3Phylogeny (briefly) Closely related to Platyhelminthes? Post Platyhelminthes?Big question: Do they have a coelom?
4Diversity Mostly free-living Primarily predators Habitats Benthic marineEx. 1: Mussel bedsEx. 2: Antarctic (big!)Some in freshwater and terrestrialA few are parasiticOne type in Dungeness crabs
5Bauplan basics Similar to Platyhelminthes Coelom? Triploblastic (distinct mesoderm muscles)Bilateral symmetry & cephalizationShare similar features of protostome developmentCoelom?
6Feeding/Digestion Eversible proboscis: Class Anopla Stored inverted within the rhynchocoelRhynchocoel from coelom?Separate from digestive systemAssociated musclesLocation/FunctionsSurface glands secreteAdhesivesToxinsKNOW how proboscis everts & captures prey!Food intake?Diagram: Pearse/BuchsbaumLiving Invertebrates
8Feeding/Digestion Eversible proboscis: Class Enopla Differences from AnoplaCommon opening with digestive system = mouthProboscis eversionEversion of foregut. Why?Stylet at end of proboscisAdditional neurotoxinsCentral channel; toxins ejected next to styletReserve stylet sac!Diagram: Pearse/BuchsbaumLiving Invertebrates
10Feeding/digestion Digestion Complete digestive system Some specialization of regionsExtra- and intracellular digestionEversible foregut extracorporealMovement through tractCiliaryPeristalsis of body wallNOTE: No muscle surrounds digestive tract!
11Circulation Closed circulatory system Partly coelomic in origin? Blood vessels and lacunaeCirculation primarily via peristalsis of body wall.Blood cells with respiratory pigments (including Hb)FunctionsTransport of nutrients, gases, hormones, waste;Additional metabolismHydrostatic skeleton
13Gas exchange Outer body surface Shape favorable S/V ratio Some larger forms: gas exchange via digestive tractIrrigation of foregut
14Osmoregulation/excretion ProtonephridiaMost important in which habitats?Absent in deep-sea, pelagic formsRole in excretion?Associated with blood vesselsBehavioral osmoregulationMucus coveringBurrowing
16Nervous system Organization (briefly) Somewhat similar to PlatyhelminthesTwo lateral nerve cordsOften an additional dorsal nerve cordCerebral ganglia more developedExtensive innervation from anterior sensory structures
17Sensory structures Adapted for active, predatory lifestyle Sensory structures concentrated at “head”Additional sensory structures on entire body
19Sensory structures Chemoreceptors Locate prey & mates Cerebral organ Function of ciliated canal?Other functions of organ?
20Sensory structures Chemoreceptors Ocelli Frontal sense organ Chemosensory?OcelliMostly pigment-cup1 pair to manySome with lensesNegatively phototaxicNemerteans usually active nocturnally
21Movement Mesoderm-derived muscles Cilia-mucus Primarily longitudinal & circularPeristalsis, etc…Fluid-infiltrated mesoderm & circulatory system allow for hydrostatic skeletonCilia-mucus
22Reproduction Asexual reproduction Transverse fission is common Small fragments new individuals
23Reproduction Sexual reproduction Gonads develop within mesenchyme Along body lengthMass matingMostly external fertilizationMay occur in mucus sacsSpawning via temporary pores or body wall ruptureSometimes internal fertilizationMales with claspers or penis
24Reproduction Sexual reproduction Early development HoloblasticSpiral cleavageDeterminate cell fateMesoderm usually from 4D cellIndirect or direct developmentPilidium larvae