Effects of temperature and salinity on the larvae of two species of rhizocephalan (Crustacea: Cirripedia)

Summary

Responses of larvae of two rhizocephalan species to changes in seawater temperature and salinity were studied under laboratory conditions. Peltogasterella gracilis parasitizes the hermit crab Pagurus pectinatus, which occurs at stable salinity and gradually changing temperature in summer. Sacculina polygenea is a parasite of the crab Hemigrapsus sanguineus, which lives in the intertidal zone in summer where salinity and temperature can fluctuate during the day. The development of both species is comprised of five naupliar stages and the cyprid stage, and it was considered successful if more than 50% of the nauplii attained the cyprid stage. P. gracilis nauplii successfully developed at 12–20°C and 30–34‰, but at 22°C successful development occurred in a narrower salinity range (32–34‰). All nauplii died both at 25°C and in 26‰. S. polygenea nauplii successfully reached the cyprid stage at higher temperatures (18–25°C) and a wider salinity range (18–34‰) than P. gracilis nauplii, but at 12°C and 16‰ larval development of S. polygenea was suppressed. Under favorable conditions, naupliar development lasted 3.5 days in P. gracilis and 2–3 days in S. polygenea. The cyprids of both rhizocephalan species demonstrated a greater resistance to temperature and salinity changes than nauplii. However, P. gracilis cyprids were active in a narrower salinity range (16–34‰), as compared to S. polygenea cyprids (8–34‰). Under favorable conditions the cyprids of both species survived for 6 to 10 days.     

Adaptive Responses of the Larvae of Cirripede Barnacle Peltogasterella gracilis to Changes in Seawater Temperature and Salinity

The responses of the larvae of the cirripede barnacle Peltogasterella gracilis (Crustacea: Cirripedia: Rhizocephala) that parasitizes the hermit crab Pagurus pectinatus to different combinations of seawater temperature (25, 22, 20, 16, and 12°C) and salinity (from 34 to 8) were studied in a laboratory. The nauplii of P. gracilis completed the entire cycle of development at 22 to 12°C in a narrow range of salinity (from 34 to 28), which agrees well with the environmental conditions of the crab hosts' habitat. At favorable temperatures (22–20°C) and salinity (34–28), the nauplii reached the cypris stage in 88 ± 2 h, while at 12°C and 34–30, the naupliar development took 156 ± 5 h. The cypris larvae appeared more resistant compared with the nauplii, in terms of changes in both the temperature and salinity of seawater. They actively swam at all experimental temperatures and in the salinity range of 34–18. At temperatures (22–16°C) and salinities (34–24) favorable for the cyprids, their longevity in plankton equaled 6–10 days. Thus, the nauplii of P. gracilis is the more vulnerable stage of development in the life cycle of this parasitic barnacle. The tolerance against changes in environmental factors is due to the adaptive capabilities of parasitic larvae and the environmental conditions in the habitats of its host, a typical marine crustacean. The insignificant parasitization rate of the hermit crab by its rhizocephalan parasite may be explained by the death of the nauplii of P. gracilis, which occurs when they enter to the surface water layer.     

Reproductive Stage of the Life Cycle in the Rhizocephalan Barnacle Polyascus polygenea (Crustacea: Cirripedia)

The specific features of the reproductive stage of the life cycle have been studied in the rhizocephalan barnacle Polyascus polygenea, a parasite of the coastal crab Hemigrapsus sanguineus. It is shown that a single crab can bear 1 to 8 externae of P. polygenea. The fecundity of the parasite depends on the size of the externae and their number on the host and may reach as much as 50000 eggs for one externa. In Peter the Great Bay, Sea of Japan, this species repeatedly reproduces during the entire spring–autumn period; externae with developing embryos in the mantle cavity occur from May to September, and planktonic larvae occur from June to October. One externa produces during the season of reproduction no less than three generations of larvae. Thus, the reproductive strategy in P. polygenea comprises a three-stage cascade of reproduction: asexual reproduction via budding of the interna; the development of several generations of one or several externae; and several reproduction cycles of each externa. This allows the parasite to produce a very great number of larvae and ensures the parasitization of a significant proportion of the host crab population. The structure of the ovaries and oogenesis in rhizocephalans and free-living cirripede barnacles have many common features, which provides evidence for integration of these two groups within one monophyletic taxon.     

Introduction to the Rhizocephala (Crustacea: Cirripedia).

Knowledge about the Rhizocephala (parasitic barnacles) has increased exponentially over the past two decades. This introduction broadly reviews this progress, touching on rhizocephalan morphology, life-cycles, larval biology, and the effects on the crustacean hosts. Members representing both orders, the Kentrogonida and Akentrogonida, are discussed. The recent discovery regarding the vermigon stage further highlights the intricacy of the kentrogonid life-cycle. Because rhizocephalans are found in most world regions, occurring on their respective hosts from the deep ocean to freshwater, their importance is now being recognized.     

Acclimation of the Sea Cucumber Apostichopus japonicus to Decreased Salinity at the Blastula and Gastrula Stages: Its Effect on the Desalination Resistance of Larvae at Subsequent Stages of Development

Apostichopus (= Stichopus) japonicus blastulae and gastrulae were acclimated for 18 h to salinities of 32 (control), 24 and 22 (the lower limit of the range of tolerance), and 20 (below the range of tolerance). Acclimation to 20 resulted in the appearance of teratic larvae, most of which subsequently died. Acclimation to 24, 22, and 20 led to a shift in the range of tolerance of the larvae at further stages of development. With a decrease in salinity, acclimated larvae developed more successfully than unacclimated larvae. Acclimated larvae attained the pentactula stage and settled at a salinity range of 32–20; unacclimated larvae, at 32–22. At different stages of development, acclimated larvae survived greater decreases in salinity than unacclimated larvae. The acclimation effects could be traced up to metamorphosis and settling, i.e., two weeks after the end of the acclimation process.     

Responses of Embryos and Larvae of the Starfish <Emphasis Type="Italic">Asterias amurensis</Emphasis> to Changes in Temperature and Salinity

We studied the effects of different combinations of temperature (5, 10, 14, 17, 20, and 22°C) and salinity (from 32 to 8‰) on the development of the starfish Asterias amurensis Lutken from Vostok Bay, Sea of Japan. Embryonic development is the most vulnerable stage; it passes successfully at 10–17°C and the salinity range of 32 to 26‰. Blastulae are the most tolerant of changing environmental factors. They survive and develop at the temperatures of 5–17°C and in the salinity range of 32–18‰. Gastrulae and bipinnariae survive under higher temperature values and salinity from 32 to 20‰. The tolerance for decreased salinity during the process of fertilization and in the latest stage of development, the brachiolaria with the developing juvenile starfish, was confined to the salinity range of 32–22‰, which agrees with the tolerance of adult starfish Asterias amurensis. Thus, for normal development of the Amur starfish in the early stages, some particular conditions of temperature and salinity are required. This is, probably, due to adaptive capabilities of each developmental stage and the peculiarities of the ecological conditions at particular depths.     

Larval Development in the Rhizocephalan Barnacle Sacculina pilosella

We studied, under laboratory conditions, the larval development of a rhizocephalan barnacle Sacculina pilosellaVan Kampen et Boschma, 1925, which parasitizes the kelp crab Pugettia quadridens(de Haan) in Vostok Bay, Sea of Japan. It is shown that at 22–23°C, the whole cycle of larval development takes about 3 days. The larvae of S. pilosellaare lecithotrophic; their development, like in other rhizocephalans, comprises five naupliar instars. Like the larvae of all sacculinids, the nauplii of S. pilosellahave no flotation collar. In their structure, the larvae of S. pilosellaare similar to the nauplii of the typical sacculina, S. carcini(elongated body outline, long furcal branches, and weakly pronounced segmentation of the abdomen). On the other hand, the characteristic outgrowth inbetween the furcal branches that is characteristic of stages IV and V in S. carciniand S. polygeneais absent in the larvae of S. pilosella.The first seta on the antennula of S. pilosellacompletely disappears only at stage IV; however, at stage III, it is already significantly reduced. No morphological differences have been revealed between male and female larvae of S. pilosellaexcept certain size differences.     

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.     

Salinity tolerance of Mytilocypris henricae (Chapman) (Crustacea,Ostracoda)

Salinity tolerance, and the effects of temperature upon it, of the Australian ostracod Mytilocypris henricae (Chapman) was determined in direct transfer experiments using adults. Animals were subjected to a combination of 11 salinities (ranging between 0.0 g · 1^–1 and 45.0 g · 1^–1) and 4 temperatures (10, 15, 20 and 25 °C). Survival was analysed using two statistical techniques: the logit linear model and the proportional hazards model. Results show that both salinity and temperature have a significant effect on survival, but there is no significant interaction between temperature and salinity.     

Modus operandi of oviposition in Dermacentor reticulatus (Acari: Ixodidae)

The process of oviposition in D. reticulatus was observed and found to be a sequence of exactly coordinated, interlocking events independent of the phase of oviposition. The average period of oviposition in the investigated ticks was 31.6 days at 20 °C and 95% relative humidity. The number of eggs deposited on each day increased until reaching a maximum on the fifth day of oviposition and then decreased continuously. As a result, most of the eggs were deposited during the initial phase of oviposition. The total number of eggs was proportional to the ticks' weight replenishment. Egg-laying commenced with the lowering of the capitulum and the simultaneous spread of the pedipalps which were lowered to the body wall embracing the genital aperture on both sides. Immediately afterwards the cuticular sac of Gene's organ was pushed out and retracted several times. At the cuticular sac's maximum extension, the vestibulum vaginae prolapsed, forming the ovipositor as an extended tube which handed over an egg to the two horns of the cuticular sac after a brief, but intensive, contact with the cuticular sac. Then the vestibulum vaginae invaginated, the pedipalps closed, and the cuticular sac was retracted. Finally, the egg was transported onto the dorsal area of the tick by means of a vigorous rising of the capitulum. During the course of oviposition most of the events, especially the period of egg embracement by the cuticular sac, were prolonged, as was the total time for laying one egg. Similarly, the intervals between successive egg-laying processes increased continuously.The number of eggs deposited was not dependent on the functional ability of Gene's organ, as shown by similar numbers of deposited eggs from ticks with and without mechanical blocking of the cuticular sac. But the participation of the organ in the process of oviposition proved to be a prerequisite for the viability of the eggs. Larvae developed and hatched only from those eggs which were deposited from ticks with an undisturbed Gene's organ. In comparison, eggs without contact to the cuticular sac of Gene's organ dried up and shrivelled immediately after being deposited and did not hatch. Consequently, it strongly suggests, together with the results from other studies, that Gene's organ covers the eggs with a secretion that prevents the loss of water.     

温度,盐度,碱度对池沼公鱼胚胎发育的影响

池沼公鱼(Hypomesus olidus Pallas)是亚冷水小型经济鱼类,栖居于淡水、河口咸淡水中。近年来国内池沼公鱼移植广泛展开,为探讨池沼公鱼对不同生态条件的生存适应能力和     

Cypris metamorphosis, injection and earliest internal development of theRrizocephalan Loxothylacus panopaei (Gissler). Crustacea: Cirripedia: Rhizocephala: Sacculinidae.

Rhizocephala is a group of crustaceans that exclusively parasitizes other crustaceans. It is taxonomically placed within the class Cirripedia, the barnacles, with which it shares a unique larval type, the cyprid. The main objective of the cyprid is to find and irreversibly attach to a suitable substratum and initiate metamorphosis. In the presumed sister group to Rhizocephala, the true barnacles or Thoracica, metamorphosis leads to a juvenile filter-feeding version of the adult organism. In Rhizocephala the female cyprid settles on the integument of a crustacean and undergoes metamorphosis into a kentrogon that possesses a hollow cuticular-tube structure, the stylet, which penetrates the integument of the host and acts as a guide tube for the prospective internal parasite. The first, hitherto unknown endoparasitic stage of a rhizocephalan, the vermigon, was recently discovered (Glenner and H?eg [1995] Nature 377:147-150) and its migration through the hemolymph of the host, as well as its internal development, was described in Glenner et al. ([2000] Mar Biol 136:249-257). The present article provides detailed information on kentrogon and vermigon formation, the injection process, and the succeeding developmental stages up to the stage of the earliest primordium reported from the literature. The anlage of the ovary is traced back to the free-swimming cypris stage and it is implied that the mesoderm and ectoderm of the endoparasite are already differentiated in the cyprid.     

Studies on the critical water mass and the rehydration potential of unfed adult Dermacentor marginatus and D. reticulatus ticks (Acari: Ixodidae)

In unfed adult Dermacentor marginatus and D. reticulatusticks survival and capability to restore water balance after loss of high percentages of exchangeable body water were investigated. Furthermore, it was examined how frequently dehydrated ticks of these species were able to rehydrate by uptake of atmospheric water vapour. The critical water mass, defined as the water mass remaining in a tick at the nonambulatory state, differed between light and heavy weight groups and averaged 62.4 and 55.8%, respectively, of the total body water of fully hydrated ticks in females, and 54.4 and 51.1% respectively, in males of D. marginatus. In D. reticulatus, the corresponding figures were 55.9 and 54.7% in females and 52.1 and 52.7% in males. All ticks survived dehydration to 50, 75 or 100% of the critical water mass, and 96.7% of the D. marginatus ticks and 95.8% of the D. reticulatus ticks compensated water losses during subsequent incubation at 95% relative humidity (r.h.) and 20°C. Unfed females and males of both Dermacentor spp. were capable to balance water loss very frequently over a period of several months. When ticks were repeatedly dehydrated at 0% r.h. for 7 days and rehydrated at 95% r.h. and 20°C, females and males of D. marginatus reached the 50% mortality after 22 and 29 cycles of de- and rehydration, respectively, during 211 and 285 days, respectively. In D. reticulatus, 50% of females and males survived 23 and 17 cycles, respectively, during 248 and 186 days, respectively. Rehydration weights were as high or even higher as those of ticks kept at permanent 95% r.h.     

The Reaction of Mytilus trossulus Larvae (Bivalvia,Mytilidae) to Desalination and Increase of Water Column Temperature

Under homogeneous salinity and temperature conditions and uniform daylight, the early larvae of the Pacific mussel Mytilus trossulus (blastulae and trochophores) accumulated in the uppermost layer of water column, while the late larvae tend to concentrate at the bottom. In a water column with a temperature or salinity gradient, the early larvae accumulated at the surface even when the salinity and temperature conditions were incompatible with their life activity. The distribution of the late larvae was different as they were able to leave water of unfavorable temperature and salinity and accumulate at the bottom.     

Cell differentiation during early development of Nassarius reticulatus L. (Gastropoda,prosobranchia)

Summary In Nassarius reticulatus the nuclei and nucleoli undergo important morphological changes from the zygote to the 16-cell stage. In the zygote and in the trefoil (2-cell) and 4-cell stage, several agranular, fibrillar nucleolus-like bodies 1 m diameter are present in the interphase nucleus. Granular nucleoli first appear at the 8-cell stage. These nucleoli have fibrillar and granular regions. The granular regions are made up predominantly of ribosome-like osmiophilic granules. From the 16 and 32-cell stage onwards, the one or two spherical nucleoli of each nucleus measure 2.5 m in diameter and show a concentric organization with a very dense central region surrounded by a broad peripheral zone containing numerous granules, possibly of ribonucleoprotein. At the same time the number of ribosome-like particles increase in the karyoplasm and that of ribosomes in the cytoplasm. These findings are surprising because in eggs with radial cleavage, which have been subjected to more detailed analysis, the first granular nucleoli appear after the end of the cleavage, at the blastula or gastrula stage. The early appearance of granular nucleoli which seem to be characteristic of several eggs with spiral cleavage is discussed in connection with biochemical data on RNA-synthesis.This investigation was supported by the Deutsche Forschungsgemeinschaft and the Stiftung VolkswagenwerkWe wish to thank Mrs. C. Mehlis for valuable technical assistance and Prof. J. Bergerard for the excellent working conditions at the Station biologique at Roscoff (France)     

Salinity and Temperature Effects on Germination for Three Salt-resistant Euhalophytes, Halostachys caspica, Kalidium foliatum and Halocnemum strobilaceum

The effects of three salinities (0, 100 and 500 mM NaCl) and four constant temperatures (10, 20, 30 and 35 °C) on seed germination of Halostachys caspica (M. B.) C. A. Mey., Kalidium foliatum (Pall.) Mop. and Halocnemum strobilaceum (Pall.) Bieb. were investigated. After seeds were treated with different concentrations of NaCl at constant temperatures of 10–35 °C for 16 days, ungerminated seeds were transferred to distilled water for 10 days to investigate the total germination; after this time, the ungerminated seeds from the 10 and 20 °C treatments were then moved to 35 °C for another 5 days to determine the final germination. The three plant species in the present experiment are salt-resistant euhalophytes growing in high saline soils in the Zhungur Basin in Xinjiang, a northwest province of China.Compared with germination under control conditions, germination percentages of all three species were not affected by 100 mM NaCl at 10–35 °C, while severely inhibited by 500 mM NaCl; germination percentages were very low at 10 °C up to 100 mM NaCl for all species; the optimum temperature for germination of H. caspica and K. foliatum was 20–30 °C, while 35 °C for H. strobilaceum, up to 100 mM NaCl; seeds did not suffer ion toxicity for all species, as evidenced by the high total germination after ungerminated seeds pretreated with 500 mM NaCl were transferred to distilled water at constant temperatures of 10–35 °C for 10 days, and the high final germination after the ungerminated seeds from the 10 and 20 °C treatments were subsequently moved to 35 °C for another 5 days; Halostachys caspica had greater sensitivity to increasing temperatures from 10 and 20 °C to 35 °C compared with the other two species.     

Comparative morphology of larvae of coastal crabs (Crustacea: Decapoda: Varunidae)

The larval development of three crabs of the Varunidae family, (Hemigrapsus sanguineus, H. penicillatus, and H. longitarsis), widely spread in Russian waters of the Sea of Japan, were studied under laboratory conditions. At a temperature of 20–22°C and a salinity of 32‰ about 30% of larvae a complete developmental cycle, including five zoeal stages and megalopa, took from 22 to 30 days. All larval stages are illustrated and described in detail. Zoea I and zoea II of the studied crabs are not distinguishable. Zoea III–V of these species differ in the number of dorsomedial setae on the abdominal somite I and in the number of setae on the posterodorsal arch. The megalopae of three Hemigrapsus species possess a different number of segments, aesthetascs and setae on the antennular exopod. In spite of the great similarity of larvae of genera Hemigrapsus and Eriocheir, the latter possesses a number of distinctive features in all developmental stages, supporting the separation of these genera.     

Cell differentiation during early development of Nassarius reticulatus L. (Gastropoda Prosobranchia)

Summary The ultrastructure of the zygote and of early segmentation stages, up to the 16-cell stage, was investigated in normal Nassarius reticulatus from Roscoff (France). This study deals predominantly with structures that remain morphologically unchanged throughout this period, such as yolk granules, lipid droplets, and multimembranous vesicles. These organelles do not change in position, fine structure, or quantity from the egg to the 16-cell stage. The cortex and the vitelline layer also remain almost unchanged until the 16-cell stage. Cortical granules could not be observed and thus the thin vitelline layer is not transformed to a thick fertilization membrane. This phenomenon seems to be related to the facts that the eggs are protected by a tough capsule and that the cells of the embryo have to incorporate extraembryonic nutrient substances. From the 2-cell stage until the 16-cell stage micropinocytotic vesicles 500–2000 Å in diameter are associated with the plasmalemma. Perhaps they help to incorporate the extraembryonic nutrient reserves. Desmosomes first appear at the 4-cell stage and are common at the 8-cell stage, when a small transitory blastocoel appears. Normally the cell borders are in close proximity during interphase. Syncytial connections between the blastomeres were not observed. Beginning at the trefoil stage the mitochondria increase in number and many apparent division stages are observed. The increase in mitochondria occurs in the perinuclear region throughout the embryo and does not result in a polar lobe especially rich or poor in mitochondria. From the 4-cell stage onwards, the number of ribosomes increases differentially in different blastomeres.Dedicated to Prof. B. Rensch on his 75th birthday. We wish to thank Mrs. C. Mehlis for her valuable technical assistance and Professor J. Bergérard for the excellent working conditions at the Station Biologique at Roscoff (France).     

Studies on survival and water balance of unfed adult Dermacentor marginatus and D. reticulatus ticks (Acari: Ixodidae)

The water content, the survival time at various relative humidities(r.h.) and the critical equilibrium activity of unfed adultDermacentor marginatus and D.reticulatus ticks were investigated at a constant temperature of20 °C. It was also examined whether these ticks use liquidwaterto compensate water loss. Both Dermacentor spp. showed nosignificant differences in water content in relation to body mass. The meanwater content of D. marginatus and D.reticulatus was 54.6% and 54.7%, respectively, in females and 56.3%and 57.0%, respectively, in males. The survival time of unfed adults prolongedwith decreasing saturation deficits. On average, males survived longer thanfemales and D. marginatus ticks survived mostly longerthanD. reticulatus ticks. The 50% mortality period rangedbetween 40 d at 33% r.h. and 420 d at 95% r.h. in D.marginatus, and between 43 d at 33 r.h. and 366 d at 95% r.h. inD. reticulatus. The critical equilibrium activity of unfedadults was estimated to be 0.84 for both species and was independent of sex.When dehydrated adult D. marginatus and D.reticulatus ticks were offered liquid water, only a few slightlygained weight while most further lost weight. Liquid water was not attractivefor dehydrated or non-dehydrated ticks and drinking was not observed. Aftersubmerging in water for 2 d, most of the dehydrated ticks had gained weight.     

The Reaction of the Starfish Asterias amurensisand Patiria pectinifera (Asteroidea) from Vostok Bay (Sea of Japan) to a Salinity Decrease

The reactions of the starfish Asterias amurensis and Patiria pectinifera that live in Vostok Bay at the salinity of 32–33 to a salinity decrease were studied under laboratory conditions. The lower limits of the desalination tolerance range of A. amurensis and P. pectinifera were, respectively, 24 and 20. A. amurensis proved to be less resistant to desalination. Under experimental conditions, all specimens of this species survived the salinity of 22, while those of P. pectinifera tolerated 18. At the same time, A. amurensis responded more actively than P. pectinifera to unfavorable changes in the environment. Turned to their dorsal side and exposed to a salinity of 16 to 32, the former reverted to the normal position within a shorter time than the latter. Being a more euryhaline species, P. pectinifera endured a salinity decrease to 6 or 8 over, respectively, 21 or 28 h. However, only 30–40% of all specimens could recover locomotory activity 12 or 8.5 h after being placed into water of normal salinity.