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the clade of Bilaterian animals excluding the acoels was recently named Nephrozoa – “animals with kidneys” Protostomes the Nephrozoan ancestor - 1st animal with an excretory system Deuterostomes Nephrozoan animals are divided into 2 major lineages that are distinguishable by features of their embryos: Protostomes Deuterostomes Nephrozoa = coelomates, animals with a true coelom (or at least, their ancestor had one) Protostomes the coelomate ancestor - 1st animal with a coelom - all its descendants got a coelom, unless it was lost Deuterostomes Platyhelminthes (flatworms) coelomate ancestor Protostomes Annelid worms Molluscs Nematodes in some groups, coelom is critical to movement & feeding ecology Arthropods Deuterostomes Platyhelminthes (flatworms) coelomate ancestor Annelid worms Molluscs Nematodes Arthropods in some groups, coelom was lost or reduced Phylum Annelida – coelomate worms ~17,000 species - coelom acts as hydrostatic skeleton allowing 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 teloblastic growth in 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 Annelida Sipuncula Echiura Pogonophora Polychaeta Clitellata segmentation Old view of coelomate worm phylogeny chetae 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 ! Old system: 2 classes of annelids (1) Polychaeta– primarily marine worms - errant (free-living) - tube-dwelling - burrowing - interstitial - planktonic - pelagic Pareurythoe Potamilla (2) Clitellata subclass Oligochaeta– earthworms subclass Hirudinoidea– leeches recent evidence: Clitellata is a clade nested within polychaetes Annelida Sipuncula Clitellata Echiura Siboglinidae 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 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” marine “polychaetes” 25 Orders, 87 Families ~8,000 spp. - parapodia (unjointed appendages) act as walking paddles or gills for 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 polychaete cross-section serially repeated segments LM dorsal blood epidermis vessel CM LM segment junction CM septum gut nephrostome ventral nerve cord ventral blood vessel have a “belly-bone” instead of our backbone nephridium CM = circular muscle ring; contracts body LM = longitudinal muscle; pull lengthwise parapodium Circular muscle Longitudinal mus. notopodium Coelom chetae oblique muscle neuropodium Asiculum Parapodium in cross-section Close-up of chetae straight, slim Notopodium Neuropodium short, hooked Dorsal view Adaptive diversification of parapodia anchoring in tubes gills parapodia in different body regions can be variously modified, some serving as gills, others in locomotion, others in feeding 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 intestine dorsal vessel = anterior flow esophagus nephridium ventral vessel lateral vessel Nervous system eyes Forebrain enervates palps, midbrain the eyes and hindbrain the nuchal organ (chemical) Primitive ventral “ladder” gradually fused, evolved into one central nerve chord palps 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 Polychaete locomotion: Variable speed Polychaete locomotion: Burrowing If septa between 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 Polychaete reproduction Benthic polychaetes form epitokes, which swim to the surface & spawn Reproductive structures are simple, often temporary ` Nereis Eunice Gametes form in coelom; released through gonoducts, nephridiopores, or simple tearing of the body wall itself 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 2-day old trochophore of Spirobranchus giganteus no mouth Later stage: segmented, or chetigerous, larva w chetae Lecithotrophic: no mouth between prototroch and metatroch bands of cilia Trochophore larva of a serpulid, posterior view Newly metamorphosed serpulid (juvenile worm) Late-stage segmented larvae Terebellid Polychaete families & their ecology order family ecology Phyllodocida Nereidae Glyceridae Polynoidae errant, predatory Spionida Chaetopteridae mucous webs, parchment tubes Terebellida Terebellidae Pectinariidae Sabellaridae deposit feeders sand tubes Sabellida Sabellidae Serpulidae Spirorbidae suspension feeders calcareous tubes often commensal 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 Order Phyllodocida Family Glyceridae - predatory - extensible proboscis with 4 teeth; used in burrowing and hunting Glycera americana Order Phyllodocida Family Polynoidae - short and flattened bodies “Scale worms” - 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) 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 Order Terebellida Family Terebellidae Thelepus crispus branchial plume - “medusa worm” has elongated tentacles used in selective deposit feeding from inside the safety of its tube (which it builds) modified prostomial appendages Deposit Feeding tentacles are hollow feeding tentacles extended to gather organic matter from surface Order Terebellida Family Pectinariidae Pectinaria californiensis, “ice cream cone worm” - selects sand grains of precise size for each region of tube 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 Order Sabellida Family Spirorbidae Major fouling organism – rapidly colonize most marine surfaces with their tiny calcareous tubes tubes encrusting a chiton’s shell valves have a large operculum, or stopper, to seal the opening of their tube after they withdraw their feeding tentacles