bodies, they've evolved unique features for life in aquatic environments. These worms play crucial roles in marine ecosystems, from filtering water to burrowing through sediments.

Beyond their ecological importance, marine worms have significant economic and medical impacts. They're used in aquaculture, serve as pollution indicators, and offer insights for biomedical research. However, some parasitic species can cause serious health issues in humans and animals.

Characteristics and Adaptations of Marine Worms

Characteristics of marine worms

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Top images from around the web for Characteristics of marine worms

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  13.3 – Superphylum Lophotrochozoa: Flatworms, Rotifers, and Nemerteans – Biology 110 PSU Dubois View original

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• Flatworms (Platyhelminthes)
  • Have soft, dorsoventrally flattened bodies well-suited for crawling in tight spaces
  • Lack a true coelom (body cavity) and are thus acoelomate, with organs embedded in mesenchyme
  • Possess a blind gut with only one opening serving as both mouth and anus (planarians)
  • Rely on specialized flame cells for excretion and diffusion through the body surface for gas exchange
  • Some species have simple eyespots for light detection and sensory cells for chemical and mechanical stimuli
• Roundworms (Nematoda)
  • Possess cylindrical, unsegmented bodies with tapered ends adapted for burrowing (hookworms)
  • Have a pseudocoelom, a fluid-filled cavity between the digestive tract and body wall
  • Feature a complete digestive system with a mouth and anus, allowing for more efficient feeding
  • Secrete a thick, protective cuticle that provides support and defense against harsh environments
  • Possess specialized sensory organs called amphids for detecting chemical cues
• Annelids (Annelida)
  • Have segmented bodies with a true coelom, allowing for efficient circulation and organ specialization
  • Possess well-developed closed circulatory systems with hearts and blood vessels for oxygen transport (earthworms)
  • Feature complex nervous systems with brains and ventral nerve cords for advanced sensory processing
  • Bear setae, tiny bristles on each segment that aid in locomotion by anchoring against the substrate
  • Often have specialized head regions with sensory organs like eyes and antennae (polychaetes)
  • Exhibit remarkable regenerative abilities, able to regrow lost body parts (some oligochaetes)

Feeding Strategies and Ecological Roles

Feeding strategies in marine worms

• Suspension feeding
  • Some annelids like feather duster worms use crown tentacles to filter suspended particles from the water
• Deposit feeding
  • Many annelids (lugworms) and flatworms ingest sediment to consume organic detritus and microbes
• Predation and scavenging
  • Predatory annelids (fireworms) and flatworms actively hunt small invertebrates or feed on carrion
• Parasitism
  • Parasitic flatworms (flukes) and nematodes live in or on hosts, feeding on tissues or body fluids (hookworms)

Ecological roles of marine worms

• Bioturbation
  • Burrowing worms mix and ventilate sediments, enhancing nutrient cycling and sediment oxygenation
• Nutrient regeneration
  • Worm waste products release nutrients like nitrogen and phosphorus, supporting primary production
• Food web dynamics
  • Marine worms are important prey items, transferring energy to fish, crustaceans, and other predators
• Habitat creation
  • Reef-building polychaetes secrete tubes that form complex structures, providing microhabitats for other species

Economic and Medical Significance

Economic and medical significance

• Aquaculture
  • Polychaete worms like Nereis are harvested for use as fishing bait and feed in shrimp farming
• Bioindicators
  • Pollution-sensitive worms (some nematodes) serve as indicators of environmental degradation
• Biomedical research
  • Planarians are studied as models for stem cell research and regenerative medicine due to their impressive regenerative capabilities
• Parasitic infections
  • Marine flatworms (schistosomes) and nematodes can infect humans and animals, causing debilitating diseases (schistosomiasis, anisakiasis)