Vellutini BC and Migotto AE (2010), Embryonic, larval, and juvenile development of ...

ECB-ART-41554

PLoS One 2010 Mar 22;53:e9654. doi: 10.1371/journal.pone.0009654.

Show Gene links Show Anatomy links

Embryonic, larval, and juvenile development of the sea biscuit Clypeaster subdepressus (Echinodermata: Clypeasteroida).

Vellutini BC , Migotto AE .

???displayArticle.abstract???
Sea biscuits and sand dollars diverged from other irregular echinoids approximately 55 million years ago and rapidly dispersed to oceans worldwide. A series of morphological changes were associated with the occupation of sand beds such as flattening of the body, shortening of primary spines, multiplication of podia, and retention of the lantern of Aristotle into adulthood. To investigate the developmental basis of such morphological changes we documented the ontogeny of Clypeaster subdepressus. We obtained gametes from adult specimens by KCl injection and raised the embryos at 26 degrees C. Ciliated blastulae hatched 7.5 h after sperm entry. During gastrulation the archenteron elongated continuously while ectodermal red-pigmented cells migrated synchronously to the apical plate. Pluteus larvae began to feed in 3 d and were 20 d old at metamorphosis; starved larvae died 17 d after fertilization. Postlarval juveniles had neither mouth nor anus nor plates on the aboral side, except for the remnants of larval spicules, but their bilateral symmetry became evident after the resorption of larval tissues. Ossicles of the lantern were present and organized in 5 groups. Each group had 1 tooth, 2 demipyramids, and 2 epiphyses with a rotula in between. Early appendages consisted of 15 spines, 15 podia (2 types), and 5 sphaeridia. Podial types were distributed in accordance to Lovén''s rule and the first podium of each ambulacrum was not encircled by the skeleton. Seven days after metamorphosis juveniles began to feed by rasping sand grains with the lantern. Juveniles survived in laboratory cultures for 9 months and died with wide, a single open sphaeridium per ambulacrum, aboral anus, and no differentiated food grooves or petaloids. Tracking the morphogenesis of early juveniles is a necessary step to elucidate the developmental mechanisms of echinoid growth and important groundwork to clarify homologies between irregular urchins.

???displayArticle.pubmedLink??? 20339592
???displayArticle.pmcLink??? PMC2842294
???displayArticle.link??? PLoS One

Genes referenced: adcy10 ago1b LOC100887844 LOC100892350 LOC100893907 LOC105439231 LOC115919910 LOC583082 pole

???attribute.lit??? ???displayArticles.show???

	Figure 1. C. subdepressus genital papillae and spawning. A Male genital papilla (arrow) releasing sperm and adjacent accessory papilla (white arrow). B Female genital papilla (arrow) releasing eggs. C Adult male releasing sperm during a spontaneous spawning event in March 8, 2007. Scale bars = 1 mm (A, B); 20 mm (C)
	Figure 2. Migration and fusion of C. subdepressus pronuclei.Montage of a single zygote during a period of 12 min 30 s after sperm entry (top). The movements of male (black dashed line) and female (white dashed line) pronuclei were outlined (bottom). Frames taken every 58 s. Scale bar =
	Figure 3. Early cleavages of C. subdepressus under light microscopy. A Two nuclei (arrows) during cariocinesis of the first cell division. B Embryo with two cells before the second cleavage; hialine layer is visible between cells (arrow). C Animal pole view of an embryo with 4 cells. D Lateral view of an embryo with 8 cells; blastomeres on the vegetal pole are smaller (bottom). E Micromeres (arrow) on the vegetal pole of an embryo with 16 cells. F Lateral view of an embryo with 16 cells. G Arrangement of micromeres and macromeres on the vegetal pole of a 16 cell embryo. H 16 cell embryo showing the mesomere arrangement on the animal pole. I Fifth division cycle showing child-micromeres (arrow) on the vegetal pole; embryo with 32 cells. J Lateral view of an embryo with 32 cells. K Vegetal pole of an embryo with 56 cells. L Lateral view of an embryo with 108 cells. Scale bars =
	Figure 4. Compactation of ectodermic cells during blastula formation. A and B show different optical sections of embryos sampled 3.5, 5.0, and 6.5 hpf. A Ectodermic cells acquired a polygonal shape and became smaller during the division cycles. B Epithelium became more uniform and cells lost the globoid shape. Scale bar =
	Figure 5. Sequential images of C. subdepressus embryos during gastrulation.Vegetal pole is bottom. A Post-hatching swimming blastula with thickened vegetal pole epithelium 9 hpf. B Initial ingression of PMC into the blastocoel 10 hpf. C Ingressed PMC aggregated on the posterior end 11 hpf. D Initial migration of PMC through the inner side of ectoderm 13 hpf; red-pigmented cells are present on the vegetal pole (not visible). E Initial invagination of the archenteron 14 hpf. F SMC ingress the blastocoel from the archenteron tip 15 hpf; PMC form lateral aggregates (arrows) and begin to secrete the skeleton. G SMC reaching the anterior pole 16.5 hpf (arrow); red-pigmented cells reached the middle region of the embryo through the ectoderm. H Final stage of archenteron invagination with SMC touching the anterior pole 19 hpf; blastocoel is populated with PMC and SMC and red-pigmented cells reached the anterior pole. Scale bars =
	Figure 6. PMC and SEM of prism larval stage of C. subdepressus. A PMC forming a ring near the posterior end 14 hpf; cells are connected by cytoplasmic bridges (arrow). B Triradiate calcareous spicule secreted by PMC initiating the formation of the larval skeleton 15 hpf. C The apical tuft (at) and future mouth (m) are present at the anterior region. On the posterior end the postoral arms (po) begin to extend and the blastopore is visible (bp). Scale bars = (A, C); (B)
	Figure 7. Gastrulation of C. subdepressus. A Time-series plots with fitted smooth curve of 4 morphometric measurements during gastrulation. The height, width, blastocoel height, and archenteron length were measured every 30 min for 8 h (12–20 hpf, except 12.5 hpf). Height and blastocoel height decreased during the period while the width showed a slight increase; archenteron elongation is continuous. B Relative amount of archenteron elongation during gastrulation calculated by the ratio between archenteron length and blastocoel height. for each timespan.
	Figure 8. Coeloms, gut, and hydropore formation in C. subdepressus. A Differentiation of a three-part gut has begun and coelomic sacs (c) were formed next to the archenteron 48 hpf. Detail shows the initial extension of the hydropore channel (arrow) from the left coelom. B Differentiated gut, mouth (m), esophagus (e), and stomach (s), after 3 d. Hidropore channel (arrow) next to the larval epithelium 3 dpf. Scale bars =
	Figure 9. Vestibule and rudiment formation in C. subdepressus larvae. A Vestibule invagination 5 dpf (arrow). B Detail of vestibule reaching the left coelomic sac. C Fusion of vestibule and left coelom (arrow). D Posterior region of a competent pluteus larva showing a well-developed rudiment (dashed line). Appendages (podia and spines – arrowheads) are present and active; developing rudiment occupied most of the body and displaced the larval gut (s). Scale bars = (A, D); (B, C)
	Figure 10. Substrate-test behaviour and metamorphosis of C. subdepressus. A Competent larvae opening the arms and exposing the vestibule pore. B Metamorphosis took approximately 1 h 30 min, from attachment to the complete regression of larval tissues. Scale bars =
	Figure 11. Morphology of postlarval juveniles of C. subdepressus. A Side view of the final stage of larval tissue regression; fragments of tissue were disrupted (arrow) near the skeleton of larval arms; a tiny sphaeridium (arrowhead) is visible between spines. B Side view showing the accumulation of larval tissues in the aboral region before the resorption. C Aboral view of A; bilaterality is not yet clearly identified. D Remnants of the larval skeleton (arrow) on the aboral surface under polarized light. E Distribution of sphaeridia (arrowhead) on the oral surface. F Different types of podia present after metamorphosis; type I (left) and type II (right) podia; circular spicule (arrow and detail). Scale bars = (F); (A, E); (D); (B, C)
	Figure 12. Formation of the lantern of Aristotle of C. subdepressus. A Rudiments of the lantern after the regression of larval tissues at the end of metamorphosis. Each set of ossicles was intercalated by a rotula (not visible) and consisted of a central tooth (arrow), two demipyramids (arrowheads), and two epiphyses (dashed line). Latter and rotula not visible because of orientation of polarized light. Asterisks mark the epiphyses of the adjacent sets. B Demipyramids (d) were formed, but not sutured together 2 dpm; teeth had narrow tips (arrow). C Demipyramids were tightly sutured into a pyramid (p) 7 dpm. D Mature teeth with ornamentation on the inner side (left). Scale bars =
	Figure 13. Postlarval appendages and lantern rudiments.Oral view representation of a postlarval juvenile after the regression of larval tissues. Ossicles of the lantern of Aristotle ossicles were present at the center of the oral region. Teeth (t), demipyramids (d), epiphyses (ep), and rotulae (r). Podia, spines, and sphaeridia are present on the calcified oral region (grey area). Dashed line delimits the second row of appendages positioned above the ambitus. Miliary spines not shown.
	Figure 14. Ambulacra of C. subdepressus juveniles. A Oral view of a juvenile showing the distribution of podial types within ambulacral zones (I–V in white circles); bbaba for type I and aabab for type II. The middle section of interambulacra are marked with dashed white lines. B Detail of ambulacrum I of a juvenile during the resorption of larval tissues. Dashed white circles mark the position of the first two podia. Type I originated on the ambulacral column Ib on the peristome edge and was not encircled by the skeleton; type II emerged from a pore in the skeleton on the ambulacral column Ia. C Ambulacrum I of a 2 months old juvenile still showing the same pattern of the younger juvenile in B. Scale bars = (A); (B, C)
	Figure 15. Aboral structures and mouth formation of C. subdepressus. A Skeletal plates on the aboral surface of a 2 d old juvenile under polarized light. B Aboral view showing the distribution of miliary spines (arrow). C Detail of a miliary (left) and primary (right) spine. D Pair of ophicephalous pedicellariae (arrows) at the posterior region of the juvenile. E Digestory track of the juvenile and fecal pellet (arrow) being released by the anus. F Side view of the mouth (arrowhead) after the opening of the peristomial membrane. G Oral view showing the mouth and peristomial membrane 7 dpm. H Juvenile 120 dpf during locomotion with podia extended anteriorly and the characteristic longer pair of posterior spines (arrows). Scale bars = (C, G); (A, D, E, F); (B); (H)
	Figure 16. Collecting sites of adult C. subdepressus.Portinho and Parcel da Praia Grande (dots) are located on the island shore of São Sebastião Channel. CEBIMar-USP (arrowhead) is located on the continent shore at the Northern region of São Paulo State. Marks every 15′. Brazil and São Paulo vector images cortesy of Felipe Menegaz and Raphael Lorenzeto de Abreu, respectively.

References [+] :

Hart, Life history evolution and comparative developmental biology of echinoderms. 2002, Pubmed, Echinobase