Molecular phylogeny of Ostracoda (Crustacea) inferred from 18S ribosomal DNA sequences: implication for its origin and diversification

Nucleotide sequences for the 18S rDNA of 17 ostracod species, representing 4 extant orders and 12 superfamilies, were determined and compared with known sequences of other crustaceans. Resulting molecular phylogenetic trees based on maximum-likelihood, maximum-parsimony, and neighbor-joining methods consistently indicated that the Podocopida plus Platycopida forms a monophyletic group, but did not indicate monophyly of the Ostracoda consisting of the four orders, Podocopida, Platycopida, Kirkbyocopida, and Myodocopida. The tree topology and the crustacean fossil record suggest that the lineage of podocopidans and platycopidans, that of kirkbyocopidans, and that of myodocopidans should have separately been established already in the Cambrian, although there is no ostracod fossil record in that time period. Close relationships between the Bythocytheroidea and Cytheroidea and among the Macrocypridoidea, Pontocypridoidea, and Cypridoidea can safely be postulated, but other relationships among podocopidan and platycopidan superfamilies could not be resolved from the 18S rDNA data. The polychotomous relationship among five lineages of the podocopidan and platycopidan superfamilies, i.e. Cytherelloidea, Bairdioidea, Darwinuloidea, Bythocytheroidea plus Cytheroidea, and Macrocypridoidea plus Pontocypridoidea plus Cypridoidea, suggests that common ancestors of those lineages diverged from each other rapidly in short intervals in the early Paleozoic.     

Fatty acid composition as a dietary indicator of the invasive caprellid, Caprella mutica (Crustacea: Amphipoda)

The invasive caprellid amphipod Caprella mutica is one of the most widely dispersed marine non-native species globally. Originating in sub-boreal north-east Asia, it has now been found in both the northern and the southern hemispheres. One potential reason why this species is such a successful invader is its ability to utilise a wide variety of food sources. The contribution of different food sources to the diet of C. mutica was estimated using fatty acids as biomarkers. Caprella mutica was collected from three field sites, including sea cages stocked with Atlantic salmon Salmo salar, shellfish longlines stocked with the blue mussel Mytilus edulis and mooring lines marking the Loch Linnhe Artificial Reef (>2 km from caged finfish aquaculture), where established populations of this species are known to occur. In addition, the fatty acid compositions of C. mutica held in aquaria and either fed the microalga, Dunaliella tertiolecta, or the diatom, Phaeodactylum tricornutum, for a period of 21 days were investigated. The fatty acid composition of the diatom and the microalgal diets was also examined. The results showed that C. mutica contained high levels of polyunsaturated fatty acids, particularly 20:5(n-3); other dominant fatty acids included 18:1(n-9), 22:6(n-3) and 16:0 (in decreasing order based on abundance). Significant differences in the fatty acid profiles between caprellids fed on the microalgae and the diatom diets and between C. mutica collected from the field sites were observed. These results provide evidence that lipid biomarkers can be successfully used to provide evidence of feeding strategy for C. mutica and that the flexibility observed in this strategy may play an important role in its invasion success.     

On the ecology of Heterocypris salinus,H. incongruens and Cypridopsis aculeata (Crustacea: Ostracoda) from Baltic brackish-water rockpools

The ostracod fauna of Baltic brackish-water rockpools is made up of two groups: permanent members of the pools, and occasional guests from the littoral zone. The former group consists of Heterocypris salinus, H. incongruens and Cypridopsis aculeata. These species are characterized by rapid development (which starts when the water temperature approaches 15°C), a short life span, and 2 or 3 separate generations during the summer and autumn. The number of generations is determined by water temperature. Hibernation always takes place as eggs. Hatching and development during the late spring or early summer has been found to be mostly simultaneous. The spawning of the 3 species always starts epidemically. Reproduction is entirely parthenogenetic in the investigated area. Under natural conditions, C. aculeata may be found with either H. salinus or H. incongruens, but these two latter species have never been recorded together. H. incongruens is less tolerant to high salinities than the other 2 species and, even after successive adaptation, it does not resist salinities higher than 16. H. salinus has been found in 35.2 S in the field, and has been kept in 30 S in the laboratory after successive adaptation. The optimum salinity-temperature range for this species is 5 to 10 S and 15°C, when both survival and development are considered. Corresponding figures for C. aculeata are 0.5 to 20 S and 15°C, although this species, like H. salinus, survives longest at 5°C. The very rapid development, parthenogenetic reproduction and short life span of these species must be considered as favourable adaptations to the variable and unstable environment of the rockpool ecosystems.     

Reproductive bioenergetics within the summer and winter generations of Euchaeta norvegica (Copepoda)

The predatory copepod Euchaeta norvegica from Korsfjorden, western Norway, has a half-year life cycle. Egg sacs produced by the winter generation are heavier on average than those produced by the summer generation. This is probably determined by the supply of food during the breeding period rather than by the average weight of mature females at the beginning of the breeding period. Measurements on individuals from a Swedish fjord show that the respiratory rate is relatively low and stable over the year. Bioenergetic budgets for the period prior to and during breeding reveal pronounced differences between individuals from the summer and winter generation, the latter being the more efficient at converting energy from a lower trophic level. It is suggested that the most important environmental factor governing this is the abundance of prey organisms.     

Brood size and chemical composition of Pareuchaeta norvegica (Crustacea: Copepoda) in Loch Etive,Scotland

Brood size and chemical composition (carbon, nitrogen, and ash) of Pareuchaeta norvegica in Loch Etive, Scotland have been determined. From 23 to 37 eggs were found in each egg mass (mean=30 eggs). The eggs are oval; the mean size of the longer axis is 438 m. Variation in egg mass (as dry weight) is related to increase in dry weight of the maternal body. an increase of 1 mg in maternal body dry weight produces an increase of 0.03 mg dry weight in the egg mass. Carbon content increases with increasing body dry weight both in pre-spawning and spent females, but nitrogen content decreases with increasing body weight. Thus, the carbon:nitrogen ratio increases with increasing body dry weight. The carbon content of an egg mass ranges from 61.4 to 65.3%, and nitrogen content from 9.6 to 13.2% of the total dry weight. Some examples of partitioning of chemical components of the maternal body into the egg mass are also described.     

Hood construction as a spacing mechanism inCleistostoma kuwaitense (Crustacea: Ocypodidae)

The ocypodid crabCleistostoma kuwaitense inhabits the upper shores of the mudflats of Kuwait, where it constructs a semi-permanent mud hood over the entrance to its burrow. Between September and November 1986, data were collected on the distribution and orientation of the hoods and their openings to investigate the crab's social spacing system. Irrespective of density, the distribution of burrow hoods is non-random, tending towards a regular dispersion. A contributory factor for this dispersion pattern is that the surface hoods tend to increase the distance between adjacent burrows. The hood openings are randomly distributed with respect to compass direction but avoid directly facing those of nearest neighbours. In the absence of burrow plugging and eviction as used by other ocypodid crabs, construction of elongated hoods appears to be a good alternative for ensuring social spacing.     

Chemical composition of sergestid shrimps (Decapoda: Natantia) collected near Bermuda

Chemical composition was determined for Sergestes corniculum, S. grandis, S. japonicus, S. robustus and S. splendens collected in December, April and September. Protein content expressed as percent of dry weight varied from 65.7% in S. splendens to 46.8% in S. japonicus. Significant differences were noted among species in Apria and September, with highest protein values in April in S. corniculum, s. robustus and S. splendens. Lipid content expressed as percent dry weight ranged from 12.6% in S. robustus to 8.3% in s. splendens. Differences in percent lipid among species were significant in December and September with highest values in s. robustus and lowest values in S. splendens. Carbohydrate content varied from 1.0% in S. grandis to 2.5% in S. splendens. Ash and chitin were only determined for S. corniculum, S. grandis and S. splendens. Although protein and lipid content were correlated with size of shrimp analyzed, protein and lipid values in S. splendens, a species known to occur near the surface only at night, appeared to be related to seasonal zooplankton abundance in near-surface waters. Differences in lipid and protein content among species suggest that higher lipid and lower protein content occurs in species with shorter ranges of diel vertical migration.     

Length-weight relationships and coefficient of condition of Euphausia superba and Thysanoessa macrura (Crustacea: Euphausiacea) in southwest Indian Ocean during summer

Samples of antarctic euphausiids, Euphausia superba and Thysanoessa macrura were obtained during the MD 25 FIBEX expedition of the R. V. Marion Dufresne, in February 1981, to the southwest Indian Ocean. Individual and mean coefficients of condition (K _m) were calculated from variations in weight as a function of total length and of carapace length. In E. superba, no significant differences were found as a function of sex or development stage in either total length and weight or carapace length and weight. In T. macrura, a significant allometric difference emerged in the wet weight of juveniles, males and females as a function of total length, and in wet weight as a function of carapace length between adults and subadults. In both E. superba and T. macrura, wet weight as a function of total length differed significantly among stations, and also between species, with a greater weight increase for T. macrura in summer. The coefficients of condition calculated for all wet weight-total length relationships showed that the morphologically different Group II males were heavier than Group I males and mature females. K _m in T. macrura was higher for females than for juveniles or males, indicating a greater weight gain by the females. These differences probably reflect real differences in physiology and may affect the distribution of these two species.     

Observations on rock boring by Alpheus saxidomus (Crustacea: Alpheidae)

This study describes some aspects of the distribution, ecology, and rock boring behaviour of the shrimp Alpheus saxidomus Holthuis from the Pacific coast of Costa Rica. This species has a typical hammer-shaped dactylus on the first right pereiopod of females and males that shows tracks of abrasion at the hammer-head. Structural analysis of this hammer-dactylus proved that it is suited for the mechanical treatment of rocks. The very thick and calcified cuticle of the hammer is mostly formed by the sclerotinized, hard exocuticle, which has abundant pore canals.     

Offshore spawning by the portunid crabScylla serrata (Crustacea: Decapoda)

The portunid crabScylla serrata (Forskål) is shown to migrate offshore to spawn. Records of 447S. serrata caught as bycatch by trawlers in the tropical waters of northern Australia were analysed with respect to area, depth, distance offshore and month of capture as well as the sex and size of the crabs and whether the females were ovigerous. The crabs were caught mainly in three areas that correspond to the tiger prawn trawl fishery, at between 10 and 60 m depth (mean 28.5 m), 3 to 95 km offshore (mean 17.9 km). Most (87%) of the crabs were captured in October and November, which suggests they move offshore in September and October. No crabs were reported from offshore by February. Over 97% of the crabs caught offshore were female, of these 61.5% were ovigerous. The size range of females (100–109 to 200–209 mm carapace-width size classes) and males (120–129 to 200–209 mm carapace-width size classes) caught was similar. The frequent occurrence in coastal waters of females that are larger than the modal size at spawning, as well as mature females with spent ovaries, suggests that many females return to the coast after spawning. Although some species of portunid crab are euryhaline, mature females of estuarine species migrate to the sea to spawn. The migration byS. serrata described here is far more extensive than would be required to reach sea water salinities; it probably provides a dispersal mechanism for larvae to enable the megalopa stage to recruit to habitats distant from those of the parents.     

Vertical distribution and nocturnal migration of Nyctiphanes couchi (Crustacea: Euphausiacea) in relation to the summer thermocline in the Celtic Sea

Vertical distributions and nocturnal migrations of the developmental stages of Nyctiphanes couchi (Bell) in relation to the summer thermocline in the Celtic Sea, 25 to 26 August 1982, have been investigated using the Longhurst-Hardy Plankton Recorder (LHPR). The vertical distributions of the metanauplii and adult females suggest that N. couchi liberates its young within the euphotic zone as mature metanauplii which, in a matter of hours, moult into the first feeding stage (Calyptopis I). The ascent migration by adult females took a maximum of 3 h (17.10 to 20.05 hrs) and had an amplitude of 50m (54 to 4 m) from below to above the thermocline. A 7C° thermocline occurred between 20 to 30 m in these profiles. The nocturnal migrations by the females were for the purpose of breeding as well as feeding within the euphotic zone and were not influenced by the presence of the thermocline. The majority of the calyptopes and furciliae remained above the thermocline over the sampling period. The post-larval males and females migrated; their vertical distributions showed a pattern similar to those of the adult females. The larger the developmental stage, the deeper was the mode of its vertical distribution. The zooplankton dry weight in the profiles ranged from 3.74 to 6.91 g per haul (=1.85 to 3.45 g C m^-2, 0 to 100 m). The euphausiids represented 35% of total zooplankton dry weight and their migrations removed a large percentage of the total zooplankton biomass from the euphotic zone for 18 h d^-1. Such a large displacement of biomass would have a major impact on the biological interactions within the ecosystem.     

Variations saisonnières de la composition en acides gras chez Penaeus japonicus (Crustacea: Decapoda)

The lipid and fatty acid composition of male and female Penaeus japonicus Bate was investigated over a period of 11 months to determine the effects of environmental and nutritional factors such as temperature and starvation. The lipid content of the prawns increases from May to November, whereas water content decreases. We observed a time-lag between the highest lipid rate of males (in November) and that of females (in October); this is probably related to ovarian metabolism. From September to March, the high lipid content of the females coincided with a high percentage of monounsaturated fatty acids (especially 16:1 and 18:1). Winter starvation induces a decrease in palmitic acid content. As temperature decreases, the monounsaturated (16:1, 18:1) and polyunsaturated (20:4, 20:5, 22:6) fatty acids increase at the expense of the saturated fatty acids (16:0, 18:0) in the adult prawn. However, in post-larvae and juveniles, this increased rate of polyunsaturated fatty acids would be related to their particular lipid metabolism.     

Growth and moulting of Neomysis integer (Crustacea: Mysidacea)

The growth and moulting of Neomysis integer (Leach) was investigated in the field and the laboratory. In the Ythan estuary, Aberdeenshire, Scotland, monthly samples taken from November 1976 to October 1978 revealed that the summer generation juveniles and mature individuals grew at a rate of 4 to 5 mm and 1 to 2 mm monthly, respectively. The winter generation had a growth rate of 3 to 4 mm monthly for juveniles and about 1 mm for mature individuals; during the winter there was a period of 3 mo when growth was almost completely stopped. Mysids reared in the laboratory on Artemia sp. nauplii had an average daily growth rate of 0.06 mm at 9°C and 0.09 mm at 16°C. The growth factors of N. integer ranged from 3 to 17% for mature and immature individuals, respectively. Intermoult periods ranged from 3 to 7 d in immature mysids to 12 to 18 d in mature mysids. Average laboratory growth curves calculated from information on growth factors and intermoult periods indicate that at 9°C (winter generation) it takes N. integer 277 d to grow to be a 15 mm mature individual, whereas at 16°C (summer generation) it takes 188 d. N. integer moults 24 times as it grows from a juvenile to a mature individual.     

Foraminiferan (Protozoa) epizoites on Arctic isopods (Crustacea) as indicators of isopod behaviour?

A total of 38 219 specimens representing 63 species of marine isopods (Crustacea) from deep and shallow Arctic waters were studied in a search for epizoic foraminifers (Protozoa). Foraminifers occurred on 21 species, and their frequency was generally low. A total of 290 foraminifer individuals were found, of which 289 belonged to Cibicides wuellerstorfi, C. refulgens and Cibicides spp. (juveniles) (Cibicidae), while only a single individual belonged to Cornuspira sp. (Cornuspiridae). The foraminifers were most frequent on species of the families Munnidae, Ischnomesidae (suborder Asellota) and on Gnathia stygia (suborder Gnathiidea), but were totally absent from the asellote families Janiridae, Haploniscidae, Nannoniscidae and from the suborder Epicaridea. The foraminifers were mainly located on the legs (Munna acanthifera), the anterior part of the body (Haplomesus quadrispinosus, heteromesus frigidus), or on the head (G. stygia adults). The epizoic foraminifers occur mainly on epibenthic isopods, which do not or only rarely clean themselves. The foraminifers are known to prefer elevated substrata, and in this the habitat of the isopods and the foraminifers coincide. The size of individual isopods was not related to the presence or absence of foraminifers.     

Larval development of Euphausia nana (Crustacea: Euphausiacea)

The larvae of Euphausia nana Brinton in Sagami Bay and Suruga Bay, Central Japan, are described and illustrated. The furcilia stage is separated into six stages on the basis of the form of the pleopods and the number of terminal telson spines. Furcilia I, no pleopod or non-setose pleopods and seven terminal telson spines. Furcilia II, nonsetose and setose pleopods and seven terminal telson spines. Furcilia III, five pairs of setose pleopods and seven terminal telson spines. Furcilia IV, five pairs of setose pleopods and five terminal telson spines. Furcilia V, five pairs of setose pleopods and three terminal telson spines. Furcilia VI, five pairs of setose pleopods and one terminal telson spine. Segmentation of the antennal endopod and mandible palp occurred at the furcilia V stage. The dominant forms of early furcilia larvae of E. nana differed during different seasons of the year. The total lengths of calyptopis III and furcilia I to VI larvae also showed seasonal changes; they were largest in May and smallest from September to December.     

Feeding and digestion in Corophium volutator (Crustacea: Amphipoda)

New observations on the feeding behavior of Corophium volutator, collected from the Menai Strait, Anglesey, UK in 1981, show that detritus drawn into one entrance of the U-shaped burrow is pushed out at the opposing entrance either uningested or as faeces. Periodically, the amphipod turns around in the burrow and recommences feeding, so both the uningested material and the faeces may be reworked by the mouthparts. A feeding individual produces, on average, 16 faecal pellets every 10 min, at a seawater temperature of 18°C. When fed on detritus dyed with azo-carmine, approximately 12 pellets are produced before the foregut, intestine and hindgut are completely clear of previously ingested material and the dye appears in the faeces. Dye which enters the ventral caeca takes between 12 and 48 h to clear this tissue and, furthermore, it is only cleared when the amphipod is feeding. It is concluded that ingested coarse material is subjected only to a primary phase of digestion in the stomach, and that it takes 4 to 24 min to clear the gut. Fine material which enters the ventral caeca is subjected to a secondary phase of digestion and absorption which takes 24 to 48 h. Particles of thorium dioxide and ferritin incorporated in the diet are absorbed by the B- and ageing RF-cells in the ventral caeca. Non-specific esterases occur in the apical regions of the same cells, the mature cells of the anterior dorsal caeca and the cells at the anterior of the intestine. Protease activity is greatest in the lumen of the ventral caeca and the large vacuole of the B-cells. Apart from the lumen of the posterior caeca, there is some protease activity throughout the lumen of the gut. Carbohydrates were localised primarily in the R/F-cells towards the proximal region of the ventral caeca. Lipid was confined to the R/F-cells in the same region.     

Responses of wintering humpback whales (Megaptera novaeangliae) to playback of recordings of winter and summer vocalizations and of synthetic sound

Summary Three natural sounds and one synthetic sound were played back to humpback whales during their 1985 and 1986 winter residency in Hawaiian waters. Playback was conducted from a vessel positioned within visual range of an elevated shorestation equipped with a high-precision surveyor's theodolite, used to determine the positions and movements of observed whale and of the playback vessel. A playback session consisted of 20 min of pretest observation with the vessel in place and underwater speaker deployed, followed by a 20-min test phase during which sound, or a blank tape control, was introduced. A total of 143 playback sessions, involving a total of 338 pods (a single whale or a group of whales), were completed over the two winter seasons. The major response observed during playback was a rapid approach to the playback vessel, characterized in some cases by velocities up to 9 km/h and approaches to within 50 m or less. Whales approaching were mainly singletons and, secondly, apparent adult pairs. No cow-calf pair ever approached. The approach was selective: 21.6% of targeted pods approached in response to a feeding sound recorded in summer feeding grounds in Alaska; 8.3% approached in response to social sounds recorded in the Hawaiian winter grounds in the presence of large surface-active pods; 3.4% responded to playback of winter song; and 4.1% responded to playback of synthetic sound. There were no approach responses to the blank tape control. Singing whales have been identified as males by many researchers. Data from Alaska suggested that the feeding sound was produced by a female; data from Hawaii suggests that the social sounds were produced by males. The different rates of response were attributed to the behavior of sexually active males seeking to affiliate with sexually mature females. Although a female may be present in pods producing social sounds, the presence of multiple males exhibiting aggression may inhibit the approach of other males. Song did not serve as an attractant for females, as measured by direct approach, but may still serve as a basis for female choice.     

Functional morphology and significance of the circulatory system of Ostracoda,exemplified by Vargula hilgendorfii (Myodocopida)

Combined high-resolution video-recordings of live specimens, SEM and serial microtome sections were used to document the morphofunctional aspects of blood (hemolymph) circulation in Ostracoda, exemplified by the nektobenthic myodocopid Vargula hilgendorfii from Japan. The circulatory system is comprised of a single-chambered dorsal heart (pericardium, myocardium with two ostia), efferent vessels (aorta and secondary arteries) and an integumental afferent network of sinuses radiating from the adductor muscle area to a peripheral channel leading to heart. The heartbeat and the linear velocity of hemolymph in sinuses range from 0.5 to 6 times s^-1 and 200 to 1000 m s^-1, respectively. Hemocytes (10 to 17 m) of irregular shapes occur within the circulating hemolymph. This typical open circulatory system is found in most myodocope ostracodes and other crustaceans. It is totally absent in small (mostly <2 mm) ostracodes such as Podocopa. We conclude that the fluid convection of hemolymph augments the diffusion process of O₂ in larger animals. Oxygen uptake is assumed to occur preferentially through the inner (posterior) surface of the carapace where hemolymph sinuses are best developed and in close contact with sea water. Hemocytes may be involved in coagulation processes as in other crustaceans (e.g. Decapoda). Integumental circulation, preserved as anastomosing features in fossil Ostracoda, is known from the early Palaeozoic through to the Recent.     

Stranding and matting behaviour in Nyctiphanes australis (Euphausiidae: Crustacea)

Numerous stranding events of the euphausiid Nyctiphanes australis Sars on the coast of south-east Tasmania during the winter months of 1984/1985 are documented. The krill were at a reproductive stage of their life cycle. Strandings almost always occurred on calm, sunny days on beaches with a northerly aspect. Typically, barometric pressure was greater than and wind speed was less than the monthly average. No significant differences were found between stranded euphausiids and those from surface swarms, and the relationship between the two forms of behaviour in this area is discussed. A new form of behaviour termed matting was observed, in which the euphausiids aggregate dorsal-side down on the substrate in shallow water. Matting usually occurs synchronously with stranding. Laboratory experiments showed that N. australis responds to changes in both the plane of polarization and intensity of light with behaviour typical of that observed in stranding and matting events. Light appears to be a key factor mediating these types of behaviour. Hypotheses for the relationship between stranding and matting are offered.     

Reproductive behaviour and larval development of Tanais cavolinii (Crustacea: Tanaidacea)

Mature female stages of Tanais cavolinii Milne Edwards are described according to degree of oostegite development. Sexual dimorphism of the chelipeds of copulatory males is explained functionally. An aberrant marsupium consisting of two closed ovisacs with a small slit for sperm transfer protects the brood from sudden unpredictable changes in salinity. Behavioural traits, courtship, copulation, and parental care are described and compared to those of Heterotanais oerstedi Kröyer. The different habitats selected by the two species are reflected by several adaptations in their morphology and behaviour as tube dwellers. A phenomenon unique among invertebrates is that the female T. cavolinii supplies additional yolk to the larvae just before their release. The production and timing of this food supply is described and its adaptive significance is discussed.