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| Author(s): |
Bruno Cossermelli Vellutini
Total Authors: 1
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| Document type: | Master's Dissertation |
| Press: | São Paulo. |
| Institution: | Universidade de São Paulo (USP). Instituto de Biociências (IBIOC/SB) |
| Defense date: | 2008-12-11 |
| Examining board members: |
Alvaro Esteves Migotto;
Jose Roberto Machado Cunha da Silva;
Carlos Renato Rezende Ventura
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| Advisor: | Alvaro Esteves Migotto |
| Abstract | |
Embryonic, larval, and juvenile development of the sea biscuit Clypeaster subdepressus is described with light and scanning electron microscopy. The reproductive cycle of the species is analyzed based on histological sections of the gonads. The morphological evolution of the order Clypeasteroida (sand dollars and sea biscuits), about 55 million years ago, was associated with the occupation of sand beds. Data on morphology of living and fossil echinoids suggests that during the evolution of sea biscuits juvenile characters were retained into adulthood. We obtained ripe gametes by KCl injection into the perivisceral coelomic cavity of adults and fertilized the eggs in vitro. We kept embryos and larvae in cultures at 26 °C and fed larvae with microalgae. Eggs (mean diameter of 160 m) are spherical, translucent, and white. After sperm entry, the vitelline envelope hardens between 2 and 6 min; male pro-nucleus begins to migrate towards the center of the egg 5 min later, taking 12 min at 0.1 m/s to fuse with the female pronucleus. Cleavages are holoblastic with the formation of macromeres, mesomeres, and micromeres. Blastulae are formed between 3.5 and 6.5 h after fertilization (hpf), develop cilia, and hatch 7.5 hpf. Gastrulation begins on the vegetal plate with the unipolar ingression of primary mesenchyme cells 10 hpf. Archenteron extension, ingression of secondary mesenchyme cells, and the formation of larval skeleton occurs until 30 hpf. In less than 48 hpf the celomic pouches are formed and on day 3 larvae begin to feed. Hidropore opens on the abanal surface of larvae while vestibule invagination takes place between the post-oral and postero-dorsal arms on the left side 5 dpf. Vestibule fuses with the left celom forming a rudiment which develops spines and podia still inside the larvae. Larvae become competent _20 d after fertilization and only metamorphose in the morning, after contact with sand from adult populations or food. After complete eversion of the rudiment, the larval epidermis retraction takes 1 h 30 min. Post-metamorphic juveniles do not have anus or mouth; they have 15 spines and 15 podia (of 2 types); 5 sphaeridia on the oral surface; aboral surface does not have plates, except for the remnants of larval spicules. Rudiments of the Aristotles lantern are organized in 5 groups. Each group has 1 tooth, 2 hemipiramids, and 2 epiphysis; a rudiment rotula is placed between the groups. Hemipiramids are formed 2 d after metamorphosis (dpm); teeth become more robust and hemipiramids fuse into piramids 7 dpm. The digestive tract appears and the anus opens on the aboral surface 2 dpm. The peristomial membrane is functional and the mouth opens 7 dpm. Ophicephalous and tridentate pedicellariae appear on the posterior region 14 dpm and 30 dpm, respectively. Growth of juveniles reared in the laboratory was slow: post-metamorphic juveniles were _250 m in diameter and reached _500 m 8 months later. We described 6 stages of gonadal growth in males and females of C. subdepressus. We found premature stages and ripe gametes more frequently between December and March (summer), while recovery stages were dominant from May until September (winter). Females have a longer period of growing stage than males. The area occupied by the germinal epithelium on a transverse section of a gonadal lobe is lower in mature stage. Gonads are heavier during the premature stage. Data suggest that C. subdepressus from São Sebastião has an annual reproductive cycle where gonadal recovery occurs during winter, nutrient storage by October, and spawning between February and March. (AU) | |
| FAPESP's process: | 06/01898-7 - Development and reproductive cycle of the sea biscuit Clypeaster subdepressus (Echinodermata: Echinoidea) from São Sebastião, SP |
| Grantee: | Bruno Cossermelli Vellutini |
| Support Opportunities: | Scholarships in Brazil - Master |