DEVELOPMENT OF THE SEA-STAR, ASTERINA BATHERI GOTO

Using natural spawning and artificial fertilization, the entire process of development from eggs to juveniles was observed in the sea-star, Asterina batheri Goto.
The breeding season of this animal in Tsukumo Bay and Toyama Bay is estimated to be late summer. The spawned eggs are approximately 430 μm in diameter and float near the surface of sea water. They develop, through a wrinkled blastula stage by holoblastic. radial cleavage, into a pear-shaped brachiolaria bearing 3 blunt brachiolar arms. Metamorphosis takes place while the brachiolariae are swimming. Ten days after fertilization, metamorphosis is complete; the resulting juveniles are about 800 μm in diameter and colored pale brown with a green tint. They bear 2 pairs of tube-feet and a terminal tentacle in each arm.
Development of this species is thus of the direct type, and very similar in every respect to that of Asterina coronata japonica , which is closely related to the present species.     

Evaluation of the attachment strength of individuals of Asterina gibbosa (Asteroidea, Echinodermata) during the perimetamorphic period

A turbulent channel flow apparatus was used to determine the adhesion strength of the three perimetamorphic stages of the asteroid Asterina gibbosa, i.e. the brachiolaria larvae, the metamorphic individuals and the juveniles. The mean critical wall shear stresses (wall shear stress required to dislodge 50% of the attached individuals) necessary to detach larvae attached by the brachiolar arms (1.2 Pa) and juveniles attached by the tube feet (7.1 Pa) were one order of magnitude lower than the stress required to dislodge metamorphic individuals attached by the adhesive disc (41 Pa). This variability in adhesion strength reflects differences in the functioning of the adhesive organs for these different life stages of sea stars. Brachiolar arms and tube feet function as temporary adhesion organs, allowing repetitive cycles of attachment to and detachment from the substratum, whereas the adhesive disc is used only once, at the onset of metamorphosis, and is responsible for the strong attachment of the metamorphic individual, which can be described as permanent adhesion. The results confirm that the turbulent water channel apparatus is a powerful tool to investigate the adhesion mechanisms of minute organisms.     

Evaluation of the attachment strength of individuals of Asterina gibbosa (Asteroidea,Echinodermata) during the perimetamorphic period

Abstract

A turbulent channel flow apparatus was used to determine the adhesion strength of the three perimetamorphic stages of the asteroid Asterina gibbosa, i.e. the brachiolaria larvae, the metamorphic individuals and the juveniles. The mean critical wall shear stresses (wall shear stress required to dislodge 50% of the attached individuals) necessary to detach larvae attached by the brachiolar arms (1.2 Pa) and juveniles attached by the tube feet (7.1 Pa) were one order of magnitude lower than the stress required to dislodge metamorphic individuals attached by the adhesive disc (41 Pa). This variability in adhesion strength reflects differences in the functioning of the adhesive organs for these different life stages of sea stars. Brachiolar arms and tube feet function as temporary adhesion organs, allowing repetitive cycles of attachment to and detachment from the substratum, whereas the adhesive disc is used only once, at the onset of metamorphosis, and is responsible for the strong attachment of the metamorphic individual, which can be described as permanent adhesion. The results confirm that the turbulent water channel apparatus is a powerful tool to investigate the adhesion mechanisms of minute organisms.     

Development and metamorphosis of the sea-star, Astropecten scoparius Valenciennes.

1. Astropecten scoparius develops to a bipinnaria with simple ciliary bands and short bipinnari arms through a wrinkled blastula by holoblastic, radial cleavage. 2. About seven days after insemination, the posterior portion of the bipinnaria becomes swollen and fine spicules appear on it, while the anterior portion, the stalk, remains unchanged. 3. Metamorphosis takes place gradually at the posterior portion, while the metamorphosing bipinnaria is pelagic. Two weeks after insemination, the stalk rapidly shrinks and the larva sinks to the bottom. 4. About 18 days after insemination, the juvenile completes metamorphois with the opening of the mouth. The newly metamorphosed juvenile is 600 mu in diameter and each arm bears two pairs of the tube-feet, each having a sucker at the tip, and one terminal tentacle with red eye-spot. 5. The aboral skeletal system of the juvenile immediately after metamorphosis is composed of one central, one madreporic, ten radial and interradial plates, in addition to five terminal plates on the arms. 6. The juveniles smaller than about one cm in R do not bear some of the diagnostic features in this species. 7. A characteristic feature of the development of Astropecten, i.e., the lack of a brachiolaria stage, is stressed. The term "nonbrachiolarian type" is tentatively proposed to distinguish the development of Astropecten and Luidia, which do not pass through a brachiolaria stage, from the usual indirect type of development.     

Larval survival and growth of Arbacia punctulata (Echinodermata: Echinoidea) fed with five micro-algae at two salinities

Fertilized eggs from an spontaneously spawn of thirty sexually mature sea urchins (Arbacia punctulata) were incubated to complete embryonic development. The echinopluteus larvae (3 ind/ml) were distributed into 50 plastic containers (25 containers at 30 psu and 25 containers at 40 psu) and fed on Tetraselmis chuii, Nannochloropsis oculata, Isochrysis galbana, Chaetoceros gracilis and C. calcitrans under a natural photoperiod. The water of the containers was partially renewed (75%) everyday. Larval anatomic development aspects, daily survival and growth were determined. The growth was determined through postoral arms and body length measurement, and body diameter of twelve larvae during metamorphosis. During the planktonic larval phase, only the I. galbana diet produced similar results for both salinities. The relative growth of larvae was isometric (I) for larvae fed on I. galbana at two salinities and positive allometric for those fed on C. gracilis and C. calcitrans at both salinities. In this study A. punctulata started metamorphosis at day 14 and was completed 30 days after fecundation. Significant differences were detected in post-settlement body growth between the two salinities (F = 23.58, p < 0.05): growth was better for larvae at 30 psu (final body diameter was 3.14 +/- 0.44 mm). The final rate of planktonic larvae was highest with I. galbana (58.33%). For juveniles the rate was 6.48% for those fed on C. gracilis (40 psu in both larvae and juveniles). We recommend the use of this diet and 40 psu for survival or 30 psu for growth.     

Reproduction and development of the conspicuously dimorphic brittle star Ophiodaphne formata (Ophiuroidea)

Ophiodaphne formata is a conspicuously dimorphic ophiuroid; the disk diameters are approximately 1 mm for males and 5 mm for females. The dwarf male clings to the larger female, with the oral surfaces and bursae of the paired ophiuroids closely appressed. Moreover, the female of each pair adheres aborally to the oral surface of a host sand dollar, Astriclypeus manni. Spawning and external fertilization occur in August, at Tsuruga Bay, Sea of Japan. Development of the dimorphic brittle star O. formata is described for the first time, from spawning through metamorphosis, with special attention to the formation of the skeletal system and the external morphology of early juveniles. Fertilized eggs are about 90 microm in diameter, pale pink, and negatively buoyant. The embryos undergo equal, total, and radial cleavage, and the larval skeleton first forms as a pair of tetraradiate spicules. Larval development proceeds to an 8-armed planktotrophic ophiopluteus, with skeletal elements that consist of a body rod and two recurrent rods. Three weeks after fertilization, all the pluteal arms, except for the postero-lateral arms, are absorbed, and the metamorphosing larvae sink to the bottom. Metamorphosis is completed 21.5 days after fertilization, and the resulting juvenile is pentagonal and approximately 270 microm in diameter. The smallest specimen (480 microm in disk diameter) collected by field sampling exhibited male features on the skeletal plates of the jaw and disk. Sexual dimorphism, the peculiar pairing behavior, and the close relationship with the host sand dollar may have evolved as distinct reproductive characteristics in this ophiuroid with its typical ophiopluteus larvae.     

Adaptations to benthic development: functional morphology of the attachment complex of the brachiolaria larva in the sea star Asterina gibbosa

The asteroid Asterina gibbosa lives all its life in close relation to the sea bottom. Indeed, this sea star possesses an entirely benthic, lecithotrophic development. The embryos adhere to the substratum due to particular properties of their jelly coat, and hatching occurs directly at the brachiolaria stage. Brachiolariae have a hypertrophied, bilobed attachment complex comprising two asymmetrical brachiolar arms and a central adhesive disc. This study aims at describing the ultrastructure of the attachment complex and possible adaptations, at the cellular level, to benthic development. Immediately after hatching, early brachiolariae attach by the arms. All along the anterior side of each arm, the epidermis encloses several cell types, such as secretory cells of two types (A and B), support cells, and sensory cells. Like their equivalents in planktotrophic larvae, type A and B secretory cells are presumably involved in a duo-glandular system in which the former are adhesive and the latter de-adhesive in function. Unlike what is observed in planktotrophic larvae, the sensory cells are unspecialized and presumably not involved in substratum testing. During the larval period, the brachiolar arms progressively increase in size and the adhesive disc becomes more prominent. At the onset of metamorphosis, brachiolariae cement themselves strongly to the substratum with the adhesive disc. The disc contains two main cell types, support cells and secretory cells, the latter being responsible for the cement release. During this metamorphosis, the brachiolar arms regress while post-metamorphic structures grow considerably, especially the tube feet, which take over the role of attachment to the substratum. The end of this period corresponds to the complete regression of the external larval structures, which also coincides with the opening of the mouth. This sequence of stages, each possessing its own adhesive strategy, is common to all asteroid species having a benthic development. In A. gibbosa, morphological adaptations to this mode of development include the hypertrophic growth of the attachment complex, its bilobed shape forming an almost completely adhesive sole, and the regression of the sensory equipment.     

Larval morphometrics and influence of adults on settlement in the gregarious ophiuroid Ophiothrix fragilis (Echinodermata)

The development of Ophiothrix fragilis was documented using light microscopy, and the allometry of larval growth was quantified. Larval development to the suspended juvenile stage took 21 days under conditions that were probably optimal compared to those in the plankton. Larval shape changed through development as the larval body and arms grew. Growth of the posterolateral larval arms was continuous throughout development, even during metamorphosis when the larva became endotrophic. During this period, these larval arms function as locomotory organs, and their continuous growth is probably essential to support the juvenile as it increases in density through development of its calcareous plates. In induction assays using adult conspecifics, initiation of metamorphosis was spontaneous. Release of the posterolateral arms was induced by the presence of adults. This response is likely to enhance a juvenile's chance of recruiting to a suitable habitat in the Ophiothrix fragilis beds of the North Sea.     

Juvenile production of the red sea urchin Strongylocentrotus franciscanus (Echinodermata: Echinoidea) in Baja California, Mexico

The red sea urchin Strongylocentrotusfranciscanus (Agassiz 1863) is harvested commercially in Baja California, Mexico, since 1970; however, in the last ten years the capture per unit effort (CPUE) has decreased from 310 kg/fishing unit/day to 120 kg/fishing unit/day. For this reason, actions were taken to develop a culture technology allowing massive production of juveniles for re-stocking natural populations or for growing them commercially. We summarize some of the basic studies and main achievements in this effort. In Baja California, considerably faster larval development (approximately 21 days) has been attained than in the US northwest coast (62 days). Spawning of red sea urchins was routinely induced with KCI while egg fertilization was performed using a 100,000-sperm/ml solution. Six microalgae species were tested and Rhodomonas sp. produced the best larval development. The mean survival rate at the end of the larval period was 25%, but results varied widely with bactch. From the feed ratios tested, best results were obtained using 7000 cel/ml during the first week of larval development, followed by 10,000 cel/ml during the second and 15,000 cel/ml during the third week. KCl proved the most consistent metamorphic inducer, regularly yielding metamorphosis percentages higher than 90%. Metamorphosis was considered complete when the functional jaw that juveniles use for first benthic feeding appeared (as soon as 20 days after induction). With this method several thousands of red sea urchin juveniles were produced. They reached up to 1.5 mm in size during the first 50 days of culture after metamorphosis, showing the great potential for mass production of this species in the laboratory.     

CHANGES IN ACTIVITIES OF CREATINE KINASE, ARGININE KINASE AND THEIR MULTIENZYME FORMS DURING EMBRYONIC AND LARVAL DEVELOPMENT OF SEA URCHINS

The presence and the changes of CPK and APK have been studied during larval development through metamorphosing of Hemicentrotus pulcherrimus, Anthocidaris crassispina and Pseudo-centrotus depressus . While no CPK activity was found in the unfertilized eggs and the embryos of early developmental stages, APK was quite active throughout these stages. At the late 8-armed pluteus stage just prior to metamorphosis, CPK first became active. Electrophoretically this CPK was identical with one of three CPK forms of sperm, tube feet and esophagus but not with two CPK forms of lantern muscle. APK in the unfertilized eggs and early embryos was electrophoretically separated into two distinct molecular forms, one of which disappeared during the late larval stages. The persisting form of larval APK was identical with a single APK form present in the adult muscular tissues.     

Adhesive papillae on the brachiolar arms of brachiolaria larvae in two starfishes, Asterina pectinifera and Asterias amurensis, are sensors for metamorphic inducing factor(s)

It has been hypothesized by Barker that starfish brachiolaria larvae initiate metamorphosis by sensing of metamorphic inducing factor(s) with neural cells within the adhesive papillae on their brachiolar arms. We present evidence supporting Barker's hypothesis using brachiolaria larvae of the two species, Asterina pectinifera and Asterias amurensis. Brachiolaria larvae of these two species underwent metamorphosis in response to pebbles from aquaria in which adults were kept. Time-lapse analysis of A. pectinifera indicated that the pebbles were explored with adhesive papillae prior to establishment of a stable attachment for metamorphosis. Microsurgical dissections, which removed adhesive papillae, resulted in failure of the brachiolaria larvae to respond to the pebbles, but other organs such as the lateral ganglia, the oral ganglion, the adhesive disk or the adult rudiment were not required. Immunohistochemical analysis with a neuron-specific monoclonal antibody and transmission electron microscopy revealed that the adhesive papillae contained neural cells that project their processes towards the external surface of the adhesive papillae and they therefore qualify as sensory neural cells.     

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.     

The larvae of Diadema setosum (Leske, 1778) (Camarodonta: Diadematidae) from South China Sea

Abstract

Diadema setosum (Leske, 1778) develops from small isolecithal eggs with a diameter of 84 ± 3 μm. Embryonic development took about 6.5–7 h and finished when a blastula left the fertilization envelope and became a larva. At this stage, the first pigment cells had appeared. At 23 h a prism developed; at 44 h a pluteus with one pair of arms had appeared; at 45 h of development plutei had two pairs of arms. The pigment cells colour the pluteus of D. setosum dark red. When 20-day-old larvae were mechanically stimulated, they flared their arms which may be defensive behaviour. During further development, the post oral arms of plutei grew to 1900 μm or more. Metamorphosis took place at about 40–45 days. At this time, five primary ambulacral podia were visible within the larval body. The duration of metamorphosis from the moment of larval settlement until the juvenile sea urchins began to move along the bottom was 40–60 min. The diameter of the test of the newly metamorphosed juvenile sea urchins was about 500 μm.     

Short-term fluctuation in salinity promotes rapid larval development and metamorphosis in Dendraster excentricus

The effect of constant and fluctuating salinity on larval development and metamorphosis of the sand dollar Dendraster excentricus was investigated in the laboratory. Sand dollar larvae at different stages of development were kept either at 32‰ (controls), exposed to constant low salinity (22‰) throughout development, or exposed to fluctuating salinity (i.e. transferring larvae from 32‰ to 22‰ for 7 days then back to 32‰ for the rest of their development). Larvae exposed to constant low salinity were significantly smaller but developed all larval arms at a slower rate than larvae in all other treatments. Larvae exposed to fluctuating salinity recovered and developed significantly longer larval arms and bigger rudiments than larvae kept at constant low salinity. Larvae exposed to fluctuating salinity produced more juveniles than larvae at constant high salinity (32‰), while those at constant low salinity produced few or no juveniles. Four-arm larvae exposed to fluctuating salinity produced significantly more juveniles than six-arm larvae exposed to the same treatment. Transferring competent 8-arm larvae from 31‰ to 15‰ for 2 days then back to 31‰, induced metamorphosis with juvenile production being significantly higher than for those kept at a constant salinity of 20, 25 and 31‰. This study indicates that a short-term decrease in salinity might induce metamorphosis for this species.     

Peptidergic and serotonergic immunoreactivity in the metamorphosing ophiopluteus of Ophiactis resiliens (Echinodermata, Ophiuroidea)

Abstract. Antibodies against the echinoderm-specific neuropeptide S1 and against 5HT were used to examine the fate of the larval nervous system during metamorphosis in the ophiuroid Ophiactis resiliens . In contrast to most echinoderms, the onset of peptidergic and serotonergic expression was delayed to the advanced ophiopluteus stage, in particular for 5HT. In advanced ophioplutei, peptidergic immunoreactivity was located in simple fibres associated with the ciliated bands, a stomach nerve ring, and cells along the antero-lateral arms. 5HT immunoreactivity was concentrated in 2 oral ganglia in the adoral projections, located at the posterior rim of the mouth. Clusters of 5HT-positive cells were also found along the antero-lateral arms. The ophiopluteus lacked a serotonergic (or peptidergic) anterior ganglion. In echinoids, holothuroids, and crinoids, anterior ganglia are thought to have a sensory role in settlement and metamorphosis. Given that ophioplutei metamorphose in the plankton and that larval structures degenerate before settlement, the absence of apical ganglia correlates with the lack of a functional role for larval structures in substrate selection and settlement. Although most of the larval nervous system degenerated during metamorphosis, the adoral projections and associated oral ganglia appeared to be incorporated into the juvenile mouth, suggesting a potential role for larval neurons in contributing to oral neuronal structures in the adult. S1-positive neurons and fibres in the rudiment developed de novo and in parallel with development of the epineural canal. This structure gives rise to the primordia of the adult circumoral nerve ring and radial nerves, indicating that differentiation of the adult nervous system begins in the early stages of metamorphosis.     

The combined effect of temperature and salinity on development of the sea star Asterina pectinifera

The effect of various combinations of temperature, which increases from 14°C up to 25°C in the summer season, and salinity, which varies from 34 to 12‰ in the early stages of development of the sea star Asterina (= Patiria) pectinifera (Müller et Troschel) from Vostok Bay, Sea of Japan, was studied. The most vulnerable process in the early ontogenesis of A. pectinifera is its embryonal development, which is completed successfully within narrow ranges of temperature (20–22°C) and salinity (34–26‰). The ability of gametes to fertilize was retained in wider ranges of temperature and salinity. The dipleurula was the most responsive of the larval stages; the resistance of blastula, bipinnaria, and brachiolaria at ages of 12.5 and 15.5 days was almost the same for fluctuations of temperature from 14 up to 25°C and salinity from 34 to 18 and 16‰ Settling of the brachiolaria and completion of metamorphosis were also responsive to variations in the environmental factors. Settling of the larvae was faster at 17°C without illumination (on the 22nd–24th days of development) than at 22°C with the day-night mode (27th–28th day of development). The lack of light apparently had a positive effect on the settling of the brachiolaria.     

The importance of larval eyes in the polychaete Capitella teleta: effects of larval eye deletion on formation of the adult eye

In many marine invertebrates with biphasic life cycles, juvenile/adult traits begin to develop before metamorphosis. For structures that are present at multiple developmental stages, but have distinct larval and adult forms, it is unclear whether larval and adult structures have shared or distinct developmental origins. In this study, we examine the relationship between the larval and adult eyes in the polychaete Capitella teleta. In addition, we describe a novel marker for larval and juvenile photoreceptor cells. Infrared laser deletion of individual micromeres in early embryos suggests that the same micromeres at the eight‐cell stage that are specified to generate the larval eyes also form the adult eyes. Direct deletion of the larval eye, including the pigment cell and the corresponding photoreceptor cell, resulted in a lack of shading pigment cells in juveniles and adults, demonstrating that this structure does not regenerate. However, a sensory photoreceptor cell was present in juveniles following direct larval eye deletions, indicating that larval and adult photoreceptors are separate cells. We propose that the formation of the adult eye in juveniles of C. teleta requires the presence of the pigment cell of the larval eye, but the adult photoreceptor is either recruited from adjacent neural tissue or arises de novo after metamorphosis. These results are different from the development and spatial orientation of larval and adult eyes found in other polychaetes, in which two scenarios have been proposed: larval eyes persist and function as adult eyes; or, distinct pigmented adult eyes begin developing separately from larval eyes prior to metamorphosis.     

An extraordinarily long larval duration of 4.5 years from hatching to metamorphosis for teleplanic veligers of Fusitriton oregonensis

Veliger larvae of the NE Pacific snail Fusitriton oregonensis were reared in culture for 4.5 to 4.6 years from hatching to metamorphosis and through postlarval growth to reproduction. Larval shells grew in length from 0.20 to 3.9 mm. Late veligers grew slowly, but shell sizes increased even in the 4th and 5th years. Widths of larval shells at late stages equaled or exceeded those of the protoconchs of two juveniles from the field. Cultured larvae did not metamorphose until presented with subtidal rocks and associated biota. There was no indication of larval senescence: the first 2 years of postmetamorphic shell growth were slightly faster, and time from metamorphosis to first reproduction (3.3 years) was slightly less than for an individual that had developed to metamorphic competence in the plankton. A 4.5-year larval phase exceeds previous estimates for teleplanic larval durations and greatly exceeds estimates of the time for transport across oceans. This extraordinarily long larval period may exceed the usual duration in nature but shows that larval periods can be much longer than previously suspected without complete stasis in growth and with little if any loss of viability.     

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.