Reproduction and development of Sabella media,a sabellid polychaete with extratubular brooding

Known reproductive patterns in the polychaete family Sabellidae include: (1) broadcasting of gametes, (2) depositing of benthic egg masses, (3) brooding outside the lip of the tube, and (4) brooding within the tube. There is little information for sabellids in the third category; there-fore we have studied the reproductive biology of Sabella (=Demonax) media (Bush), one of the few species known to brood its early developmental stages outside the tube. A total of 32 adults of S. media with egg cocoons were collected from the surfaces of compound ascidians (Aplidium sp. and Didemnum sp.) and from holdfasts of a brown alga (Hedophyllum sessile) at Eagle Cove, San Juan Island, Washington, USA, from June 1981 through June 1982, between tidal levels of 0.0 and 0.6 m. The donutshaped cocoons, each containing over 1 000 eggs, are deposited just outside the tube aperture from April through September. Larval development takes place within the cocoon through the 3-setiger stage, at which time the larvae emerge (about 8 d after egg deposition). The newly hatched larvae are demersal and swim near the bottom of the culture dish for 1 d before settlement. Metamorphosis takes nearly a week, and initial formation of the tube is also gradual. The reproductive patterns within the family Sabellidae are discussed, and the adaptive significance of extratubular brooding considered.     

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.     

Reproduction, larval development and functional relationships of the burrowing, spionid polychaete Dipolydora armata with the calcareous hydrozoan Millepora complanata

Dipolydora armata (Langerhans, 1880) is a small (4 to 5 mm) spionid polychaete found burrowing in the calcareous hydrozoan Millepora complanata Lamarck, 1816, on coral reefs at Barbados, West Indies. It excavates complex networks of interconnecting burrows and forms aggregations of worms in cavities within branches of the coral. Adult worms have a mixed feeding mode (suspension feeding and deposit feeding). Size–frequency distributions of worms in branch samples suggest that they mature in a single year and that reproduction occurs throughout the year. Burrow openings on the surface of the coral develop distinctive, erect spines caused by combined growth of worm tubes and host tissue. Millepore zooids were absent in the vicinity of tube openings and on spines, and thus the potential feeding surface of the coral will be reduced in heavily colonized branches. Burrows and openings were densest at the bases of millepore branches where weakening of the skeleton would be expected to occur. The absence of openings near the branch tips suggests difficulty in larval settlement there, amongst stinging zooids. Reproduction␣and larval development of the worms were examined, and a sequence of larval stages from one to 20 segments and a juvenile stage of 22 segments are described. Eggs are deposited in brood sacs attached to the burrow wall, and the larvae feed upon nurse eggs (adelphophagy). The presence of larvae and juveniles occurring free in the burrows suggests that larval development may be completed within the host coral as an alternative or in addition to a planktonic larval phase. Lack of provisional larval setae, early development of adult capillary setae, production of special spermatophores and a protracted breeding cycle in D. armata are all traits which would favour complete development within the host skeleton. Received: 6 March 1997 / Accepted: 25 October 1997     

Reproduction and development in the pycnogonid Pycnogonum littorale

Aspects of the reproductive biology of Pycnogonum littorale (Ström) are examined. Vitellogenesis occurs between November and August, the process resembling that in Nymphon gracile, annelids, and Limulus polyphemus, in which the majority of the yolk is synthesized within the oöcyte, with only a small contribution from outside, thus contrasting with the method in insects. The mode of formation of the mature yolk platelets shows similarities with the process described in Cambarus spp. Growth occurs in the post larva by a series of moults, and sometimes in the adult by a process not involving moults. The male usually has 9 moults and the female 10 or 11.     

Population biology and larval development of the terebellid polychaete Nicolea zostericola

A 3-year study was conducted on a population of Nicolea zostericola (Oersted: Grube, 1860) at Nahant, Massachusetts (USA), which indicated that this species has a life span of about 1 year. Spawing occurred from mid-April to early July, after a rise in sea-water temperature to about 6°C. Pair formation occurred between sexually mature adults prior to and during spawning. Eggs were deposited in cocoons, where development occurred in 14 to 22 days. Larval develomment is described along with juvenile and adult substrate preferences and behavior. The entire intertidal population disappears following the spawning season in late June, and reappears in September as a result of migration of worms from the sub-littoral zone. Oogenesis consists of 3 phases: a short gonadal and follicular phase, followed by a longer vitellogenic phase during which oocytes are free-floating in the coelomic fluid.Contribution no. 31 from the Marine Science Institute, Northeastern University, Nahant, Massachusetts, USA.     

Reproduction,development and population biology of the Caribbean ophiuroidOphionereis olivacea,a protandric hermaphrodite that broods its young

Reproduction and development of the ophiuroidOphionereis olivacea H. L. Clark, a species that broods its young, were investigated in Florida from January through December 1985 and in Belize in June 1985 and April 1986.O. olivacea has a maximum disc diameter of 5.2 mm and is a protandric hermaphrodite. Sex reversal occurs at disc diameters ranging between 2.2 and 4.0 mm; it has 400 µm diameter oocytes and is ovoviviparous. As expected from an obligate out-crosser, this ophiuroid has a similar allocation to male and female reproduction, in terms of gonad volume. Reproduction of the Florida population was monitored for one year.O. olivacea is a sequential brooder and incubates its young during the coldest months of the year. The females produce a single clutch of juveniles each year. Spawning starts in November and peaks in January and February. The ova are spawned synchronously from all the ovaries of each female into the bursae and are retained there. Fertilization is accomplished by intake of sperm into the female bursae.O. olivacea develops through a ciliated embryonic stage that appears to be a modified vitellaria larva lacking ciliary bands. These modified larvae swim in seawater in the bursae. Direct development in this species has resulted from heterochrony in the loss of ophiopluteus features. The number of brooding females in the population increases in November and reaches a maximum in March. JuvenileO. olivacea emerge from the bursae at a disc diameter of 480 µm and each arm has three segments. Recruitment was first detected in April, and juveniles were particularly abundant in June. Small size inO. olivacea is associated with paedomorphic heterochrony with precocious maturation of the males at a disc diameter of 1.5 mm, ~2 mo after taking up their free existence. Brooding as a life history mode inO. olivacea is examined and the adaptations of this species to its warm-water habitats are discussed.     

Gametogenesis in a Northumberland population of the polychaete Melinna cristata

The proliferative activity of the germinal epithelium in relation to breeding biology has been investigated in a population of the ampharetid polychaete Melinna cristata (Sars). This species is dioecious and highly gregarious, and breeds during a brief period at the end of December or beginning of January. The gonal exists in proliferative and non-proliferative states. The former begins immediately after spawning, and is maintained until September. The rate of release of gametocytes into the coelom varies during this period, with peaks in January and April. In September, DNA synthesis ceases in gonads of both males and females and no further gametocytes are released into the coelom, but primary oocytes which have completed the S phase of meiosis continue to develop and accumulate in the ovary as a population of previtellogenic oocytes which are released into the coelom immediately after spawning. This cycle of germinal epithelium activity is compared with those described in other polychaetes.     

Reproduction,larval development and post-larval growth ofNaineris laevigata (Polychaeta,Orbiniidae) in the Mediterranean Sea

To investigate the life-history adaptations of a brackish-water population ofNaineris laevigata Grube, a population from Acquatina lagoon near Lecce (Italy) was studied. Benthos and plankton samples were collected monthly over a period of ca. 2 yr (1989–1990). Observations of gametogenesis indicate that oogenesis is intraovaric, probably with autosynthetic yolk formation. Oogenesis takes about 7 mo, from November to April–May, for both proliferative and vitellogenetic phases. Reproduction is synchronized within the population. Spawning has also been obtained under laboratory conditions where larval development and post-larval growth were studied. Eggs measured 240 µm in diameter and were spawned within a gelatinous mass. The lecithotrophic pelagic stage was very short. Reproductive effort was high, probably because of high food availability and low level of competition. One of the most interesting findings was the probable presence of a resting stage in the life-cycle. The adaptive significance of enclosing the eggs in gelatiuous masses and of reducing the duration of the pelagic stage is discussed.     

Reproduction and development of Paedoclione doliiformis,and a comparison with Clione limacina (Opisthobranchia: Gymnosomata)

Observations on breeding season, copulation, spawning, and development are described for Paedoclione doliiformis, the only gymnosomatous pteropod which consistently retains external larval features throughout its life. The number of eggs spawned per individual is dependent upon temperature and availability of Spiratella retroversa, its thecosome prey. At 17° to 19°C, planktotrophic veligers hatch from floating egg masses within 3 days, and cast their shells approximately 11 days later. The resultant shell-less veligers could complete metamorphosis to the polytrochous larval stage, in which the body is encircled by 3 ciliary bands, within 12 h. Some polytrochous larvae begin feeding on veligers of S. retroversa within 2 days. Unlike other gymnosome species, there is no further change in external appearance except for growth. A comparison of reproduction and development has been made with Clione limacina, another gymnosome which competes for food with P. doliiformis in Nova Scotian (Canada) coastal waters.     

Feeding,tube-building and particle-size selection in the terebellid polychaete Eupolymnia nebulosa

The present study was aimed at obtaining new information on the feeding biology of the terebellid polychaete Eupolymnia nebulosa (Montagu). Feeding, tube-building, particle-size selection, and tentacular morphology are described. Experiments were carried out during the fall of 1984 on specimens collected in the vicinity of Banyuls-surmer, France. Feeding activity takes place almost entirely in darkness, and E. nebulosa shows a marked preference for smaller particles when feeding and selects larger ones for tube-building. The control of its activity pattern by light intensity may result in seasonal modification of its energy balance. The mechanisms controlling particle-size selection in this species are discussed.     

Distribution and feeding in the onuphid polychaete,Diopatra cuprea (Bosc)

Population density of the onuphid polychaete Diopatra cuprea is poorly correlated with particle size distribution of the substratum. It varies directly, however, with current velocity. Measurements of the volume of oxygen drawn through the tube by the inhabitants' rhythmic activities, and the volume consumed under similar conditions, indicate that the rate of oxygen utilization is unusually low; therefore, the influence of current velocity cannot be exerted through its effect on oxygen supply. We suggest that the worm's tube, which protrudes several centimeters above the substratum in the form of an inverted hook, is a food-catching device whose efficiency is governed by the volume of water flowing past. This hypothesis is supported by the identity of many species found both in the gut and on the tube. We also suggest that the tube-irrigating activities permit the animal to test the medium for the presence of chemical stimuli emanating from food caught by the tube; supra-threshold concentrations of these stimuli elicit the feeding response.     

Larger foraminifera: Reproduction and early stages of development in Heterostegina depressa

The process of reproduction (multiple fission) of the megalospheric gamont of Heterostegina depressa d'Orbigny, 1826 (Nummulitidae) is described. During this process, the protoplasm separates outside the parent test into the juveniles. The initial chambers receive some of the symbiotic algae from the parent protoplasm. The second chamber develops from the initial chamber by division, not by growth. The newly formed 2-chamber-stage receives a second set of symbiotic algae from the parent residual protoplasm. Thereafter, calcification takes place, and the first ectoplasm sheath is formed. The problem of alternation of generations is discussed. From the very small proportion of microspheric individuals found in Heterostegina species (fossil and recent) it is concluded that gamogony has been greatly reduced.     

Regeneration in the gonochoristic polychaete Ophryotrocha notoglandulata

Anterior and posterior regeneration in both male and female Ophryotrocha notoglandulata Pfannenstiel, 1972 was induced by amputation of parts of the prostomium or caudal segments. Regeneration capacity is identical in males and females. The prostomium is not necessary for caudal regeneration.     

Environmental grain and polychaete species' diversity in a bathyal benthic community

Patterns of polychaete species' dispersion in the San Diego Trough, Southern California Continental Borderland, North Pacific Ocean, at a depth of 1230 m are analyzed. Samples consist of 4 replicate 0.25-m² box cores, each partitioned into twenty-five 0.01-m² subcores, and of 1 unpartitioned core. The sampler is biased but, when this bias is taken into account, few species show strong aggregation either between or within cores. If all species are considered together as replicates, intraspecific aggregation is detected between cores, but uniform dispersion dominates within cores. Patchiness or habitat partitioning on the assayed scales can thus account for little of the extremely high species' diversity observed. Apparently due to an environmental structure having a “grain” smaller than 0.01-m², the diversity of species assumed to be sedentary is higher than the diversity of species assumed to be mobile. One evidence of such structure is a negative covariance between paraonid abundance and density of “mudballs” constructed by a cirratulid. Consideration of these results suggests that either grain specialization or simultaneous, biogenic disequilibrium or both act on spatial scales smaller than 0.01-m² to maintain high polychaete species' diversity in the San Diego Trough.     

Reproduction and development of the blue coralHeliopora coerulea (Alcyonaria: Coenothecalia)

Up to the present time, the reproductive cycle and larval development ofHeliopora coerulea, living fossil and sole member of the alcyonarian order Coenothecalia, have been undescribed. Populations ofH. coerulea studied on the Great Barrier Reef between 1984 and 1989 were found to have separate sexes and an annual gametogenic cycle. Mature eggs were large (>800µm diam), and their development was initiated internally. There appeared to be a lunar or semi-lunar periodicity in reproductive behaviour, with brooding of larvae commencing around either full or new moon. Development proceeded via superficial cleavage and a solid stereoblastula. Subsequent development took place on the surface of the colony, within a temporary brood-space created by protracted distension of the polyps. Larvae lacked zooxanthellae and were brooded for between 6 and 14 d prior to leaving the colony. Reproduction and development reflected the taxonomic affinities ofH. coerulea, but brooding and embryological development also appeared to be constrained by its morphology. Reproductive and larval characteristics ofH. coerulea may offer a partial explanation of the current biogeographic range ofH. coerulea.     

Benthic polychaete assemblages and their relationship to the sediment in Port Madison,Washington

Two indices of community association and a 3 dimensional ordination of stations were used to elucidate the relationship between small-scale changes in species, composition of polychaete assemblages and changes in the physical character of the sediment, at 9 stations along a 1.5 km subtidal transect. There were no faunal or physical discontinuities that might have been used to delineate boundaries of polychaete communities, except at a very shallow station where the effects of extreme fluctuations of temperature and salinity were evident. The degree of similarity between assemblages was related to the similarity of the sediments at the different stations. In particular, the changes in species composition appeared to correspond most clearly to differences in the clay content of the sediment.     

Maturation,epitoky and regeneration in the polychaete Eunice siciliensis under field and laboratory conditions

In the gonochoric polychaetous annelid Eunice siciliensis Grube, germ cells only develop in the posterior segments of the worm; these segments subsequently differentiate into an epitokous portion separating at maturity from the infertile body part. As in the Pacific and Atlantic palolo worms, the epitokous portions die some hours after spawning. Laboratory investigations revealed that the anterior parts of spawned worms survive and regenerate genital segments. After a period of at least 8 months, paired gonads are developed in these segments. Gonia proliferating later from the germinal tissue are released from gonadal sacs into the coelomal cavities, where gamete development occurs. A reproductive epitokous portion does not mature and separate until the second year of cultivation; it is followed by caudal regeneration. These facts and the observation that only about 50% of the individuals obtained from samples of coralligène were sexually differentiated, led to the conclusion that E. siciliensis probably has a bi-annual reproductive cycle. Caudal regeneration does not depend on the presence of a prostomia hormone. The ability to form posterior regenerates is inherent to the parapodial segments of all body regions, except for mature genital segments. This is also valid for the formation of morphologically different secondary prostomia. However, for initiation and further promotion of gametogenesis and epitokous development, at least one gonadotropic factor originating from the prostomium is required. Neurosecretory cells within the brain suggest this factor(s) to be of neuro-endocrine nature. Specimens developing secondary prostomia were found both under field and laboratory conditions. In several cases, sexual development took place, and even epitokous portions were separated from such individuals. From this it appears that the gonadotropic functions are re-established by the regenerated prostomia in order to ensure reproduction in individuals accidentally deprived of the anterior end. The possible rôle of temperature and light as environmental factors involved in the control of normal and regenerative growth, of sexual development and reproduction is discussed.     

Dietary study of the midwater polychaete Poeobius meseres in Monterey Bay,California

This study presents the first quantification of the diet of a gelatinous midwater organism on a temporal basis. Using the Monterey Bay Aquarium Research Institute's remotely operated vehicle Ventana, regular collections of the polychaete Poeobius meseres (Heath, 1930) over a 1 yr period (October 1990 to November 1991) in Monterey Bay yielded intact organisms for the study of feeding behavior and quantitative analysis of stomach contents. In situ observations showed P. meseres feeding in two different ways: (1) by deployment of a mucus web in the water column that passively collects particles for consumption; and/or (2) by grasping detrital material in the water column with its ciliated tentacles. Stomach-content analyses showed that P. meseres is primarily coprophagic, its diet being dominated by fecal pellets from euphausiids and copepods. These fecal pellets appear to provide P. meseres with essentially all its carbon. Although fecal pellets were the most important food item volumetrically, P. meseres also consumed large numbers of diatoms and small numbers of dinoflagellates, chrysophytes, radiolarians, foraminiferans and eggs. The diet of P. meseres appears to reflect primary productivity in the surface waters, with different food items predominant in the diet at different times of the year. Pennate diatoms were most abundant in the diet during the fall, centric diatoms were most abundant during the sumnier, and fecal pellets during the winter. The composition of P. meseres diet suggests that this and other midwater gelatinous organisms have a significant role in the remineralization of particles as they sink from the surface to the deep sea.     

Natural variations in tissue concentration of copper,zinc and iron in the polychaete Nereis diversicolor

This study was undertaken to investigate the natural variation of heavy metals in the polychaete Nereis diversicolor O. F. Müller and to examine this variation with respect to physiological and environmental parameters. During a 2 yr period from October 1980 to October 1982, concentrations of copper, zinc and iron in N. diversicolor from the Tees Estuary, North East England, were found to vary significantly with time. A seasonal influence on whole body copper concentration, in part related to the reproductive cycle, was observed. Zinc concentrations in N. diversicolor increased during periods of rapid growth and may represent a physiological demand for this metal. Whole body concentrations of iron appeared to be independent of size of worm, sexual maturation and sediment concentrations.     

Chaotic genetic patchiness and high relatedness of a poecilogonous polychaete in a heterogeneous estuarine landscape

The genetic structure of benthic marine invertebrates is often described as “chaotic” when genetic structure cannot be explained and barriers to dispersal and gene flow cannot be identified. Here, chaotic patterns of genetic structure for the polychaete Pygospio elegans (Claparède) sampled at 16 locations from the heterogeneous Isefjord–Roskilde Fjord estuary complex in Denmark were found. There was no isolation by distance, and the geography of the estuary complex did not seem to pose a barrier to dispersal and gene flow in this species. We investigated whether characteristics of the environment could be related to the genetic structure and possibly restrict gene flow in this species. Additionally, since P. elegans is poecilogonous, producing larvae with different pelagic developmental periods, we investigated whether observed developmental modes in the samples might clarify the genetic patterns. None of the tested factors explained the population genetic structure. However, a high degree of relatedness among individuals in almost all samples was found. Samples with a larger percentage of young individuals had more related individuals, suggesting that different cohorts could be comprised of individuals with different degrees of relatedness. Relatedness within a site could be increased by limited larval dispersal, collective dispersal of related larvae, sweepstakes reproductive success, or asexual reproduction, but distinguishing between these requires further study. Using a “seascape genetics” approach allowed us to investigate some of the numerous potential factors that could influence population genetic structure in a poecilogonous species.