Reproduction and larval morphology of broadcasting and viviparous species in the Cryptasterina species complex

The Cryptasterina group of asterinid sea stars in Australasia comprises cryptic species with derived life histories. C. pentagona and C. hystera have planktonic and intragonadal larvae, respectively. C. pentagona has the gonochoric, free-spawning mode of reproduction with a planktonic lecithotrophic brachiolaria larva. C. hystera is hermaphroditic with an intragonadal lecithotrophic brachiolaria, and the juveniles emerge through the gonopore. Both species have large lipid-rich buoyant eggs and well-developed brachiolariae. Early juveniles are sustained by maternal nutrients for several weeks while the digestive tract develops. C. hystera was reared in vitro through metamorphosis. Its brachiolariae exhibited the benthic exploration and settlement behavior typical of planktonic larvae, and they attached to the substratum with their brachiolar complex. These behaviors are unlikely to be used in the intragonadal environment. The presence of a buoyant egg and functional brachiolaria larva would not be expected in an intragonadal brooder and indicate the potential for life-history reversal to a planktonic existence. Life-history traits of species in the Cryptasterina group are compared with those of other asterinids in the genus Patiriella with viviparous development. Modifications of life-history traits and pathways associated with evolution of viviparity in the Asterinidae are assessed, and the presence of convergent adaptations and clade-specific features associated with this unusual mode of parental care are examined.     

Lectin histochemistry of the hyaline layer around the larvae of Patiriella species (Asteroidea) with different developmental modes.

Larvae of sea stars are surrounded by an extracellular matrix called the hyaline layer. The lectin-binding properties of this matrix were investigated in an ultrastructural study of Patiriella species having different modes of development. The planktonic bipinnaria and brachiolaria of P. regularis and the planktonic brachiolaria of P. calcar demonstrated the same labeling of the hyaline layer for three lectins: Con A, SBA, and WGA. In both species the outer coarse meshwork stained for all three lectins, whereas the intervillous layer displayed patchy labeling. In the benthic brachiolaria of P. exigua, the outer coarse meshwork displayed heavy labeling for all three lectins. The heavy labeling of the outer coarse meshwork of P. exigua compared with that of the other species suggests an increased number of lectin binding sites in the hyaline layer of this species. The similar ultrastructure and histochemistry of the hyaline layer of P. regularis and P. calcar may reflect similar requirements of their extracellular cover in their planktonic environment. Lectin labeling shows that hypertrophy of the hyaline layer of P. exigua, in particular the outer coarse meshwork, involves elaboration of the carbohydrate composition of the matrix. Modifications seen in the ultrastructure and histochemistry of the hyaline layer of P. exigua appear to be associated with the evolution of benthic development.     

Evolution of development in the sea star genus Patiriella: clade-specific alterations in cleavage

Examination of early development in five species of the Patiriella sea star species complex indicates that the ancestral-type radial holoblastic cleavage (Type I) is characteristic of P. regularis and P. exigua, whereas cleavage in species from the calcar clade followed multiple alternatives (Types II-IV) from holoblastic to meroblastic. Considering that invariant radial cleavage is thought to play a role in embryonic axis formation in echinoderms, we documented the details of blastomere formation in Patiriella sp. and followed development of the embryos. In Type II cleavage, the first and second cleavage planes appeared simultaneously at one pole of the embryo, dividing it directly into four equally sized blastomeres. In Type III cleavage, the first and second cleavage planes appeared simultaneously, followed promptly by the third cleavage plane, dividing the embryo directly into eight equally sized blastomeres. In Type IV cleavage, numerous furrows appeared simultaneously at one end of the embryo, dividing it into 32-40 equally sized blastomeres. Confocal sections revealed that embryos with cleavage Types II-IV were initially syncytial. The timing of karyokinesis in embryos with Types II and III cleavage was similar to that seen in clutch mates with Type I cleavage. Karyokinesis in embryos with Type IV cleavage, however, differed in timing compared with Type I clutch mates. Alteration in cleavage was not associated with polarized distribution of maternally provided nutrients. For each cleavage type, development was normal to the competent larval stage. Although variable blastomere configuration in the calcar clade may be linked to possession of a lecithotrophic development, other Patiriella species with this mode of development have typical cleavage. The presence of variable cleavage in all calcar clade species indicates that phylogenetic history has played a role in the distribution of this embryonic trait in Patiriella. The plasticity in early cleavage in these sea stars indicates that this aspect of early development is not constrained against change and that there are many ways to achieve multicellularity.     

Evolution of larval form in the sea star genus Patiriella: conservation and change in the larval nervous system

The organization of the peptidergic system in the larvae of Patiriella species with divergent ontogenies was compared to determine which aspects of neurogenesis are conserved and which are altered in the evolution of development in these sea stars. P. regularis has ancestral-type feeding bipinnaria and brachiolaria larvae and the organization of the nervous system, in association with feeding structures, paralleled the bilateral larval body plan. P. calcar and P. exigua have non-feeding planktonic and benthic brachiolariae, respectively, and there was no trace of the neuronal architecture involved with feeding. The nervous system in the attachment stage brachiolaria was similar in all three species and neuronal organization reflected larval symmetry. Delayed expression of peptidergic lineages to the brachiolaria stage in the lecithotrophs indicates heterochronic change in the timing of neurogenesis or deletion of the ancestral early neurogenic program. The bipinnarial program is suggested to be a developmental module autonomous from the brachiolar one. With a divergence time of less than 10 Ma, the evolution of development in Patiriella has resulted in extensive reduction in the complexity of the larval nervous system in parallel with simplification in larval form. There is, however, strong conservation in the morphology and neuronal architecture of structures involved with settlement.     

Cellular Events of Wrinkled Blastula Formation and the Influence of the Fertilization Envelope on Wrinkling in the Seastar Patiriella exigua

Like many echinoderms, the seastar, Patiriella exigua has a wrinkled blastula rather than the smooth-walled blastula typical of most phyla. The cellular events of wrinkled blastula formation in P. exigua were documented using light, confocal and electron microscopy. Wrinkled blastulae have a highly infolded epithelium. Prior to wrinkling, the blastomeres are cuboidal with lipid droplets and yolk granules distributed throughout their cytoplasm. During wrinkling, the cells become columnar and the lipid and yolk reserves become redistributed to the basal and apical ends of the cells, respectively. Gastrulae have a tall columnar epithelium, with a basal accumulation of lipid. Interdigitation of numerous cell projections, including short lateral processes, basal lamellipodia and apical filopodia, assists in maintaining epithelial integrity during wrinkling. Apical filopodia have not been observed in other echinoderm embryos. Although 1 M urea caused elevation of the fertilization envelope, the embryos did not expand into the newly-created space. This is suggested to be due to the adhesive properties of the hyaline layer. Embryos removed from their envelope were enlarged with shallower and fewer wrinkles compared with controls. It appears that the integrity of the hyaline layer and fertilization envelope both influence the compact wrinkled profile of P. exigua blastulae.     

The embryonic development of the marine caddis fly. Philanisus plebeius Walker (Trichoptera: Chathamidae)

1. P. plebeius, a trichopteran with marine intertidal larvae, oviposits in the coelom of a starfish, Patiriella exigua. Oviposition occurs mainly in the spring and autumn months. 2. In spite of the intracoelomic location of the embryos, the development of P. plebeius follows an unmodified trichopteran mode, including the characteristic blastokinesis. Nutrients are not supplied to the caddis embryos by the host starfish. 3. Hatching takes place in the starfish coelum after 17-18 days. The newly hatched caddis larvae quickly escape to their rock pool habitat. 4. The form of the female ovipositor indicates that other species of Chathamidae utilize starfish species as oviposition hosts. 5. This mode of oviposition offers protection to the caddis embryos in the intertidal habitat.     

Some Like It Fat: Comparative Ultrastructure of the Embryo in Two Demosponges of the Genus Mycale (Order Poecilosclerida) from Antarctica and the Caribbean

During embryogenesis, organisms with lecithotrophic indirect development usually accumulate large quantities of energetic reserves in the form of yolk that are necessary for larval survival. Since all sponges have lecithotrophic development, yolk formation is an ineludible step of their embryogenesis. Sponge yolk platelets have a wide range of morphological forms, from entirely lipid or protein platelets to a combined platelet showing both lipids and proteins and even glycogen. So far, there are no comparative studies on the nature and content of yolk in congeneric species of sponges inhabiting contrasting environments, which could have putative effects on the larval adaptation to environmental conditions. Here, we have taken advantage of the worldwide distribution of the sponge genus Mycale, in order to compare the embryogenesis and yolk formation in two species inhabiting contrasting latitudinal areas: M. acerata from Antarctic waters and M. laevis from the Caribbean. We have compared their brooded embryos and larvae using scanning and transmission electron microscopy, and calculated their energetic signatures based on the nature of their yolk. While the general morphological feature of embryos and larvae of both species were very similar, the main difference resided in the yolk nature. The Antarctic species, M. acerata, showed exclusively lipid yolk, whereas the Caribbean species, M. laevis, showed combined platelets of lipids and proteins and less frequently protein yolk platelets. The larvae of M. acerata were estimated to possess a two-fold energetic signature compared to that of M. laevis, which may have important ecological implications for their survival and for maintaining large population densities in the cold waters of the Southern Ocean.     

Vestigial ophiopluteal structures in the lecithotrophic larvae of Ophionereis schayeri (Ophiuroidea)

Evolution of echinoderm development from a feeding to a non-feeding mode can be examined by studying non-feeding larvae with structures that appear to be vestiges derived from a feeding ancestral state. The lecithotrophic larvae of the Australian brittle star Ophionereis schayeri possess such features, and the early development of this species was documented by light and scanning electron microscopy. The embryos undergo irregular cleavage, resulting in the formation of different sized blastomeres, with subsequent development through a wrinkled blastula stage. The lecithotrophic larva of O. schayeri possesses several vestigial ophiopluteal structures, including a continuous ciliated band, a larval gut, and a larval skeleton. The ciliated band is a reduced expression of the continuous ciliated band typical of ophioplutei. The larval gut is a transiently complete system, but an esophageal plug and rapid closure of the blastopore renders it nonfunctional. The larval skeleton, though reduced, consists of four rods corresponding to the body, posterolateral, anterolateral, and postoral rods characteristic of an ophiopluteus. Due to a heterochrony in larval skeletogenesis, the postoral rods develop early and simultaneously with the other rods. Compared with the larvae of other lecithotrophic ophiuroids, the larva of O. schayeri is one of the most reduced ophiopluteal forms reported to date.     

Maternal factors and the evolution of developmental mode: Evolution of oogenesis in Heliocidaris erythrogramma

 Evolutionary change in developmental mode in sea urchins is closely tied to an increase in maternal provisioning. We examined the oogenic modifications involved in production of a large egg by comparison of oogenesis in congeneric sea urchins with markedly different sized oocytes and divergent modes of development. Heliocidaris tuberculata has small eggs (95 μm diameter) and the ancestral mode of development through feeding larvae, whereas H. erythrogramma has large eggs (430 μm diameter) and highly modified non-feeding lecithotrophic larvae. Production of a large egg in H. erythrogramma involved both conserved and divergent mechanisms. The pattern and level of vitellogenin gene expression is similar in the two species. Vitellogenin processing is also similar with the gonads of both species incorporating yolk protein from coelomic and hemal stores into nutritive cells with subsequent transfer of this protein into yolk granules in the developing vitellogenic oocyte. Immunocytology of the eggs of both Heliocidaris species indicates they incorporate similar levels of yolk protein. However, H. erythrogramma has evolved a highly divergent second phase of oogenesis characterised by massive deposition of non-vitellogenic material including additional maternal protein and lipid. Maternal provisioning in H. erythrogramma exhibits recapitulation of the ancestral vitellogenic program followed by a novel oogenic phase with hypertrophy of the lipogenic program being a major contributor to the increase in egg size. Received: 12 August 1998 / Accepted: 25 November 1998     

The life history of Philanisus plebeius Walker (Trichoptera: Chathamiidae), a caddisfly whose eggs were found in a starfish

Abstract.

• 1 Philanisus plebeius had a univoltine life cycle with adults present from November to April in the South Island of New Zealand. Males predominated in light trap collections in all months and the mean size of adult insects declined over the flight period.
• 2 There are probably seven larval instars which inhabited the marine intertidal zone and fed primarily on non-calcareous algae. Pupae were found only on the red alga, Corallina officinalis.
• 3 Caddisfly eggs were found during most of the year in the coelom of an intertidal starfish, Patiriella regularis. Oviposition is probably through the popular pores and newly hatched larvae may leave the host via the same route or through the stomach wall.
• 4 Egg development time was greater than 30 days at 16–18°C.
• 5 P.plebeius probably colonized New Zealand from Australia after the unusual oviposition behaviour had evolved in association with the Australian cushion star, Patiriella exigua. P.regularis is less abundant and occurs lower on the shore than P.exigua and may be inaccessible to some caddisflies which oviposit amongst intertidal algae.

     

Convergent maternal provisioning and life-history evolution in echinoderms

In marine invertebrates, the frequent evolution of lecithotrophic nonfeeding development from a planktotrophic feeding ancestral developmental mode has involved the repeated, independent acquisition of a large, lipid-rich, usually buoyant egg. To investigate the mechanistic basis of egg-size evolution and the role of maternally provisioned lipids in lecithotrophic development, we identified and quantified the egg lipids in six sea urchin species and five sea star species encompassing four independent evolutionary transformations to lecithotrophy. The small eggs of species with planktotrophic development were dominated by triglycerides with low levels of wax esters, whereas the larger eggs of lecithotrophs contain measurable triglycerides but were dominated by wax ester lipids, a relatively minor egg component of planktotrophs. Comparative analysis by independent contrasts confirmed that after removing the influence of phylogeny, the evolution of a large egg by lecithotrophs was correlated with the conspicuous deposition of wax esters. Increases in wax ester abundance exceeded expectations based solely on changes in egg volume. Wax esters may have roles in providing buoyancy to the egg and for postmetamorphic provisioning. Experimentally reducing the amount of wax esters in blastula stage embryos of the lecithotroph Heliocidaris erythrogramma resulted in a viable but nonbuoyant larvae. During normal development for H. erythrogramma, wax ester biomass remained constant during development to metamorphosis (five days postfertilization), but decreased during juvenile development before complete mouth formation (12 days postfertilization) and was further reduced at 18 days postfertilization. The function of wax esters may be specific to the lecithotrophic developmental mode because there were negligible wax esters present in competent pluteus larvae of Strongylocentrotus drobachiensis, a planktotrophic species. These data suggest that this seminal evolutionary modification, the production of a large egg, has been accomplished in part by the elaboration of a preexisting oogenic component, wax esters. The modification of preexisting oogenic processes may facilitate the observed high frequency of transformations in larval mode in marine invertebrates.     

Characterization of the lecithotrophic larval development of the temperate New Zealand asterinid Stegnaster inflatus

In the family Asterinidae, development through a planktonic lecithotrophic brachiolaria larva is common and has evolved independently several times. Here, we describe the lecithotrophic development of the asterinid Stegnaster inflatus, a species endemic to New Zealand. Early development through the blastula and gastrula stages is short, with hatching at the brachiolaria stage occurring within 48 hr. After hatching, larvae are negatively buoyant, and without aeration remain near the bottom of the culture containers. The settled benthic juvenile stage was reached in ~2 weeks. The brachiolaria of S. inflatus shares common characteristics with the planktonic brachiolaria of other asterinids in that the brachiolar attachment apparatus comprises three brachia and a central adhesive disc, although the latter is thin and appears to be reduced. Mortensen (1925, Videns kabelige Meddelelser fra Dansk naturhistorisk Forening i København, 79 (15), 261‐420) had hypothesized that individuals of S. inflatus might brood within the “cave” formed in the interambulacral space between the arms. We found no evidence for brooding, but hypothesize that S. inflatus may have demersal development, on or near the bottom, which has implications for larval dispersal and population structure.     

Comparison of laboratory-reared eggs, embryos and larvae of five labrid fishes

Eggs, embryos and larvae of five labrid fishes, Thalassoma cupido, Pteragogus flagellifer, Pseudolabrus japonicus, Halichoeres tenuispinnis, and H. poecilopterus, reared in the laboratory are described and compared. The eggs were buoyant and spherical, with a single, spherical oil globule. P. japonicus eggs were unique in lacking melanophores on the oil globule. Eggs of the remaining species closely resembled each other, except in diameter. Incubation periods were short, ranging from ca. 19 h in H. poecilopterus to ca. 31 h in P. japonicus. The newly-hatched embryos also resembled each other, having a short tail and large oval or pear-shaped yolksac, the anterior tip of which extended beyond the snout. The single oil globule was located at the anterior tip of the yolk. As the yolksac diminished with growth, its anterior tip moved posteriorly. The yolk and oil globule were completely absorbed 3 or 4 days after hatching. In all free embryos and larvae except for Pteragogus flagellifer, needle-like projections appeared on both the dorsal and anal finfold margins 12 h to 1 day after hatching. Although morphology of free embryos and larvae of all five species was very similar, differences in pigmentation, location of the anus, and the needle-like projections were apparent. Artificial keys to the newly-hatched embryos and larvae are given.     

Viviparity in the sea star Cryptasterina hystera (Asterinidae)--conserved and modified features in reproduction and development

Cryptasterina hystera has a highly derived life history with intragonadal development and juveniles that emerge from the parent's reproductive tract. The gonads are ovotestes with developing eggs separated from sperm by follicle cells. C. hystera has typical echinosperm that must enter the gonoduct of conspecifics to achieve fertilization. During oogenesis, an initial period of yolk accumulation is followed by hypertrophic lipid deposition, the major contributor to the increase in egg size. 1-Methyladenine induces egg maturation and ovulation, but the spawning component of the hormonal cascade is suppressed. This is the major alteration in reproduction associated with evolution of viviparity in C. hystera. The switch to viviparity was not accompanied by major change in gonad structure, indicating there were few or no anatomical constraints for evolution of a marsupial function for the gonad. Despite their intragonadal habitat, the brachiolaria are equipped for a planktonic life, swimming in gonadal fluid. During the gastrula stage, lipid provisions are released into the blastocoel where they are stored for juvenile development. The eggs of C. hystera have light and dark cytoplasmic regions that mark animal-vegetal polarity. The dark pigment provided a marker to follow the fate of vegetal cells. Live birth is rare in the Echinodermata and the incidence of this form of brooding in the phylum is reviewed.     

Maternal provisioning in Ophionereis fasciata and O. schayeri: brittle stars with contrasting modes of development

Evolutionary change from planktotrophic to lecithotrophic development in echinoderms is closely tied to an increase in maternal provisioning. We provide the first data on the major energetic constituents in the eggs of two ophiuroids, the planktotroph Ophionereis fasciata (egg diameter 103 microm) and the lecithotroph O. schayeri (egg diameter 248 microm), to document changes in maternal investment associated with the switch to lecithotrophy in O. schayeri. Lipid classes in the eggs of the two species did not differ except for the presence of small amounts of wax esters in the eggs of O. schayeri. Production of a large egg in O. schayeri is mostly due to enhanced deposition of one energy-storage lipid, triglyceride. The eggs of O. schayeri are not simply scaled-up versions of the ancestral-type eggs of O. fasciata. The relationship between lipid and protein content and egg volume conformed to the relationship previously established for echinoderm eggs. Surprisingly, total lipid and protein data for the eggs of O. schayeri grouped with data for the eggs of planktotrophic echinoderms. The eggs of O. schayeri are small compared with those of other echinoderms with lecithotrophic development, and their energetic contents may approach the minimum provisions necessary to permit development without feeding.     

Developmental fate of the yolk protein lipovitellin in embryos and larvae of winter flounder, Pleuronectes americanus.

The developmental fate of the vitellogenin-derived yolk protein, lipovitellin (Lv), was investigated in winter flounder embryos and yolk-sac larvae. Since Lv is present as only one major polypeptide in ovulated winter flounder eggs, unlike the multiple yolk polypeptides found in the mature eggs of most teleosts, this system is presented as a simpler model of yolk protein structure and utilization during teleostean development. Winter flounder Lv is cleaved during embryogenesis from a 94 kD polypeptide at fertilization to 67 kD and 26 kD polypeptides at hatching. The rate of this proteolytic processing is slow during early embryonic development, but enters a more rapid phase between days 8 and 12 post-fertilization in embryos reared at 4-5 degrees C, and approaches 50% completion at day 10. Lv processing is essentially complete 3 days before hatching; nevertheless, major degradation of the Lv peptide by the developing winter flounder does not occur until after hatching. The Stokes radius of Lv changes only moderately following processing, from 4.50 nm in unfertilized eggs to 4.19 nm in late embryos and newly hatched larvae, whereas the processed Lv retains its heat stability relative to other yolk polypeptides. Nearly 50% of its lipid content, however, is released from the Lv particle during embryogenesis, concomitant with cleavage of the Lv 94 kD polypeptide. Lv processing may thus render a portion of the yolk protein-associated lipid more accessible to the developing embryo, whereas other yolk components are retained for later use by the winter flounder larva. Alternately, removal of lipid may lead to proteolytic vulnerability of the Lv polypeptide. In either case, only a portion of the lipid moiety of the Lv particle appears to play a significant nutritive role for the embryo, whereas its protein component is reserved for larval use. J. Exp. Zool. 284:686-695, 1999.     

Development of the hyaline layer around the planktonic embryos and larvae of the asteroid Patiriella calcar and the presence of associated bacteria

Summary

The hyaline layer (HL) around the embryos and larvae of Patiriella calcar is examined by transmission electron microscopy. P. calcar hatches at the gastrula stage and develops through a lecithotrophic planktonic brachiolaria. The hyaline layer of unhatched P. calcar is poorly developed and is comprised of wispy fibrils scattered among the epithelial microvilli. Fibrils are also occasionally seen associated with the inner surface of the fertilization envelope. By the hatched gastrula stage, the hyaline layer is organized into three strata: the intervillous layer, the supporting layer and the coarse outer meshwork layer. Seven-day-old brachiolaria also have a hyaline layer comprised of three strata. In these larvae the supporting layer elevates away from the epithelial surface due to the tuft-like organization of the underlying microvilli. This results in the formation of local outpockets giving the surface of the HL a lobed appearance. Bacteria are occassionally seen in the intervillous layer, particularly in association with the outpockets. These bacteria are phagocytosed by the epithelial cells and, in larvae that have bacteria, may play an augmentive role in larval nutrition. The structure of the hyaline layer of P. calcar is compared with that of the hyaline layer of other Patiriella species to determine if it is more similar to the external coats around its planktonic (P. regularis) or benthic (P. exigua) developing congeners. The comparison shows that the hyaline layer of P. calcar is virtually identical to that of P. regularis, a similarity that may reflect the pelagic life histories of these species.     

Reproduction and development in a vermetid gastropod, Vermetus triquetrus

Abstract. We report on a study of reproduction and development in the Mediterranean vermetid gastropod Vermetus triquetrus from the SE coast of Spain. It is a gonochoristic species. The egg capsules are attached to the inside of the shell, and females brood up to 22 capsules simultaneously (more often 4–10). The capsules hold 10–61 eggs or embryos; the uncleaved eggs are yolk-rich, with a mean diameter of 377.3 μm. A distinct polar lobe occurs during the first cleavage, and blastomere D has discernible qualities after the 4-cell stage. The formation of the mesentoblast 4d occurs at the transition from the 24-cell stage to the 25-cell stage. Gastrulation begins after the 36-cell stage. Internal yolk is the major source of nutrition for the encapsulated embryos, but some nurse eggs (∼ 12%) and some sibling larvae are also ingested by the developing embryos. Hatching occurs during the swimming/crawling pediveliger stage, and metamorphosis is completed outside the capsules soon after hatching. Hence, larval development in Vermetus triquetrus is lecithotrophic intracapsular, with a short free-swimming/crawling phase.     

Evolution of marine invertebrate reproductive patterns

A simple model of the evolution of reproductive patterns in marine benthic invertebrates is presented. The aim is to discuss the dichotomous distribution of forms into those which produce a large number of small eggs with planktotrophic development, and those which produce a small number of large eggs with direct or lecithotrophic development. The fecundity of adult individuals is assumed to be inversely proportional to egg size, and the mortality of planktonic larvae is assumed to be density independent and size dependent. The growth of planktonic larvae is assumed to be sigmoid with metamorphosis occurring at a given size. The model concludes that there are at most two evolutionarily stable egg sizes. Depending on larval growth rate and death rate, the metamorphosis size, a smaller egg size, or both may be evolutionarily stable. The predictions of the model are compared to patterns observed in nature. Illustrative data are supplied mainly from prosobranch molluscs.     

Effects of egg size on the development time of non-feeding larvae

The evolution of egg size in marine invertebrates remains a topic of central importance for life-history biologists, and the pioneering work of Vance has strongly influenced our current views. Vance's model and most models developed since have assumed that increases in egg size result in an increase in the prefeeding period of marine invertebrate larvae. For lecithotrophic species, this means that the entire development period should be correlated with egg size. Despite the importance of this assumption, it has not been tested at the appropriate scale-within species. We investigated the effects of egg size on development time for three lecithotrophic species from two phyla: the ascidians Phallusia obesa and Ciona intestinalis, and the echinoid Heliocidaris erythrogramma. We found that within individual broods of eggs, larger eggs took longer than smaller eggs to develop or become metamorphically competent larvae. It has long been recognized that producing larger eggs decreases fecundity, but our results show that increasing egg size also carries the extra cost of an extended planktonic period during which mortality can occur. The substantial variation in egg sizes observed within broods may represent a bet-hedging strategy by which offspring with variable dispersal potentials are produced.