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CHAPTER TWO- IMPORTANCE OF THE LARVAL STAGE IN THE LIFE HISTORY OF MARINE INVERTEBRATES, SPECIFICALLY ASTEROIDS: A REVIEW 2.1. Introduction An animal starts its development as a zygote. The amount of development that takes place before and after hatching varies considerably from group to group, and frequently from species to species within the same group (Thorson, 1950). There are phyla, such as the Entoprocta in which all known species have larvae. In other phyla, such as the Chaetognatha all individuals hatch in a form resembling minuscule adults. They have no larvae, and development is assumed to be direct. However, in most phyla there is a mixture of developmental modes, some species with larval stages, and some without. In the words of Young (2002) “Indeed, larval development is the most common developmental pathway in the animal kingdom. Representing the future generations of most marine animals, larvae are, in a very real sense, the lifeblood of the sea”. Species that never had a larval phase throughout their evolutionary history or phylogeny show primary direct development. Those without larvae, but that at some point during evolution have evolved from species with larvae, show secondary direct development (Strathmann, 1993; Nielsen, 1998). Jägersten (1972) affirms that there are no factual cases of primary direct development, but Williamson (1992) identifies this category for some phyla such as the Chaetognatha, that show no trace of a larval form at any time during their evolutionary history. With respect to time spent in larval stage, some organisms like the polychaete genus Spirorbis, have a larval life of only a 25
few hours, whereas other species such as the European eel Anguilla anguilla Linnaeus, takes three years to complete its larval development (Williamson, 1992). After a series of cleavages (Fig. 2.1) all metazoan embryos pass through the blastula stage before hatching. At this stage the dividing cells form a more or less hollow sphere, with a fluid filled space within called a blastocoel (Fig. 2.2). In most phyla embryonic development continues further although in many echinoderms the cells of the blastula are ciliated and the animal hatches in this stage (Williamson, 1992). In the following stage, the gastrula, a tube-like inner layer of cells called the archenteron, or primitive gut, is formed. The internal end of the archenteron is closed, and the opening at the vegetal pole is called the blastopore (Figs. 2.2, 2.3). Ectoderm Endoderm Primary mesenchyme Fig.2.1. Cleavage in Deuterostomes showing the cell divisions from the original zygote to the late divisions prior the blastula stage. Abbreviations: an 1 , an 2 refer to cells derived from the animal half; veg 1, veg 2 refer to cells derived from the vegetal half (Modified from Barnes et al. 2001). 26
Page 1 and 2: University of Southampton Research
Page 3 and 4: Graduate School of the National Oce
Page 5 and 6: UNIVERSITY OF SOUTHAMPTON ABSTRACT
Page 7 and 8: Marthasterias glacialis (ECHINODERM
Page 9 and 10: Acknowledgments I know everybody sa
Page 11 and 12: Prière de l’étoile de mer Seign
Page 13 and 14: species of asteroid Patiriella para
Page 15 and 16: embryonic tolerances could determin
Page 17 and 18: dispersed over great distances and
Page 19 and 20: lecithotrophic development. The pre
Page 21 and 22: al., 1997). In a review (Vrijenhoek
Page 23 and 24: Although larval dispersal and settl
Page 25: larvae of shallow water echinoids f
Page 29 and 30: een defined as a unique sequence of
Page 31 and 32: therefore a developing form may wel
Page 33 and 34: adults” that have the definitive
Page 35 and 36: The dipleurula is the hypothetical
Page 37 and 38: among tunicate tadpoles, sponge and
Page 39 and 40: Fig.2.4. Bipinnaria larvae of the a
Page 41 and 42: In marine invertebrates there is a
Page 43 and 44: independent of habitat or mode of n
Page 45 and 46: whether juveniles derived from larv
Page 47 and 48: and the northern Mediterranean have
Page 49 and 50: Wares (2001) performed phylogenetic
Page 51 and 52: Fig. 3.2. A. Marthasterias glaciali
Page 53 and 54: 3.2.2- Temperature/pressure effects
Page 55 and 56: Pressure was applied using an Enerp
Page 57 and 58: Fig. 3.7. Bippinaria larvae of Mart
Page 59 and 60: X Data were abnormal. At 150 and 20
Page 61 and 62: X Data all the embryos were abnorma
Page 63 and 64: X Data blastulae, at 200atm 90% of
Page 65 and 66: 50atm more than 90% of embryos were
Page 67 and 68: Those data (Young et al., 1997; Ped
Page 69 and 70: Percentage of individuals swimming
Page 71 and 72: that settling invertebrate larvae d
Page 73 and 74: CHAPTER FOUR- REPRODUCTIVE FEATURES
Page 75 and 76: In 1973, Vance proposed a theoretic
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Species Volume Energy Dev Class Ref
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4.1.2- Body Size The reproductive o
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Species Depth of max. Depth range (
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arm, and the minor radius (r), from
Page 86 and 87:
From Eqs.1 and 3 we obtain the esti
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Data on maximum body size, maximum
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250 200 Body size (mm) 150 100 50 0
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Fig. 4.7. Hierarchical cluster anal
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(Hymenaster membranaceus Thomson).
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gamete production at low population
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varies depending on the vitellogeni
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size, high fecundity, small egg siz
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strategy described by Winemiller an
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It seems that evolutionary features
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strategy stablished by the Winemill
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which normal embryonic/larval devel
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Larval dispersal from eight populat
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These results are very important si
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possibility. The opportunistic spec
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hypothesis that the Mesozoic and ea
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Barnes, H. and H.T. Powell. 1951. T
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Chester, C.M. 1996. The effect of a
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Crisp, D.J. 1978. Genetic consequen
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David, B., A. Guille, J-P. Féral a
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Grant, A. 1983. On the evolution of
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Inaba, D. 1934. On some holothurian
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of the 6 th International Echinoder
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Lieberkind, I. 1926. Ctenodiscus au
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McEdward, L.R. and S.F. Carson. 198
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Minchin, D. 1987. Sea-water tempera
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Pawson, D.L. 1976. Some aspects of
Page 140 and 141:
Pingree. R.D., B. Sinha and C.R. Gr
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Savidge, G., H.J. Lennon, and A.D.
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Shilling, F.M. and D.T. Manahan. 19
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Turner, R.L. and J.M. Lawrence. 197
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Vickery, M.S. and J.B. McClintock 2
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(Eds.): Reproduction Genetics and D
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