Ovary structure and oogenesis in Cirratulus cirratus (Polychaeta: Cirratulidae)

Oogenesis in polychaetes has, in most species, two main phases: a coelomic phase during which vitellogenesis occurs, and an ovarian phase. Details of the latter are known in very few species. Efficient reproduction requires coordination between these two phases of oocyte differentiation. The ovaries of Cirratulus cirratus (O. F. Müller) occur 2/segment throughout the fertile region of the body; 5 main stages of oocyte differentiation can be recognised on them: stem cells, oogonia, premeiotic oocytes, early oocytes and terminal oocytes. A quantitative study of the composition of the ovary throughout the reproductive cycle shows that the ovary size is approximately constant, but that the percentage of cells in the terminal oocyte stage is reduced to zero prior to spawning. This stage in oocyte differentiation is therefore a critical one, at which oogenesis may be arrested. The ovary alternates between a proliferative phase when the terminal oocytes are present, and a non-proliferative phase when they are absent. The overall rate of germ cell production for each ovary is low, less than 1 cell/ovary/day, and the, ovary tissue turnover time is greater than 2 years. A qualitative model describing the production of oocytes is presented, and the implications of the low rate of germ cell production are discussed. A low rate of germ cell proliferation, as in Cirratulus cirratus, implies that the rate of oocyte output into the coelom will be controlled by factors influencing the later stages of ovarian oocyte differentiation.     

Stereological methods applied to reproductive cycle of Tapes rhomboides

A population of Tapes rhomboides (Pennant) in the Bay of St. Malo, France, was studied for one and a half years (July 1984–October 1985) to determine spawning frequency and fecundity under natural conditions, using the techniques of qualitative histological staging, condition index calculation and quantitative stereology. Spawning took place twice a year, in late May and in July/September. There was an extended winter resting period. Gonad development and oocyte production were positively correlated with female body size. The annual fecundity in a 40 mm clam was about 5x10⁵. Stereological techniques provided accurate information on oocyte dynamics within a gonad and the relationship with atretic processes. Each oocyte generation from the onset of the cycle to the winter resting stage was spawned eventually if conditions were suitable, or the oocytes were resorbed. Atresia of oocytes was seen throughout the reproductive period, but especially after the spring spawning and at the end of the summer.     

Observations on the reproductive cycles of Monodonta lineata,Gibbula umbilicalis and G. cineraria

Monthly samples of gonads of 3 common species of intertidal trochids, Monodonta lineata (da Costa), Gibbula umbilicalis (da Costa) and G. cineraria (L.) were fixed for examination by light microscopy. Numbers and proportions of immature and mature oocytes in sections of ovaries were determined. In M. lineata and G. umbilicalis, the annual reproductive cycles were very similar, the testis and ovary of both species being empty brown structures from September to January/February, when gametogenesis began and the gonads began to swell and turn green in both sexes. As ripening continued, the ovary remained green in G. umbilicalis, but in M. lineata turned greygreen by the end of May. The testis of both species changed, to yellowish in G. umbilicalis and creamy-pink in M. lineata. Spawning occurred throughout summer and early autumn, and the gonads reverted to their former empty state. These changes were matched by the increase and subsequent decrease in proportion of ripe oocytes in the gonad. Some ripe oocytes are not shed during the spawning season, but no evidence of cytolysis of such oocytes was found. In G. cineraria, in contrast, the ovary remained green and swollen and the testis remained creamy-white and packed with sperm throughout the year. The proportion of ripe to unripe oocytes in the ovary fluctuated for the entire sampling period, and did not indicate the time of spawning. In the testis of all three species, spermatogonia were rarely seen, and spermatid stages were uncommon.     

Reproduction in the sea pen <Emphasis Type="Italic">Pennatula phosphorea</Emphasis> (Anthozoa: Pennatulacea) from the west coast of Scotland

Reproduction in the sea pen Pennatula phosphorea Linnaeus 1758 was investigated in a population located in southern Loch Linnhe, west Scotland. This was accomplished through analysis of trends in oocyte size-frequency distribution and fecundity over a 12-month period. Pennatula phosphorea is dioecious and the study population exhibited a sex ratio of 1:1. Oogenesis in female P. phosphorea is characterised by the maintenance of a large pool of small oocytes throughout the year of which a small proportion (<30%) mature synchronously and are broadcast-spawned during the summer months of July and/or August. Although spawning occurs annually, the duration of oogenesis exceeds 12 months. Initial oocyte generation is best described as ‘quasi-continuous’ as it may be suppressed during winter. The timing and periodicity of oogenesis and spawning may be related to seasonal environmental cues and it is proposed that annual spawning constitutes a brief and synchronous event. Fecundity is high in P. phosphorea, typically up to 50 oocytes per polyp and 40,000 oocytes per colony in medium to large colonies. Although mean polyp fecundity increased with colony size (axial rod length) there was no seasonal fluctuation in this measure of relative fecundity. Since only a small proportion of oocytes present are spawned each year, the present study advises caution when making inferences regarding the seasonal output of viable oocytes, especially on occasions where the definition of fecundity or the details of the oogenic cycle of a species are unclear. Pennatula phosphorea produces large oocytes (>500 μm), indicative of the production of lecithotrophic larvae; this may confer certain advantages with respect to larval longevity and survival.     

Multi-year observations on the gametogenic ecology of the Antarctic seastar <Emphasis Type="Italic">Odontaster validus</Emphasis>

This study reports the first multi-year observations on the reproductive patterns for an Antarctic predator/scavenger, Odontaster validus (Koehler 1912). Seastars were collected monthly from a shallow site (15–20 m depth) near the British Antarctic Survey (BAS) Rothera Research Station (Adelaide Island, 67°34′S 68°08′W) from July 1997 to January 2001. Reproductive condition, oocyte size frequencies and spermatogenesis were examined in at least ten seastars each month using histological and image analysis techniques. Gonad indices (GI) and pyloric caeca indices (PI) were also examined in the same samples. Female and male GIs varied seasonally, in parallel with a reduction in the proportion of large oocytes and mature sperm in the gonad in August to mid-October following winter spawning. Despite there being remarkable consistency in the timing of spawning from year to year, differences in the reproductive condition of individuals were apparent. Patterns in the digestive tissues also varied with season, peaking in December and reaching a minimum in February in two of the three study years. This weaker annual pattern may partly reflect the varied diet of this predator/scavenger species, which is not directly dependant on the timing and magnitude of the annual phytoplankton bloom. Pooled oocyte size distributions and residual analysis suggested that oogenesis progressed over 18–24 months, with the largest of the two size classes (maximum diameter = 183 μm) being spawned annually. This pattern of oocyte growth and spawning was previously reported in the early 1960s for an O. validus population from McMurdo Sound, which lies south of Rothera by 10° latitude. The extremely catholic diet of this predator/scavenger suggests the reproductive patterns of the seastar will be less susceptible to changes in food supply compared to polar suspension feeders or deposit feeders. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Reproductive cycle of the subarctic brooding asteroid Leptasterias polaris

The reproductive cycle of the large brooding seastar Leptasterias polaris Müller and Troschel was examined over an 18-month period in the St. Lawrence Estuary, Québec, Canada. There is a distinct annual cycle with spawning over several months in the autumn. The female has an unusual cycle in that the ovary only slightly decreases in size during spawning, and the size structure of the oocyte population is remarkably stable throughout the year. The major annual change observed in the oocyte population is the development of a small number of 600-to 800- oocytes prior to spawning and their loss during spawning. This stability, combined with the lack of evidence of phagocytosis, suggests that oocyte development takes place over many years. By contrast, the developmental cycle of the testis is similar to that of most echinoderms. The large reservoir of oocytes probably guarantees a steady annual recruitment, and brooding during the winter probably minimizes metabolic costs for the female and ensures the release of the juveniles when conditions are favourable in the spring and summer.     

Reproduction and reproductive variability in the coral Pocillopora verrucosa from the Republic of Maldives

The sexuality, reproductive mode, and timing of reproduction of Pocillopora verrucosa from the Republic of Maldives, Indian Ocean, were assessed using serial histological sections. These showed that P. verrucosa is an annual simultaneous hermaphrodite, with gonads arranged in two opposing arcs of alternating testes and ovaries, six gonads in each arc. No planulae were observed in any dissection or histological analysis carried out, therefore making brooding unlikely. Broadcast spawning is inferred from the disappearance of mature gametes from samples collected between late March and April 1991. Mean oocyte size at spawning was 53.5 m and mean potential fecundity was 7300 ooctyes cm^-2yr^-1. The reproductive pattern of P. verrucosa in the Maldives is compared to that of the same species in different locations, the short breeding season in March to April occurring earlier in the Maldives than in Red Sea populations. The maximum mean oocyte diameter found in Maldivian specimens was much smaller than elsewhere. The year-to-year variation in numbers of oocytes/polyp within single colonies, and the variation between colonies within the population was significant (p<0.01). Therefore, it is possible that fecundity is not a good variable to use when monitoring stress on coral reefs unless larger numbers of estimates can be routinely made. Some colonies contained immature oocytes at spawning that were not released and continued to grow to approximately twice the size of the spawned oocytes that were presumed to be mature. These unspawned oocytes were oosorbing, and were characterised by the presence of zooxanthellae and large numbers of vacuoles in their cytoplasm. This gradual expansion and oosorption of unspawned oocytes has not been documented previously for corals.     

Seasonal variations in biochemical constituents during the reproductive cycle of the female dog cockle Glycymeris glycymeris

In an attempt to describe the biochemical events associated with the main stages of the annual and reproductive cycles of the female dog cockle Glycymeris glycymeris L., we studied seasonal variations in the various stages of oocyte development of the ovaries, and the glycogen, total protein and total lipid content of five body tissues – adductor muscle, foot, tunic coat, visceral mass and mantle. From November 1991 to November 1994, microscopic examination of the ovaries and measurement of the tissue concentrations of glycogen, total proteins and total lipids in these five body tissues were made monthly on ten female dog cockles originating from the sea area around Douarnenez (south Brittany, France). Morphological studies revealed that in the population investigated the annual cycle is characterised by three major periods: a first period of vitellogenesis extending from February/March to April/May and preceding a spawning in spring; a second period of vitellogenesis extending from May/June to September/October and leading to either no spawning, a single autumnal spawning event, or to two spawning events in summer and autumn; and a third period extending from October/November to February/March and characterised by a high level of oocyte lysis. In the muscular body tissues of the dog cockle, i.e. the adductor muscles, the foot and the tunic coat (the muscular envelope containing the visceral mass), the concentrations of glycogen, total proteins and total lipids underwent very similar variations during the annual cycle. During each stage of vitellogenesis, a typical glycogen–protein–lipid sequence was observed in the muscular tissues that was characterised firstly by a peak of glycogen concentration 2 to 3 mo before spawning, followed by a peak in total proteins 1 mo before spawning, and finally by a peak in lipid content just before spawning. A similar glycogen–protein–lipid sequence was also recorded in the first half of the winter period. However, these events were followed by general atresia affecting all oocytes in the gonad. Maximum energetic value of biochemical constituents in females coincided with peaks in lipid content in the visceral mass and mantle. These biochemical events occurred principally immediately before and at the end of oocyte lysis (December/January). A drop in the total energetic value, affecting mainly the visceral mass and the mantle, was recorded each year during the period January to March, coinciding with the period of shell growth in this species. Our data clearly indicate that in female G. glycymeris all muscular tissues contribute to the storage of glycogen and proteins, and suggest that glycogen may be the source of energy triggering vitellogenesis. Biochemical and microscopic observations revealed that oocyte development takes place during the first half of winter, but that these oocytes undergo atresia in December/January. The metabolites produced from oocyte lysis could contribute to somatic growth, which occurs in late winter. Received: 3 March 1997 / Accepted: 23 July 1997     

Annual reproductive cycle of the chiton Acanthopleura japonica

Annual reproductive cycle of the chiton Acanthopleura japonica (Lischke) was studied by observing both gonad index and histological features from October 1980 to October 1981. No significant changes in each factor were observed from October to April. Increased values of gonad index and spermatogenesis or vitellogenesis in gondas were observed from May to September. In the same time, gonad index decreased and sperms or oocytes in gonalds disappeared in the days around spring tide, and they were recovered around neap tide. Suggested spawning around spring tide from May to September is also supported by the occurrence of released eggs in the days around the new and full moons.     

Fecundity of the chokka squid Loligo vulgaris reynaudii on the southeastern coast of South Africa

Potential fecundity in Loligo vulgaris reynaudii was estimated to be about 17 000 eggs, calculated as the total number of discernible oocytes in the ovary and oviduct. Squid were observed to spawn up to 8140 eggs over a 36 h period in captivity. First estimations of actual fecundity are therefore between 8000 and 17 000 eggs. Factors complicating a more accurate estimation of actual fecundity in this species include difficulties with aquarium maintenance, their behaviour of spawning over a protracted period and in multiple sites, and atretic oocytes observed in both developing and mature ovaries. Detailed morphological and histological analysis of gonads collected at regular intervals over a complete spawning season will allow a more precise calculation of actual fecundity. Received: 9 October 1998 / Accepted: 22 April 1999     

Social inhibition of maturation in females of the temperate wrasse Pseudolabrus celidotus and a comparison with the blennioid Tripterygion varium

In two temperate reef fish, Pseudolabrus celidotus (Bloch and Schneider) and Tripterygion varium (Bloch and Schneider) studied near Leigh, New Zealand, most spawning activity was concentrated during the first 2 months of spawning seasons which lasted about 5 months. In P. celidotus, maturation and spawning of first-year females (0+) was delayed with respect to older (1+yr) females. Within the 0+ age class, the minimum size of maturation declined as the spawning season proceeded. However, in all females of T. varium, ripening and spawning took place over the same time ranges. Observations on the seasonal patterns of female aggression suggested that larger female P. celidotus were socially inhibiting the maturation of small females. The level of interaction was high compared to that in T. varium, and reached a peak over the onset of the spawning season. This hypothesis was tested by the removal of larger (1+yr) female P. celidotus from a field population. The remaining 0+ females increased in ovary weight and matured earlier than those in an undisturbed area. We argue from this experiment that it is of advantage for P. celidotus females to spawn early in the season and of advantage to inhibit other females from doing so. Two possible reasons are suggested, the first applying to sexchanging species such as P. celidotus, the second to temperate-water fishes in general.     

Factors affecting the spawning period of sardine in two highly oligotrophic Seas

Ovarian histology and weight dynamics of reproductive and somatic tissues were used to investigate seasonality of spawning and factors affecting reproductive period in two E Mediterranean sardine, Sardina pilchardus, populations (central Aegean and Ionian Seas), between September 1999 and May 2001. Despite similarities in the general spawning pattern of the two populations, i.e. protracted spawning season during the colder months of the year, reproductive period in the Ionian was shorter and lagged behind the Aegean by 2–3 months. In both Seas, reproductive period was influenced by body size as smaller females tended to have both shorter and delayed spawning season. Whereas hepatosomatic index (HSI) was consistently higher in reproductively active females during the whole spawning period, seasonality of spawning did not match variations of HSI. In both Seas fluctuations of HSI matched the spring burst of primary productivity and were followed by fluctuations in somatic condition and mesenteric fat by a 2 months’ lag. Somatic condition and reproductive activity displayed inverse seasonal patterns, implying that egg production in sardine basically relies on visceral and muscular fat deposits, accumulated during the summer growing season. Reliance of egg production on past energetic reserves suggests that sardine is a capital breeder, which is a rather efficient strategy in such oligotrophic habitats as the E Mediterranean, where winter spawning is accompanied by a particular decline in adult preying fields.     

Gametogenesis and spawning periodicity in the fan worm <Emphasis Type="Italic">Sabellastarte spectabilis</Emphasis> (Polychaeta: Sabellidae)

The sabellid polychaete Sabellastarte spectabilis (Grube 1878) was collected at approximately monthly intervals from January 2002 to December 2003 from intertidal and subtidal reefs near the Hawaii Institute of Marine Biology in Kane’ohe Bay, Hawaii, USA (21°N, 157°W). Gametogenesis and spawning periodicity were investigated using histological techniques and induction of spawning trials. Worms were characterized into four discrete reproductive stages based on histological evidence: (1) No evidence of reproductive activity in the coelom (sex cannot be determined), (2) Only coelomocytes present in the coelom (sex cannot be determined), (3) Some gametes present in the coelom (sex can be determined) and (4) Coelom densely packed with gametes (sex can be determined). The small hermaphroditic portion of the population was not used in this study. Stage 4 worms were present over an extended period of time (females, March–December and males, March–November) indicating a potentially broad reproductive season. No correlation between day length and maturation stages in S. spectabilis was detected. However, the statistical model Y = ([394.26 × X] − [7.793 × X ²]) − 4960.781 where Y the % frequency of Stage 4 worms and X the mean monthly water temperature explained 44% of the variation between water temperature and % frequency of Stage 4 worms. Maturation appeared to coincide with water temperatures of 24–25°C (March–September) after which there is a reduction in the % frequency of stage 4 individuals. Induction of spawning trials conducted between May and January showed the month of October with a significantly higher percent success than any other month investigated. According to all available information (e.g., natural spawning in water tables, histological data, induction of spawning trials, correlation of maturation stages with observed changes in average monthly water temperature.), there is an apparent peak in reproductive activity (spawning) within a broad maturational season, which may be influenced by water temperature.     

Reproductive cycle of two populations of Ophionereis schayeri (Ophiuroidea) in New South Wales

Reproduction of two populations of Ophionereis schayeri (Müller and Troschel) in New South Wales was investigated from November 1991 through January 1993. The reproductive cycle was documented by histological examination of the gonads and by image analysis to determine the oocyte size-frequency distributions. Both populations of O. schayeri were mature in December and January and had a major summer spawning period between January and February. Thereafter, the condition of the gonads exhibited interindividual variability, with asynchronous low-intensity gamete release through August. O. schayeri has the potential to spawn for up to 8 mo of the year. This breeding pattern with synchronous spawning in summer and asynchronous gamete release through winter was similar in both populations. During autumn and winter, the gonads contained developing gametes and advanced gametes ready for spawning. The eggs spawned by O. schayeri during these seasons started their growth during the previous spring vitellogenic period, and continued to grow through summer. Upon reaching full size, they were stored for spawning outside the main breeding period. Spring is marked by increased spermatogenic and vitellogenic activity followed by maturation and spawning. Throughout their development, the oocytes of O. schayeri are surrounded by a follicle consisting of periodic acid-Schiff-positive (PAS+) haemal fluid and PAS+ yolk by the oocytes. In the testes, the haemal sinus projects into the centre of the spermatocyte columns, thus appearing to play a nutritive role in support of both oogenesis and spermatogenesis. Late vitellogenic oocytes of O. schayeri are firmly anchored to the germinal epithelium by an attachment complex consisting of specialised attachment cells and basophilic strands that radiate between the oolemma and the nucleus. Spawning is associated with rupture of the follicles, which remain as prominent, empty U-shaped profiles in the ovaries. O. schayeri produces copious numbers of 200 m-diam oocytes, suggesting that this species is a broadcast spawner and that it has a modified ophiopluteus or vitellaria larva.     

Seasonality of coral reproduction in the Dampier Archipelago,northern Western Australia

Coral spawning in Western Australia (WA) occurs predominantly in the austral autumn in contrast to the Great Barrier Reef (GBR) on Australia’s east coast where most spawning occurs in spring. Recent work, however, suggests a second spawning period in northern WA with at least 16 Acropora spp spawning in spring or early summer. This discovery has initiated a re-examination of reproductive seasonality in northern WA, particularly on inshore reefs adjacent to large development projects, such as the site of this study in Mermaid Sound, in the Dampier Archipelago. Three locally abundant taxa, Porites spp, Pavona decussata and Turbinaria mesenterina were sampled monthly from September 2006 to May 2007 to determine sexuality, the mode of reproduction and the time of gamete maturity. All three taxa were gonochoric broadcast spawners. Porites spp. colonies were mature in November and December, P. decussata in March and April. In contrast, most colonies of T. mesenterina contained mature gametes for up to 5 months beginning in November, suggesting either individuals are releasing gametes on multiple occasions, or they retain mature gametes for more than 1 month. Field surveys to determine the reproductive status of the remaining coral assemblage were conducted prior to the full moon in October 2006 and March 2007. Only four species contained mature gametes in October 2006. In contrast, 55 species contained mature gametes in March 2007. We conclude that the major spawning season of corals on shallow-inshore reefs in the Dampier Archipelago is autumn, although taxa that spawn in spring and summer include Porites spp., Acropora spp. and possibly T. mesenterina that are numerically dominant at many of these sites. Consequently, management initiatives to limit the exposure of coral spawn to stressors associated with coastal development may be required in up to five months per year.     

Biology of penaeid prawns in the Suez Canal lakes

A study was made from January 1988 to March 1989 of the penaid prawns in the Great Bitter Lake and Lake Timsah located in the central part of the Suez Canal. Two species of Red Sea origin were investigated,Metapenaeus stebbingi andTrachypenaeus curvirostris; the former is by far the commoner. Both species displayed seasonal breeding over the period April to October, with peaks in the early and late parts of the season.M. stebbingi had two main cohorts each year. A spring-spawned cohort survived 16 mo, and attained modal sizes of 23 mm carapare length (CL) for females and 16 to 17 mm CL for males. The autumn-spawned cohort survived 13 mo, and reached modal sizes of 20 mm and 15 mm CL for males and females, respectively. The reasons for the success ofM. stebbingi in the Canal lakes, in contrast to other Lessepsian penaeids which have flourished in the Mediterranean Sea, have been considered. The main factors are that it is essentially a shallow-water species, with excellent tolerance of salinity variations and adverse environments. However, the Canal lake populations have smaller maximum sizes, and mature earlier, than those in open seas.     

Ovary development at the onset of gametogenesis is genetically determined and correlated with reproductive traits at maturity in shrimp <Emphasis Type="Italic">Litopenaeus (Penaeus) vannamei</Emphasis>

Besides some mammals and a few model organisms, the presence of genetic variation in ovary or gonad development at ages before that of reproduction has not been established for marine oviparous species nor has the correlation with reproductive traits at maturity. In this investigation, ovary development was evaluated for genetic variability in a full-sib family structured population of subadult shrimp. The numbers of each oocyte type that were present were counted, measured, and used to evaluate the following traits: total oocyte number, mean oocytes diameter, and ovary maturity (OM). The total ovary area was also measured for each female. Genetic variation was assessed through the estimation of the parameter ‘heritability’. The heritability (h ²) of total number of oocytes was zero, but large heritability values were seen for mean oocytes diameter (h ²=0.57±0.27) and OM (h ²=0.71±0.26). Family means correlations between traits in subadults with traits measured in their full-sibs when adults (days to first spawn, total number of spawns, total fecundity, and fecundity at first spawn) indicated the existence of some significant associations between reproductive traits at the two ages. These findings point toward an early genetic determination of reproductive capacity in this crustacean.     

Gonad morphology and oocyte development in<Emphasis Type="Italic"> Pseudocalanus</Emphasis> spp. in relation to spawning activity

Gonad maturation processes were studied in Pseudocalanus spp. females from Georges Bank and Cape Cod Bay (northwest Atlantic) using a combination of morphological analysis and experiments. For light microscopy of the oocytes, females of different maturation stages were preserved immediately after capture. The maturation processes during the spawning cycle were described from observations of live females which were exposed to feeding and starvation at two temperatures, 8 and 15°C, for 12 days. The gonad morphology of these females was examined in 24 h intervals, and spawning events were recorded. Both light microscopy and whole animal observation revealed that oocytes during maturation change in shape and size, in the morphology of the nucleus, and in the appearance of the ooplasm. Due to these modifications of oocyte morphology and due to oocyte migration, the morphology of the gonads changed distinctly during a spawning cycle. Five oocyte development stages were identified by light microscopy and related to a macroscopic system of four gonad development stages, that can be applied to whole animals and allows the identification of females ready to spawn. The experiment showed that food and temperature had strong effects on gonad maturation processes. High proportions of mature females were found when food was available, whereas the proportion of immature females increased shortly after exposure to starvation. Compared to 15°C, gonad maturation at 8°C was prolonged and thus spawning frequency was lower. The final maturation processes at food saturated conditions were slower than the embryonic development, and no indication was found that mature oocytes are stored in the diverticula waiting to be released. The duration of the interspawning interval would thus be determined by the duration of final oocyte maturation which is dependent on both temperature and food supply.Communicated by O. Kinne, Oldendorf/Luhe     

Reproduction of a Northumberland population of the polychaete Cirratulus cirratus

A population of Cirratulus cirratus (O. F. Müller) was sampled from September 1966 to September 1968. The population is found intertidally in crevices at Cullercoats Bay, Northumberland (UK). Measurements of the sexual maturity and size of the animals have been made. The breeding season is not restricted, spawning occurs in the population asynchronously throughout the year. Ripe worms and worms that have just spawned are invariably present, but the majority of females are always at intermediate stages of oogenesis. Adult males, however, always contain active spermatozoa. Females, but not males, are devoid of coelomic gametes after spawning; a new generation of coelomic oocytes begin to accumulate in the coelom after 30 days. The growth of the coelomic oocytes is relatively slow, the coelomic phase of oocyte development takes between 1 and 2 years for completion. The coelomoducts which serve for the emission of the gametes are described. An interpretation of the female population structure based upon length and sexual maturity data suggests that most females survive to spawn 2 or 3 times, and some to spawn 4 or 5 times. They grow in length by about 2 cm in the period between successive spawnings. The reproduction of Cirratulus cirratus is compared with that of other annelid species breeding throughout the year, and this unusual mode of reproduction is discussed.     

Reproductive patterns in the Antarctic brachiopod Liothyrella uva

The reproductive cycle of the Antarctic articulate brachiopod Liothyrella uva (Broderip, 1833) is described from monthly samples collected between September 1985 and July 1987 from a population at Signy Island, Antarctica. Spermatogenesis and oogenesis are described for the first time in this species. Surface dried-tissue masses for a standard individual (41 mm shell length) were calculated for the digestive diverticula, gut, lophophore and gonad from monthly dissections of 15 brachiopods. Seasonal patterns, with summer peaks, were observed in the digestive diverticula and gut. The lophophore and gonad masses did not exhibit seasonal trends. Females showed a sharp decrease in proportion of large oocytes between October and November in 1986, suggesting spawning during this period. There was no similar decrease during the same period in 1985. Mean percent spermatozoa measurements revealed a large increase in November 1985 and a rapid decline in December 1985. This suggested a large spawning event for males in 1985 which was not repeated the following year. These data indicate large inter-annual differences in reproductive activity as well as differences between males and females. They also suggest the possibility of sperm storage by females. Brood characteristics were also highly variable. The smallest brooding female was 31.5 mm in length. Some females brooded more than one developmental stage simultaneously, and variation in brood size (numbers of embryos or larvae held in the lophophore) and brood composition between individuals was high. All samples collected throughout the 2 yr period contained some females with broods. The data suggest that the reproductive strategy of L. uva is highly plastic, and that there may be three reproductive periodicities on seasonal, annual and inter-annual time scales. Received: 16 May 1997 / Accepted: 2 March 1998