The unprecedented level of diversity recorded among the clones of self-fertilizing gynogenetic unisexuals and self-fertilizing simultaneous hermaphrodites challenges current ideas on the predominant role of recombination in promoting evolution of biological diversity. Though limited to a few species, the existence of self-fertilizing and cyclical sex changing hermaphrodites remains a puzzle to many geneticists and endocrinologists. Within a few days after the removal of a harem master or mistress, a successor changes sex and takes over the harem - the causes for the sex changing mechanism pose many challenges to socio-ecologists and behaviour specialists. This book is a synthesis of relevant and recent information on sexuality of fishes and points towards new directions of desired research.

First to look at fungi from the angle of biodiversity. As no college/university offers degree courses in Mycology, the book explains the need for such innovative courses, which are academically and economically important. Highlights the global cost of beneficial and harmful fungi, and brings to light many companies producing fungal based enzymes.

To identify factors those accelerate/decelerate species diversity To quantify identified environmental factors and life history traits that accelerate/decelerate species diversity

The polyphyletic Protozoa have explored the possibility of performing almost all metazoan functions with a few subcellular organelles. Their unicellularity and structural simplicity have (i) limited diversity to 32,950 species, (ii) restricted spatial distribution to aquatic habitats (94%, against 15% in Metazoa), (iii) demonstrated the ubiquitous dominance of clonality, (iv) reduced sexualization in 50% species, (v) facilitated the use of vegetative gametes in 40% species and (vi) secondary loss of sex in 10% species. With the fastest multiplication rates, i.e. once every 6-60 hours, they occur in high densities of 105-106 cell/ml. Their diverse and complicated life cycles are described in 30 types. Being risky, the cycle involves two hosts in < 2,000 parasitic species and injective transmission mode by sanguivorous insects and ticks in < 300 species. Their radial symmetry has accelerated diversity more than in radially symmetric less speciose Porifera (8,553 species), Cnidaria (10,856) and Echinodermata (7,000). In them, diversity is decelerated in the following descending order: symmetry > clonality > hermaphroditism > motility. Motility ranges from 2-3 m for Rhizopoda to 400-2,000 m for Ciliophora. Not surprisingly, 6,800 species of arcellinids, filosians and formainifers are testated or shelled. Within 1,229 sessile species, the peritrichid and suctorian ciliates are better adapted to coloniality. Unlike those of many Metazoa, the protozoan cyst is a dynamic stage, in which clonal or sexual reproduction occurs. Over 81% protozoans encyst, as it ensures (i) 90% survival during unfavorable conditions (against 15 in 12% non-encysted protozoans), (ii) genome transfer through generations, (iii) dispersal into new habitats and (iv) transmission to new hosts. Their mean body size ranges from 2 m to 2 mm - a range over 1,000-times - only 8% aquatic metazoans cover a similar size range. In comparison to 77% macrophagy in Metazoa, only 46% protozoans are macrophagous predators. Within motile microphagy, protozoans filter 3-2 times smaller food particle at 50% cheaper clearance cost. This efficiency has expanded microphagy to 15% in protozoans, against 3% in Metazoa. Hence, their turnover rate in trophic dynamics is twice faster than that of metazoans. Foraminifers serve as ecological sensitive indicators in petroleum exploration and rise in sea level. For the first time, incidences of clonality and meiosis as well as symbiosis and parasitism have been shown to hint at the origin and evolution of different protozoan taxonomic groups during the geological past.

To identify some life history features of plants and environmental factors that accelerate species diversity and others decelerating it. To quantify and bring light to these features and highlight new findings. To bridge relevant information on aquatic and terrestrial plants on these aspects.

This book is a comprehensive elucidation on aspects of reproduction and development in platyhelminthes covering from acoelids to taeniids. With the unique presence of neoblasts, turbellarians serve as a model for studies on cancer and senescence. Of ~ 27,000 species, ~ 77% are parasites; they are harmful to man and his food basket from livestock and fish. The stress hormone, cortisol level is responsible for susceptibility and resistance of the host. In digeneans, the propagatory multiplication potency is retained by all the larval forms and in either direction in sporocyst. The higher clonal diversity, mixing and selection in Second Intermediate Host (SIH) may purge inbreeding depression suffered by the fluke on propagatory multiplication in First Intermediate Host (FIH). Of 12,012 digeneans, 88% may engage 33,014 potential SIH species. They have the choice to select one among the available/awaiting 3.5 host species. The motility of vertebrate host and euryxenic flexibility/scope for selection of SIH species has increased lineage diversification in digeneans. The life cycle of cestodes is divided into aquatic and terrestrial patterns. The former includes (i) oncosphere and (ii) coracidium types and the latter (iii) hexacanth-cysticercoid, (iv) hexacanth-tetrathyridium and (v) hexacanth-cysticercus types. The share for the oncosphere, coracidium and hexacanth types is 17.0, 29.5 and 46.5%, respectively. The staggering fecundity and adoption of the intermediate host in the herbivorous/insectivorous food chain have enriched Taenioidea as the most (2,264) speciose order. Sex specific genes Smed-dmd 1 and macbol have been identified, and neuropeptides and dipeptides are involved in sexualization. Trematodes are unable to parasitize elasmobranchs, as they cannot suck body fluid/blood containing a high level of urea. Relatively higher fecundity supplemented with propagatory multiplication, incorporation of SIH in 88% species, clonal selection in SIH, and euryxenic flexibility and the widest choice for selection of SIH have led to the highest lineage diversification to render digeneans as the most speciose order in Platyhelminthes.

To identify factors those accelerate/decelerate species diversity To quantify identified environmental factors and life history traits that accelerate/decelerate species diversity

The 26 recognized minor phyla comprise aberrant clades, as most of them terminate as blind offshoots. Untied from the discussion on their phylogenesis of minor phyla, this book is largely devoted, for the first time, to aspects of reproduction and development in minor phyletics. The minor phyla are not as speciose (1,795 species/phylum) as the major phyla (157,066 species/phylum) are. The accumulation of deleterious genes causes inbreeding depression among progenies arising from parthenogenesis, clonal multiplication and selfing hermaphrodites. The reason for the limited species diversity in minor phyla is traced to (i) eutelism in 65.7% of minor phyletics and (ii) existence of 21.6% clonals, (iii) 6.4% parthenogens and (iv) 1.2% selfing hermaphroditism. Gonochorism obligately requires motility to search for a mate. The combination of low motility and gonochorism from Placozoa to hemocoelomatic minor phyla has limited diversity to < 1,000 species. Over 19% of minor phyletics are hermaphrodites. With the need to manifest and maintain dual sexuality, fecundity of hermaphrodites may be reduced to 50% of that in gonochores. Adopting an array of strategies, < 100 hermaphrodites are selfers. In eutelics, mitotic division is ceased in somatic cells after hatching. For the first time, the prevalence of eutelism has been brought to light in numbers of all the six pseudocoelomate phyla and priapulids. Eutelism limits fecundity to 30-300 eggs in free-living pseudocoelomates, priapulids and possibly other hemocoelomates. In them, sperm production is less than that of egg production; as a result, a large fraction of their eggs is sterile. With a high proportion of non-eutelic gametic cells (35%), Nematoda and possibly Nematomorpha and Acanthocephala are more fecund than rotifers, in which the proportion is 15%. Briefly, the reasons for the limited species diversity in minor phyletics are traced to eutelism, parthenogenesis and clonal multiplication. Surprisingly, parthenogenesis and clonal multiplication mutually eliminate each other. This is also true of hermaphroditism and parthenogenesis. However, clonal multiplication is prevalent from structurally simplest Placozoa to the most complex Ascidiacea, except in pseudocoelomates and hemocoelomates. A limited number of cells and cell types, and the consequent structural simplicity facilitate manifestation of parthenogenesis in pseudocoelomates and parasitism in Mesozoa, Myxozoa, 59% of Nematoda, Nematomorpha, Acanthocephala and Pentastomida. Despite hermaphroditism, Bryozoa (5,700 species) and Ascidiacea (3,000 species) are speciose among minor phyla. For the first time, the importance of fusion of fragments or colonies - an event equivalent to gamete fusion at fertilization - is recognized as a source of new gene combination. Besides, the colonies in these minor phyla degenerate and regenerate more or less regularly. Only the fittest degenerated colonies may be rejuvenated and regenerated.

Echinoderms and prochordates occupy a key position in vertebrate evolution. The genomes of sea urchin share 70% homology with humans. Researches on cell cycle in sea urchin and phagocytosis in asteroids have fetched Nobel Prizes. In this context, this book assumes immense importance. Echinoderms are unique, as their symmetry is bilateral in larvae but pentamerous radial in adults. The latter has eliminated the development of an anterior head and bilateral appendages. Further, the obligate need to face the substratum for locomotion and acquisition of food has eliminated their planktonic and nektonic existence. Egg size, a decisive factor in recruitment, increases with decreasing depths up to 2,000-5,000 m in lecithotrophic asteroids and ophiuroids but remains constant in their planktotrophics. Smaller (< 18 mm) ophiuroids do not produce a lecithotrophic eggs but larger (> 110 mm) asteroids generate planktotrophic eggs only. Publications on sex ratio of echinoderms indicate the genetic determination of sex at fertilization but those on hybridization, karyotype and ploidy induction do not provide evidence for heterogametism. But the herbivorous echinoids and larvacea with their gonads harboring both germ cells and Nutritive Phagocytes (NPs) have economized the transportation and hormonal costs on gonadal function. Despite the amazing potential just 2 and 3% of echinoderms undergo clonal reproduction and regeneration, respectively. Fission is triggered, when adequate reserve nutrients are accumulated. It is the most prevalent mode of clonal reproduction in holothuroids, asteroids and ophiuroids. However, budding is a more prevalent mode of clonal reproduction in colonial hemichordates and urochordates. In echinoderms, fission and budding eliminate each other. Similarly, autoregulation of early development eliminates clonal reproduction in echinoids and solitary urochordates. In pterobranchs, thaliaceans and ascidians, the repeated and rapid budding leads to colonial formation. Coloniality imposes reductions in species number and body size, generation time and life span, gonad number and fecundity as well as switching from gonochorism to simultaneous hermaphorditism and oviparity to ovoviviparity/viviparity.

This book is perhaps the first attempt to comprehensively project the uniqueness of molluscs, covering almost all aspects of reproduction and development from aplacophorans to vampyromorphic cephalopods. Molluscs are unique for the presence of protective external shell, defensive inking, geographic distribution from the depth of 9,050 m to an altitude of 4,300 m, gamete diversity, the use of nurse eggs and embryos to accelerate the first few mitotic divisions in embryos, the natural occurrence of androgenics in a couple of bivalves, viable induced tetraploids, gigantism induced by elevated ploidy, the complementary role played by mitochondrial genome in sex determination by nuclear genes and the uptake and accumulation of steroid hormone from surrounding waters. In molluscs, sexuality comprises of gonochorism (< 75 %) and hermaphroditism, which itself includes simultaneous (> 24%), protandry (< 1 %), Marian and serial. In them, the presence of shell affords iteroparity and relatively longer life span in prosobranchs and bivalves but its absence semelparity and short life span in opisthobranchs and cephalopods. Within semelparity, gonochorism facilitates faster growth and larger body size but hermaphroditism small body size. In them, sex is irrevocably determined at fertilization by a few unknown genes and is not amenable to any environmental influence. However, the sex determining mechanism is more a family trait in bivalves. Primary sex differentiation is also fixed and not amenable to environmental factor but secondary differentiation is labile, protracted and amenable to environmental factors. Both sex differentiation and reproductive cycle are accomplished and controlled solely by neurohormones. In these processes, the role of steroid hormones may be alien to molluscs.

This book is a concise informative elucidation of all aspects of reproduction and development in annelids covering from arenicola to tubifex. Annelids flourish between 4,900 m depth to 2,000 m altitude; some of them occur in unusual habitats like hydrothermal vents and subterranean aquatic system (stigobionts). A few have no gut and acquire adequate nutrients through osmotrophism and/or engaging symbiotic microbes. In the absence of exoskeleton to escape predation, the 17,000 speciose annelids have explored bewildering modes of reproduction; not surprisingly, 42-47% of them are brooders. With 13,000 species, polychaetes are gonochores but some 207 species of them are hermaphrodites. Clitellates are all hermaphrodites; of them, 76 species are parthenogens, of which 56 are earthworms. Regenerative potency of annelids ranges from an organ to an entire worm from a single 'seminal' segment. The head, tail and both together can be regenerated 21, 42 and 20 times, respectively. However, the potency is limited to ~1% of polychaetes and < 2% of oligochaetes. In oligochaetes, the chloragogue temporally separates regeneration and reproduction but sedentary polychaetes undertake them together at the reduced reproductive output. Only 79 polychaete and 111 oligochaete species have the potency for clonal reproduction. Within families, the potency ranges from 2% in spionids to 54% in naidids. Epitoky, a spectacular and unique phenomenon, involves the transformation from benthic to meroplanktonic reproductive morphism. It occurs in 106 errant polychaete species. The larger glycerides, nereidids and eunicids use muscular energy to climb < 50 m vertical distance. But the small phyllodocids and cteniodrilids may reduce buoyancy to climb 1,000-4,000 m vertical distance. Heterogamatic sex determination is reported to occur only in six polychaete species, although karyotype is known for 83 annelid species. In temperate polychaetes, a dozen neuroendocrines, arising mostly from the 'brain' regulates reproductive cycle. A complete chapter devoted to vermiculture, (i) recognizes the fast-growing candidate species, (ii) distinguishes 'layers' from 'brooders', (iii) indicates that the harvest of oligochaetes may reduce the input of nitrogenous fertilizer in the ricefield, and (iv) explores the scope for increasing wealth from waste.

This book is a concise informative elucidation of all aspects of reproduction and development in annelids covering from arenicola to tubifex. Annelids flourish between 4,900 m depth to 2,000 m altitude; some of them occur in unusual habitats like hydrothermal vents and subterranean aquatic system (stigobionts). A few have no gut and acquire adequate nutrients through osmotrophism and/or engaging symbiotic microbes. In the absence of exoskeleton to escape predation, the 17,000 speciose annelids have explored bewildering modes of reproduction; not surprisingly, 42-47% of them are brooders. With 13,000 species, polychaetes are gonochores but some 207 species of them are hermaphrodites. Clitellates are all hermaphrodites; of them, 76 species are parthenogens, of which 56 are earthworms. Regenerative potency of annelids ranges from an organ to an entire worm from a single 'seminal' segment. The head, tail and both together can be regenerated 21, 42 and 20 times, respectively. However, the potency is limited to ~1% of polychaetes and < 2% of oligochaetes. In oligochaetes, the chloragogue temporally separates regeneration and reproduction but sedentary polychaetes undertake them together at the reduced reproductive output. Only 79 polychaete and 111 oligochaete species have the potency for clonal reproduction. Within families, the potency ranges from 2% in spionids to 54% in naidids. Epitoky, a spectacular and unique phenomenon, involves the transformation from benthic to meroplanktonic reproductive morphism. It occurs in 106 errant polychaete species. The larger glycerides, nereidids and eunicids use muscular energy to climb < 50 m vertical distance. But the small phyllodocids and cteniodrilids may reduce buoyancy to climb 1,000-4,000 m vertical distance. Heterogamatic sex determination is reported to occur only in six polychaete species, although karyotype is known for 83 annelid species. In temperate polychaetes, a dozen neuroendocrines, arising mostly from the 'brain' regulates reproductive cycle. A complete chapter devoted to vermiculture, (i) recognizes the fast-growing candidate species, (ii) distinguishes 'layers' from 'brooders', (iii) indicates that the harvest of oligochaetes may reduce the input of nitrogenous fertilizer in the ricefield, and (iv) explores the scope for increasing wealth from waste.

This book is the first to report that research in allogenics/xenogenics has conclusively shown that fishes have retained bisexual potency even after sexual maturity and spermiation. The XY genotype found in the unexpected female phenotypes sired by supermales (Y1Y2) and androgenic males (Y2Y2) points out the need to employ sex specific molecular markers to identify the true genotype of a juvenile, which matures either as a male or female, depending upon the sex of its pair (female or male) and thereby critically assessing the environmental role in sex determination. This book is meant to assist molecular biologists in the search of sex determining gene(s), fishery biologists endeavouring to develop techniques for profitable monosex aquaculture and ecologists interested in conservation of fishes and their genomes.

A comprehensive elucidation of sex differentiation gonochoric and hermaphroditic fishes, this book examines sex chromosomes and sex determining genes, through sex differentiation genes and steroid receptor genes and to stem cells and germ cells. It emphasizes the need to search for more than one sex determining gene residing on different chromosomes, traces the origin of hermaphrodites from secondary gonochores, and explains the conservation of homologous sex differentiation and steroid receptor genes among gonochores and hermaphrodites. The author highlihgts that the changes in the phenotypic morphotypes among gonochores is intrasexual but intersexual among hermaphrodites and identifies the optimal broodstock size, the appropriate candidate species for bait and food fishes and recognizes that the fishes do undergo menopause and reproductive senescence, which has an implication on the production of stem cells. He shows that the analysis of steriles and mutants has demonstrated the value of fishes as a system for genetic dissection of human development and diseases.

Dating back to the early Cambrian period, crustaceans had ample time to undertake endless experimentation with form and function. Today, no other group of plants or animals on the planet exhibit the range of morphological diversity seen among extant Crustacea. With more than 52,000 species, they are placed fourth in terms of overall species diversity. This book comprehensively elucidates the reproduction and development of all the taxonomic groups of Crustacea and bridges the gap between conventional zoologists and molecular biologists. Reproductive modes from the point of embryonic stem cells and primordial germ cells is discussed with a special section on cysts.

This book is the first to report that research in allogenics/xenogenics has conclusively shown that fishes have retained bisexual potency even after sexual maturity and spermiation. The XY genotype found in the unexpected female phenotypes sired by supermales (Y1Y2) and androgenic males (Y2Y2) points out the need to employ sex specific molecular markers to identify the true genotype of a juvenile, which matures either as a male or female, depending upon the sex of its pair (female or male) and thereby critically assessing the environmental role in sex determination. This book is meant to assist molecular biologists in the search of sex determining gene(s), fishery biologists endeavouring to develop techniques for profitable monosex aquaculture and ecologists interested in conservation of fishes and their genomes.

Fish constitute an important natural renewable resource and any reduction in their ability to propagate as a result of human interference may have significant socioeconomic consequences. The negative effect of human activity on sex differentiation and reproductive output in fish is so diverse that it has been difficult to encompass it in a single book. This book serves as the first attempt to do so. Unlike in mammals, the expression of a host of sex differentiation genes in fish is mostly controlled by environmental factors. Not surprisingly, environmental sex differentiation is ubiquitous in fish. Overexploitation by capture fisheries does not disrupt sex differentiation but crowding in aqua-farms does, by reducing accessibility to food supply. Some of the man-made chemicals routinely used worldwide mimic endogenous hormones. For example endosulfan, which is widely used in developing countries, disrupts endogenous hormones and feminizes fish. For the first time, this book views endocrine disruption from the point of labile early life and non-labile adult stages. It shows that sex can irreversibly be reversed, when exposed to endocrine disrupting chemicals (EDCs) during early labile stages but reversibly impairs reproductive output on exposure to EDCs during non-labile adult stage. A consequence of climate change, elevated temperature, and declining oxygen and pH levels is that it masculinises genetic female fish. Fish display a remarkable ability to postpone the labile period. Besides postponement, some primary and tertiary gonochores have two distinct labile periods amenable to temperature and hormonal manipulations. Hermaphrodites have retained the period until the end of the adult stage and are capable of sex change/reversal more than once in both male and female directions.

Half of the 12 papers are research reports selected from the presentations to an international conference at Manonmaniam Sundaranar University on an undisclosed date. The others are reviews of literature on the same theme of advanced technologies in fisheries and marine sciences. Among the topics are gene transfer to germline and somatic tissues of

Dating back to the early Cambrian period, crustaceans had ample time to undertake endless experimentation with form and function. Today, no other group of plants or animals on the planet exhibit the range of morphological diversity seen among extant Crustacea. With more than 52,000 species, they are placed fourth in terms of overall species diversity. This book comprehensively elucidates the reproduction and development of all the taxonomic groups of Crustacea and bridges the gap between conventional zoologists and molecular biologists. Reproductive modes from the point of embryonic stem cells and primordial germ cells is discussed with a special section on cysts.

Echinoderms and prochordates occupy a key position in vertebrate evolution. The genomes of sea urchin share 70% homology with humans. Researches on cell cycle in sea urchin and phagocytosis in asteroids have fetched Nobel Prizes. In this context, this book assumes immense importance. Echinoderms are unique, as their symmetry is bilateral in larvae but pentamerous radial in adults. The latter has eliminated the development of an anterior head and bilateral appendages. Further, the obligate need to face the substratum for locomotion and acquisition of food has eliminated their planktonic and nektonic existence. Egg size, a decisive factor in recruitment, increases with decreasing depths up to 2,000-5,000 m in lecithotrophic asteroids and ophiuroids but remains constant in their planktotrophics. Smaller (< 18 mm) ophiuroids do not produce a lecithotrophic eggs but larger (> 110 mm) asteroids generate planktotrophic eggs only. Publications on sex ratio of echinoderms indicate the genetic determination of sex at fertilization but those on hybridization, karyotype and ploidy induction do not provide evidence for heterogametism. But the herbivorous echinoids and larvacea with their gonads harboring both germ cells and Nutritive Phagocytes (NPs) have economized the transportation and hormonal costs on gonadal function. Despite the amazing potential just 2 and 3% of echinoderms undergo clonal reproduction and regeneration, respectively. Fission is triggered, when adequate reserve nutrients are accumulated. It is the most prevalent mode of clonal reproduction in holothuroids, asteroids and ophiuroids. However, budding is a more prevalent mode of clonal reproduction in colonial hemichordates and urochordates. In echinoderms, fission and budding eliminate each other. Similarly, autoregulation of early development eliminates clonal reproduction in echinoids and solitary urochordates. In pterobranchs, thaliaceans and ascidians, the repeated and rapid budding leads to colonial formation. Coloniality imposes reductions in species number and body size, generation time and life span, gonad number and fecundity as well as switching from gonochorism to simultaneous hermaphorditism and oviparity to ovoviviparity/viviparity.

Of all vertebrates, fish exhibit unparalleled diversity of sexual plasticity and flexibility, ranging from gonochorism to unisexualism, and exceptional patterns of functional hermaphroditism. Fish farming and monosex aquaculture have led to reproductive dysfunction with males producing less milt, and females failing to ovulate and spawn. This book brings together relevant information on the role of the endocrine system on sexual differentiation in fish, and bridges the gap between molecular endocrinologists and fishery scientists.

This book is perhaps the first attempt to comprehensively project the uniqueness of molluscs, covering almost all aspects of reproduction and development from aplacophorans to vampyromorphic cephalopods. Molluscs are unique for the presence of protective external shell, defensive inking, geographic distribution from the depth of 9,050 m to an altitude of 4,300 m, gamete diversity, the use of nurse eggs and embryos to accelerate the first few mitotic divisions in embryos, the natural occurrence of androgenics in a couple of bivalves, viable induced tetraploids, gigantism induced by elevated ploidy, the complementary role played by mitochondrial genome in sex determination by nuclear genes and the uptake and accumulation of steroid hormone from surrounding waters. In molluscs, sexuality comprises of gonochorism (< 75 %) and hermaphroditism, which itself includes simultaneous (> 24%), protandry (< 1 %), Marian and serial. In them, the presence of shell affords iteroparity and relatively longer life span in prosobranchs and bivalves but its absence semelparity and short life span in opisthobranchs and cephalopods. Within semelparity, gonochorism facilitates faster growth and larger body size but hermaphroditism small body size. In them, sex is irrevocably determined at fertilization by a few unknown genes and is not amenable to any environmental influence. However, the sex determining mechanism is more a family trait in bivalves. Primary sex differentiation is also fixed and not amenable to environmental factor but secondary differentiation is labile, protracted and amenable to environmental factors. Both sex differentiation and reproductive cycle are accomplished and controlled solely by neurohormones. In these processes, the role of steroid hormones may be alien to molluscs.

This book is a comprehensive elucidation on aspects of reproduction and development in platyhelminthes covering from acoelids to taeniids. With the unique presence of neoblasts, turbellarians serve as a model for studies on cancer and senescence. Of ~ 27,000 species, ~ 77% are parasites; they are harmful to man and his food basket from livestock and fish. The stress hormone, cortisol level is responsible for susceptibility and resistance of the host. In digeneans, the propagatory multiplication potency is retained by all the larval forms and in either direction in sporocyst. The higher clonal diversity, mixing and selection in Second Intermediate Host (SIH) may purge inbreeding depression suffered by the fluke on propagatory multiplication in First Intermediate Host (FIH). Of 12,012 digeneans, 88% may engage 33,014 potential SIH species. They have the choice to select one among the available/awaiting 3.5 host species. The motility of vertebrate host and euryxenic flexibility/scope for selection of SIH species has increased lineage diversification in digeneans. The life cycle of cestodes is divided into aquatic and terrestrial patterns. The former includes (i) oncosphere and (ii) coracidium types and the latter (iii) hexacanth-cysticercoid, (iv) hexacanth-tetrathyridium and (v) hexacanth-cysticercus types. The share for the oncosphere, coracidium and hexacanth types is 17.0, 29.5 and 46.5%, respectively. The staggering fecundity and adoption of the intermediate host in the herbivorous/insectivorous food chain have enriched Taenioidea as the most (2,264) speciose order. Sex specific genes Smed-dmd 1 and macbol have been identified, and neuropeptides and dipeptides are involved in sexualization. Trematodes are unable to parasitize elasmobranchs, as they cannot suck body fluid/blood containing a high level of urea. Relatively higher fecundity supplemented with propagatory multiplication, incorporation of SIH in 88% species, clonal selection in SIH, and euryxenic flexibility and the widest choice for selection of SIH have led to the highest lineage diversification to render digeneans as the most speciose order in Platyhelminthes.