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Sponges

the clade of Bilaterian animals excluding the acoels was recently named Nephrozoa – “animals with kidneys”. Sponges. Cnidarians. acoel flatworms. Protostomes. the Nephrozoan ancestor - 1 st animal with an excretory system. Deuterostomes. Sponges.

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Sponges

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  1. the clade of Bilaterian animals excluding the acoels was recently named Nephrozoa – “animals with kidneys” Sponges Cnidarians acoel flatworms Protostomes the Nephrozoan ancestor - 1st animal with an excretory system Deuterostomes

  2. Sponges Nephrozoan animals are divided into 2 major lineages that are distinguishable by features of their embryos: Cnidarians acoel flatworms Protostomes Deuterostomes

  3. Sponges Nephrozoa= coelomates, animals with a true coelom (or at least, their ancestor had one) Cnidarians acoel flatworms Protostomes the coelomate ancestor - 1st animal with a coelom - all its descendants got a coelom, unless it was lost Deuterostomes

  4. Platyhelminthes (flatworms) Annelid worms Molluscs Nematodes Arthropods Protostomes coelomate ancestor in some groups, coelom is critical to movement & feeding ecology Echinoderms Chordates Deuterostomes

  5. Platyhelminthes (flatworms) Annelid worms Molluscs Nematodes Arthropods in some groups, coelom was lost or reduced coelomate ancestor Echinoderms Chordates

  6. ~17,000 species Phylum Annelida – coelomate worms - coelom acts as hydrostatic skeletonallowing worms to crawl (polychaetes), dig (earthworms), inflate body regions - embryos develop through spiral cleavage, leading to a trochophore larval stage (shared with molluscs) - segmented bodies divided into repeating blocks (metamerism) - formed by teloblasticgrowthin larvae - blocks of segments are specialized for different functions - complete digestive system; excretory system w/ metanephridia - closed circulatory system; well-developed nervous system - chetae: spines sticking out of epidermis for movement, defense

  7. Annelida SipunculaEchiuraPogonophora PolychaetaClitellata segmentation Old view of coelomate worm phylogeny chetae

  8. Former Coelomate Worm “Phyla” Segmented (now Family Sibloglinidae) Pogonophora– deep-sea tube worms Vestimentifera– giant vent worms Non-segmented: Sipuncula Echiura – innkeeper worms All are now just clades nested within Annelida !

  9. Old system: 2 classes of annelids (1) Polychaeta– primarily marine worms - errant (free-living) - tube-dwelling - burrowing - interstitial - planktonic - pelagic (2) Clitellata subclass Oligochaeta– earthworms subclass Hirudinoidea– leeches Pareurythoe Potamilla recent evidence: Clitellata is a clade nested within polychaetes

  10. Annelida Sipuncula Clitellata Echiura Siboglinidae

  11. Used to be: Sipuncula Echiura Pogonophoran Annelida Polychaeta Clitellata DNA data shows all these groups belong to one big clade, interspersed among different polychaete groups

  12. Annelida Problem: now, no group we can call “polychaetes” – same as “Annelida” if you include these 4 clades in “Polychaeta” – paraphyletic group if you exclude these 4 but keep using name “polychaete”

  13. marine “polychaetes”25 Orders, 87 Families ~8,000 spp. • - parapodia(unjointed appendages) act as walking paddles • or gillsfor respiration • numerous chetae (bristles) on parapodia, each derived • from a single epidermal cell • - reproductive structures may be simple or temporary • foregut modified as eversible proboscis for feeding • great habitat diversity • (mostly marine) • - head elaborated into two regions: • prostomium with tentacles and • palps, and peristomium

  14. polychaete cross-section serially repeated segments CM segment junction LM dorsal blood vessel LM epidermis CM septum gut nephrostome ventral nerve cord ventral blood vessel nephridium have a “belly-bone” instead of our backbone CM = circular muscle ring; contracts body LM = longitudinal muscle; pull lengthwise

  15. parapodium Circular muscle notopodium Longitudinal mus. Coelom chetae oblique muscle neuropodium Asiculum

  16. Parapodium in cross-section Close-up of chetae straight, slim Notopodium Neuropodium short, hooked

  17. Dorsal view

  18. Adaptive diversification of parapodia gills anchoring in tubes parapodia in different body regions can be variously modified, some serving as gills, others in locomotion, others in feeding

  19. Circulatory system of Nereis • No hearts; contractions • of dorsal vessel & • body wall controls • blood flow • - In species w/ incomplete • septa, blood cells flow • through continuous coelom • - hemoglobins & • other respiratory • pigments dorsal vessel = anteriorflow esophagus nephridium ventral vessel intestine lateral vessel

  20. Nervous system eyes Forebrain enervates palps, midbrain the eyes and hindbrain the nuchal organ (chemical) palps Primitive ventral “ladder” gradually fused, evolved into one central nerve chord

  21. Polychaete locomotion Parapodia move out of phase lateral undulations. Chetae contact the substrate, push off with each stroke Coelomic cavities in each segment are hydraulically isolated from each other, allowing independent movement of segments

  22. Polychaete locomotion: Variable speed

  23. Polychaete locomotion: Burrowing If septabetween coelomic spaces are absent, contraction of 1 area produces extension of another region (fluid is continuous) Circular muscles make movements possible that aren’t available to nematodes, which have only longitudinal muscles

  24. Polychaete reproduction Benthic polychaetes form epitokes, which swim to the surface & spawn Reproductive structures are simple, often temporary Gametes form in coelom; ` released through gonoducts, nephridiopores, or simple tearing of the body wall itself Nereis Eunice

  25. There are a range of larval forms, but most pass through a trochophore larva stage early in development Trochophore locomotory band of cilia Juvenile worm Growth zone

  26. 2-day old trochophore of Spirobranchus giganteus Later stage: segmented, or chetigerous, larva w chetae no mouth Lecithotrophic: no mouth between prototroch and metatroch bands of cilia

  27. Newly metamorphosed serpulid (juvenile worm) Trochophore larva of a serpulid, posterior view

  28. Late-stage segmented larvae Terebellid

  29. Polychaete families & their ecology order family ecology Phyllodocida Nereidae errant, predatory Glyceridae Polynoidae often commensal Spionida Chaetopteridae mucous webs, parchment tubes Terebellida Terebellidae deposit feeders Pectinariidae sand tubes Sabellaridae Sabellida Sabellidae suspension feeders Serpulidae calcareous tubes Spirorbidae

  30. Order Phyllodocida Family Nereidae • one pair of large curved • jaws, held inside body • until deployed to catch • prey • bodies typically homonomous: • all segments are alike

  31. Order Phyllodocida Family Glyceridae - predatory - extensible proboscis with 4 teeth; used in burrowing and hunting Glycera americana

  32. Order Phyllodocida Family Polynoidae “Scale worms” - short and flattened bodies - homonomous; few segments of fixed number - dorsum covered by scales called elytrae - 1 pair of jaws - often commensal on other invertebrates: live on them, neither hurt (parasite) nor help (mutualist)

  33. Order Spionida Family Chaetopteridae worm out of tube - adult body is highly tagmatic: front and back ends are very different (heteronomous) - trap suspended particles by pulling water through a mucous web - web is balled up, consumed, re-spun every 18 minutes - parchment tube is home to many commensal organisms tube, often in U-shape

  34. Order Terebellida Family Terebellidae Thelepus crispus branchial plume - “medusa worm” has elongated tentacles used in selective depositfeedingfrom inside the safety of its tube (which it builds)

  35. modified prostomial appendages Deposit Feeding tentacles are hollow feeding tentacles extended to gather organic matter from surface

  36. Order Terebellida Family Pectinariidae Pectinaria californiensis, “ice cream cone worm” - selects sand grains of precise size for each region of tube

  37. Order Sabellida Family Serpulidae Spirobranchus sp. “Christmas tree worm” - build calcareous tubes - often imbedded in rocks or coral heads - compound eyes on tentacles; shadows trigger rapid withdrawal

  38. Order Sabellida Family Spirorbidae Major fouling organism – rapidly colonize most marine surfaces with their tiny calcareous tubes have a large operculum, or stopper, to seal the opening of their tube after they withdraw their feeding tentacles tubes encrusting a chiton’s shell valves

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