Method for distinguishingLimnodrilus hoffmeisteri andLimnodrilus claparedeianus (Oligochaeta,Tubificidae) and its applicability in Lake Suwa

It is still next to impossible to distinguish species using immature worms of theLimnodrilus genus. A method was developed to separate mixed immature populations ofLimnodrilus hoffmeisteri andLimnodrilus claparedeianus into each species. The ratio of setal upper tooth length to lower tooth length, inL. hoffmeisteri andL. claparedeianus, ranged from 0.9 to 1.6 and from 1.3 to 2.1, respectively. Even if the median value of the frequency overlapped, this indistinguishable portion did not exceed 6% of each population.     

Cocoon deposition of Rhyacodrilus hiemalis Ohtaka (Tubificidae) in Lake Biwa,Japan

The larval stages of the mud prawn Upogebia africana were reared in the laboratory, from hatchings of females collected in the Mgazana estuary, South Africa. The larvae were tested for the combined effects of temperature and salinity in a factorial designed experiment, using 3 females and 2 replicates of 10 larvae per combination. Combinations were made from 5 temperatures (15, 20, 25, 30 and 35 °C) and 4 salinities (15, 25, 35 and 45). Results were tested by ANOVA and multiple regression was applyed to generate contour models by polynomial equation. Results showed that U. africana develops optimally in near to sea water salinity at around 25 °C, with slightly wider tolerance to low salinity in zoeal stage I, and with increased moult rate at lower salinity in late stages. A comparison with similar experimental results for other species is made, namely in view of the life cycle strategies for dispersal and return migration.     

On the Systematic Position of Rhyacodrilus prostatus Knöllner (Oligochaeta, Tubificidae)

New material of the marine tubificid Rhyacodrilus prostatus Knöllner, 1935 is examined and redescribed as Phallodrilus prostatus (Knöllner) comb. n. The main reason for the decision of this systematic position is the presence of a second pair of prostate glands, previously not reported, attached to the ectal end of the atria.     

A revision of Lycodrilus phreodriloides (Oligochaeta, Tubificidae)

The taxon Lycodrilusphreodriloides Michaelsen, 1905 is fully described for the first time. It is now recognized as Baikalodrilus phreodriloides (Michaelsen) comb.n., a member of the Tubificidae. This is the last of the original Lycodrilus species to be reclassified.     

A generic revision of the Phallodrilinae (Oligochaeta, Tubificidae)

The generic classification of the subfamily Phallodrilinae (with a total of 252 species) is revised according to phylogenetic principles. Morphological character patterns are assessed under the principle of maximum parsimony, but due to the poor resolution and instability in the resulting cladograms, the analysis is supplemented with intuitive weighting of synapomorphic similarities. Thirty-one genera are recognized. The former definition of the type genus Phallodrilus Picrantoni, 1902, is revised and the members of this genus are reclassified into 20 taxa, each hypothesized to be monophyletic: Phallodrilus s.str . (revised to contain the type species only), Somalidrilus gcn.n., Milliganius gen.n., Phallodriloides gen.n., Albanidrilus gen.n., Abyssidrilus gen.n., Paraktedrilus gen.n., Uniporodrilus Erséus, 1979, Inermidrilus gen.n., Gianius gen.n., Mexidrilus gen.n., Peosidrilus Baker & Erséus, 1979, Atlantidrilus Erséus, 1983, Thalassodrilus Brinkhurst, 1963, Pirodrilus gen.n., Pirodriloides gen.n., Marionidrilus gen.n., Pectinodrilus gen.n., Pacifidrilus gen.n. and Pseudospiridion gen.n. Nine new species are described from the Northwest Atlantic: Phallodriloides pinnulatus sp.n., Abyssidrilus opulentus sp.n., A. potens sp.n., A. altoides sp.n., Mexidrilus obtusus sp.n., Peosidrilus dalei sp.n., P. aduncus sp.n., P. riseri sp.n., and Atlantidrilus hamulus sp.n. The genus Discordiprostatus Baker, 1982, is synonymized with Nootkadrilus Baker, 1982.     

Life-cycle and karyology of Branchiura sowerbyi Beddard (Oligochaeta,Tubificidae)

Data on the life-cycle of a population of Branchiura sowerbyi Beddard in a water-lily tank at the Botanical Garden in Padua are reported. The breeding period is from April to July, after which the reproductive system is partially resorbed (August–September) and reformed later in the autumn. The karyology of the species was also studied, and revealed 38 mitotic chromosomes in the gonia, and 19 bivalents in the primary spermatocytes and in the primary oocytes.     

Seasonal Vertical Migration and Aestivation of <Emphasis Type=Italic>Rhyacodrilus hiemalis</Emphasis> (Tubificidae,Clitellata) in the Sediment of Lake Biwa,Japan

The vertical distribution of the tubificid worm Rhyacodrilus hiemalis Ohtaka, the numerically dominant species of oligochaete in the littoral of Lake Biwa, was studied with special reference to seasonal vertical migration in the lake sediment. Monthly collections of lake sediment cores were made using PVC tubes. Core sections of sample sediments ranged from 76 to 117 cm. The vertical distribution of the worms showed no diurnal variation; therefore diel vertical migration was not evident. Seasonal downward migration started in April, and upward migration started in October. From December to March, almost all worms remained in the near-surface sediment layer (surface to 30 cm deep), while from July to September almost all worms remained deeper than 30 cm. However, few individuals migrated deeper than 90 cm. No discontinuous layers were found in grain size composition, water content, loss on ignition, particulate carbon, nitrogen or phosphorus. In deep sediment there was no free oxygen, as evidenced by negative ORP values. For 4 months in summer, R. hiemalis aestivated, probably utilizing anaerobic respiration. It appeared that R. hiemalis moved deeper in the sediment in response to sediment temperature, because sediment temperatures in the deep layers seemed to converge at around 20–21 °C in the summer months. The life history traits of seasonal vertical migration and summer aestivation perhaps arose as an adaptation to the climatic conditions accompanying the geographical origin of R. hiemalis, and they also serve to minimize predation risk during summer when most invertebrate predatory fishes are active.     

Observations on the population dynamics of Potamothrix hammoniensis (Michaelsen, 1901) (Tubificidae,Oligochaeta) in Lake Isacova in the Danube Delta

The Danube Delta is one of the widest wetland systems in Europe and Lake Isacova is one of the biggest lakes in the Delta. The oligochaete community in the Lake comprised 52% of the total benthic fauna and Potamothrix hammoniensis (Michaelsen, 1901) (Tubificidae, Oligochaeta) represented more than 90% of the oligochaetes sampled. During September 1991 – August 1994, the proportion of ovigerous individuals of P. hammoniensis represented less than 20% of the total population, with localised differences in the Lake occurring over time. Breeding and cocoon production in the study period started in March of the year, when the water temperature was about 7 °C, and lasted until May 1992 and June 1993, respectively. The newly hatched individuals reached the highest proportion in May. Although large individuals were found again by the end of September (1991) and the beginning of October (1993), no spermatozeugmata in their spermathecae or cocoons were observed during November and October, respectively. Member of this cohort bred and started cocoon deposition during the following spring, after about 11 months of maturation (from April to March). A second, less intensive period of breeding was recorded during August 1992 and this lasted until the beginning of September 1993. However, cocoons from this latter period did not show embryonic growth and hatching until the autumn floods bring oxygenated water to the bottom level. This resulted in a period of rapid development followed by the mass hatching of cocoons. These specimens needed a maximum of 9 month (from October to July) to reach sexual maturity.     

Taxonomic Revision of the Marine Genus Heterodrilus Pierantoni (Oligochaeta,Tubificidae)1

Marine tubificids possessing trifid anterior setae are morphologically and taxonomically reviewed, on the basis of material from the Atlantic and Pacific Oceans. Heterodrilus Pierantoni, 1902 is revised to include thirteen species, H. arenicolus Pierantoni, 1902, H. minisetosus sp.n.H. ascensionensis sp.n. H. queenslandicus (Jamieson, 1977), H. lacertosus sp.n. H. scitus sp.n. H. keenani sp.n. H. claviatriatus sp.n. H. subtilis (Pierantoni, 1917), H. jamiesoni sp.n. H. occidentalis sp.n. H. pentcheffi sp.n. and H. bulbiporus sp.n. The genus is briefly defined: marine tubificids with trifid setae in preclitellar segments (with H. subtilis as the only exception); paired spermathecae located in segment X; vasa deferentia entering apical, ental ends of slender, ciliated atria, which bear broadly attached masses of prostate glands; paired male pores, and generally with penial setae arranged in bisetal bundles. Heterodriloides gen.n. is established for H. quadrithecatus sp.n. distinguished from Heterodrilus by two main features: its spermathecae are located in XII, with a supplementary pair generally located in XI; and its vasa enter the ectal part of the atria. Giereidrilus gen.n. a third genus with trifid setae, is established to include Phallodrilus ersei Giere, 1979 and G. inermis sp.n. Both species have unpaired spermathecal and male pores, and their atria are not ciliated. Heterodrilus, Heterodriloides and Giereidrilus are placed in the subfamily Rhyacodrilinae Hrabě, 1963.     

Redescriptions of Phallodrilus parthenopaeus Pierantoni and P. obscurus Cook (Oligochaeta, Tubificidae)

The type species of Phallodrilus Pierantoni, 1902, P. parthenopaeus Pierantoni, 1902; is redescribed on the basis of new material from W Scotland. The species is characterized by its specific spermathecal and penial setae, its very slender atria, and its long spermathecal ducts. Sexually fully mature specimens of P. obscurus Cook, 1969 are described for the first time, on the basis of material from New Jersey (E USA). The new material shows that this species possesses 5 to 9 penial setae in each ventral bundle of segment XI, and that its atria are coated with a relatively thick musculature.     

Quantitative observations on the population ecology of Branchiura sowerbyi (Oligochaeta,Tubificidae)

Cohorts of Branchiura sowerbyi were reared at different temperatures and initial population densities in order to obtain data suitable for the interpretation of population dynamics in field populations. Percent hatching from cocoons reaches its maximum at 25 °C and decreases towards lower and higher temperatures. Embryonic development time, T_E, was measured and the relative threshold temperature, 10 °C, calculated by extrapolation. The degree day requirement for embryo development is 195 °C d. The time of first cocoon laying (T_gm) was observed and the ratio T_E/T_gm was seen to fit with that of other tubificid species cultured so far. Embryo mortality is rather high, while worm mortality is low or very low. Fecundity increases from 15 to 20 °C but decreases at 25 °C. A mathematical model for the simulation of population densities with four size-stage compartments is suggested. It could be used for the optimization of worm uptake (simulated as stage specific mortality) in mass cultures reared for the production of Branchiura, to be used as food for fish fingerlings.     

New and Little-Known Species of Deep-sea Tubificidae (Oligochaeta) from the North-West Atlantic

Eight species of Tubificidae are reported from deep-sea samples taken south of Massachusetts. Phallodrilus grasslei sp. n., with heavily muscular vasa deferentia, and penial setae, two per bundle, oriented with ectal ends obliquely pointing towards the anterior, and P. rostratus sp. n., with a long and narrow, snout-like prostomium, heavily muscular, tripartite atria, and small, hooked penial setae, about five per bundle, are described. Phallodrilus biparis Erséus, previously known only from off France in the north-east Atlantic, is reported and depicted. Taxonomic notes are provided for Adelodrilus voraginus (Cook), A. fimbriatus Erséus, Bathydrilus asymmetricus Cook, and B. atlanticus Erséus. The depth distribution of all eleven deep-sea tubificid species known to occur south of Massachusetts are briefly discussed.     

Correlation Between Urea and Other Chemical and Biological Parameters in Waters of Lake Suwa,Japan

The vertical profiles of chemical and biological parameters, including urea concentration, have been measured periodically since February of 1977 at a central station in Lake Suwa, which is one of the typical eutrophic lakes in Japan. The seasonal trend in the standing stock of urea in the central water column, together with the ratio of urea versus total inorganic nitrogen in the euphotic zone from 12 March, 1977 to 25 July, 1978, are presented. The possible importance of bacterial decomposition of dead phytoplankton as a urea source in natural waters is demonstrated by this study. At times, a highly significant correlation between the vertical profile of urea and vertical distributions of other chemical and biological parameters which were also measured was found. An apparent in situ utilization of urea by phytoplankton is suggested on the basis of vertical profiles of urea and other chemical and biological parameters.     

Olavius cornuatus sp.n. (Oligochaeta, Tubificidae) from Georges Bank (NW Atlantic)

Olavius cornuatus sp.n. is described from Georges Bank off Massachusetts. It is distinguished from other species of Olavius Erséus, 1984 by its curved, horn-shaped atria ending in large, protrusible penes and up to six ectally hooked penial setae per bundle.     

Growth of Tubifex tubifex Müller (Oligochaeta,Tubificidae) under Various Trophic Conditions

Growth of Tubifex tubifex on highly caloric activated sludge and poor in organic matter natural silt was experimentally studied. The relationship between oxygen consumption rate, weight, and caloric value of T. tubifex body in culture on activated sludge was determined to calculate the growth efficiency (K₂ = P/P + R). The growth rate has been determined, and models of T. tubifex growth are given under various trophic conditions conforming to results of the experiment. Somatic growth, generative growth and life span of this species were compared on the basis of the experiments and literature. Acceleration of growth and prolongation of life under conditions of caloric food and delay of these processes in silt poor in organic matter have been established and measured. T. tubifex was found to have advantages as compared to other tubificid species in response to increasing amounts of nutrient food in waters polluted by organic matter and, therefore, to produce abundant populations under these conditions.     

Marine Tubificidae (Oligochaeta) of Antarctica, with descriptions of three new species of Phallodrilinae

Five species of Tubificidae are recorded from Antarctic waters: Torodrilus lowryi Cook, 1970, Torodrilus sp. (subfamily Rhyacodrilinae), Marionidrilus antarcticus sp. n., M. weddellensis sp. n., and Thalassodrilus bicki sp. n. (subfamily Phallodrilinae); only T. lowryi was known from Antarctica before. The status of the two Southern Hemisphere genera Torodrilus Cook, 1970, and Marionidrilus Erséus, 1992, are discussed; although the taxonomic position of the two new species of Marionidrilus is somewhat uncertain. Thalassodrilus bicki , however, appears closely related to Northern Hemisphere taxa.