Scanning electron microscopy of the placental interface in the viviparous lizard Sceloporus jarrovi (Squamata: Phrynosomatidae)

Placental membranes mediate maternal‐fetal exchange in all viviparous reptilian sauropsids. We used scanning electron microscopy to examine the placental interface in the mountain spiny lizard, Sceloporus jarrovi (Phrynosomatidae). From the late limb bud stage until birth, the conceptus is surrounded by placental membranes formed from the chorioallantois and yolk sac omphalopleure. The chorioallantois lies directly apposed to the uterine lining with no intervening shell membrane. Both fetal and maternal sides of the chorioallantoic placenta are lined by continuous layers of flattened epithelial cells that overlie dense capillary networks. The chorioallantoic placenta shows specializations that enhance respiratory exchange, as well as ultrastructural evidence of maternal secretion and fetal absorption. The yolk sac placenta contains enlarged fetal and maternal epithelia with specializations for histotrophic nutrient transfer. This placenta lacks intrinsic vascularity, although the vascular allantois lies against its inner face, contributing to an omphallantoic placenta. In a specialized region at the abembryonic pole, uterine and fetal tissues are separated by a compact mass of shed shell membrane, yolk droplets, and cellular debris. The omphalopleure in this region develops elongate folds that may contribute to sequestration and absorption of this material. Fetal membrane morphogenesis and composition in S. jarrovi are consistent with those of typical squamates. However, this species exhibits unusual placental specializations characteristic of highly placentotrophic lizards. J. Morphol., 2011. © 2011 Wiley‐Liss, Inc.     

Placentation in the lizard Gerrhonotus coeruleus with a comparison to the extraembryonic membranes of the oviparous Gerrhonotus multicarinatus (Sauria,Anguidae)

Paraffin sections of an ontogenetic series of embryos of the viviparous lizard Gerrhonotus coeruleus and the oviparous congener G. multicarinatus reveal that although general features of the development of the chorioallantoic and yolk sac membranes are similar, differences are evident in the distribution of the chorioallantoic membrane in late stage embryos. An acellular shell membrane surrounds the egg throughout gestation in both species although the thickness of this structure is much reduced in G. coeruleus over that of G. multicarinatus. The initial vascular membrane to contact the shell membrane in both species is a trilaminar omphalopleure (choriovitelline membrane) composed of ectoderm, mesoderm of the area vasculosa, and endoderm. This transitory membrane is replaced by the vascularized chorioallantois as the allantois expands to contact the inner surface of the chorion. Prior to the establishment of the chorioallantois at the embryonic pole, a membrane begins to form within the yolk ventral to the sinus terminalis. This membrane, which becomes vascularized, extends across the entire width of the abembryonic region and isolates a mass of yolk ventral to the yolk mass proper. The outer membrane of the yolk pole is a nonvascular bilaminar omphalopleure (chorionic ectoderm and yolk endoderm). In G. multicarinatus the bilaminar omphalopleure is supported internally by the vascularized allantoic membrane, whereas in G. coeruleus the allantois does not extend beyond the margin of the isolated yolk mass and the bilaminar omphalopleure is supported by the vascularized intravitelline membrane. Both the chorioallantoic placenta (uterine epithelium, chorionic ectoderm and mesoderm, and allantoic mesoderm and endoderm) and the yolk sac placenta at the abembryonic pole (uterine epithelium, chorionic ectoderm, and yolk sac endoderm) persist to the end of gestation in G. coeruleus.     

Morphogenesis of placental membranes in the viviparous,placentotrophic lizard Chalcides chalcides (Squamata: Scincidae)

In the scincid lizard Chalcides chalcides, females ovulate small ova and supply most of the nutrients for development by placental means. The yolk is enveloped precocially by extraembryonic ectoderm and endoderm during the gastrula stage, establishing a simple bilaminar yolk sac placenta. The shell membrane begins to degenerate at this time, resulting in apposition of extraembryonic and maternal tissues. A true chorioplacenta has developed by the early pharyngula stage, as has a choriovitelline placenta and the first stages of an omphaloplacenta. Although the choriovitelline membrane disappears rapidly, the omphaloplacenta spreads to occupy the entire abembryonic pole. The yolk cleft is not confluent with the exocoelom, and no omphalallantoic placenta develops. By the limb-bud stage, an allantoplacenta has been established, with a mesometrial placentome composed of interdigitating ridges of chorioallantois and uterine mucosa. The discovery of five distinct placental arrangements in this species, three of which are transitory and two of which have not previously been recorded in reptiles, emphasizes the need for accounts that specify ontogenetic stages and the precise identity and composition of squamate placental membranes. Contrary to previous interpretations, the pattern of extraembryonic membrane development in C. chalcides is evolutionarily conservative, despite the presence of a reduced yolk mass and cytological specializations for nutrient transfer. Our observations indicate that substantial placentotrophy can evolve in squamates without major modifications of morphogenetic patterns. J Morphol 232:35–55, 1997. © 1997 Wiley-Liss, Inc.     

Of birds and mice: hematopoietic stem cell development

For many years it has been assumed that the ontogeny of the mammalian hematopoietic system involves sequential transfers of hematopoietic stem cells (HSCs) generated in the yolk sac blood islands, to successive hematopoietic organs as these become active in the embryo (fetal liver, thymus, spleen and eventually bone marrow). Very little was known about early events related to hematopoiesis that could take place during the 4.5 day gap separating the appearance of the yolk sac blood islands and the stage of a fully active fetal liver. Experiments performed in birds documented that the yolk sac only produce erythro-myeloid precursors that become extinct after the emergence of a second wave of intra-embryonic HSCs from the region neighbouring the dorsal aorta. The experimental approaches undertaken over the last ten years in the murine model, which are reviewed here, led to the conclusion that the rules governing avian hematopoietic development basically apply to higher vertebrates.     

In vitro development of murine T cells from prethymic and preliver embryonic yolk sac hematopoietic stem cells.

Mature T cells are derived from prethymic stem cells, which arise at one or more extrathymic sites and enter and differentiate in the thymus. The nature of these prethymic stem cells is a critical factor for the formation of the T-cell repertoire. Although the bone marrow of adult mice can provide such stem cells, their origin during murine embryogenesis is still undetermined. Among potential sites for these progenitor cells are the fetal liver and the embryonic yolk sac. Our studies focus on the yolk sac, both because the yolk sac appears earlier than any other proposed site, and because the mammalian yolk sac is the first site of hematopoiesis. Although it has been shown that the yolk sac in midgestation contains stem cells that can enter the thymic rudiment and differentiate toward T-cell lineage, our aim was to analyze the developmental potential of cells in the yolk sac from earlier stages, prior to the formation of the liver and any other internal organ. We show here that the yolk sac from 8- and 9-day embryos (2-9 and 13-19 somites, respectively) can reconstitute alymphoid congenic fetal thymuses and acquire mature T-cell-specific characteristics. Specifically, thymocytes derived from the early embryonic yolk sac can progress to the expression of mature T lymphocyte markers including CD3/T-cell receptor (TCR), CD4 and CD8. In contrast, we have been unable to document the presence of stem cells within the embryo itself at these early stages. These results support the hypothesis that the stem cells capable of populating the thymic rudiment originate in the yolk sac, and that their presence as early as at the 2- to 9-somite stage may indicate that prethymic stem cells found elsewhere in the embryo at later times may have been derived by migration from this extra-embryonic site. Our experimental design does not exclude the possibility of multiple origins of prethymic stem cells of which the yolk sac may provide the first wave of stem cells in addition to other later waves of cells.     

Reproduction,placentation, and embryonic development of the Atlantic sharpnose shark,Rhizoprionodon terraenovae

The Atlantic sharpnose shark Rhizoprionodon terraenovae (Richardson) is a small carcharhinid that is a common year-round resident along the southeast coast of the United States. It is viviparous and its embryos develop an epithelio-vitelline placenta. Females enter shallow water to give birth in late May and early June. Mating occurs shortly after parturition, and four to seven eggs are ovulated. Fertilized eggs attain the blastoderm stage in early June to early July. Separate compartments for each egg are formed in the uterus when the embryos reach 3–30 mm. Embryos depend on yolk for the first 8 weeks of development. When embryos reach 72 mm their yolk supply is nearly depleted and they shift to matrotrophic nutrition. When the embryos reach 40–55 mm, placental development begins with the vascularization of the yolk sac where it contacts the uterine wall. Implantation occurs at an age of 8–10 weeks by which time the embryos reach 70–85 mm. The expanding yolk sac engulfs the maternal placental villi, and its surface interdigitates with the villi to form the placenta. The rest of the lumenal surface of the uterus is covered by non-placental villi that appear shortly after implantation. Histotrophe production by the non-placental villi begins just after their formation. The placenta grows continuously during gestation. The egg envelope is present throughout gestation, separating maternal and fetal tissues. Embryos develop numerous appendiculae on the umbilical cord. Young sharks are born at 290–320 mm after a gestation period of 11 to 12 months. © 1993 Wiley-Liss, Inc.     

Development of yolk sac and chorioallantoic membranes in the Lord Howe Island skink,Oligosoma lichenigerum

Development of the yolk sac of squamate reptiles (lizards and snakes) differs from other amniote lineages in the pattern of growth of extraembryonic mesoderm, which produces a cavity, the yolk cleft, within the yolk. The structure of the yolk cleft and the accompanying isolated yolk mass influence development of the allantois and chorioallantoic membrane. The yolk cleft of viviparous species of the Eugongylus group of scincid lizards is the foundation for an elaborate yolk sac placenta; development of the yolk cleft of oviparous species has not been studied. We used light microscopy to describe the yolk sac and chorioallantoic membrane in a developmental series of an oviparous member of this species group, Oligosoma lichenigerum. Topology of the extraembryonic membranes of late stage embryos differs from viviparous species as a result of differences in development of the yolk sac. The chorioallantoic membrane encircles the egg of O. lichenigerum but is confined to the embryonic hemisphere of the egg in viviparous species. Early development of the yolk cleft is similar for both modes of parity, but in contrast to viviparous species, the yolk cleft of O. lichenigerum is transformed into a tube‐like structure, which fills with cells. The yolk cleft originates as extraembryonic mesoderm is diverted from the periphery of the egg into the yolk sac cavity. As a result, a bilaminar omphalopleure persists over the abembryonic surface of the yolk. The bilaminar omphalopleure is ultimately displaced by intrusion of allantoic mesoderm between ectodermal and endodermal layers. The resulting chorioallantoic membrane has a similar structure but different developmental history to the chorioallantoic membrane of the embryonic hemisphere of the egg. J. Morphol. 2012. © 2012 Wiley Periodicals, Inc.     

Observations on the Oman Shark,Iago omanensis (Triakidae), with emphasis on the morphological and cytological changes of the oviduct and yolk sac during gestation

The shark Iago omanensis (Triakidae, Selachia) is encountered in large populations in the Gulf of Aqaba, Red Sea, at depths of 150–1,500 m. It is a placental viviparous species, reproductive all year round and giving birth to four (occasionally five) young of 170- to 180-mm total length (TL). Its distribution and morphometrics, as well as histological and cytological changes in the oviducts, were studied. The ratio of weight of the female genital organs to body weight changes from 0.7% in nongravid females to 19.8% in the final stages of pregnancy. The ripe, liberated eggs, which are 11–12 mm long and 5 mm wide, pass through the nidamental gland and settle in the uterus. The embryo attains 9- to 11-mm TL and settles on a protruding ridge of the submucosa, covered with a microvillar endometrium. At this site of attachment, a placenta is formed and the participating uterine endometrium and wall of the yolk sac undergo profound histocytological changes, forming two parts of this organ. Three forms of food provisioning occur in the growing embryos: (1) lecithotrophic, based on yolk transported from the egg to the embryonic gut via the umbilical cord; (2) mixed food provision, during which, in addition to nourishment provided via the umbilicus, food is transported across the placenta through transfer from the female blood vascular system to the embryonic yolk sac via the trophic villi of the yolk sac; and (3) histotrophic, when all yolk reserves have been used and nutrition is provided from the so-called “milk” within the yolk sac, metabolized by the trophic structures of the sac and transported by blood vessels. Despite the gradual utilization of yolk, the yolk sac mass initially increases from 0.5–1.0 cc to 2.0–2.2 cc with the addition of primary and secondary trophic villi until, during the final stages of embryogenesis, it decreases again to 1.4–1.6 cc. Neonate juveniles are 35–40 times heavier than the original eggs. J. Morphol. 236:151–165, 1998. © 1998 Wiley-Liss, Inc.     

In vitro activation of the in vivo colony-forming units of the mouse yolk sac.

Experiments were performed to investigate the presence of colony-forming units (CFU) in the mouse embryonic yolk sac during the developmental period in which the yolk sac is the sole hemopoietic organ. Injection of yolk sac cell suspensions from normal embryos into syngeneic, lethally irradiated adult recipients evoked a very low number of spleen colonies. However, prior cultivation of yolk sacs in vitro caused a dramatic increase in the spleen colony-forming capacity--as high as 84-fold--following 48 hours in culture. The yolk sac origin of the spleen colonies was confirmed by: (a) Chromosomal marker analysis; (b) dose-response analysis; (c) demonstrating that the above colonies were not of endogenous origin induced by the mere injection of grafted cells. We conclude that the yolk sac contains many precursors of colony-forming cells which though undetectable by immediate grafting apparently become activated in culture by an as yet unknown induction process.     

Proteolytic activity in the yolk sac membrane of quail eggs.

Extraembryonal degradation of yolk protein is necessary to provide the avian embryo with required free amino acids during early embryogenesis. Screening of proteolytic activity in different compartments of quail eggs revealed an increasing activity in the yolk sac membrane during the first week of embryogenesis. In this tissue, the occurrence of cathepsin B, a lysosomal cysteine proteinase, and cathepsin D, a lysosomal aspartic proteinase, has been described recently (Gerhartz et al., Comp Biochem Physiol, 118B:159-166, 1997). Determination of cathepsin B-like and cathepsin D-like proteolytic activity in the yolk sac membrane indicated a significant correlation between growth of the yolk sac membrane and proteolytic activity, shown by an almost constant specific activity. Both proteinases could be localized in the endodermal cells, which are in direct contact to the yolk. The concentration of proteinases in the endodermal cells appears to be almost unaltered in the investigated early stage of quail development, whereas the amount of endodermal cells increases rapidly, seen by a complicated folding of the yolk sac membrane. In the same cells quail cystatin, a potent inhibitor of quail cathepsin B (Ki 0.6 nM), has been localized at day 8 of embryonic development. Approximately at this stage of development, the quail embryo stops metabolizing yolk. In conclusion, it is strongly indicated that the amount of available free amino acids, produced by proteolytic degradation and supporting embryonic growth, is regulated by the growth of the yolk sac membrane.     

Development of erythroid and myeloid progenitors in the yolk sac and embryo proper of the mouse.

In this study, we have mapped the onset of hematopoietic development in the mouse embryo using colony-forming progenitor assays and PCR-based gene expression analysis. With this approach, we demonstrate that commitment of embryonic cells to hematopoietic fates begins in proximal regions of the egg cylinder at the mid-primitive streak stage (E7.0) with the simultaneous appearance of primitive erythroid and macrophage progenitors. Development of these progenitors was associated with the expression of SCL/tal-1 and GATA-1, genes known to be involved in the development and maturation of the hematopoietic system. Kinetic analysis revealed the transient nature of the primitive erythroid lineage, as progenitors increased in number in the developing yolk sac until early somite-pair stages of development (E8.25) and then declined sharply to undetectable levels by 20 somite pairs (E9.0). Primitive erythroid progenitors were not detected in any other tissue at any stage of embryonic development. The early wave of primitive erythropoiesis was followed by the appearance of definitive erythroid progenitors (BFU-E) that were first detectable at 1-7 somite pairs (E8.25) exclusively within the yolk sac. The appearance of BFU-E was followed by the development of later stage definitive erythroid (CFU-E), mast cell and bipotential granulocyte/macrophage progenitors in the yolk sac. C-myb, a gene essential for definitive hematopoiesis, was expressed at low levels in the yolk sac just prior to and during the early development of these definitive erythroid progenitors. All hematopoietic activity was localized to the yolk sac until circulation was established (E8.5) at which time progenitors from all lineages were detected in the bloodstream and subsequently in the fetal liver following its development. This pattern of development suggests that definitive hematopoietic progenitors arise in the yolk sac, migrate through the bloodstream and seed the fetal liver to rapidly initiate the first phase of intraembryonic hematopoiesis. Together, these findings demonstrate that commitment to hematopoietic fates begins in early gastrulation, that the yolk sac is the only site of primitive erythropoiesis and that the yolk sac serves as the first source of definitive hematopoietic progenitors during embryonic development.     

Chondroitin sulfate synthesis by mouse embryonic, extraembryonic, and teratoma cells in vitro

Sulfated glycosaminoglycan (GAG) synthesis by primary cultures of embryo, yolk sac, and trophoblast was compared with synthesis by the same tissues in utero. In general, the in vivo and in vitro results were in good agreement. As was the case in vivo, the three tissues synthesized chondroitin-4-sulfate and chondroitin-6-sulfate (but no dematan sulfate) at characteristic ratios.Cultured embryos are already capable of synthesizing chondroitin sulfates, primarily chondroitin-4-sulfate, before, or at, the 64-cell stage. During the attachment and initiation of outgrowth stages, blastocysts synthesize more chondroitin-6-sulfate than chondroitin-4-sulfate. Thereafter, progressively more chondroitin-4-sulfate is synthesized so that the 4:6 ratio increases, resembling that of trophoblast cells.Blastocyst-derived cell lines and teratoma cell cultures were also studied. One blastocyst-derived line, MB4, synthesized GAG with a pattern similar to that of yolk sac, which it resembles biochemically in other respects as well. The GAG profile of MB2, a parietal endoderm-like cell line resembled neither that of embryo, yolk sac, nor trophoblast cells. Embryonal carcinoma (undifferentiated teratoma) cells had a chondroitin sulfate pattern different from that of most of the other cultures.     

Expression of the 14 kDa and 16 kDa galactoside-binding lectins during differentiation of the chick yolk sac

The gastrulating chick embryo expresses two galactoside-binding lectins of 14 kDa and 16 kDa. These lectins are present in the area pellucida and area opaca, and in the latter are concentrated in the endoderm. Since the area opaca is the progenitor of the yolk sac, we studied the galactose-binding lectins during the development of this extraembryonic organ. In the yolk sac, lectin expression surges between 2 and 4 days, and thereafter remains constant throughout development. Using monoclonal antibodies (mAbs) specific to the 16 kDa yolk sac lectin, and a panel of polyclonal antibodies to the 14 kDa and 16 kDa lectins we studied lectin expression. The mAbs inhibit the hermagglutinating activity of extracts from chick yolk sac, embryonic pectoral muscle, and adult liver, but have no effect on the hemagglutinating activity of extracts from the adult intestine. Immunolocalization studies with the mAbs and polyclonal antibodies indicate that in the less differentiated endodermal cells of the area vitellina the 16 kDa lectin is present in discrete lectin-rich inclusions. In contrast, within the maturing endodermal epithelium of area vasculosa the 16 kDa lectin is present around the intracellular yolk platelets, and is associated with the cytoplasmic matrix. The 16 kDa lectin is also found at the apical cell surface of the yolk sac epithelium, in some regions closely associated with the plasma membrane. The 14 kDa lectin is distributed intracellularly surrounding the yolk platelets of the maturing yolk sac endoderm. The surge in expression of the 16 kDa lectin at the time of expansion of the area opaca suggests that it may be involved in the spreading of this area. Our findings also indicate that as the yolk sac endoderm differentiates into an epithelium intracellular lectin expression changes from predominantly organelle associated to cytoplasm associated. The association of both lectins with yolk suggest that the lectins may also be involved in the processing of intracellular and extracellular yolk proteins. These results, in con junction with previous findings indicating the presence of these lectins in the extracellular matrix (Didier et al., Histochemistry 100:485, 1993; Zalik et al., Intl J Dev Biol 38:55–68, 1994) indicate that these lectins play multiple roles in embryonic development.     

Free amino acids in the early cleavage stages of the rabbit egg

In the first half of gestation, mouse yolk sac contains levels of N-acetyl-β-hexosaminidase activity and a ratio of N-acetyl-β-hexosaminidase: β-glucuronidase much higher than those of other embryonic tissues or the decidua. The properties of the yolk sac enzyme are very similar to those in the other tissues, suggesting that the observed difference in activity is quantitative rather than qualitative. In blastocyst cultures, the vesicular growths derived from the inner cell mass possess patterns of N-acetyl-β-hexosaminidase activity similar to yolk sac in vivo, but different from trophoblast cells developing in the same cultures. It is therefore proposed that the vesicular growths contain at least some differentiated yolk sac cells.     

Ontogeny of the immune system of fish

Information on the ontogeny of the fish immune system is largely restricted to a few species of teleosts (e.g., rainbow trout, catfish, zebrafish, sea bass) and has previously focused on morphological features. However, basic questions including the identification of the first lympho-hematopoietic sites, the origin of T- and B-lymphocytes and the acquisition of full immunological capacities remain to be resolved. We review these three main topics with special emphasis on recent results obtained from the zebrafish, a new experimental model particularly suitable for study of the ontogeny of the immune system because of its rapid development and easy manipulation. This species also provides an easy way of creating mutations that can be detected by various types of screens. In some teleosts (i.e., angelfish) the first blood cells are formed in the yolk sac. In others, such as zebrafish, the first hematopoietic site is an intraembryonic locus, the intermediate cell mass (ICM), whereas in both killifish and rainbow trout the first blood cells appear for a short time in the yolk sac but later the ICM becomes the main hematopoietic area. Erythrocytes and macrophages are the first blood cells to be identified in zebrafish embryos. They occur in the ICM, the duct of Cuvier and the peripheral circulation. Between 24 and 30 hour post-fertilization (hpf) at a temperature of 28 degrees C a few myeloblasts and myelocytes appear between the yolk sac and the body walls, and the ventral region of the tail of 1-2 day-old zebrafish also contains developing blood cells. The thymus, kidney and spleen are the major lymphoid organs of teleosts. The thymus is the first organ to become lymphoid, although earlier the kidney can contain hematopoietic precursors but not lymphocytes. In freshwater, but not in marine, teleosts the spleen is the last organ to acquire that condition. We and other authors have demonstrated an early expression of Rag-1 in the zebrafish thymus that correlates well with the morphological identification of lymphoid cells. On the other hand, the origins and time of appearance of B lymphocytes in teleosts are a matter of discussion and recent results are summarized here. The functioning rather than the mere morphological evidence of lymphocytes determines when the full immunocompetence in fish is attained. Information on the histogenesis of fish lymphoid organs can also be obtained by analysing zebrafish mutants with defects in the development of immune progenitors and/or in the maturation of non-lymphoid stromal elements of the lymphoid organs. The main characteristics of some of these mutants will also be described.     

Embryo implantation and proteinase activities in a marsupial (Macropus eugenii)

Summary Embryo implantation remains superficial (epithelio-chorial type) in most marsupials including the Macropodidae, but does involve formation of specialized contact zones of the trophoblast with the uterine epithelium. Since in eutherian mammals proteinases appear to play a central role in implantation-initiation mechanisms, a systematic histochemical investigation of proteinase patterns as related to implantation was performed in the tammar wallaby, Macropus eugenii (Macropodidae).Tammar uteri with embryos were collected at diapause and at days 7, 17, 18, 19, 20, 21 and 26 of the 27-day gestational period. Proteinase patterns were studied using a sensitive histochemical gelatin-substrate-film test previously optimized for the detection of trophoblast-dependent proteinase (blastolemmase) in the rabbit. Proteinase patterns were correlated with light-microscopical morphology of the processes of shedding of the extracellular embryo coverings (shell membrane) and attachment of the trophoblast to the uterine epithelium.At acid pH values an intracellular proteinase is detected in yolk sac endoderm and trophoblast as well as in endometrial glands and certain stromal cells. This enzyme is proposed to be a cathepsin indicating high catabolic activity connected particularly with protein transport from the endometrium into the yolk sac. Peak activity is found in the avascular (bilaminar) yolk sac at the phase when contact with the endometrium is being established.A particularly interesting proteinase active at alkaline pH values is detected in the trophoblast-endoderm complex. This enzyme appears to be extruded into the interface between trophoblast and uterine epithelium where it shows maximal activity for only approximately one day, around day (18-)19, exclusively in the bilaminar (avascular) yolk sac. The activity is correlated with the process of shedding of the extracellular embryo coverings (shell membrane) and of subsequent attachment of the trophoblast to the uterine epithelium, in the bilaminar but not the trilaminar (vascular) yolk-sac region. This is the first report on an extracellular (alkaline) proteinase activity possibly serving a specific function in embryo implantation in a marsupial.Abreviations BYS bilaminar (avascular) yolk sac membrane = bilaminar omphalopleure - dp.c. days post coitum - d RPY days after removal of pouch young - TYS trilaminar (vascular) yolk sac membrane = trilaminar omphalopleure Preliminary reports on portions of these investigations were presented at the 14th Annual Meeting of the Society for the Study of Reproduction 1981 (Biol Reprod 24 Suppl 1, p 78 A, 1981) and at the 3. Arbeitstagung der Anatomischen Gesellschaft 1982 (Anat Anz 153, 268, 1983)     

Larval ontogeny and morphology of giant trahira Hoplias lacerdae

In the present study, the morphology and behaviour of giant trahira Hoplias lacerdae larvae were investigated, from hatching to complete absorption of the yolk sac, under laboratory conditions. In the first day post‐hatching (dph), the larvae presented a big ovoid‐shaped yolk sac that underwent regression during larval ontogeny. The mouth opened 3 dph, when the pectoral fins were evident. From this day, the larvae were able to perform sudden bursts of activity and appear to be able to swim a few centimetres before sinking again. The branchial apparatus was defined at 5 dph, and by 6 dph the operculum was formed. The internal organs such as intestine, liver, kidney and external sensorial structures were present at 7 dph. The yolk sac remained until 7 dph.