The ultrastructure of the protonephridial system of Götte's larva of Stylochus mediterraneus (Polycladida, Platyhelminthes)

The protonephridial system of Götte's larva of Stylochus mediterraneus was studied by electron microscopy. There is one protonephridium on each side of the body, formed by one terminal and one canal cell. The terminal filtration apparatus is formed by a single cell (the terminal cell) with several globular processes, the largest of which includes the nucleus. Fingers of cytoplasm (leptotriches) from each process penetrate the lumen surrounding the bundle of cilia and fingers from adjacent processes interdigitate to form a pattern of convoluted slits which constitute the weir. The single canal cell is inserted internally to the terminal cell at the top of the weir and encloses the lumen without a junction. Septate junctions are present between the terminal and canal cells. The lumen of the canal cell is smooth-walled for most of its length and cilia arise and terminate at all levels of the terminal and canal cells. Posterior to the larval mouth opening, the canal cell crosses the epithelium and the lumen ramifies to form the excretory opening. The terminal apparatus closely resembles that found in the freshwater planarian Bdellocephala brunnea .     

Influence of salinity on early development in the spined loach

Spined loach Cobitis taenia developed successfully between 0·12 and 4·80‰ salinity. At 6·00‰, net production was strongly reduced, and development failed at or above 7·20‰. Below 0·12‰ S, net production became variable, indicating restrictive effects. In comparison with other primary freshwater fish species C. taenia has a low sensitivity to salinity. The upper limit for early development was equal to the highest salinity under which C. taenia adults are found along the Baltic coast. Therefore, salinity should not limit early development within the brackish habitats of spined loach.     

Comparing salinity tolerance in embryonic and larval development of two species of water strider,Aquarius paludum and Gerris latiabdominis (Hemiptera: Gerridae)

Water strider Aquarius paludum (Fabricius) is a cosmopolitan species colonizes mainly freshwater but occasionally brackish habitats throughout the Palearctic and Oriental regions. Water strider Gerris latiabdominis (Miyamoto) is a common species in Japan lives in temporary habitats as freshwater paddy fields. These two species often occur syntopically. We investigated differences in the developmental response to brackish water during embryonic and larval stages between the two species. Eggs were exposed to 0–1.8% NaCl solutions within 24 h of oviposition. Larvae of G. latiabdominis were exposed to salinities of 0, 0.5%, and 0.9% from the first instar until adult emergence. Limits of NaCl concentration for hatching were 1.3% and 1.0% for A. paludum and G. latiabdominis, respectively. The hatching rate of G. latiabdominis was lower than that of A. paludum at salinities ≥0.9%. The period of embryonic development of G. latiabdominis was more prolonged than that of A. paludum at a given salinity. Although the salinity tolerance of G. latiabdominis was lower than that of A. paludum, our results suggest G. latiabdominis has the physiological capacity to expand into brackish waters. High and low salinity tolerances of A. paludum and G. latiabdominis, respectively, reflect the relatively wide range of habitat salinities utilized by A. paludum and the relatively restricted habitats preferred by G. latiabdominis. The high salinity tolerance of A. paludum could be an important factor contributing to their cosmopolitan distribution because high tolerance to salinity means the possibility of them to be dispersed via ocean or sea to other continents and islands.     

Influence of temperature and salinity on embryonic development ofParacentrotus lividus (Lmk, 1816)

The combined effects of temperature and salinity on early development of the sea urchinParacentrotus lividus (Lmk, 1816) are reported. The optimal temperature-salinity combinations for development are 18 °–20 °C and 34–35‰; there is a significant temperature-salinity interaction. The optimal conditions found in the experiments are above the mean yearly values for the sampled population's environment (North Adriatic Sea), being more similar to those of the Tyrrhenian Sea. These results suggest that embryonic tolerances to temperature and salinity are under genetic and not environmental control.     

温度、盐度对龟足胚胎发育和幼虫生长的联合影响

龟足(Capitulum mitella Linnaeus)在我国主要分布于长江口以南海浪剧烈冲击的暴露型岩相海岸的中、高潮区,是一种颇具养殖潜力和市场前景的新品种。研究温度(24、27、30、33℃)和盐度(28,31,34)对龟足胚胎发育和幼虫生长的协同影响,可为龟足的人工育苗提供依据。结果如下(1):33℃-28温盐度组合胚胎发育时间最短144h,27℃-28温盐度组合胚胎相对孵化率最高。温度与盐度对胚胎发育时间没有显著影响;但温度和盐度对胚胎孵化率有极显著影响,温度与盐度间的交互作用显著。胚胎发育最适宜的温盐度组合是27℃-28。(2):27℃的3个盐度组、30℃-31温盐度组合无节幼虫持续时间最短。在同一盐度条件下以27℃的存活率较高,在同一温度条件下以盐度31的存活率较高,其中以27℃-31温盐度组合的存活率最高;存活率1和存活率2分别高达99.0%、90.7%。27℃-28、27℃-31温盐度组合变态率最高,变态率分别为81.8%、73.7%。34高盐组幼虫的存活率和变态率均很低甚至为零。温度和盐度对幼虫存活率和变态率有极显著影响,两者的交互作用极为显著。综合无节幼虫持续时间、存活和变态情况,27℃-31温盐度组合为幼虫生长发育的最佳组合条件。龟足胚胎发育、无节幼虫的生长和变态对温度盐度的敏感性有所不同,这是由龟足的自身繁殖特点及生活环境决定的。     

Embryonic and larval development of the peanut worm Phascolosoma agassizii (Keferstein 1867) from the Sea of Japan (Sipuncula: Phascolosomatidea)

All stages of the embryonic and larval development of Phascolosoma agassizii from Peter the Great Bay (Sea of Japan) were studied and illustrated using light and electron microscopy. The eggs of P. agassizii have the form of an ellipsoid (long and short axes about 100 and 70?µm, respectively). Egg cleavage is typical, spiral, and unequal. Gastrulation occurs by epiboly. This species possesses two pelagic larval stages, a lecithotrophic trochophore and a planktotrophic pelagosphera. The transformation of trochophore into pelagosphera occurs 80–90?h after fertilization. After 120–180?h, the larva has developed all systems of organs characteristic of the pelagosphera and is capable of feeding. At day 10, pelagospheras can settle, for some time, on the aquarium bottom and move on a ciliated lip, collecting food with the aid of a buccal organ. In addition, the larvae periodically attach themselves to the aquarium bottom or to the surface film of the water by means of a terminal organ. The trunk of the larva elongates by enlargement of the region behind the dorsal anal opening, which is located almost in the middle of the trunk region in the 15-day old larva. In the laboratory, 1-month old larvae spend the greater part of time in the attached state. Being attached by a glandular terminal organ to the aquarium bottom, they characteristically bend the body, actively feeding on microalgae from the substratum surface. The differences in the development of P. agassizii in the isolated West-Pacific and East-Pacific populations are shown and discussed.     

Mating behavior,spawning, parental care,and embryonic development of some marine pseudocerotid flatworms (Platyhelminthes: Rhabditophora: Polycladida) in Singapore

The reproductive biology of tropical marine cotylean polyclads is presently poorly known. Reproductive aspects of 16 polyclad species from the family Pseudocerotidae in the genera Acanthozoon, Nymphozoon, Phrikoceros, Pseudobiceros, Pseudoceros, Thysanozoon, and Tytthosoceros from Singapore were documented for the first time. Penis fencing was observed to be just a mating ritual and not necessary for insemination, not always aggressive, and could also result in eventual reciprocal insemination. Results showed that all species underwent similar embryonic developmental stages and hatched as Müller's larvae. Only Pseudoceros concinnus and Pseudoceros laingensis, with mean developmental times of >20 days and mean brood sizes of <1,000 eggs, displayed long‐term parental care. Polyclads producing larger brood sizes had shorter developmental times and only covered their egg masses for about one day. Phrikoceros baibaiye and Pseudobiceros spp. produced egg capsules with pointed opercula, whereas all other species possessed smooth, rounded opercula. All genera hatched with brownish‐orange larvae, except for Pseudoceros spp., which hatched with reddish‐purple larvae regardless of the initial embryo color (either grayish‐yellow or reddish‐purple). These could potentially complement current taxonomic characters in distinguishing polyclad genera and species.     

Stylochus (Imogene) matatasi n. sp. (Platyhelminthes,Polycladida): pest of cultured giant clams and pearl oysters from Solomon Islands

A large polyclad flatworm has been consistently found associated with mortalities of the cultured giant clam,Tridacna gigas (L.) and the fouling pearl oysterPinctada maculata (Gould) in Solomon Islands.Stylochus (Imogene) matatasi n. sp. is described and a brief account of its biology is given.ICLARM Contribution # 856.ICLARM Contribution # 856.     

Spectral reflectance of Thalassia testudinum (Hydrocharitaceae) seagrass: low salinity effects

Massive anthropogenic changes in estuarine salinities, from manipulations of freshwater flows, are again occurring through governmental projects “correcting” past freshwater alterations. The downstream effects of increased freshwater on seagrass meadows, a major fisheries and ecosystem habitat, are not clear. Spectral responses to low salinities were quantitatively delimited for the important habitat seagrass Thalassia testudinum utilizing spectral reflectance measurements for the first time (non-invasive sampling). Over a range of salinities (32–16 parts per thousand sea salts [ppt] for 24 h) and spectra (308–1138 nm), Thalassia specimens showed statistically significant differences in spectral values (P < 0.05) between treatments at normal (32 ppt) and 50% reduced (16 ppt) seawater. Mature blades yellowed at low salinities. Reflectance changes at 525 nm and 650–680 nm at low salinities suggested changes in xanthophylls and chlorophylls. Four indices were also used to characterize the reflectance spectra to delineate the effect of the salinity changes: (1) The normalized difference vegetation index (NDVI) for mature blades reduced at 16 ppt from that at 32 ppt. (2) The chlorophyll normalized difference index (Chl NDI) suggested chlorophyll content decreases in response to reduced salinity. (3) The structure independent pigment index (SIPI), higher in mature blades at 16 ppt than new blades, indicates a higher carotenoid : chlorophyll ratio in mature blades. (4) The photochemical reflectance index (PRI) suggested a lower photochemical efficiency at lower salinities. The main low-salinity effect on Thalassia physiology delineated herein is likely through changes in pigmentation (decreases in chlorophyll and changes in xanthophyll cycle epoxidation).     

Larval development of nemerteans of the genus Quasitetrastemma (Nemertea: Monostilifera)

Data on the larval development of Quasitetrastemma stimpsoni and Q. nigrifrons are presented. In both species, fertilization is external; the development passes through a free-swimming larval stage, the “hidden larva.” The larva has three pairs of eyes. After settling, the eyes of the second pair fuse with eyes of the first pair or are completely reduced. The basis and stylets are formed in 7–8 days after fertilization. Larvae of Q. stimpsoni settle on day 9–10 after fertilization; and Q. nigrifrons, on day 7–8.     

盐度对军曹鱼胚胎和仔鱼发育的影响

观察比较了不同盐度梯度(20、23、26、29、32、35、38、41和44)下军曹鱼受精卵的沉浮性、孵化率和畸形率以及测定了不同盐度梯度(10、14、18、22、26、30、34、38、42和44)下仔鱼不投饵存活系数SAI值。结果表明,受精卵在海水盐度32以上为完全浮性,26以下为完全沉性。军曹鱼受精卵孵化的最适盐度范围为29～38,适宜盐度范围为26～41,其中23～26和41～44分别视为受精卵孵化在低盐区和高盐区的两个临界区域,在此盐度上下,军曹鱼受精卵孵化率大幅度下降而仔鱼畸形率大幅度上升。试验盐度范围内军曹鱼仔鱼SAI值为2.32～16.24,仔鱼生长和存活的最适盐度范围为26～34,适宜盐度范围为22～38,而盐度18～22及38～42可分别视为军曹鱼仔鱼存活率在低盐区和高盐区的两个临界区域。     

Preliminary results on the effects of salinity and settling conditions on megalopal metamorphosis of fiddler crab Ilyoplax pusilla

Metamorphosis of fiddler crab Ilyoplax pusilla larvaefrom megalopal to first crab stage wasstudied in laboratory experiments under variousconditions of salinity and substratum. The hatchedzoea metamorphose through five stages before reachingmegalopal stage. The megalops were placed in a 20 mlPetri dishes (2–3 megalops/dish), with salinities of10, 20 or 30 . Each salinity level was tested eitherwith or without sandy mud substratum. Thirty to 35megalops were used in each of the six treatments. Theexperiment was carried out at a water temperature of28 ±0.5°C and with daily feeding of the diatomChaetoceros gracilis. Treatment of 20 salinity andsandy mud substratum revealed the highest metamorphicrate (87%), while in contrast no metamorphosis wasobserved at 30 salinity withoutsandy mud substratum. Duration of the metamorphosiswas about 16 days. Numerous malformed juvenile crabswere observed in treatments conductedwithout sandy mud substratum.     

盐度对条石鲷胚胎发育的影响

为了确定条石鲷胚胎孵化的适宜盐度,在试验水温为23.0℃～25.2℃条件下,设置了8个盐度组进行条石鲷胚胎孵化试验,研究了盐度对条石鲷胚胎发育的影响。结果表明:低盐度和高盐度对胚胎有持续性伤害,均可造成胚胎和卵黄球在卵裂期收缩而死亡,一部分胚胎在原肠期之后收缩死亡;低盐度可造成初孵仔鱼畸形率增加,主要引起仔鱼脊柱"L"形和"C"形弯曲,而高盐度可导致胚体胚孔关闭以后尾部的畸形发育;通过分析各盐度组的孵化率、仔鱼畸形率和盐度之间的关系,得出健康仔鱼比例(PHL)和盐度(S)的关系式为PHL=-0.0018S2-0.1135S-0.8853(R2=0.948),以PHL70%为适宜孵化盐度范围,以PHL90%为最适孵化盐度范围,由此确定在23.0℃～25.2℃条件下,条石鲷的适宜孵化盐度范围为21～42(PHL70%),最适为30～33(PHL90%)。     

Effect of daily salinity fluctuation on the intraspecific interactions of a euhalophyte (Suaeda salsa) along a salinity gradient

每日盐度波动对真盐生植物盐地碱蓬种内相互作用沿盐度梯度的影响 土壤盐度的异质性是河口潮间带的一个突出的环境特征,影响植物的生长和盐沼中生物相互作用的转变。本研究旨在探究盐度梯度和盐度波动对一种真盐生植物的种内相互作用的交互影响。     

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.     

Larval development of the rhizocephalanSacculina polygenea (Crustacea: Cirripedia)

Larval development of the rhizocephalanSacculina polygenea (Crustacea: Cirripedia: Rhizocephala) parasitizing the coastal crabHemigrapsus sanguineus was studied in Vostok Bay, the Sea of Japan. At 22–23°C, the entire cycle of larval development takes 2.5 days and includes five naupliar stages and one cypris stage. Like other rhizocephalans, the larvae ofS. polygenea are lecithotrophic and only grow slightly in size in the course of development, and like all sacculinids, they have no flotation collar. The naupliar stages IV and V have a tubercle between the furcal rami; this tubercle is absent in the larvae of the genusPeltogasterella, but it has been described inS. carcini. The first seta of the antennule only disappears completely at the fourth stage, although it is markedly reduced at the third stage. No morphological differences, except differences in size, are found between male and female nauplii.     

Early development of milkfish: effects of salinity on embryonic and larval metabolism, yolk absorption and growth

During embryogenesis of Chanos chanos , more than half of the yolk was consumed and the majority of it was converted into larval tissue. Salinity affected both yolk absorption and embryonic and larval growth. Larvae hatched in 20% had larger yolk reserves but were smaller and grew more slowly than larvae in 35 and 50%. Larvae hatched in 35 and 50% had equal amounts of yolk but those from 35% were larger. Oxygen consumption rates increased during development (from 0.06 ± 0.01 μl O₂ egg^–1 h^–1 by blastulae to 0.37 ± 0-01 μl O₂ egg^–1 h^–1 by prehatch embryos and 0–43 ± 0–03 μl O₂ larva ^–1 h ^–1 by newly-hatched larvae) and were significantly affected by salinity. Eggs and yolk-sac larvae incubated in 35% consumed more oxygen than those in the low and high salinities. Salinity affected both the rate and pattern of yolk utilization but salinity-related differences in metabolism, yolk absorption, and growth were not related directly to the osmotic gradient. Low salinity retarded yolk absorption while high salinity reduced yolk utilization efficiencies. Differences in oxygen consumption rates were probably related to variations in the relative amounts of metabolically active embryonic and larval tissue and/or higher activity levels rather than differential osmoregulatory costs. 35% is probably the most suitable salinity for incubation and larval rearing of milkfish.     

Morphological studies on the early development of Taenia taeniaeformis larvae in susceptible mice

Bortoletti G. and Ferretti G. 1985. Morphological studies on the early development of Taenia taeniaeformis larvae in susceptible mice. International Journal for Parasitology15: 365–375. Taenia taeniaeformis larvae which develop into infective strobilocerci in C3H mice have been studied from the 5th to the 15th day of development (L5–L15), both at light and electron microscope level. The L5 were initially compact, without a central cavity but then become vacuolized. Until stages L7–L8 they were surrounded by a perilarval amorphous layer (PAL) made up of a finely granular material which prevented the host cells from making contact with the larval tegument. The larval volume increased considerably between stages L6 and L8, remained unchanged from L9 to L13, but continued to increase thereafter. The larval cellular layer, which appeared as a single, large ‘syncitial system’, grow until stages L14–L15 when the scolex anlagen began to form. The tegument was initially incompletely organized and was covered by microvilli. These were completely replaced by microtriches from stage L8 onward. Sometimes both microvilli and microtriches were together observed in stage L7. Microvilli fragments, sometimes beaded, could be observed at L5 within the damaged cytoplasm of host cell debris. Very often they were branched at different heights, especially in stages L5–L7. In L10–L15 all undamaged microtriches increased in density and formed bundles which invaded the host cells. In stages L5–L8 and in some L9, muscular bundles started to become organized inside the tegumental distal cytoplasm (TDC), and after become independent in the subtegumental cellular layer (SCL). Until L8–L9 the larvae were surrounded by host cells debris. From stages L8–L10 onwards the adjacent host cells were less damaged though the larval microtriches penetrated them deeply. In stages L5–L7 neutrophils together with macrophages and some damaged hepatocytes were detected, while eosinophils were present only from L8 onward. In the other stages neutrophils clearly diminished in numbers, whereas macrophages had increased. No mastcells and few plasma cells were observed.     

Lecithotrophic development and metamorphosis in the Indo-West Pacific brittle star Ophiomastix venosa (Echinodermata: Ophiuroidea)

Summary

The larval development of the ophiocomid ophiuroid Ophiomastix venosais described using SEM. The gastrula transforms into a uniformly ciliated early larva which progressively changes into a lecithotrophic late premetamorphic larva with a continuous bilateral ciliated band. This stage is short-lived and equivalent to a highly reduced ophiopluteus. Comparisons between O. venosa and other ophiuroid species whose development has been investigated suggest that, whatever the developmental mode (lecithotrophic or planktotrophic), a pluteus stage always occurs in ophiuroids with planktonic development. Two metamorphic stages were identified, the late metamorphic larva differing from the early one by the closure of the larval mouth. The appearance of the permanent mouth marks the end of the metamorphosis. The postlarva still possesses remnants of larval features. The transformation of the reduced ophiopluteus into a barrel-shaped metamorphic larva with transverse ciliated bands, a vitellaria larva, is followed. The possible occurrence of a unique type of metamorphic larva in non-brooding ophiuroids is discussed. Verification of this, however, needs further SEM investigations on metamorphic larva from species having “regular” planktotrophic development.     

Effects of salinity on larval and early juvenile growth of an extremely euryhaline crab species,Armases miersii (Decapoda: Grapsidae)

The neotropical crab Armases miersii (Rathbun, 1897) breeds in supratidal rock pools, where great salinity variations occur. In laboratory experiments, all larval stages and the first juveniles were reared at six different salinities (5–55 PSU, intervals of 10 PSU). In five series of experiments, exposure to these conditions began either from hatching (Zoea I) or from the onset of successively later stages (Zoea II, III, Megalopa, Crab I). Growth was measured in terms of dry weight, carbon, nitrogen and hydrogen content. At osmotically extreme conditions (5 and 55 PSU, resp.), all stages showed minimum biomass accumulation; this was consistent with maximum mortality and longest duration of development (data presented in a separate paper). Successively later exposure to these salinities tended to reduce these effects. Lowest mortality and shortest time of development occurred generally at 15–25 PSU, indicating an optimum at moderately reduced salinities. This response pattern, however, was not congruent with that observed in growth. Biomass accumulation was initially maximum within a wide range of salinities (15–45 PSU), but in the Zoea II and III stages, this range tended to narrow and to shift towards higher salinities (35–45 PSU). These trends reversed in the Megalopa and Crab I, where maximum growth occurred again in a wider range and at lower salinities (15–35 PSU). The reduction of zoeal growth in moderately dilute media (15–25 PSU), which were optimal for survival and development, is interpreted as an energetic cost of hyper-osmoregulation, which begins already at hatching. Five PSU caused hypo-osmotic stress, exceeding in the long term the larval capacity for hyper-regulation. Poor zoeal survival and growth at 55 PSU are interpreted as effects of hyper-osmotic stress. In the Megalopa and Crab I, reduced growth at salinities 35 PSU may reflect the energetic costs of hypo-osmoreguation beginning in these stages. Our data suggest that the physiological adaptations of larval and early juvenile A. miersii allowing for survival and development in a physically harsh and unpredictable habitat imply a trade-off with reduced growth, due to energetic costs of osmoregulation.