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“time after emerging (hatching) from the primary egg membrane”. This limits the term significantly. On the other hand, there are pelagic propagules that undergo direct development and consequently qualify as larvae only in the sense that they are dispersed by water movements (McEdward, 1992). The third definition of a larva is basically morphogenetic. For this definition, larva is the premetamorphic consequence of type 1 embryogenesis, a type of specification of cell fates that is fundamentally different in invertebrate larvae, until metamorphosis (Davidson, 1991; Davidson et al., 1995; Hall and Wake, 1999). The problem with this definition if that it applies most specifically to larvae that are strictly indirect-developing, such as those of echinoderms, in which there is a considerable degeneration (reabsortion) of larval tissues at metamorphosis, but it is not similarly applicable to all invertebrate larvae. Finally, McEdward & Janies (1993) suggest it is important to recognize that there cannot be an absolute distinction between larvae and mesogens (see pag. 21), because the evolution from indirect to direct development usually involves the successive reduction and elimination of larval structures. Thus, in order to answer the questions about “what is a larva?” and “what is not?” McEdward & Janies (1993) propose that a larva will only be a larva when the strictest morphological and developmental features are taken into account. Everything else-including a mesogenis not. 2.2.3. Juvenile The expression “juvenile” has been used in a very broad sense. At one extreme, it makes reference to “post-larval” stages, either directly following rapid metamorphosis from a definite larval stage or at some point, not adequately defined, during a prolonged, gradual metamorphosis. At the other extreme, juveniles are “pre- 31
adults” that have the definitive adult morphology, but are small and/or not sexually mature. According to the definitions of McEdward and Janies, (1993), a juvenile 1) has attained the adult body plan (symmetry, general body shape), 2) is a form in which the major systems are functional (especially locomotion and feeding), with the exception of reproduction, and 3) excludes the transitional period during metamorphosis. 2.2.4. Metamorphosis Definitions of metamorphosis usually affirm it involves a change in form and function that is accomplished over a relatively short period of time and defines the transition from larva to adult (Burke, 1989).These definitions have been often restricted to cases where there is a drastic and rapid change in morphology. However, it would be more useful to consider metamorphosis as the transition from the larval body plan to the juvenile body plan, regardless of the rate or magnitude of the change (McEdward & Janies, 1993). 2.2.5. Indirect development This refers to the pattern of development in which the embryo is followed by intermediary stages with structural features that are not directly implicated in the morphogenesis of a juvenile. These intermediary stages are larvae, and the construction of their specialized structure and transitory body plan, followed by metamorphosis, defines the indirect nature of a developmental succession. 2.2.6. Direct development This refers to the pattern of development in which the embryonic stages are followed directly by the morphogenesis of the juvenile, without an intervening larval stage. This development possibly will involve short, simple ontogenetic sequences or long, complex series. In contrast to indirect development, the juvenile develops 32
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 and 26: larvae of shallow water echinoids f
Page 27 and 28: few hours, whereas other species su
Page 29 and 30: een defined as a unique sequence of
Page 31: therefore a developing form may wel
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
Page 77 and 78: Species Volume Energy Dev Class Ref
Page 79 and 80: 4.1.2- Body Size The reproductive o
Page 81: Species Depth of max. Depth range (
Page 84 and 85:
arm, and the minor radius (r), from
Page 86 and 87:
From Eqs.1 and 3 we obtain the esti
Page 88 and 89:
Data on maximum body size, maximum
Page 90 and 91:
250 200 Body size (mm) 150 100 50 0
Page 92 and 93:
Fig. 4.7. Hierarchical cluster anal
Page 94 and 95:
(Hymenaster membranaceus Thomson).
Page 96 and 97:
gamete production at low population
Page 98 and 99:
varies depending on the vitellogeni
Page 100 and 101:
size, high fecundity, small egg siz
Page 102 and 103:
strategy described by Winemiller an
Page 104 and 105:
It seems that evolutionary features
Page 106 and 107:
strategy stablished by the Winemill
Page 108 and 109:
which normal embryonic/larval devel
Page 110 and 111:
Larval dispersal from eight populat
Page 112 and 113:
These results are very important si
Page 114 and 115:
possibility. The opportunistic spec
Page 116 and 117:
hypothesis that the Mesozoic and ea
Page 118 and 119:
Barnes, H. and H.T. Powell. 1951. T
Page 120 and 121:
Chester, C.M. 1996. The effect of a
Page 122 and 123:
Crisp, D.J. 1978. Genetic consequen
Page 124 and 125:
David, B., A. Guille, J-P. Féral a
Page 126 and 127:
Grant, A. 1983. On the evolution of
Page 128 and 129:
Inaba, D. 1934. On some holothurian
Page 130 and 131:
of the 6 th International Echinoder
Page 132 and 133:
Lieberkind, I. 1926. Ctenodiscus au
Page 134 and 135:
McEdward, L.R. and S.F. Carson. 198
Page 136 and 137:
Minchin, D. 1987. Sea-water tempera
Page 138 and 139:
Pawson, D.L. 1976. Some aspects of
Page 140 and 141:
Pingree. R.D., B. Sinha and C.R. Gr
Page 142 and 143:
Savidge, G., H.J. Lennon, and A.D.
Page 144 and 145:
Shilling, F.M. and D.T. Manahan. 19
Page 146 and 147:
Turner, R.L. and J.M. Lawrence. 197
Page 148 and 149:
Vickery, M.S. and J.B. McClintock 2
Page 150 and 151:
(Eds.): Reproduction Genetics and D
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