MSc I Sem I Practical II PDF

Developmental Biology - I PSMAZOP102  PAGE EXPERIMENTS NOS. 1)To observe sperm and ova in ovotestes of Achatina fulica (garden snail) with suitable staining 1-4 techniques. 2) To obse...

Developmental Biology - I PSMAZOP102  PAGE EXPERIMENTS NOS. 1)To observe sperm and ova in ovotestes of Achatina fulica (garden snail) with suitable staining 1-4 techniques. 2) To observe development of Caenorhabditis elegans. 5-6 3) To culture Drosophila to study its life cycle. 7-11 4) To observe stages of Tribolium or Sitophilus to 12 understand indirect development in animals. 5) To study Gemmule in Sponge. 13 6) To study larvae of non-chordates: 14-25 ▪ Porifera – Amhiblastula 14 15 ▪ Cnidaria (Coelenterata) – Planula 16-17 ▪ Platyhelminthes – Redia and Cercaria ▪ Annelida and Molluscs – Trochophore 18 ▪ Mollusca – Glochidium and Veliger 19-20 ▪ Echinodermata – Auricularia, Echinopluteus and 21-23 Ophiopluteus ▪ Hemichordata – Tornaria 24 7) Temporary mounting of life forms of crustacean: (Nauplius, Zoea, Mysis, Megalopa and Alima) 26-30 8) To study Life cycle of Insects: Lepisma, Cockroach, Butterfly / Moth 31-33  To observe sperm and ova in ovotestes of Achatina fulica (garden snail) with suitable The animals staining used in techniques (Page this work are 1-4) Gastropods, Molluscs, Pulmonates belonging to the order of Stylommatophores, the family of Achatinidae, the genus Achatina and the Species fulica (Bowdich, 1720). The snails from the natural and breeding environment were used for this histological study. Achatina fulica being a protandrous hermaphrodite animal, the better it was possible to first detect male gametes in the ovotestis at early stages and then female gametes.  The snails from the natural environment have been collected on sandy soils and in areas devoid of herbs and indeed justify the weak development of gametes. As for the speed of the maturation of gamete in Achatina fulica from the breeding environment, the early maturation would probably be due to a good breeding environment and the food. As factors such as air humidity, temperature and photoperiod affect snail breeding. A low relative humidity causes estivation in the snail, a phenomenon that causes growth disorders. Too high temperature would lead to conditions that are not in favour of the growth and reproduction of snails. The genital system of Achatina fulica: The ovotestis is true multilobate. The ovotestis duet is divisible into an apical portion, an ovisperm vesicle and a basal portion bearing a talon, and ending in carrefour. Spermatozoa are found stored in the ovisperm vesicle throughout the year. The spermoviduct is fairly long and all along its length the narrow sulcus is incompletely separated from the wide uterus. The vas deferens is continuous with the sulcus and ends in the penis, while the uterus continues as the oviduct ending in vagina. The penis has a vergie and a preputial region..  The apical vagina is narrow and tubular and the basal vagina bears a swelling. Both the penis and the vagina open in the genital atrium. The spermatheca is large. The albumen gland is large and communicates with the carrefour through a narrow, small duct. The prostatic acini are many and all open in the sulcus except a few opening in the basal uterus. Ovotestis, albumen gland and prostate exhibit seasonal periodicity. Calcic glands are present in the uterine wall and secrete the egg shell The genital system of Achatina fulica: According to the different length classes established as well as the original environment, we proposed that the cycle of gametogenesis could be divided into 4 stages in the male and in the female as well: Stage 1: Beginning of maturation: phase of sexual rest, acini are therefore reduced to islets of quiescent gonies. Stage 2: Maturation: the gonies multiply by successive mitosis. Acini are poorly developed in number and volume in the connective tissue. The side walls of the tubules are lined with primary cells which have a large nucleus and have a scanty cytoplasm. Stage 3: Advanced maturation: the cells remain adherent to the side wall of the acini but enter into growth, this corresponds to the phase of vitellogenesis. As a result of the increase in size of the acini, the connective tissue has almost disappeared. Stage 4: Maturity: the acini are then completely filled with mature oocytes (with a relatively homogeneous size), which present a very distinct nucleus and sometimes even the very visible nucleolus. The Maturity Phase of gametes of Achatina fulica Spermatozoa Ovum  Structure of Sperm & Egg of Achatina fulica Sperm: Sperm is elongated with total length of 800 micron with body divisible into head & filament. Head id pear shaped with pointed anterior process, having large flattened nucleus curved to assume shape like that of a spoon bowl. When viewed from nuclear side up it gives a triangular appearance. The nuclear material extends to the glycogen filled cytoplasm from base of which axoneme arise, which extends posteriorly into slender, flexible filament. Ovum: Ovum is very tiny and creamy white, flaccid and spent in post reproductive stage and recently spawned but prior to egg-laying, the albumen gland is lemon yellow and translucent. Eccentrically located female pro-nucleus with abundant yolk & cytoplasm. Stainning ovotestes of Achatina fulica to observe Sperm & Egg Giemsa is not a single dye but it is a mixture of several dyes viz. methylene blue & its oxidation products the azures ass well as eosin yellow. The quality of the stain varies with the proportion of different dyes mixed.. Reqiurements: Alcohol fixed smears, Geimsa stain (dissolve 1g Giemsa powder in 50mL Glycerine & mix well. Warm the mixture at 60 degrees Celcius for 2hrs. Add 10mL methanol & filter), distilled buffered water (Mix 3.76g Disodium hydrogen phosphate, 2.10g Potassium dihydrogen phosphate in 1000mL D/W, Adjust pH to 7.2 by adding Disodium hydrogen phosphate) Alcohol grades (70%) Acetone Procedure: Bring down the smear to water. Stain it with Giemsa stain for 15-20min. Transfer the smear to dilute Giemsa prepared by using D/W (1:2) & allow it to remain there for 30min. Rinse with 70% alcohol Give two dips in Acetone. Clear in Xylene Mount in DPX Results: Nuclei are stained reddish purple rest of the cell stains blue, Sperm head with nucleus stains purple. Chromosomes also stain purple  To observe development of Caenorhabditis elegans (Page 5-6) The nematode worm Caenorhabditis elegans is a small (1mm long), unsegmented, vermiform, free-living soil nematode. It is a relatively simple and precisely structured organism, extensively used as a model organism for molecular and developmental biology. The body of an adult C. elegans hermaphrodite contains exactly 959 somatic cells, whose entire lineage has been traced through its transparent cuticle. Its genome has also been entirely sequenced, the first-ever for a Reasons for Selection as Model Organism It has a rapid period of embryogenesis (about 16 hrs.), which it can accomplish in a petri dish. It has relatively few cell types. The predominant adult form is hermaphroditic, with each individual producing both eggs and sperm. Roundworms can reproduce either by self-fertilization or by cross- fertilization. The cell lineage of Caenorhabditis elegans is entirely invariant from one individual to the next. C. elegans also has a small number of genes for a multicellular organism about 19,000. Pre- Embryonic Development The embryo of the nematode C. elegans progresses through several distinctive phases in developing towards the first larval stage, when the embryonic worm first emerges from the eggshell. These phases/stages can be subdivided as follows:  Fertilization: After fertilization a single- cell diploid embryo occurs in spermatheca of adult hermaphrodite. The fertilized embryo becomes covered by a membrane that may prevent polyspermy, which is followed by the formation of a harder eggshell consisting of three layers secreted by egg. The newly fertilized embryo exits prophase arrest and leaves the spermatheca to continue its development in the uterus.  Proliferation: After fertilization, the single-cell embryo begins a series of cell divisions. During this phase, all embryonic cells look similar in their cytoplasmic structures and begin short-distance migrations away from their sister cells, through a process that has been termed “global cell sorting”. Early proliferation events span from 0 to 150 min post-fertilization (at 22°C) and take place within the uterus. Proliferation events continue in later stages, including gastrulation and morphogenesis. Certain daughter cells always undergo immediate programmed cell death (apoptosis), while their sister cells continue to proliferate and develop. Gastrulation: Starting at 30 cell stage, gastrulation encompasses the process by which single cells begin to become internalized and migrate into the center of the embryonic mass to eventually create separate ectodermal, endodermal and mesodermal compartments. Continued global cell sorting results in many functional cell groups becoming established by proximity rather than by sisterhood. Morphogenesis: This phase overlaps with end of gastrulation when most cells have ended proliferation and are joining tissue subgroups. Cells become structurally specialized to adopt shapes and cell contents that reflect their eventual cell fate within specialized tissue compartments. Much directed cell migration occurs where certain cells extend sheet-like arms to enfold their neighbours or penetrate through narrow passages inside the developing tissues. Some tissues become syncytial with the disappearance of intervening cell membranes. Terminal differentiation occurs without many additional cell divisions. Elongation: Once the embryo’s developing tissues begin to form a longer worm-like shape, they become folded within the eggshell. Early elongation events begin around 350min after the first cleavage and involve both microfilaments and microtubules. Moving through the comma, two-fold and finally the three- fold stage, the embryo decreases in circumference and increases in length until it is ready for hatching. Elongation occurs coincidentally with later stages of morphogenesis. Quickening: The first signs of muscle movement are seen around 430min and by the three-fold stage, the worm can move in a coordinated fashion within the egg. A series of squeezing events and later, active wriggling motions, precedes hatching. These squeezing activities surely aid in further elongation of the animal, though they occur quite late. Quickening occurs Hatching: When the embryo contains about 600 cells and many immature tissues, the young L1 larva breaks through the eggshell to emerge into the world. At this point, the L1 larva will begin postembryonic development where it will grow ten-fold in length and ten-fold in breadth before achieving adulthood. Post-embryonic development: Under environmental conditions favorable for reproduction, hatched larvae develop through four larval stages viz. L1, L2, L3 and L4 in just 3 days at 20°C. When conditions are stressed due to food insufficiency, excessive population density or high temperature, C. elegans can enter an alternative third larval stage, L2d, called the dauer stage (Dauer is German for permanent). Dauer larvae are stress-resistant; they are thin and their mouths are sealed with a characteristic dauer cuticle and cannot take in food. They can remain dormant in this stage for a few months. The stage ends when conditions improve favour further growth of To culture Drosophila to study its life cycle (Page 7-11)  The fruit fly Drosophila melanogaster has been extensively studied for over a century as a model organism for genetic investigations. It also has many characteristics that make it an ideal organism for the study of animal development and behavior, neurobiology, and  Developmental Stages of Drosophila melanogaster The development of Drosophila can be divided into the following stages: Embryogenesis 1. Fertilization Fertilization of Drosophila can only occur in the region of the oocyte that will become anterior of the embryo. 2. Cleavage Eggs undergoes superficial cleavage with large mass of centrally located yolk confines cleavage to the cytoplasmic rim of the egg & cells do not form until the nuclei have divided. The zygote nucleus undergoes several mitotic divisions within the central portion of the egg. In Drosophila, 256 nuclei are produced by a series of eight nuclear divisions averaging 8 minutes each. The nuclei then migrate to the periphery of the egg, where the mitoses continue. During the ninth division cycle, about five nuclei reach the surface of the posterior pole of the embryo. These nuclei become enclosed by cell membranes and generate the pole cells that give rise to the gametes of the adult. Most of the other nuclei arrive at the periphery of the embryo at cycle 10 and 3. Blastoderm Formation The oocyte plasma membrane folds inward between the nuclei, partitioning off each somatic nucleus into a single cell creating the cellular blastoderm, in which all the cells are arranged in a single-layered jacket around the yolky core of the egg. The formation of the cellular blastoderm involves a microtubules and microfilaments with approximately 6000 cells formed within 4 hours of fertilization. 4. The Midblastula Transition After the nuclei reach the periphery, cycles 1–10 are each 8 minutes long whle cycle 13, the last cycle in the syncytial blastoderm, takes 25 minutes to complete. Cycle 14, in which the Drosophila embryo form cells is asynchronous. Some groups of cells complete this cycle in 75 minutes, whereas other groups of cells take 175 minutes. Transcription from the nuclei is greatly enhanced at this stage. This slowdown of nuclear division and the concomitant increase in RNA transcription is often referred to as the midblastula 5. Gastrulation Gastrulation begins at the time of the midblastula transition to segregate the presumptive mesoderm, endoderm and ectoderm. The prospective mesoderm about 1000 cells constituting the ventral midline of the embryo folds inward to produce the ventral furrow that eventually pinches off to become a ventral tube within the embryo. It then flattens to form a layer of mesodermal tissue beneath the ventral ectoderm. The prospective endoderm invaginates as two pockets at the anterior and posterior ends of the ventral furrow. The pole cells are internalized along with the endoderm & the embryo bends to form the cephalic furrow. The ectodermal cells on the surface and the mesoderm undergo convergence and extension, migrating toward the ventral midline to form the germ band that includes all the cells forming the trunk of the embryo. The germ band extends posteriorly and wraps around the dorsal surface of the embryo. Thus, at the end of germ band formation, the cells destined to form the most posterior larval structures are located immediately behind the future head region. At this time, the body segments begin to appear, dividing the ectoderm and mesoderm. 6. Body Segmentation The germband (ventral blastoderm) is the main trunk region. The process of germband extension pushes the posterior end over dorsal side. The first signs of segmentation grooves appear to outline parasegments which give rise to segments. Segments are formed from the posterior of one parasegment and the anterior of the next. There are 14 parasegments: 3 mouths, 3 thoracic, 8 abdominal. 7. Larval Stages The larva is a white, segmented, worm-shaped burrower with black mouthparts (jaw hooks) in the narrower head region. For tracheal breathing, it has a pair of spiracles at both the anterior and posterior ends. Since insect skin will not stretch, the young small larvae must periodically shed their skins (cuticle) in order to reach adult size. There are two such molts in Drosophila larval development that are accompanied by shedding of the mouthparts as well as the skins. During each period between molts, the larva is called an instar, i.e. the first instar is between hatching and the first molt. After the second molt, the larva feed until ready to pupate. At this stage, the larva crawls out of the food medium onto a relatively dry Pupal Stage Soon after everting its anterior spiracles, larval body shortens and cuticle get harden and pigmented. A headless and wingless pre-pupa forms followed by the formation of the pupa with everted head, wing pads and legs. The puparium thus utilizes the cuticle of the third larval instar. The adult structures that seem to appear first during the pupal period have actually been present as small areas of dormant tissues as far back as the embryonic stage. These localized pre-adult tissues are called imaginal discs (Analgen). The main function of the pupa is to permit the development of the Anlagen to adult proportions. The breakdown of larval tissues to furnish material and energy for this development is a prime feature of pupal metabolism. Adult Stage Adults exhibit typical insect anatomy, including compound eyes, body (head, thorax, and abdomen), wings and six jointed legs. The various types of bristles and hairs on the body are characteristics used to identify different phenotypes of flies. 8. Significance of Studies on Drosophila Development Drosophila and human development are homologous processes. They utilize closely related genes working in highly conserved regulatory To observe stages of Tribolium or Sitophilus to understand indirect development (Page 12)  Adult Tribolium beetles are 3-5 mm in size. Some such as T. brevicornis (B4 mm) and T. freemani (B5 mm) are visibly larger than other species such as T. audax, T. anaphe, T. castaneum and T. confusum (B3 mm or smaller). Adults are sexually dimorphic. The sexes may be significantly different from each other in body size. In some species, such as T. brevicornis, males may be larger than females but in others including T. confusum, there may be a tendency for females to be larger. T. castaneum adult males are distinguishable from females because of the presence of setiferous glands (“sex patches”) on their first pair of legs, which are absent in females. Similarly, in T. confusum, only males have these glands but they appear on each pair of appendages.  Beetle life cycles include four stages: egg, larva, pupa, and adult. The microscopic eggs of tenebrionids are ovoid and bright white. In T. castaneum and T. confusum, embryogenesis typically lasts 3.5-5 days in ideal laboratory conditions. The larvae are worm-like and yellowish. In optimal conditions, this stage is typically about 2-3 weeks for T. castaneum and T. confusum. The pupae are light colored, and either white or yellowish. Lateral on each abdominal segment they carry gin traps, ie, outgrowths with strongly sclerotized teeth. Pupae are not capable of locomotion though they may wriggle (with the movement originating in the abdomen). This wriggling movement moves the gin traps of two abdominal segments relative to each other thus “biting” potential predators. The sexes are dimorphic and easily discernable as pupae, because the females have larger genital papillae compared to those found on the male pupae. In a favorable environment, the pupal stage may last 5-6 days in  The typical life cycle from egg to adult in laboratory strains of T. castaneum and T. confusum may be as short as 3-4 weeks in optimal conditions of food, temperature, and humidity. However, the rate of development from egg to adult varies vastly among species and may be as long as almost 9 weeks for some species of flour beetles. Developmental time varies even among different strains of a species. In addition to genetics, environmental factors such as temperature, humidity, and food also influence development. Adults may live more than 3 years, though a life span of 1-6 months is more typical in laboratory settings. In general, the life span of virgin adults in laboratory conditions for T. castaneum and T. confusum beetles is 7-11 months. Fecundity of T. castaneum females drops after 3-4 months as their germ cells get used up.  Study of Gemmule in ▪ Gemmules Sponge: are asexuallyPage 13 masses of the produced cells forming Internal buds capable to develop into the new organism. ▪ Gemmules are produced to survive in the harsh environmental conditions & for the germination. ▪ Archaeocytes of sponges are totipotent cells loaded with the food material in the form of lipoprotein or glycoprotein taking part in the formation of gemmules. ▪ Then the mobile amoebocytes start moving & is surrounded by the central mass of the archeocytes & start secreting the thick solid chitin around the archeocytes thus forming a layer around it. ▪ After this there is secretion of the spicules by the scleroblasts in between the inner membrane & outer membrane. ▪ A tiny opening called micropyle present on the The study of larvae of non- chordates: (Page 14-25) Amphiblastula larva ▪ In sponge sexual reproduction results in formation of larva called an amphiblastula (e.g. Sycon, Oscarella, etc.). ▪ The body is some what ovoid in form and is comprised of an anterior half of small flagellated micromere cells and a posterior half of large non-flagellated macromere cells. ▪ It encloses a small cavity the inside of which is filled with amoebocytes. ▪ It develops from stomoblastula through a process of inversion. ▪ It leads a free swimming existence for some times and then settles down at bottom and gives rise to young sponge through embolic Planula larva ▪ A planula is the free-swimming, flattened, ciliated, bilaterally symmetric larval form of various cnidarian species & also in some species of Ctenophores. ▪ The planula forms either from the fertilized egg of a medusa in Scyphozoans & Hydrozoans or from a Polyp in Anthozoans. ▪ Depending on the species, the planula either metamorphoses directly into a free-swimming, miniature version of the mobile adult form or navigates through the water until it reaches a hard substrate where it anchors & grows into a polyp. ▪ The planulae of the Scyphozoans lack mouth & Redia larva ▪ The redia larva will give 15 to 20 cercaria larvae. They are liberated from the redia larva through birth pore. ▪ It is oval in shape with tail with 0.25mm to 0.35mm in length. ▪ The cuticle covering will show backwardly directed spines. ▪ Two suckers are present, Oral sucker around mouth & ventral sucker. ▪ The digestive system starts with mouth, opens into pharynx, oesophagus & intestine divided into two branches. ▪ More flame cells are present, all of them open into excretory tubules. The two excretory tubules will unite at the posterior end & become excretory bladder. It gives an excretory tube. It divides into two, which opens out through nephridiopore. Cercaria larva ▪ Cercaria larva is the fourth larval stage in the life- cycle of Liver fluke. It is a free living stage produced by the redia larva. ▪ It has a flat and oval body about 35mm in length & a long muscular undulating tail. ▪ Cercaria has two suckers an anterior, oral sucker surrounding the mouth & a ventral sucker situated in the middle of the body. ▪ Body space is filled with parenchyma & contains a few cystogenous glands on each side forming cyst of the future larva. ▪ The alimentary canal consists of mouth, muscular pharynx, oesophagus & bifurcated & inverted Y- shaped intestine. ▪ It also possesses an excretory bladder with a pair of protonephridial canals & a number of flame cells. ▪ Cercaria also has two large non-functional penetration glands as well as rudiments of reproductive organs which have originated from Trochophore larva ▪ Trochophore is a small, translucent, free- swimming larva characteristic of marine annelids & most groups of molluscs. ▪ Trochophores are spherical or pear-shaped & are girdled by a ring of cilia of pre-oral circlet or prototroch above the mouth & the metatroch around the pygidium or anus. ▪ These ciliary bands are support in locomotion & feed­ing. ▪ The anterior end of the body is broader than the posterior end & it exhibits bilateral symmetry. ▪ There is no coelom at this stage but only a spacious blastocoel encloses the mouth, alimentary canal, anus & a pair of Glochidium larva ▪ Glochidium is a microscopic larval stage of freshwater mussels (Unio). ▪ Body is an undivided mass with presence of a bivalve shell, with valves united dorsally & flat ventrally. ▪ The ventral ends of the valves curve & bear spines. ▪ The mantle lines the valves of the shell & bears brush-like hairs. ▪ An adductor muscle at the base of the shell connects the valves. ▪ Presence of a byssus gland near ad­ductor muscle & a long byssus thread present. ▪ The glochidium larva attaches itself to the gill of a fresh water fish by the byssus thread. Veliger larva ▪ Veliger are planktonic larvae of many bivalve & gastropod molluscs characterized by a shell, foot & velum. ▪ A larval mollusc in the stage when it has developed the velum is named as Veliger larva ▪ Velum is a lobed, ciliated structure used for swimming & feeding. ▪ The velum is derived from the prototroch - a pre-oral ciliated band in the trochophore larva. ▪ A dorsal shell gland secretes the shell of the veliger. ▪ The shell of a bivalve veliger is bi- valved while the shell of a gastropod Auricularia larva ▪ Auricularia is a bilaterally symmetrical larva of Holothuria. ▪ After gastulation & formation of coelomic sacs & gut the embryo becomes a free swimming larva called auricularia larva, within 3 days. ▪ It is transparent, pelagic about 0.5 to 1mm in length. Its swims about by a ciliated band which forms preoral loop & an anal loop. ▪ Internally, larva has a curved gut with sacciform stomach, hydrocoel & right & left somatocoels. ▪ After a free swimming plantkonic existence, the bilateral larva undergoes metamorphosis in which the radial symmetry of the adult is developed. Echinopluteus larva ▪ Echinopluteus ia a larva of Echinoidea. Gastrula becomes conical, one side of which flattens to form the oral surface. ▪ Stomodaeal invagination communicates with archenteron & the gut is differentiated into mouth, oesophagus, stomach & intestione. ▪ Larva begins to form projections which develop into six arms, namely, preoral, antrolateral, anterodorsal, postoral, postero-dorsal & posterolateral. ▪ Posterolateral arms are very short & direct outwards or backwards. ▪ Tips of the arms are pigmented & are supported by calcareous skeletal rods. ▪ Locomotion is by ciliated bands. Ophiopluteus larva ▪ Ophiopluteus is the free swimming larva in brittle stars. It is similar to echinopluteus of echinoids with the only difference that the former has fewer arms than the later. ▪ The posterolateral arms are the longest & directed forward. After gastrulation the arms develop gradually. Posterolateral arms are formed first. ▪ After 4, 10 & 18 days anterolateral, postoral & posterodorsal arms develop respectively. ▪ Ciliated bands accompany the arms edges & support locomotion. ▪ Internally the larva contains coelomic chambers & archenteron. Tornaria larva ▪ A tornaria larva is the planktonic larva of some species of Hemichordata, Similar in appearance to the bipinnaria larvae of starfishes. ▪ It has an oval, transparent body measuring upto 3mm ▪ At its anterior end, it bears a tuft of cilia & a pair of eye spots. ▪ The gut is differentiated into oesophagus, Stomach & intestine. ▪ The cilia form two bands on the body surface. ▪ The anterior ciliary band follows a winding course over most of the water current towards the mouth. ▪ The posterior is in the form of a thin sac  Temporary mounting of life forms of Staining crustacean: and mounting (Page techniques are 26-30) primarily used for microscopic examination and anatomical studies of plankton. This technique is best suited for animals which are transparent such as invertebrate larval forms of crustacean. Methods: Fixing & Preservation: Preserve the plankton sample in 5-10% Formalin or Absolute alcohol for few days prior to mounting. Reagents: 1% Alcoholic Eosin, Glycerin, Acid-alcohol (70% ethanol and a few drops of concentration HCl). Procedure: Sort different larval forms from the plankton sample & transfer in petri dish. Wash with distilled water. Immerse the specimens in alcoholic eosin stain, Immersion time may vary with the nature as well as thickness of the integument from 2-5 min. Specimens should be washed in distilled water after staining. Excess stain may be removed by immersing the specimens in a mixture of acid-alcohol. Nauplius larva ▪ It is the first larvae hatched from egg in most of the crustaceans. ▪ It is free swimming larvae, minute & microscopic. ▪ The body has indistinct regions like a simple median eye also called as nauplius eye, three pair of jointed appendages (uniramous antennule, biramous antennae & mandible). ▪ Mandibles along with antennae are helpful in food collection. ▪ In some forms nauplius larva develops straight away into adult, but in many other crustacean forms it gives rise to other intermediate larval forms like metanauplius, Zoea larva ▪ Zoea is the second important larva of Crustacea, after the nauplius larva. ▪ The zoea is characterized by a distinct cephalothorax & abdomen, 8 pair of appendages & buds of 6 more & resembles the adult. ▪ The cephalothorax is immensely developed & covered by a helmet-like carapace, which is produced into two long spines, anterior median rostral & a posterior median dorsal. ▪ Two lateral spines are also present. ▪ The paired lateral & stalked compound eyes become well-formed but remaining 6 pair of thoracic appendages appears in the form of bud. ▪ The long abdomen is distinctly made of 6 Mysis larva ▪ In Penaeus, the zoea larva, instead of converting into the megalopa stage, moults into the post larval mysis larva. ▪ It has 13 pairs of appendages. ▪ All the thoracic appendages are biramous. ▪ Even the 5 pairs of posterior thoracic legs are biramous with flagellar exopodites which take up the locomotory function. ▪ The abdomen develops similar to that of the adult form, with 5 pairs of biramous pleopods & a pair of uropods & a telson. ▪ The mysis larva metamorphosis Megalopa larva ▪ In true crabs, the zoea larva or metazoea larva passes through successive moults into the post larval megalopa stage. ▪ It has a broad & crab-like unsegmented cephalothorax. ▪ The carapace is produced anteriorly into a median spine. ▪ The eyes are large, stalked & compound. ▪ All the thoracic appendages are well formed of which the last 5 pairs are uniramous. ▪ The abdomen is also well formed, Alima larva ▪ The so-called alima larva of Squilla hatches out from the egg directly ▪ It is a modified zoea larva form. ▪ It is a pelagic larva, having a glass- like transparency & occurring in large numbers in the plankton. ▪ It has a slender form & a short & broad carapace. ▪ All the head appendages are present. ▪ But only is 6-segmented, having 4 or 5 pairs of pleopods. ▪ The alima larva differs from the zoea larva in the armature of the telson & a very large raptorial  Significance of Larval forms According the biogenetic law proposed by Haeckel, ontogeny recapitulates phylogeny. This in other words means that, the successive stages of individual development correspond with successive ancestors in the line of evolutionary descent. ▪ Nauplius larva occurs in the development of all the crustaceans and so it was considered as the ancestral form of crustaceans. ▪ The old idea of recapitulations stands greatly modified now-a- days and the crustacean larval forms are now regarded to be the larval reversions of simpler crustacean ancestors. ▪ The larval forms are useful for finding out homologies and the affinities among various groups. ▪ The animals which pass through similar stages are closely related. ▪ Larvae are helpful in wide range distribution of species and also in keeping the food reserves of eggs to a minimum.  To study Life cycle of Insects: The word “metamorphosis” (Page 31-33) comes from the Greek which means to transform. Metamorphosis is the process of transformation of an immature larval individual into sexually mature reproducing adult. The transformed adult is completely different from larvae in form, structure and habit. It is the way insects grow and mature. Their lives are divided into separate stages for resting, growing and reproducing. Insects grow in stages and the cycle of stages is metamorphosis. For many insects, the stages are so different from one another that you might not recognize them as the same animal. There are four types of metamorphosis in insects namely, No-metamorphosis, Complete metamorphosis, Gradual metamorphosis, Incomplete metamorphosis. Most insects begin life as an egg and hatch within a few days of being laid. But there are some insects that will live through an entire season as an egg before hatching. The insects that stay in the egg longer need more time to grow and become strong enough to live outside of the egg. Lepisma ▪ These insects are ametabolous i.e. they undergo no metamorphosis. (Page ▪ In this type, the newly hatched creature 31) looks like an adult except in size and differences in armature of spines and setae. ▪ Females deposit a few eggs at a time in narrow cracks and may produce up to 100 eggs during a normal life span. ▪ Immature silverfish hatch from the eggs within a few weeks and begin growing and molting. After several molts, the insects reach the adult stage and begin reproducing. ▪ Maturation times vary depending on temperature. ▪ They hatch from the egg looking like Cockroach ▪ This type of incomplete metamorphosis is also known as paurometabolous/gradual (Page development. In this type, the newly 32) hatched young ones resemble the adult in general body form but lacks wings and external genital appendages. ▪ The young nymphs undergo several nymphal stages through successive moulting to transform into adult. ▪ Cockroaches, along with many other species, emerge from eggs as nymphs. ▪ Nymphs are very similar in physiology and morphology to an adult cockroach, therefore it's an incomplete metamorphosis or change. ▪ Nymph stages are called instars and each one is numbered after each molt. ▪ The difference between adult and nymph Butterflies/Moths ▪ This type of metamorphosis is also known as holometabolous development. In this type, four (Page metamorphic stages are included namely egg, 33) larva, pupa and adult. ▪ After hatching larva moults several times to become fully grown one. It later becomes a pupa within a secreted case called as puparium. Inside the puparium, the pupa differentiates into adult and then breaks open the case to emerge out. ▪ Eggs are laid on plants by the adult female butterfly. These plants will then become the food for the hatching caterpillars. ▪ Larva/caterpillar if the insect is a butterfly or a The caterpillar eat & as it grows it splits its skin and sheds it about 4 or 5 times. The caterpillar has a few tiny eyes, stubby legs & very short antennae. ▪ Pupa of butterflies is also called a chrysalis. Depending on the species, the pupa may suspended under a branch, hidden in leaves or buried underground. The pupa of many moths is protected inside a cocoon of silk. ▪ Adult have long legs, long antennae and compound eyes. They can also fly by using their Read Also... 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