Environmental transmission of a sulfur-oxidizing bacterial gill endosymbiont in the tropical lucinid bivalve Codakia orbicularis.

Codakia orbicularis is a large tropical member of the bivalve mollusk family Lucinidae which inhabits shallow-water sea-grass beds (Thalassia testudinum environment) and harbors sulfur-oxidixing endosymbiotic bacteria within bacteriocytes of its gill filaments. When a C. orbicularis-specific 16S rDNA (DNA encoding rRNA) primer is used with a bacterium-specific 16S rDNA reverse primer in amplifications by PCR, the primer set was unsuccessful in amplifying symbiont DNA targets from ovaries, eggs, veligers, and metamorphosed juveniles (600 microns to 1 mm in shell length) cultivated in sterile sand, whereas successful amplifications were obtained from gill tissue of adult specimens and from metamorphosed juveniles (600 microns to 1 mm in shell length) cultivated in unsterilized sea-grass bed sand. To ascertain the presence of the symbiont target in juveniles, restriction fragment length polymorphism analysis, Southern blotting, and transmission electron microscopy were used. Specific hybridizations and observation of endosymbiotic bacteria in the gills of numerous juveniles cultivated in unsterilized sea-grass bed sand showed that the sulfur-oxidizing endosymbionts of C. orbicularis are environmentally transmitted to the new generation after larval metamorphosis.     

The biology of the Northeastern Pacific Turridae. V. Demersal development,synchronous settlement and other aspects of the larval biology of Oenopota levidensis

Summary

The larval development and metamorphosis of a turrid gastropod is described for the first time. This snail, Oenopota levidensis, is typical of the boreal genus Oenopota, which has over 150 described species. Development to a veliger occurs within a lenticular capsule in about 50 days. The capsules hatch to release veligers which swim for less than a week. The remainder of their planktotrophic larval period is spent demersally. Demersal veligers assumed one of two characteristic postures; they remain on the bottom with the velum either extended laterally or folded over the shell. These demersal veligers continue development and metamorphose after another 25 days. The majority of the veligers in the 55 cultures examined metamorphosed and settled within a 96-h period, even though their oviposition occurred over a 47-day period. Potential selective forces leading to this synchronous settlement are proposed.     

REPRODUCTIVE BIOLOGY OF THE SESSILE GASTROPOD VERMICULARIA SPIRATA (CERITHIOIDEA: TURRITELLIDAE)

The reproductive and developmental biology of the sessile gastropodVermicularia spirata (Philippi, 1836), collected from the FloridaKeys, was studied from living and preserved material. Individualsof this species attach themselves to a variety of substrata,but were mainly found embedded in the white sponge Geodia gibberosa.Pallial reproductive structures of both sexes of V. spiratawere found greatly to resemble those of Turritella communis,a free-living member of the same family. In both species, animalsof both sexes have open pallial ducts formed by two wide, recurvedlaminae. In the female of V. spirata, the laminae of the pallialoviduct serve as a capsule gland; a pair of side pockets representa fertilization pouch (possibly doubling as a copulatory bursa)and a seminal receptacle. The functional significance of theextensive, open, pallial sperm duct is not yet clear. Vermiculariaspirata is a protandrous hermaphrodite, and small males arefree-living; they become attached at about the time they undergosex reversal. Fertilization is probably brought about by malescrawling close to the apertures of the large, sessile femalesbefore releasing sperm. Egg capsules are brooded in the females'mantle cavities. Ova of about 300 µm diameter give riseto large (about 600 µm long) swimming-crawling veligerlarvae with shells of two and a half whorls. The veligers arecapable of metamorphosis at the time of hatching, but siblingsfrom one brood metamorphosed over a two-week period in the laboratory.Juvenile snails grew rapidly by filtering phytoplankton addedto their culture water. The life history of V. spirata is welladapted to assure fertilization and recruitment in a speciesotherwise committed to a sessile, filter-feeding existence. (Received 3 February 1989; accepted 19 April 1989)     

OBSERVATIONS ON THE GROWTH, REPRODUCTION AND FEEDING OF THE NUDIBRANCH ARMINA TIGRINA

One specimen of the sand-burrowing nudibranch Armina tigrinaRafinesque was collected from South Carolina in June. The specimendeposited a single egg mass of approximately 6500 white eggswhich developed into lecithotrophic veligers in 8 days at 23°C.Of the veligers which metamorphosed, 9 lived 4–5.5 months(i.e. the life cycle was subannual). Eight individuals reachedsexual maturity in about 80 days. Copulation began at a bodylength of 24 mm and oviposition at 28 mm. During the 1.5 monthegg-laying period, each individual laid 2–4 wavy egg masseswith 2000–7000 eggs per mass. Death followed oviposition.Average growth rate of fed and starved pre-ovipositional nudibranchswas 3.4% and 0.9% per day respectively. Growth rate of ovipositingspecimens was 0.6% or less per day. Based on average feedingrates, each nudibranch consumed approximately 1.6 g damp weightof Renilla reniformis (one small colony) between metamorphosisand egg laying and 6.1 g damp weight (about two average colonies)from egg laying to death. Feeding efficiency is presumably increasedby interlocking and abutting radular teeth. Egg diameters reportedfor Armina tigrina from South Carolina and Florida were 199µm and 82 µm respectively. This difference suggeststhe existence of two species of Armina or ne species with twogeographically separated developmental types. Current address: Marine Science Institute, Northeastern University,Nahant, Massachusetts 01908. U.S.A. (Received 10 April 1980;     

SPAWNING AND LARVAL DEVELOPMENT OF CLYPEOMORUS CLYPEOMORUS JOUSSEAUME 1888 IN WALTAIR COAST

Clustering and pairing of the two sexes of the prosobranch Clypeomorusclypeomorus Jousseaume, 1888 was observed during the spawningperiod. The eggs are released in the form of a thin filamentwhich folds in a definite fashion and forms a ribbon. Thereare two larval stages in development, the trochophore and theveliger. The maximum number of trochophores wasobserved 13 hoursand the maximum number of veligers 18 hours after fertilization.The swimming-crawling stage was also observed. (Received 5 July 1979;     

Reproduction in Halopteris (Sphacelariales)

Oogamy is recorded in five southern species of Halopteris. Ineach the gametangia and asexual sporangia occur in similar sori,although situated on separate plants. The plurilocular antheridiaand the unilocular oogonia occur within one and the aame sorus.In both the dehiscence is apical. In H. congesta fertilization has been observed in cultures.The polarity of the zygote is established by the direction ofthe first-formed wall. Early divisions convert it into a nodulecomposed of small cells. First rhizoids appear and then cylindricalshoots arise from the opposite pole. Sporelings of five NewZealand species of Halopteris have been raised in culture. Theconditions in the culture greatly affected the character ofthe sporelings, the simplest of which at the end of 2 months'growth were only uniseriate filaments. The best developed sporelingshad a compact basal disc with up to four upright shoots showingthe beinnings of branching.     

Gill filament differentiation and experimental colonization by symbiotic bacteria in aposymbiotic juveniles of Codakia orbicularis (Bivalvia: Lucinidae)

Summary

Codakia orbicularis is a tropical lucinid harboring gill endosymbionts which are environmentally transmitted from a free living-symbiont form to the new host generation after metamorphosis. Structural changes occurring in the cellular organization from incomplete gill filaments in young aposymbiotic juveniles to full differentiated gill filaments containing bacterial endosymbionts in reared symbiotic juveniles, were analyzed for juveniles from 250 μm to 2 μm shell-length. Aposymbiotic juveniles possess differentiated gill filaments with ciliated, intermediary, and lateral zones similar to those described in wild juveniles, except for the bacteriocytes which are lacking. Granule cells, which progressively differentiate during the morphogenesis of the gill filament, do not appear as a consequence of symbiosis. Experimental colonization of aposymbiotic juveniles by the free-living symbiont form has been obtained through the addition of unsterilized sand collected from the natural habitat of C. orbicularis. Two days after exposure to crude sand, symbiosis-competent bacteria enter by endocytosis at the apical pole of undifferentiated cells which progressively differentiate into classical bacteriocytes similar to those found in the adult gill filaments. Undifferentiated cells of aposymbiotic gill filaments remain receptive to bacteria several months after metamorphosis, and become bacteriocytes when aposymbiotic juveniles get contact with the symbiont free-living form. Therefore, the environmental transmission of symbionts does not appear to be restrained to a defined period of time during post-larval development in C. orbicularis.     

Morphology and development of a new species of Balanoglossus (Hemichordata: Enteropneusta: Ptychoderidae) from Shimoda, Japan

The morphology and development of a new species of the genus Balanoglossus belonging to the family Ptychoderidae are described in detail. This acorn worm was collected from the sandy seashore in the cove near Shimoda Marine Research Center, University of Tsukuba (Shimoda, Shizuoka Prefecture, Japan). This acorn worm is easily distinguished from other balanoglossids by a characteristic hepatic region. There are two kinds of hepatic saccules: large, dark-colored saccules in the anterior region and small, light-colored saccules in the posterior region. Between the two subregions of the hepatic region, there is a small region that has no or tiny saccules. This species does not form distinct burrows or mounds of casts. The breeding season is in winter. The process of embryogenesis from fertilization to metamorphosis was observed. A shift in seawater temperature from about 13 degrees C to about 9 degrees C induced gamete release. Two days after fertilization, embryos hatched and became typical feeding tornaria larvae. Two months after fertilization these larvae metamorphosed into juveniles and began their benthic life.     

GLOCHIDIA OF THE FRESHWATER MUSSEL LAMPSILIS OVERWINTERING ON FISH HOSTS

Largemouth Bass were infected with glochidia of the freshwatermussel Lampsilis cardium. Three fishes each were held at 4.5,10, and 15.5°C; five fish were held at 21°C. By 64 days,metamorphosed juveniles were found in the 15.5 and 21°Ctrials but not in the 5.5 and 10°C trials, indicating thatthe lower threshold temperature for metamorphosis was between10 and 15.5°C for the duration. In a second experiment,Largemouth Bass were infected with glochidia of L. cardium andheld at 10°C. A sample of fishes was removed monthly andbrought to 21°C. Numbers of glochidia that metamorphosedafter being warmed were compared to the number that metamorphosedwithout warming. The percentage that metamorphosed after warmingdecreased linearly with time. At one month, 100% of the glochidiametamorphosed after warming. This decreased to 80% by two months,to 30% by four months and 3% by six months. Although this post-warmingpercentage decreased with time, the total percentage of metamorphosedjuveniles (at all temperatures) was not correlated with time.Controls kept at 21°C required three weeks to reach peakmetamorphosis, but test subjects subjected to 10°C requiredless than nine days to metamorphose once warmed. Many overwinteringglochidia therefore complete a portion of their developmenton the host at winter temperatures, but stop short of excystment.Some glochidia metamorphosed without being warmed, but thisphenomenon is not understood. This study confirms that glochidiamay overwinter on hosts, with some glochidia persisting formore than six months before metamorphosing when warmer conditionsreturn. (Received 29 September 1998; accepted 18 January 1999)     

EXTRA-CAPSULAR YOLK BODIES IN THE EGG MASSES OF SOME TROPICAL OPISTHOBRANCHIA

Seventeen species of opisthobranch molluscs from Enewetak, MarshallIslands were found to deposit bodies of yolk within their gelatinousegg masses external to the capsules which surround the ova.These observations bring the total number of opisthobranch speciesin which extra-capsular yolk is known to 26. This study reviewsprevious reports of extra-capsular yolk and contributes newdata on the egg masses and developmental characteristics ofspecies in which it is known to occur. The various types ofyolk body found are detailed and categorized, and original observationson the deposition of yolk bodies and their fate during, andsubsequent to embryonic development presented. To date, extra-capsular yolk bodies have been found only withinthe egg masses of species of Chromodoris and Cadlinella (Nudibranchia:Chromodorididae), Elysia (Sacoglossa: Elysiidae), and Bosellia(Sacoglossa: Polybranchiidae). Three types of yolk body arerecognized: (1) cap-like yolk bodies associated with individualcapsules, (2) discrete yolk bodies strewn throughout the eggmass, and (3) continuous or discontinuous yolk strings. Direct consumption of yolk bodies by newlyhatched veligers ofChromodoris albopunctatus (Garrett) is described. In most otherspecies, the yolk disappears during the course of developmentand is probably of nutritive value to the embryos. The availabledata suggest that chromodorid species which utilize extra-capsularyolk during the course of development produce relatively largerlarvae than species with comparably sized ova that do not. (Received 25 November 1982;     

Development of eggs and larvae of the flounders Rhombosolea tapirina and Ammotretis rostratus (Pisces: Pleuronectidae)

The stages of development of laboratory-reared eggs and larvae of Rhombosolea tapirina and Ammotrelis rostratus are described. They both exhibited á typical pleuronectid pattern of development. At ambient seawater temperature of 11.1–13.8° C R. tapirina eggs hatched 83–93 h after fertilization and larvae metamorphosed c. 65 days later at mean length of 8.83 mm. Hatching of A. rostratus eggs occurred 93–105 h after fertilization and larvae metamorphosed after c. 69 days (mean length 11.21 mm) at 12.7–16.5° C. The two species can be readily separated by their morphology, meristics and pigmentation. In particular, the eggs differ in diameter, only R. tapirina larvae possess a pair of spines in the otic region, and juvenile A. rostratus have only a left pelvic fin.     

Heterochrony, cannibalism, and the evolution of viviparity in Salamandra salamandra

The way in which novelties that lead to macroevolutionary events originate is a major question in evolutionary biology, and one that can be addressed using the fire salamander (Salamandra salamandra) as a model system. It is exceptional among amphibians in displaying intraspecific diversity of reproductive strategies. In S. salamandra, two distinct modes of reproduction co-occur: the common mode, ovoviviparity (females giving birth to many small larvae), and a phylogenetically derived reproductive strategy, viviparity (females producing only a few large, fully metamorphosed juveniles, which are nourished maternally). We examine the relationship between heterochronic modifications of the ontogeny and the evolution of the new reproductive mode in the fire salamander. The in vitro development of embryos of ovoviviparous and viviparous salamanders from fertilization to metamorphosis is compared, highlighting the key events that distinguish the two modes of reproduction. We identify the heterochronic events that, together with the intrauterine cannibalistic behavior, characterize the derived viviparous reproductive strategy. The ways in which evolutionary novelties can arise by modification of developmental programs can be studied in S. salamandra. Moreover, the variation in reproductive modes and the associated variation of sequences of development occur in neighboring, conspecific populations. Thus, S. salamandra is a unique biological system in which evolutionary developmental research questions can be addressed at the level of populations.     

Testing the evolutionary constraints of metamorphosis: The ontogeny of head shape in Triturus newts

In vertebrates with complex, biphasic, life cycles, larvae have a distinct morphology and ecological preferences compared to metamorphosed juveniles and adults. In amphibians, abrupt and rapid metamorphic changes transform aquatic larvae to terrestrial juveniles. The main aim of this study is to test whether, relative to larval stages, metamorphosis (1) resets the pattern of variation between ontogenetic stages and species, (2) constrains intraspecific morphological variability, and (3) similar to the “hour‐glass” model reduces morphological disparity. We explore postembryonic ontogenetic trajectories of head shape (from hatching to completed metamorphosis) of two well‐defined, morphologically distinct Triturus newts species and their F1 hybrids. Variation in head shape is quantified and compared on two levels: dynamic (across ontogenetic stages) and static (at a particular stage). Our results show that the ontogenetic trajectories diverge early during development and continue to diverge throughout larval stages and metamorphosis. The high within‐group variance and the largest disparity level (between‐group variance) characterize the metamorphosed stage. Hence, our results indicate that metamorphosis does not canalize head shape variation generated during larval development and that metamorphosed phenotype is not more constrained relative to larval ones. Therefore, metamorphosis cannot be regarded as a developmental constraint, at least not for salamander head shape.     

Laboratory spawning, larval development, and metamorphosis of the limpets Lottia digitalis and Lottia asmi (Patellogastropoda, Lottiidae)

Abstract. This study describes and compares laboratory spawning, larval development, and metamorphosis in the patellogastropod limpets Lottia digitalis and Lottia asmi. Both species were dioecious and freely spawned their gametes, which were fertilized externally. Eggs from L. digitalis and L. asmi averaged 155 and 134 μm in diameter, respectively. Early cleavage patterns were typical of other patellogastropods. Swimming trochophore larvae had developed ∼ 15 hours after fertilization, and ultimately developed into lecithotrophic veliger larvae that reached metamorphic competence at 5.25–5.5 days after fertilization (13°C). Food particles were frequently visible in the gut of newly metamorphosed individuals one day after settlement, and adult shell growth was typically initiated within 2–4 days of settlement. Small egg size in L. asmi , relative to other eastern Pacific lottiids, may be directly related to the need for high fecundity in this small-bodied species; however, developmental information is available for relatively few lottiid species. Because broadcasting lottiids do not secure egg masses in safe microhabitats for development, this reproductive mode may have been conducive to their ecological radiation into novel habitats.     

西藏真蚋一新种(双翅目：蚋科)

西藏真蚋一新种（双翅目：蚋科）邓成玉,张有植,薛群力,陈汉彬（成都军区卫生防疫队成都６１００６１）（贵阳医学院贵阳５５０００４）１９８９年５月,作者在进行西藏亚东烟类调查时,发现烟属真纳亚属一新种,现记述如卜。新纤细真纳Ｓｉｔｈｄｓ（ＥＭｂｏｄｓｎ们...     

Freezing injury to ovules, pollen and seeds in winter rape

Winter rapeseed (Brassica napus, cv. Samouraï) flowersearly in spring and, under field conditions, short freezingperiods can occur. Unacclimatized plants were freeze-stressed(–3°C for 4 h) at different developmental stages ofbuds, open flowers and seeds. The dissection of pistils from stressed plants showed that freezingresults in shrivelled ovules. We assessed freezing injury onthe basis of per cent of shrivelled ovules: ovule sensitivitybegins early (8 d before anthesis) but increases up to anthesis.Crosspollination of stressed pistils with non-stressed pollenshowed that recording of freeze-injured ovules is a good methodfor early estimation of the effect of stress on seed yields. On the other hand, stress does not reduce the viability of pollen,except when it was applied at the binucleate pollen stage. Useof frozen pollen x nonstressed pistils has little effect onseed yields. Freeze injury on seeds was assessed by seed filling:seeds are very susceptible just after fertilization until 20d after fertilization (DAF). Freezing seems to inhibit seedfilling. A germination test of stressed seeds during their developmentindicated that embryo viability is not affected if the stressoccurs after 35 DAF. As the embryos develop, resistance to stressincreases. Key words: Brassica napus, rapeseed, freeze injury, pollen and ovule, seed filling     

Gill ultrastructure and symbiotic bacteria in Codakia orbicularis (Bivalvia,Lucinidae)

Summary The cellular organization of the gill, which harbors symbiotic bacteria, is described in juveniles and adults of Codakia orbicularis, a large tropical Lucinidae. The ciliary zone is similar in every species of Lucinidae described and includes the large clear cell which has been previously described as an intermediary cell. The intermediary zone is composed of a few narrow unciliated cells, which bind adjacent filaments together and constitute channels through which sea water circulates along the abfrontal part of the filaments. The lateral zone is more complex in C. orbicularis than in other Lucinidae, being composed of four cell types and differentiated into two distinct regions. The bacteriocytes and intercalary cells occupy the outermost bacteriocyte zone, while mucocytes and numerous cells crowded with proteinic, cystine-rich granules constitute the innermost secretory zone which has not been described in other species. The newly described granule cells are considered to be a key factor in the storage and metabolic conversion of sulfur compounds.     

Polyploidy induced by hydrostatic pressure in rainbow trout, Salmo gairdneri Richardson

Triploid rainbow trout were produced by hydrostatic pressure applied to eggs 40 min after fertilization. Treatment for 10 min with or without exposure to 2% ether produced high hatching rates. Nuclear measurements from serial section of 40-day-old fry and from blood smears of 5-month-old juveniles showed that the proportion of triploid individuals was 80–90%. Ether treatment alone did not induce triploidy. Attempts to produce tetraploids by hydrostatic pressure treatment of eggs at 8 h after fertilization failed. Parallel results were also obtained with heat shock.     

Direct development of the brittle star Amphiodia occidentalis (Ophiuroidea, Amphiuridae) from the northeastern Pacific Ocean

Abstract. The highly modified development of the brittle star Amphiodia occidentalis is described from post-fertilization to the juvenile stage. Fertilized eggs are negatively buoyant, ∼190 μm in diameter, surrounded by a thick hyaline layer and a tough fertilization envelope. After gastrulation, embryos flatten into a bilaterally symmetrical disk with a U-shaped ridge surrounding an indented stomodeum on the oral surface. Internally, a ring of ∼22 calcitic ossicles grows at the edge of the disk. Vestigial ophiopluteal structures such as a ciliated band, paired larval spicules, or larval arms are not expressed during development. Although the fertilization envelope disintegrates on day 3, developmental stages remain immotile for five more days until they move with podia. At hatching, five hydrocoelic lobes are evident on the left side of the post-gastrula, and these migrate clockwise around the stomodeum, establishing pentamerous radial symmetry. Central and radial plates originate on the right side and migrate to a dorsocentral location as pentamerous symmetry is established. Development of the juvenile oral skeletal frame follows closely that described by Hendler (1978) for Amphioplus abditus except that A. occidentalis did not form buccal scales. The juvenile mouth opened by day 12. Fifty-five days after fertilization, juveniles had not added their first arm segments, although the first lateral arm plates had appeared. Developmental stages identical to those described here have been found in plankton tows taken in Oregon usually after storms that bring high waves. The unusual development of this species probably occurs in both benthic and pelagic environments.