On some freshwater harpacticois from Japan,closely related to Canthocamptus mirabilis Štěrba

Preliminary comparisons are presented, of certain diagnostic characters of four species of Canthocamptus, all the specimens examined here being collected from freshwater bodies throughout Japan. The geographical distribution of each species is also discussed.Contribution No. 69 from the Itako Hydrobiological Station, Ibaraki University.     

Response of harpacticoid copepods to habitat structure at a deep-sea site

Given the quiescent physical environment and the low rates of bioturbation in the deep sea, biologically produced structures, such as animals tubes, may play an important role in creating habitat heterogeneity. In San Diego Trough, the cirratulid polychaete Tharyx luticastellus builds and inhabits a robust mud concretion (a mudball). Mudballs are abundant and persist after the worm has died or abandoned them. Our analysis of twelve 6.6-cm-diameter cores from 32° 51.02 N, 117° 46.97 W, taken with the submersible SEA CLIFF, indicate that one of 29 species of harpacticoids common in San Diego Trough is associated with Tharyx mudballs. This species (of the genus Heteropsyllus) responded only to mudballs containing worms, suggesting that any effects of the inanimate structure were not the cause of the association. We could detect no difference in bacterial numbers in sediments between control and occupied-mudball samples. This result suggests that the response does not result from gross differences in food levels near a mudball, but the possibility that there are differences in some preferred food cannot be discounted. An univestigated possibility is that Heteropsyllus responds to occupied mudballs because the worm's presence deters some (presumably small) predator.     

The biology and morphology of the marine harpacticoid copepod Heteropsyllus nunni Coull, during encystment diapause

Heteropsyllus nunni Coull, a meiobenthic harpacticoid copepod is the marine crustacean to undergo a state of diapause within a cyst. A 12 month field study indicated H. nunni adults reached peak population densities in winter, with nauplii maturing in the spring, becoming adults by April or May.At the last stage of development, a mature but unmated adult, they begin to prepare for encystment diapause. The copepods remain within their cyst in a state of diapause for 3–4 months during the summer only. Studies on the effects of temperature and photoperiod suggested that these two environmental cues are not crucial for induction or termination of diapause. Low temperature delayed development and time to encystment, while high temperatures accelerated development, making the time to encystment shorter. There were males than females in the cysts in laboratory experiments. Upon excystment, the copepods mate, and females begin egg production within one week. Adults that have excysted and mated die after a few weeks of active reproductive effort. Nauplii go on to mature and begin the univoltine diapause/reproductive cycle.The copepods prepare for dormancy in two ways: they begin to produce and store two types of secretory products to be used in cyst construction; then they produce large quantities of lipid to be used as a nutrient supply throughout diapause. Histochemistry of the cyst-building material indicated the lower urosome is full of two chemically different products. Dorsally, there is a storage sac of proteinaceous material. The ventral sac of secretory product is a mucopolysaccharide. The copepod builds the spherical cysts in a matrix of small and large sand grains. The cysts fit tightly around the ventral portion of the animal in the its flexed position: however, there is a large space between the cyst and the sides of the copepod.Biochemical analysis of the cyst showed it is composed of an amino acid complex similar to collagenous material. Scanning electron microscopy revealed a complex of large cuticular pores located in the lower urosome and caudal rami. There are specific pores for secretion of the two cyst-building products.     

Effect of increased pCO2 in seawater on survival rate of different developmental stages of the harpacticoid copepod Tigriopus japonicus

The rapid increase in carbon dioxide levels in seawater is causing ocean acidification and is expected to have significant effects on marine life. To explore the ability of the harpacticoid copepod Tigriopus japonicus to adapt to an increased concentration of dissolved carbon dioxide (CO₂) in seawater, we compared the survival rates of adult and nauplius stages at 400, 1000, and 1550?ppm pCO₂ over a 14-day period. The survival rate of T. japonicus dramatically decreased over time with increase in pCO₂ concentration. At 1550?ppm, the survival rate showed a decrease of more than 20% at the end of the experimental period over that at 400?ppm. Furthermore, the survival rate decreased by a greater amount at all concentrations in nauplii than in adults, with a greater effect in wild-collected specimens than in culture-derived individuals. The results suggest that future ocean acidification may negatively influence the sustainability of T. japonicus and thus may eventually influence benthic ecosystems.     

Towards a revision of the genus Parastenocaris Kessler, 1913: establishment of Simplicaris gen. nov. from groundwaters in central Italy and review of the P. brevipes-group (Copepoda, Harpacticoida, Parastenocarididae)

A new genus Simplicaris (Copepoda, Harpacticoida, Parastenocarididae) is established to accommodate two species collected from deep groundwater in Italy, S. lethaea sp. nov. and S. veneris (Cottarelli & Maiolini, 1980) comb. nov. Parastenocaris hippuris Hertzog, 1938 and P. aedes Hertzog, 1938 are ranked as incertae sedis within the genus. Members display complete absence of leg 5 in both sexes and an unusual elongation of the first exopodal segments of legs 1–4, in which exp-1 is distinctly longer than exp-2 or -3, or as long as exp-2 and -3 combined. As the systematic status of the family Parastenocarididae and of the type genus Parastenocaris is still in flux, a list of phylogenetically informative characters is proposed, along with a discussion of their various states in representative members of the family. The genus Parastenocaris sensu stricto is redefined to comprise only the brevipes -group. The remaining members of the genus are considered Parastenocaris sensu lato pending a thorough revision of the family.  © 2004 The Linnean Society of London, Zoological Journal of the Linnean Society , 2004, 140 , 417−436.     

Harpacticoid copepods associated with the seagrass Halophila ovalis in the Ashtamudi Estuary,south-west coast of India

A temporal study of harpacticoid copepod populations associated with the seagrass Halophila ovalis was undertaken in the Ashtamudi Estuary, south-west coast of India. A total of 19 species representing 8 families was recorded in this assemblage. Harpacticoids formed 7.52% of the total phytal meiofauna. At the species level, harpacticoids exhibit parallel assemblages with phytal zones, found in other localities.     

Vertical distributions of a planktonic harpacticoid and a calanoid (Copepoda) in a meromictic Antarctic lake

Lake Abraxas (68° 29 S., 78° 17 E.) has been cut off from the sea for c. 6000 yr. In December, 1985, it had an ice cover 1.38 m thick, a thermocline at 5.2 m, and zero oxygen at 17.7 m and below. The salinity of the oxylimnion was in the range 14–19 g 1^–1. The calanoid, Paralabidocera antarctica (I. C. Thompson), had a maximum density just above a thermocline at 5.0 m, at which depth adult males outnumbered females almost 3 : 1. Immediately beneath the ice adult females outnumbered males 4 : 1. Immature copepodite stages were more abundant relative to adults near the oxycline than at higher levels. The planktonic harpacticoid, Amphiascoides sp., had a maximum density close to the oxycline at 17.2 m.     

Assessing the diversity of New Zealand freshwater harpacticoid copepods (Crustacea: Copepoda) using mitochondrial DNA (COI) barcodes

Taxonomic and ecological studies of freshwater harpacticoid copepods are limited globally by the ability to easily and accurately identify specimens. Here, we test the use of the mitochondrial cytochrome c oxidase subunit I (COI) gene locus as a tool for assessing the diversity of freshwater Harpacticoida. We obtained sequences from New Zealand harpacticoid copepods, representing two families, five genera and nine species, including the non-indigenous Elaphoidella sewelli. All species were delineated by the COI gene. However, high intraspecific diversity was evident among populations of Elaphoidella bidens (>12%), and between North and South Island populations of Bryocamptus pygmaeus (>18%), potentially indicating the presence of morphologically cryptic taxa. We suggest that mitochondrial DNA (COI) sequences can provide a useful tool for the routine identification of freshwater harpacticoid copepods. Applications of these data will include assessing species diversity and biogeography as well as assisting with the detection of non-indigenous species.     

The estimation of individual dry weight and standing crop of harpacticoid copepods

Individual dry weights have been calculated for ten species of harpacticoid copepods including epibenthic and interstitial forms. The data have been used to calculate a linear relationship between body length and weight enabling the individual dry weight of any harpacticoid of known body length to be estimated. The length-weight relationship has been used to estimate the standing crop of harpacticoids from three different sediment types. In all cases the estimated values were within 20% of the actual standing crop as determined directly by weighing.     

A complete enzymatic capacity for biosynthesis of docosahexaenoic acid (DHA, 22 : 6n–3) exists in the marine Harpacticoida copepod Tigriopus californicus

The long-standing paradigm establishing that global production of Omega-3 (n–3) long-chain polyunsaturated fatty acids (LC-PUFA) derived almost exclusively from marine single-cell organisms, was recently challenged by the discovery that multiple invertebrates possess methyl-end (or ωx) desaturases, critical enzymes enabling the biosynthesis of n–3 LC-PUFA. However, the question of whether animals with ωx desaturases have complete n–3 LC-PUFA biosynthetic pathways and hence can contribute to the production of these compounds in marine ecosystems remained unanswered. In the present study, we investigated the complete enzymatic complement involved in the n–3 LC-PUFA biosynthesis in Tigriopus californicus, an intertidal harpacticoid copepod. A total of two ωx desaturases, five front-end desaturases and six fatty acyl elongases were successfully isolated and functionally characterized. The T. californicus ωx desaturases enable the de novo biosynthesis of C₁₈ PUFA such as linoleic and α-linolenic acids, as well as several n–3 LC-PUFA from n–6 substrates. Functions demonstrated in front-end desaturases and fatty acyl elongases unveiled various routes through which T. californicus can biosynthesize the physiologically important arachidonic and eicosapentaenoic acids. Moreover, T. californicus possess a Δ4 desaturase, enabling the biosynthesis of docosahexaenoic acid via the ‘Δ4 pathway’. In conclusion, harpacticoid copepods such as T. californicus have complete n–3 LC-PUFA biosynthetic pathways and such capacity illustrates major roles of these invertebrates in the provision of essential fatty acids to upper trophic levels.