Annelida Polychaeta Larva = Trochophore Band of cilia around body; tuft on apex

1. Arenicola • Annelida • Polychaeta • Larva = Trochophore • Band of cilia around body; tuft on apex • Same larval stage in Mollusca • Diverse lifestyles • Errant vs. Sedentary • Errant: Free-living predators • Often well-developed eyes and sense organs, jaws • Deposit feeders • Nonselective • Selective • Suspension feeders • Active • Passive • Solitary • Colonial • Reproduction Fig. 9-25 Fig. 9-25 Amphitrite

3. Arenicola marina Fig. 13-23

5. Annelida • Polychaeta • Larva = Trochophore • Band of cilia around body; tuft on apex • Same larval stage in Mollusca • Diverse lifestyles • Errant vs. Sedentary • Errant: Free-living predators • Often well-developed eyes and sense organs, jaws • Deposit feeders • Nonselective • Selective • Suspension feeders • Active • Passive • Solitary • Colonial • Reproduction Chaetopterus Phragmatopoma californica

8. Annelida • Polychaeta • Larva = Trochophore • Band of cilia around body; tuft on apex • Same larval stage in Mollusca • Diverse lifestyles • Errant vs. Sedentary • Errant: Free-living predators • Often well-developed eyes and sense organs, jaws • Deposit feeders • Nonselective • Selective • Suspension feeders • Active • Passive • Solitary • Colonial • Reproduction Nereis succinea Wikipedia

9. Epitoky Fig. 9-27

10. Annelida • Sipuncula (class) • Peanut worms • Exclusively marine (250+ species) • Most common in shallow water • Unsegmented bodies up to 35 cm long • Studded introvert used for locomotion • Cryptic • Burrow in sediments or hide in shelters • Deposit or suspension feeders • Consume detritus and microbes • Dioecious • External fertilization Sipunculus nudus glaucus.org.uk

11. Annelida • Echiura (class) • Exclusively marine (~150 species) • Deposit feeders • Non-retractable proboscis • Live in U-shaped or L-shaped burrows • Typically small; may get large in deep sea • Dioecious broadcast spawners

12. Annelida • Pogonophora (class) • Beard worms • Long, thin worms (~135 species) • Most common in deep sea • No mouth or gut • Not parasitic • Anterior tuft of up to several thousand tentacles • Tentacles absorb dissolved nutrients • Symbiotic bacteria in trophosome utilize nutrients to manufacture food • Vestimentifera • Large deep-sea animals • Found at many hydrothermal vents

14. tolweb.org • Nematoda • Free living and parasitic forms • Cosmopolitan/Ubiquitous • Mostly in sediments (free living) or hosts (parasitic) • Common in fine muds • Organic rich areas • Described species: 28,000+ (>55% parasitic) • May be up to 500,000 species total! • Extremely abundant!! • Up to hundreds of individuals per ml of sediment • 90,000 in one rotting apple (not marine) • Hydrostatic skeleton • Longitudinal muscles only • Move by whipping back and forth

15. Benthos – Soft Bottom • Species Composition • Animals often categorized by size and location • Location: epifauna vs. infauna • Megafauna • No standard definition • Some infaunal macrofauna would be considered megafauna if exposed • Nearly absent from sandy beaches • High energy environment • Pressure from terrestrial predators • Conspicuous but less important ecologically than smaller, more abundant organisms • More important in low energy environments

16. Benthos – Soft Bottom • Species Composition • Macrofauna • Large enough to be retained on 0.5 mm sieve • Low diversity on beaches compared to less dynamic areas • In terms of biomass, most important taxa are • Burrowing bivalves • Polychaetes • Crustaceans • All these taxa are: • Mechanically resistant to sediment movement (bivalves) • Highly mobile (polychaetes) • Both (crustaceans) • Typically display zonation on shorelines

17. Fig. 14-10

18. Fig. 13-31

19. Benthos – Soft Bottom • Species Composition • Meiofauna • Pass through 0.5 mm sieve but large enough to be retained on 62 μm sieve • Sometimes termed interstitial fauna: live in spaces between sand grains • Very diverse group vs. others inhabiting sand beaches • Many individuals move among sediment grains but may or may not displace them in bulk like burrowing macrofauna • Endobenthic: larger than interstitial spaces, displace particles while moving • Mesobenthic: move within interstitial spaces, do not displace particles while moving • Most meiofauna mesobenthic in medium to coarse sediments, endobenthic in very fine sediments

20. Fig. 13-29

21. Loricifera • Benthos – Soft Bottom • Species Composition • Meiofauna • Many taxa represented: Mollusks, crustaceans, worms from several phyla, etc. • Some groups entirely or almost entirely meiofaunal (Ex: kinorhynchs, gastrotrichs, loriciferans) Kinorhyncha Nematoda Gastrotricha

22. Benthos – Soft Bottom • Species Composition • Meiofauna • Body trends in meiofauna include • Reduced body size • Especially striking in groups whose members typically are large (e.g. Mollusca, Echinodermata) • Vermiform or flattened shape • Flexibility and maneuverability • Flattened shape  Increased surface area for DOM uptake • Strengthened body design • Protects against abrasion and crushing • Adaptations may include protective spines or scales (gastrotrichs), well-developed cuticle or exoskeleton (nematodes, crustaceans), internal skeleton of calcareous spicules (ciliates, sea slugs) • Many soft-bodied animals can contract strongly to protect against mechanical damage • Adhesive and gripping structures • Adhesive glands, hooks, suckers, claws • Statocysts • Sensory organs that detect gravity and help animals to orient correctly within sediments

23. Benthos – Soft Bottom • Species Composition • Meiofauna • Most are: • Deposit feeders (gastrotrichs, nematodes) • Predators (hydroids, flatworms) • Microherbivores (scraping diatoms or algae off sand grains; ostracods, harpacticoid copepods) • Some suspension feeding species, primarily sedentary animals like bryozoans and tunicates • Reproduction • Most have low fecundities, due primarily to small body size • Many species produce only 1-10 eggs at a time • 98% of meiofaunal species lack pelagic larvae • Young are brooded or eggs may be attached to sand grains; young hatch as benthic juveniles • No pelagic dispersal phase; dispersal through entrainment in water currents, attachment to feet of mobile organisms (e.g. seabirds)