Invertebrate Embryology and Reproduction

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Invertebrate Embryology and Reproduction
Copyright
Dedication
Contents
Preface
Acknowledgements
1 Chapter Outline
	Historical Review
		Descriptive phase
		Discovery of the microscope
		Comparative phase
			Embryology and other subjects
				Cell theory
				Chromosome theory
				Genetics and gene theory
				Phylogeny and recapitulation theory
				Retention theory
		Experimental phase
		References
2 Chapter Outline
	Introduction
		Gametogenesis and gametes
			Origin of the germ cell (gametocyte) in some cnidarians
				In Obelia sp.
				In Eudendrium sp. (loss of medusoid phase)
				In Hydra sp.
			Natural phenomena indicating the identification of primordial gonocytes (germ cells)
			Features of the nucleus
				Chromatin diminution in Ascaris
				Chromosome elimination in Sciara
			Features of the cytoplasm
				Localized cytoplasmic factors in germ-cell determination
			Formation of gametes (gametogenesis)
				Oocyte growth (deutoplasmogenesis) or vitellogenesis
					Deutoplasmogenesis in Portunus pelagicus (in view of histochemistry)
						Predeutoplasmic oocyte
						Deutoplasmic oocytes (secondary vitellogenesis phase)
					Deutoplasmogenesis in Asterina pectinifera (in view of cytology)
				Meiotic arrest in animal oocytes
				Life span of gametes
					Senescence of spermatozoa
					Senescence of egg
			Structure of gametes
				Structure of the sperm
					Evolution of the sperm cell
						The typical marine spermatozoon
							The acrosome
							The nucleus
							The centrioles and the anchoring structures
							The axoneme
							Mitochondria
				The mature egg (the unfertilized egg)
					Cortical granules
					Exocytosis
					Fate of cortical granule membrane after exocytosis
			Types of gametes
				Types of sperm
				Types of eggs
					Egg membranes
			Maturation of gametes
				Oocyte maturation
				Spermatozoon maturation
		Fertilization (L., FERTILIS = TO PRODUCE; TO BEAR; AND FREVO = TO BEAR)
			Description of fertilization reaction in sea urchin eggs
			Formation of the fertilization membrane
			Up-to-date concept of the process of fertilization
				I-Cell adhesion (recognition and contact between sperm and egg)
				II-Regulation of sperm entry into the egg and prevention of polyspermy
					Ion-dependent changes in membrane potential (polysperm block)
					Other plasma membrane polyspermy blocks
						Echiuroids, annelids, and molluscs
					Elevation of the fertilization envelope
						Formation of fertilization membrane
					Various secretory products released by cortical granules
					Release of peroxide to inactivate sperm
			Other activities performed by cortical granules
				Hardening of the fertilization envelope
				Role of calcium in the initiation of the cortical granule reaction
				III-Fusion of the haploid nuclei of the egg and sperm
				IV-Activation of egg metabolism to start development
		Development
			Early development
				Cleavage
				Blastulation
				Gastrulation
		References
Kingdom Protista
3 Chapter Outline
	Phylum Protozoa
		Class 1: Mastigophora (GREEK MASTIX, ‘WHIP’, AND PHOREIN, ‘TO BEAR’), [FLAGELLATA] (LATIN FLAGELLUM, ‘WHIP’)
			Chlamydomonas
				Habitat
				Morphology
				Reproduction
					Asexual reproduction
						Zoospore formation or binary fission (as in the majority of flagellates).
						Aplanospore formation.
						Palmella stage.
					Sexual reproduction
						Isogamous reproduction.
						Anisogamous reproduction.
						Oogamous reproduction.
					Zygote and zygospore
			Volvox (family: Volvocidae)
				Volvox habitat
				Morphology
				Reproduction
					Asexual reproduction
					Sexual reproduction
			Wonderful features of Volvox
		Class 2: Sarcodina (Amoebae) (GREEK SARCOS, ‘FLESHY’)
			Family: Difflugiidae
			Difflugia sp. (Borradaile et al., 1977, p. 78)
				Habitat
				Reproduction
					Sexual reproduction
				Habitat
				Morphology
			Family: Actinophyridae (Hartmann, 1913)
			Actinophrys
				Morphology
				Reproduction
		Class 3: Sporozoa (GREEK SPORA, ‘SEED’)
			Example: Eimeria spp.
			Monocystis
				Reproduction and/or life cycle
		Class 4: Ciliophora (LATIN CILIUM, ‘EYELID’)
			Habitat
			Paramecium (slipper animalcule)
				Morphology
				Reproduction
					Asexual reproduction
					Sexual reproduction
				Conjugation in Paramecium
					Cell adhesion
						Agglutination
						Holdfast union
						Paroral union
					Fusion of the meiotically reduced haploid genome
					Development of a new cell line
		References
Kingdom Animalia
	Table of classification of Kingdom Animalia
Subkingdom Parazoa
4
Chapter Outline
	Phylum Porifera
		Definition
		Historical review
		General characteristics
		Classification (according to various sources)
			Another view for class Demospongiae
			Another recent view
		Embryological characteristics of Porifera
		Reproduction
			Agametic reproduction
				Budding
				External bud formation
				Internal buds (gemmule formation)
				Other agametic types of reproduction
					Reduction bodies
					Fragmentation
			Factors influencing agametic reproduction
			Regeneration
			Gametic reproduction
				Sexual differentiation
				Gonads
				Origin of the germ cells
				Gametogenesis
					Spermatogenesis
						Structure of the fully formed spermatozoon
					Oogenesis
					Reproductive behaviour and spawning
					Fertilization
				Development
		Class Calcarea
			Subclass Calcaronea
				Leucosolenia variabilis
					Inversion
					Amphiblastula larva (free swimming period)
					Metamorphosis and settlement
						Reproduction
						Spermatogenesis
						Oogenesis
						Embryogenesis
						Formation of the larva
						The fully formed larva
							Gametogenesis
				Development of Sycon raphanus
			Subclass Calcinea
				Calcinea larva
			Hexactinellida (Hyalospongiae)
				Reproduction
				Oopsacas minuta Topsent, 1927
					Development of Oopsacas
			Demospongiae
				Tetractinomorpha (Tetraxonida)
				Example: 1—Donatia deformis (Thiele)
			Viviparous sponges
				Example: 2—Plakina monolopha (Maas, 1909)
				Example: 3—Spongia officinalis Lenneaus
				Example: 4—Stylocordyla borealis Loven, 1868
				Example: 5—Carnivorous Asbestopluma occidentalis
		Nutrition of embryos
		Larval release
		Larval behaviour and settling
		Metamorphosis
		Oviparous sponges
		Types of larvae
			I Parenchymula larva
			II Amphiblastula larva
			III Simple blastula (undifferentiated blastula) (coeloblastula)
		Biological associations
		References
Diploblastica
5 Chapter Outline
	Phylum Cnidaria
		Definition
		General characteristics
		Classification
		Body plan of Cnidaria
		Reproduction
			Agametic reproduction
				Class Hydrozoa
				Other types of agametic reproduction
				Class Scyphozoa
				Class Anthozoa
			Regeneration
			Gametic reproduction
				Origin of germ cells
				Gonadogenesis
				Gametogenesis
					Spermatogenesis
					Oogenesis
				Gametes
				Spawning (release of gametes)
				Brooding
				Cnidarian embryogenesis
					Fertilization
					Cleavage
					Blastulation
					Gastrulation
					Larval forms
					Larval settling
					Postembryonic development (metamorphosis)
		Class Hydrozoa
			Origin of germ cells, sex determination, and sex inversion in medusae of the genus Clytia (Hydrozoa, Leptomedusae): The inf ...
			Obelia geniculata
				Development of the medusa
				Structure of the medusa
				Gametic reproduction
				Origin of the germ cells
				Development
			Eucheilota paradoxica
				Formation of frustules, polyps, and persistent stages
			Bougainvillea fructuosa
			Tubularia mesembryanthemum
				Embryogenesis
				Formation of actinula larva
				Actinula larva
			Eudendrium racemosum (Cavolini, 1785)
				Metamorphosis
			Development of Gonionemus depressum
			Hydra vulgaris
				Fertilization (Hydra carnea)
				Cleavage and blastulation
				Gastrulation
				Cyst formation
				Hatching of embryo
			General development of siphonophora
				Bargmannia elongata
					The deep-sea siphonophore
					The siphonosome cormidial organization
					The siphosome: The growth zone and budding sequence
				Nanomia bijuga
		Class Scyphozoa [Subphylum Medusozoa Peterso (Lawley et al., 2016)]
			Subclass Stauromedusa
				Stylocoronella riedli
			Subclass Discomedusae
				Order Coronatae
					Ex. Nausithoë aurea
						Spermatogenesis
						Oogenesis
						Embryogenesis
				Order Semaeostomeae
					Development of Aurelia aurita
					Planula larva
					Larval settlement and onset of metamorphosis
					Late metamorphosis: The formation of tentacles and gastric pouches
				Other Semaeostomeae Scyphozoa
				Order Rhizostomae
					Genus Mastigias
					Cassiopea andromeda Forskål, 1775
						Agametic reproduction
						Development
						Strobilation
					Cotylorhiza tuberculata
						Reproductive system
						Spermatogenesis
						Oogenesis
						Fertilization
						Embryology
						Release of the embryos
						Planula
						Settlement
						The polyp
						The scyphistoma
					Lychnorhiza lucerna
		Class Cubozoa Werner, 1973 (Lawley et al., 2016)
			Tripedalia cystophora
			Charybdaea marsupialis
			Carybdea marsupialis
			Carybdea sivickisi
				Sexual maturation
				Courtship, spermatophore formation and sperm-transfer
				Dehiscence of the spermatophore and fertilization
				Histology of the female gonad and putative spermathecae
				Settlement and development of embryos
			Copula sivickisi
				Structure of the gonads of C. sivicksi
				Spermatozeugmata
				Spermatozoon
				Female gonad with attached spermatozeugmata
				Fertilization
			Alatina cf. moseri (Mayer, 1906)
				Agametic reproduction
				Cyst formation
				Metamorphosis
				Young medusa
			Morbakka virulenta
		Class Anthozoa
			Subclass Ceriantipatharia
				Order Antipatharia
					Agametic reproduction
					Gametic reproduction
					Ex. Cirrhipathes anguina
						Mature male polyp
						The mature sperm
						Mature female polyp
						Spawning
					Ex. Antipathes Pallas, 1766
				Order Ceriantharia
					Ex. Pachycerianthus multiplicatus
					Ex. Cerianthus Iloydii
						Ex. Tubipora
			Subclass Octocorallia (Alcyonaria)
			Soft corals
				Order Stolonifera
				Order Alcyonacea
					Alcyonium digitatum (dead man’s fingers)
					Alcyonium coralloides
					Heteroxenia fuscescens (Ehrenberg, 1834)
						Agametic reproduction
							Budding
							Transverse fission
							Pinnitomy
							Gametic reproduction
								Spermaries
								The ovum
								Fertilization
								Embryology
								Gonads and gametogenesis
								Spawning
								Fertilization
								Cleavage
								Blastula
								Spermatogenesis
								Oogenesis
								Spawning
								Gametes
								Fertilization and development
							Spawning
							Cleavage
							Gastrulation
							Formation of the stomodaeum and gastrodermis
					Xenia umbellata
					Capnella gaboensis Verseveldt, 1977
				Order Gorgonacea (horny corals)
					Sea fan and Corallium
					Junceella fragilis Ridley
					Anthoplexaura dimorpha Kûkenthal, 1908
			Subclass Hexacorallia (Zoantharia)
				Sea anemones and stony corals
				Order: 	Actiniaria (sea anemones)
					Sea anemones
					Nematostella vectensis
					Sagartia troglodytes
					Halcampa duodecimcirrata
					Epiactis japonica
					Tealia crassicornis
					Cribrinopsis japonica
				Order Scleractinia
					True or stony corals
					Astrangia danae
					The reef-building coral Acropora spp.
						Galaxea fascicularis
						Dipsastraea (Favia) speciosa
		References
6 Chapter Outline
	Phylum Ctenophora
		Definition
		Distinctive features
		Classification
			Bases of taxonomy
			Hormiphora plumosa
			Reproduction
				Regeneration
				Brooding
				Gametic reproduction
					Origin of the germ cells and gonads
					Gonads
					Gametogenesis
						Spermatogenesis
						Mature sperm
						Oogenesis
						Oogenesis in Gastrodes
							Spawning
					Development
						Embryonic development
						Fertilization
						Cleavage
						Gastrulation
						Larval types
			Mnemiopsis leidyi
				Cell lineage experiments
			Organogenesis
				Comb plates
				Stomodeal pharynx
				Sense organ
				Nervous system
				The gastrovascular system
			Hatching
			Brooding
		References
Triploblastica
Acoelomata
7 Chapter Outline
	Phylum Platyhelminthes, Turbellaria
		Definition
		Introduction
		Distinctive features
		Classification
			Two theories concerning the origin of Platyhelminthes
		Order Acoela
			Acoel Polychoerus carmelensis
				Morphology of gametes
				Mating (Costello and Costello, 1938)
				Development of simple egg (Acoela)
					Polychoerus carmelensis
					The acoel Neochildia fusca
						The acoel Convolutriloba longifissura
		Reproduction
			Agametic reproduction
				Occurrence and types
			Gametic reproduction
			Reproductive system
				Method for obtaining eggs (Kato, 1968)
				How to prepare embryos
					Gametogenesis
						Spermatogenesis
							Spermatozoa
							Polymorphism of sperm
							Mechanisms of sperm transfer in Turbellaria
						Oogenesis
							Oocytes (ova)
					Copulation and/or fertilization
						Oviposition
		Order Polycladida
			Development of another simple egg
				Cleavage of this simple egg (Kato, 1968)
				Gastrulation
				Indirect development
					Formation of Müller’s larva
						Metamorphosis of Müller’s larva
						Hoploplana inquilina (Polycladida, Acotylea)
					Götte’s larva (Stylochus sp.)
			Larvae of flatworms Polycladida
				Direct development in Polycladida
					Acotylea Notoplana humilis
		Order Rhabdocoela
			Dalyellid flatworm, Gieysztoria superba
				Juvenile of Gieysztoria
			The rhabdocoel Mesostoma lingua
			Comparison between Gieysztoria and Mesostoma
			The Rhabdocoel Macrostomum sp.
				Juvenile of Macrostomum sp.
		Order Tricladida
			Epimorphosis
			Morphallaxis
			Development of composite egg (Tricladida)
				Dendrocoelum lacteum
				Girardia tigrina (Girard, 1850)
		References
8 Chapter Outline
	Phylum Nemertinea
		Definition
		Introduction
		Distinctive features
		Classification (ACCORDING TO VARIOUS SOURCES)
		Reproduction
			Reproductive system
			Gametic reproduction
				Gametogenesis
					Spermatogenesis
						Structure of the spermatozoon.
							Formation of the prospective body wall.
							Fusion of the discs.
							Development and/or structure of the organs
							Proboscis
							Nervous system
							Body wall
							Nephridia
							Muscles
							Body cavity
							Alimentary canal
							Embryonic development
							Cleavage
							Blastula.
							Pilidium larva
							Juvenile development in M. alaskensis
							Juvenile rudiment development
							The nervous system.
				Oogenesis
				Spawning
				Fertilization
			Egg activation and the first block to polyspermy
			Obtaining material
			Double eggs in Nemertinea
			Early development
				Cleavage
				Blastula
				Gastrulation
			Indirect development
				Pilidium larva
					The structure of pilidium larva
					Metamorphosis of pilidium larva
						Desor larva
						Schmidt’s larva
						Iwata’s larva
						Lineus ruber (Schmidt’s larva)
						Structure of Schmidt’s larva
						Metamorphosis of Schmidt’s larva
						Development of the proboscis
						Early juvenile
				Micrura alaskensis
			Direct development
				Procephalothrix simulus
		References
Pseudocoelomata
9 Chapter Outline
	Phylum Nematoda
		Definition
		Historical review
		General characters
		Classification
		Reproduction
			Agametic reproduction
			Parthenogenesis
			Gametic reproduction
				Sexual dimorphism
				Spicules
				Intersexes
				Hermaphroditism
				Reproductive system
				Origin of germ cells and gonads
				Gametogenesis
					Spermatogenesis
					Oogenesis
				Reproductive behaviour
					Sex attractants
				Copulation
				Fertilization
		Development
			Early embryology
			Cleavage
				One- to two-cell stage (first cleavage)
				Two- to four-cell stage (second cleavage)
				Chromatin diminution
				Four- to eight-cell stage (third cleavage)
				Eight-cell to 16-cell stage (fourth cleavage)
				Fifth cleavage—Blastula
			Gastrulation
		Hatching
		Embryological peculiarities
		Postembryonic development
			Life cycles
			Anabiosis
		Caenorhabditis elegans
			Nomenclature
			Historical review
			Sex differentiation
			Reproductive system
			Gonadogenesis
			Gametogenesis
			Gametes
			Development
				Embryogenesis
				Gastrulation
				Polarity
				Postembryonic development
				Dauerlarva
		Variation in nematode embryology
		References
Coelomata
Supraphylum Arthropods Mandibulata
10 Chapter Outline
	Phylum Crustacea, Pennant (1777)
		Definition
		Historical review
		General characters
		Classification
			Branchiopoda (Greek branchia, ‘gill’)
				Anostraca (Greek a, ‘not’ and ostracon, ‘shell’)
					Morphology
				Reproductive systems
				Example Artemia sp.
					The male reproductive system
					Female reproductive system
					Early development (embryology)
						Cleavage
						Presumptive areas of the blastula
						Gastrulation
							Differentiation of the embryo
						The hatched nauplius
					Parthenogenesis
				Diplostraca
					Morphology
				Reproductive system
					Development (embryology)
						Gametes: Oogenesis
					Cleavage
					Presumptive areas of the blastula
					The presumptive stomodaeum and proctodaeum
					The presumptive mesoderm
					The presumptive ectoderm
					Gastrulation.
					Differentiation of the embryo
			Cirripedia (Latin cirrus, ‘curl’, and pous, ‘foot’, includes barnacles)
				Thoracica (Greek thorax, ‘chest’)
				Reproductive system
					Dwarf males
				Copulation
				Fertilization and brooding
			Development
				Gametes
				Cleavage
				Presumptive midgut
				Presumptive stomodaeum and proctodaeum
				Presumptive mesoderm
				Presumptive ectoderm
				Gastrulation
				Differentiation of the embryo
				Metamorphosis of the larvae
			Malacostraca (Greek malakia, ‘softness’, and ostrakon, ‘shell’)
				Hoplocarida (Greek hoplon, ‘weapon’, and karis, ‘shrimp’)
					Ex. Squilla
					Definition
					History
					Habitat and behaviour
					Morphology
					Sexual dimorphism
					Reproductive systems
					Formation of the sperm cord
					Courtship and copulation
					Development (embryology)
						Gametes
						Early embryology
						Postembryology (larval development)
				Eucarida (Greek eu, ‘true’, and karis, ‘shrimp’)
				Order Decapoda (Greek deca, ‘ten’, and pous, ‘foot’)
					Penaeoidea
						Definition
						Habitat
					Family Penaeidae Bate, 1881
					Penaeus kerathurus
						Morphology and sexual dimorphism
						Reproductive systems
							Male reproductive system
								Formation of the spermatophore of P. kerathurus
									Initial formation of a sperm mass
									The two ducts of the ascending limb
									The deposition of the main layers of the body and the wing
									Preliminary connection of the two parts of the spermatophore
									The descending limb
									Role of the distal vas deferens
									The terminal ampoule
								The external appearance of the fully formed spermatophore of P. kerathurus
								Chemical composition of the spermatophore of P. kerathurus
									The absence of chitin
									Distribution of lipids
									Distribution of proteins
									Distribution of carbohydrates
									Argentaffin material in the spermatophore
									Hardening of the spermatophore of P. kerathurus
							Female reproductive system
								Copulation
								Development
									Gametes
									Spawning
									Fertilization
									Early embryology
									Larval development
					Astacidea (Astacura)
						Definition
						Habits and habitat
						Morphology and sexual dimorphism
						Reproductive systems
							Formation of the spermatophore of A. leptodactylus
							The fully formed spermatophore of Astacidea
							The ultrastructure of astacid sperm
						Copulation
						Spawning
						Brooding
						Development
							Formation of gametes
								Spermatogenesis
								Oogenesis
									Annual cycle of ovary development in sexually mature crayfish
						Early embryological studies
						Astacus fluviatilis Fabricius, 1775
							Up-to-date embryological studies on Astacidae
							The Japanese Cambaroides japonicus
							Parthenogenetic Marmorkrebs Procambarus fallax
						Hatching
							Postembryonic development
							Maternal care in Astacidea
							Parthenogenesis
					Brachyura Latreille, 1803
						Definition
						Habits and habitat
						Morphology and sexual dimorphism
						Reproductive systems
							The male system
								Formation of the spermatophore of P. pelagicus
									Formation of the sperm masses (role of the testis)
									The mature follicle
									The spermatozoa
									Deposition of the main layers of the spermatophore (role of the PVD)
									Role of the MVD
									Role of the DVD
								Moulding of the spermatophore of P. pelagicus
								Structure of the spermatophore of P. pelagicus
								Chemical composition of the spermatophore of P. pelagicus
									Absence of chitin
									Distribution of lipids
									Distribution of proteins
								Formation of the spermatophore of C. danae Smith, 1869
								Formation of the spermatophore of Chionoecetes opilio
									Spermatid differentiation
							The female system
								Copulation
								Duration of copulation in Brachyura
								Formation of the spermatheca
									Precopulation stage
									Fresh-copulation stage
										Plug of the female P. pelagicus
										Formation of the plug
									Late-copulation stage
										Chemical structure of the plug
										Hardening of the plug
								Maturation of the ovaries
									Precopulation stage
									Fresh-copulation stage
									Late-copulation stage
									Prespawn stage
										Deutoplasmogenesis
									May-spawn stage (ovigerous female)
									Inter-spawn stage
									September-spawn stage
										Egg-membranes
								Embryology
								Hatching
								Postembryonic development (larval development)
								Artificial insemination
								Embryogenesis of artificially inseminated eggs
								Utilization of lipovitellin during embryogenesis
		References
11 Chapter Outline
	Phylum Mollusca
		Definition
		General features of Mollusca
		Classification of Mollusca
			Class- Amphineura
				Polyplacophora
					Reproduction
						Agametic reproduction
						Gametic reproduction
							Dimorphism
							Hermaphroditism and sex ratio
					Anatomy of the reproductive system
					Gametogenesis
						Oogensis
						Spermatogenesis
							Reproductive behaviour and spawning
					Early development
						Cleavage
						Gastrulation
					Larval development
						Larval eye
						Foot and pedal gland
						The shell
					Settlement and metamorphosis
					Brooding and ovoviviparity
					Later development (Wada, 1968)
						The eyes
						The aesthetes
						The nervous system
						The head
				Monoplacophora
				Aplacophora
					Early development
					Larval development
					Metamorphosis
			Class- Gastropoda
				Reproduction
					Agametic reproduction
					Gametic reproduction
						Dimorphism
						Hermaphroditism
						Protandric hermaphrodites
						Reproductive system
					Eremina ehrenbergi
						The hermaphrodite gonad
						The hermaphrodite duct
							The talon
							Albumen gland
						Spermoviduct
						The male side of the system
							The vas deferens
							The penis
							The genital atrium
						The female side of the system
							The oviduct
							The spermatheca and spermathecal duct
							The vagina
							The accessory organs of the vagina
								The mucous glands
								The dart sac and dart
									The dart
						Gametogenesis
							Spermatogenesis
								Structure of the fully mature spermatozoa
								Abnormal spermatogenesis
								Other examples of dimorphism of sperm in Mollusca
								Functions of abnormal spermatozoa
							Spermatophores
								Eremina ehrenbergi
							Oogenesis
							The spherical oocyte
							Gonad of Melampus coffeus
						Back to E. ehrenbergi
							Sperm pathway and spermatophore formation
								Spermatophore formation
								Copulation
							Pathway of the foreign sperm
							The pathway of the oocyte
								The egg/fertilization
									The fully formed egg
									Back to Gastropoda, In general
									Reproductive behaviour
										Spawning aggregation
										Sex recognition
										Copulation
										Brooding behaviour
										Spawning and rearing of youngs
					Adalaria proxima
						Fertilization
						Early development
							Cleavage
								Cleavage of Trochus (Annelidan mode)
								Cleavage of Ilyanassa obsoleta
							Differentiation of germ layers
								Segregation of ectoderm
								Differentiation of ento-mesoblast
								Ecto-mesodermal cells
							Blastulation
							Gastrulation and gastrula stage
								Types of gastrulation
									Invagination (emboly)
									Epiboly
									Multipolar proliferation (ingrowth)
						Larvae (trochopore and veliger stages)
							Shell formation
							Foot, pedal gland, statocysts
							Radula sac
							Velum
							Head vesicle
							Digestive system
						Later development
							Torsion
							Coiling of the visceral hump
							Detorsion
								Echinospira larvae
								Trophon geversianus (Pallas, 1774)
		References
12 Chapter Outline
	Cephalopoda (Siphonopoda)
		General characters
		Classification
			According to Gardiner (1972)
			According to Borradaile et al. (1977)
		Reproduction
			Agametic reproduction
			Gametic reproduction
				Sexual dimorphism
				The reproductive systems
					The male system
						The testis.
						The gonoduct.
					The vas deferens
						Proximal region.
						Main region.
						Distal region.
					Needham’s organ
			Spermatophores
				Spermatophore of Sepia officinalis
					Tunics
					Connectives
					Spermatophoric cord
					Ejaculatory apparatus
				Dehiscence of the spermatophore
				Spermatozoa of Sepia officinalis
				Formation of the spermatophore
					Role of the testis (spermatogenesis)
						Testicular duct.
					Role of the PVD
					Role of the MVD
					Role of the DVD
					Role of Needham’s sac
				Hardening of the spermatophore
					The female system
						Buccal seminal receptacle.
						The ovary.
							Ovulation.
							Fertilization.
							The egg.
		Reproductive behaviour, mating, copulation, and spawning
		Development
			Cleavage
			Formation of germ layers from the blastoderm
		Organogenesis
		References
Phylum Chordata
13 Chapter Outline
	Subphylum Urochordata (Tunicata)
		Definition
		General characters
		Class Ascidiacea
			Characteristics
			Classification
				Order 1- Enterogona
				Order 2- Pleurogona
			Reproduction
				Agametic reproduction
				Gametic reproduction
					Gametogenesis
						Spermatogenesis
							The sperm
						Oogenesis
							The fully grown oocyte
						Spawning
						Fertilization
				Early development (embryogenesis)
					Maturation and ooplasmic segregation
					Cleavage (second phase of embryogenesis)
					Gastrulation and neurulation
						Gastrulation
						Neurulation
					Morphogenesis and cell differentiation
				Hatching
				Structure of fully formed larva
					Metamorphosis
					Differentiation of adult organs
						Endostyle
						Atrium
						Alimentary canal
						The nervous system
				Time required for development
				Experimental studies
					Metamorphosis
		References
Further Reading
Index
	A
	B
	C
	D
	E
	F
	G
	H
	I
	J
	K
	L
	M
	N
	O
	P
	Q
	R
	S
	T
	U
	V
	W
	X
	Y
	Z
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