OEB51 Lecture 7 Introduc2on to the Protostomes Spiralia & Ecdysozoa Annelida Ctenophora Animals Porifera Placozoa Cnidaria Xenacoelomorpha Parahoxozoa Ambulacraria Echinodermata Hemichordata Planulozoa Deuterostomia Cephalochordata Chordata Urochordata Bilateria Craniata Chaetognatha Bryozoa Entoprocta Cycliophora Nephrozoa Annelida Trochozoa Mollusca Nemertea Brachiopoda Phoronida Spiralia Gastrotricha Protostomia Platyhelminthes Gnathostomulida Micrognathozoa Gnathifera Rotifera Nucleariida Orthonectida Fungi Dicyemida Opisthokonta Filasterea Priapulida Ichthosporea Scalidophora Holozoa Animals Loricifera Choanoflagellata Kinorhyncha Nematoida Nematoda Ecdysozoa Nematomorpha Tardigrada Panarthropoda Onychophora Arthropoda Echinoderm and hemichordate germ layer fate maps Primus (2005) Dev Biol Urochordate and cephalochordate germ layer fate maps A: Urochordate B: Cephalochordate Ctenophora Animals Porifera Placozoa Cnidaria Xenacoelomorpha Parahoxozoa Ambulacraria Echinodermata Hemichordata Planulozoa Deuterostomia Cephalochordata Chordata Urochordata Bilateria Craniata Chaetognatha Bryozoa Entoprocta Protostomes Cycliophora Nephrozoa cons+tute 95% Annelida Trochozoa Mollusca Nemertea of all animal Brachiopoda Phoronida diversity! Spiralia Gastrotricha Protostomia Platyhelminthes Gnathostomulida Micrognathozoa Gnathifera Rotifera Nucleariida Orthonectida Fungi Dicyemida Opisthokonta Filasterea Priapulida Ichthosporea Scalidophora Holozoa Animals Loricifera Choanoflagellata Kinorhyncha Nematoida Nematoda Ecdysozoa Nematomorpha Tardigrada Panarthropoda Onychophora Arthropoda Protostome characters found in the literature • The blastopore becomes the mouth (but there are many excep2ons) • Spiral cleavage(but this is only in Spiralia) • Mesoderm derived from the mesentoblast, usually 4d (but this is only in Spiralia) • Schizocoelous coelom formaon, where the coelom forms from the rim of the blastoderm (but there are many excep2ons) • Trochophore larva (but this is only in Spiralia) • Apical nervous center (brain) and ventral nerve cord How is ventral defined in these two protostomes? SPIRALIA (= LOPHOTROCHOZOA) Animals with spiral development Trochophores Lateral and Apical Views – Third Cleavage Acila castrensis Spiral cleavage general proper2es I • Conspicuous cleavage paerns – Strongly conserved blastomere fates – Generally accepted notaon for blastomeres: Conklin 1897 Crepidula – First cleavage oZen along plane defined by apical pole and sperm entry point, determining secondary axis (DV) – Paern usually easier to recognize in small, yolk-free eggs (50-300um) – In larger eggs the yolk “distorts” the paern • no direct correlaon between cleavage paern and amount of yolk • Most have typical trochophore larva – Platyhelminthes and nemertenes have modified trochophores • Developmental mode: – Some have direct development – Some have indirect development • Oral/aboral axis fixed during oogenesis • Polar bodies at apical pole • Fer2lizaon occurs before the end of meiosis Spiral cleavage general proper2es II • Four cell stage: – A/C quadrants = L/R – B/D quadrants are anterior/ventral and posterior/dorsal – May be equal sized blastomeres or unequal (From 2 cell stage) – D quadrant usually larger than others • Typical spiral cleavage has – Four micromere quartets – Mesoderm and germline formaon from 4d cell • Prototroch typically derived from – 1a2 1d2: primary trochoblasts – 1a1222 1c1222: accessory trochoblasts – 2a1 2c1: secondary trochoblasts • Mesoderm derived from two blastomere groups – Endomesoderm from 4d cell – Ectomesoderm from micromeres of second and third quartets Spiral cleavage general proper2es II Spiral cleavage general proper2es II • Four cell stage: – A/C quadrants = L/R – B/D quadrants = anterior/ventral and posterior/dorsal – D quadrant usually larger than others • Typical spiral cleavage has – Four micromere quartets • 1st quartet: 3rd cleavage (8 cells) • 2nd quartet: 4th cleavage (16 cells) • 3rd quartet: 5th cleavage (64 cells) • 4th quartet: 6th cleavage (128 cells) Asymmetric segregaon • During early cleavage, different regions of cytoplasm are segregated into different blastomeres • The cytoplasmic “determinants” determine the cell fate of the recipient blastomeres • This accounts for the generally mosiaic ( = determinate = non-regulave) development seen in most spiralians Limacina sp. 430430CHAPTERCHAPTER THIRTEEN THIRTEEN TrochophoreUNCORRECTED larvaUNCORRECTED PAGE PAGE PROOFS PROOFS FigureFigure 13.35 13.35GrowthGrowth of a trochophoreof a trochophore larva. larva. (A) Trochophore (A) Trochophore larva oflarva Arenicola of Arenicola. Note Notethe teloblastic the teloblastic (4d) mesodermal(4d) mesodermal bands bands destined destined to form to formthe metameric the metameric coelomiccoelomic spaces. spaces. (B,C) (B,C)Two stagesTwo stages in the in development the development of Eteone of Eteone. (B) Early-stage. (B) Early-stage segmentation.segmentation. (C) Juvenile, (C) Juvenile, showing showing the fates the offates the of larval the larvalregions. regions. Oligochaeta.Oligochaeta.NowhereNowhere is the is divergence the divergence of the of clite- the clite- llate llateannelids annelids from from the polychaetesthe polychaetes more more apparent apparent than thanin the in major the major differences differences in reproductive in reproductive and lifeand life historyhistory strategies. strategies. The evolutionThe evolution of new of newreproductive reproductive Figure 13.35 Growth of a trochophore larva. (A) Trochophore stylesstyles unquestionably unquestionably contributed contributed greatly greatly to the to suc- the suc-ecaelarvaecae(seminal of(seminal Arenicola receptacles) receptacles). Note thethat teloblastic open that opento the(4d) to outside mesodermalthe outside via viabands cessfulcessful invasion invasion of freshof fresh water water and andland landby theby theseparatedestinedseparate pores to pores (Figure form (Figure the 13.36). metameric 13.36). coelomic spaces. (B,C) Two oligochaetesoligochaetes and hirudinoideans.and hirudinoideans. Ofstages majorOf inmajor theimportance development importance to theof to Eteone overallthe . overall(B) reproductive Early-stage reproductive OligochaetesOligochaetes are hermaphroditic are hermaphroditic and usually and usually possess possessstrategysegmentation.strategy of oligochaetes of oligochaetes (C) Juvenile, is a unique isshowing a unique region the region fates of glandular of of the glandular larval distinctdistinct and complexand complex reproductive reproductive systems, systems, including includingtissueregions.tissue called called the clitellum the clitellum(Latin(Latin for “saddle for “saddle”) (Figure”) (Figure permanentpermanent gonads. gonads. Furthermore, Furthermore, various various parts parts of the of the13.36A).13.36A). This structureThis structure is a principal is a principal anatomical anatomical feature feature reproductivereproductive apparatus apparatus are restricted are restricted to particular to particular seg- seg-unifyingunifying the Oligochaeta the Oligochaeta and the and Hirudinoidea the Hirudinoidea as the as the ments,ments, usually usually in the in anteriorthe anterior portion portion of the of wormthe wormclitellateclitellate annelids. annelids. The clitellum The clitellum has the has appearance the appearance of a of a (Figure(Figure 13.36 13.36). The). arrangementThe arrangement of the of reproductive the reproductive sys- sys-thickthick sleeve sleeve that partiallythat partially or completely or completely encircles encircles the the temstems facilitates facilitates mutual mutual cross-fertilization cross-fertilization followed followed by bywormworm’s body.’s body. It is formed It is formed of secretory of secretory cells withincells within the the encapsulationencapsulation and depositionand deposition of the of zygotes. the zygotes. epidermisepidermis of particular of particular segments. segments. The exact The exactposition position of of The maleThe male system system includes includes one or one two or pairstwo pairs of testes of testesthe clitellumthe clitellum and the and number the number of segments of segments involved involved are are locatedlocated in one in or one two or specifictwo specific body body segments. segments. Sperm Sperm are areconsistentconsistent within within any particular any particular species. species. In freshwater In freshwater releasedreleased from from the testes the testes into theinto coelomic the coelomic spaces, spaces, where whereformsforms the clitellum the clitellum is located is located around around the position the position of the of the they theymature mature or are or picked are picked up by up storage by storage sacs (seminalsacs (seminal vesicles) derived from pouches of the septal peritoneum vesicles) derived from pouches of the septal peritoneum ▲ ▲ (Figure(Figure 13.36B). 13.36B). There There may maybe a singlebe a single seminal seminal vesicle vesicle or orFigureFigure 13.36 13.36The reproductiveThe reproductive system system of Lumbricus of Lumbricus as many as three pairs in some earthworms. When ma- and matingand mating in earthworms in earthworms (see Figure (see Figure 13.19C). 13.19C). (A) Ex- (A) Ex- as many as three pairs in some earthworms. When ma-ternal structures associated with reproduction of Lumbricus ture, the sperm are released from the seminal vesicles, ternal structures associated with reproduction of Lumbricus ture, the sperm are released from the seminal vesicles,(ventral view). (B) Segments 9–15 of Lumbricus (composite