Sulfide-oxidizing bacteria in the burrowing echinoid,Echinocardium cordatum (Echinodermata)

Symbiotic filamentous bacteria thrive in the intestinal caecum of the deposit-feeding echinoid Echinocardium cordatum. Specimens of E. cordatum were collected at Wimereux (Nord Pas-de-Calais, France) in 1991. Their symbiotic bacteria build nodules by forming multilayered mats around detrital particles that enter the caecum. The morphological features of the bacteria are those of Thiothrix, a sulfide-oxidizing genus. The filaments, which may form rosettes, are sheathed and made by a succession of hundreds of rod-shaped bacteria which store elemental sulfur in the presence of external sulfide. Live bacteria are restricted to the outer layers of the nodules. Their sulfide-oxidizing activity was investigated, using a Biological Oxygen Monitor, by measuring the O₂-consumption when reduced sulfur compounds are provided. They oxidize thiosulfate and sulfide. Optimal sulfide oxidation occurs at intermediary pO₂ (100 to 160 M O₂l^-1). Spectrophotometry has confirmed that the sulfur content of the filamentous symbiotic sulfideoxidizing bacteria depends on the presence of external sulfide. This is the first report of symbiotic intradigestive Thiothrixspp.-like bacteria; it lengthens the list of symbioses between sulfide-oxidizing bacteria and invertebrates from sulfide-rich habitats.     

Microbial activity, oxygen status and fermentation in the gut of the irregular sea urchin Echinocardium cordatum (Spatangoida: Echinodermata)

Microbial activity in the gut of the detrivore irregular sea urchin Echinocardium cordatum (Pennant) was studied by measurements of oxygen profiles, fermentation end products, C/N ratios, pH and concentrations of sulphide and sulphate in the gut segments, including the nodules of the intestinal caecum. The highest oxygen flux and consumption, and highest concentrations of short-chained fatty acids, and the lowest pH values occurred in the anterior stomach segments, including the anterior caecum. The C/N ratios indicate synthesis of microbial biomass in the caeca. The concentration of sulphate was high in the anterior stomach segments, whereas sulphide was only detectable in the nodules of the intestinal caecum. The anterior and intestinal caeca were the major sites for microbial activity, and oxidation of acetate and propionate produced in the two caeca corresponded to at least 9% of the total respiration of the sea urchin. Microbial fermentation, especially in the anterior caecum, seems to be important for the metabolism of E. cordatum, allowing the sea urchin to utilise refractile carbohydrates. The functions of the intestinal caecum are probably both residual fermentation and oxidation of accumulated sulphide. Received: 25 February 1998 / Accepted: 30 June 1998     

Functional morphology of the podia and ambulacral grooves of the comatulid crinoid Antedon bifida (Echinodermata)

Feeding units — viz. triplets of unequally-sized podia associated with protective lappets — occur all along the pinnules of adult Antedon bifida (Pennant). Small food particles are trapped by direct mucus impingement to the wall of primary and secondary podia (there are no mucus net or mucus thread helping in this process). Large particles are caught by primary and secondary podia which partly curl over them. Small particles accumulate on the collecting podia before being transferred to the groove, while large particles are transferred one by one. Transfer of particles to the groove occurs by wiping the collecting podia on the ciliary tracts against the ciliary current. When active, tertiary podia always paddle against the ciliary current. They serve in bolus formation (mucus embedding of food particles), but do not participate in bolus compaction or propulsion. Elimination of unwanted particles occur through the action of secondary podia whose movements may disrupt the lappet's palisade, thus creating a sideward current that moves particles from the groove to the outside. Typical podial triplets do not occur along brachial and calycinal grooves. Both brachial and calycinal podia function mostly in guiding and regulating particle flow. The feeding structures of early pentacrinoid larvae of Antedon bifida recall to mind those of pinnules of adult individuals. They consist of twenty-five podia arranged in five radial triplets alternating with five interradial pairs. They are similar to the pinnular feeding structures of adults in that they have both collecting (radial) and paddling (interradial) podia.     

Biochemical and morphometric study of growth in the stomach and intestine of the echinoid Lytechinus variegatus (Echinodermata)

In June 1990, previously starved Lytechnius variegatus were fed a 5% fish meal-agar diet for 32 d at 20°C and 32. Stomach and intestine indices increased by 139 and 66%, respectively, with the most growth occurring by Day 16. The stomach had a faster growth rate than the intestine, as indicated by an increase in the stomach: intestine ratio. Gonadal growth did not begin until Day 16, after substantial gut growth. DNA and morphometric analysis revealed that cellular growth in the stomach and intestine was first hyperplastic and then hypertrophic. DNA concentration and histological examination indicated that the stomach was composed of large voluminous cells, and the intestine of small cells. The stomach of starved individuals contained numerous depressions that significantly decreased in number during growth. The number of depressions significantly increased in the intestine. Lipid concentration and amount were higher in the stomach, and increased during growth by 43 and 258%, respectively, by Day 32; little change in lipid occurred in the intestine. The stomach lipid:DNA ratio increased by 66% by Day 16, with little change in the intestine. The concentration of soluble protein remained constant in the stomach, but had decreased in the intestine by Day 16. The total energy stored in the stomach and the intestine increased by 152 and 66%, respectively, by Day 32. The stomach mucosa increased in thickness and appeared to decrease its surface area. These data suggest that the stomach constitutes the primary storage organ of the gut. The intestinal mucosa also inreased in thickness but remained thinner than the stomich while apparently increasing in surface area, suggesting an enhanced role in residual nutrient absorption and ranslocation, respiration or water ion-transport.     

Digestive mechanics and gluttonous feeding in the feather starOligometra serripinna (Echinodermata: Crinoidea)

The movement and digestion of food in the gut ofOligometra serripinna (Carpenter) were studied at Lizard Island (14°3842S; 145°2710E) in the austral winter of 1986. Feather stars in the laboratory were fed a brief, small meal of brine shrimp nauplii and killed at increasing time intervals thereafter. Histological reconstructions showed that the ingested nauplii progressed along the digestive tract surprisingly quickly. Some nauplii were found in the mid and hind intestine in only 30 min, and all of the nauplii had reached the hind intestine and rectum in 1 h. Digestion of the nauplii had started at 1 h, and only a few fragments of naupliar exoskeleton remained in the hind intestine and rectum 5 h after the start of feeding. Videotape analysis showed that no fecal pellets were released during this experiment. In the natural environment ofO. serripinna, ingested particles may similarly be transported quickly to the hind part of the gut and digested there — when feather stars were fixed in the field, most of the gut contents were found in the hind intestine and rectum.O. serripinna, which efficiently rejects inert particles before they are ingested, usually defecates infrequently (probably not more than once over a span of many hours) and differs from some other feather stars that ingest numerous inert particles and defecate much more frequently. When specimens ofO. serripinna were fed continuously on brine shrimp nauplii,Artemia sp. (San Francisco strain), in the laboratory, the feather stars fed gluttonously, packing their guts with several hundred nauplii in 1 to 2 h. Thereafter, superfluous feeding began (i.e., further ingestions appeared to force undigested nauplii, some of them still living, out of the anus). These observations suggest thatO. serripinna usually feeds at relatively modest rates in its natural habitat, but can feed gluttonously to take advantage of infrequent patches of highly concentrated, nutritious particles (e.g. copepod swarms, migrating demersal zooplankton, and invertebrate gametes from mass spawnings). It is likely that such patches of nutritious particles are usually small enough to drift out of reach of the feather stars before gluttonous feeding proceeds to superfluous feeding. Opportunities for superfluous feeding in nature are probably very infrequent (e.g. ingestion of coral gametes and embryos after a mass spawning), and the feather stars evidently have no behavior that stops further ingestions after the gut becomes filled to capacity.     

Structural and functional peculiarities of the digestive system of Cucumaria frondosa (Echinodermata: Holothuroidea)

The fine structure of the intestinal epithelium of Cucumaria frondosa has been examined. The digestive cells possessed some specific ultrastructural peculiarities which testify to their participation in the transport of substances and in the processes of intracellular and cavitary digestion. The main units of the intestinal epithelium appear to be multifunctional digestive cells in which the phenomenon of compartmentalization among the organelles' groups, intended to carry out various functions, occurs. The heterogeneity of the structure of populations of the digestive cells is explained. Both primitive and progressive features of the structure of the digestive tract of C. frondosa are indicated.     

Reproductive cycle of the brooding echinoid Abatus cordatus (Echinodermata) in Kerguelen (Antarctic Ocean): changes in the organ indices,biochemical composition and caloric content of the gonads

Variations in organ indices, organic levels, organic and caloric contents of the gonads of the brooding echinoid Abatus cordatus (Verrill), collected in the Morbihan Gulf (49°30′S; 70°E) were studied over a 1 yr period (March 1978 to January 1979). In both sexes, a clear annual cycle was discernable for organ indices, and for organic and caloric contents. In contrast, the protein levels in the gonads varied moderately, while the levels of lipid and carbohydrate remained almost constant. This peculiarity sets A. cordatus apart from nearly all other echinoids characterized by an annual reproductive cycle. The male and female gonad indices change synchronously. The gonad indices double during maturation, reflecting variations in the germinal tissue. In both sexes, the maximal gonad index (at the end of March) coincides with the onset of the spawning season. The average male gonad index is 50% higher than that of the female. This difference is related to the restriction of coelomic space in the female due to development of the brood pouches. At maturity, the lipid and carbohydrate levels in the ovary are 2.8 and 2.1 times greater, respectively, than the levels in the testis, the latter having a 25% higher protein level. This disparity in organic levels reflects mainly the differences in germinal tissue composition. The female reproductive effort is higher than that of the male. The spawn energy output of a standard individual is 200 cal for a male and 228 cal for a female. The unusually lower gonad index of the female is compensated for by higher lipid and carbohydrate levels, giving the ovary a 40% higher calorific value.     

Karyotype analysis of the sea urchinParacentrotus lividus (Echinodermata): evidence for a heteromorphic chromosome sex mechanism

A consistent diploid number of 2n = 36 was determined for the sea urchinParacentrotus lividus from the Gulf of Palermo by analysis of mitotic chromosomes of both early developing embryos and male gonads. The haploid numbern = 18 was determined by counts of spermatocyte bivalents at diakinesis. A heteromorphic chromosome sex mechanism of the XY type is likely present in this species. This is indicated by the occurrence of a chromosomal pair, pair No. 2, which is heteromorphic in both morphology and size in about 50% of the mitotic figures (metaphases and anaphases) of einbryos. In addition, heteromorphism of the same pair of chromosomes occurred during spermatogonial metaphases in the five male specimens investigated here. The detection of a low chromosome number (2n = 36) compared to other echinoids (2n = 42 to 44), a heteromorphic chromosome sex system and the involvement of three chromosome pairs in nucleolar organization (NORs) provide evidence of the specialization of theP. lividus karyotype.     

Effects of current speed on filtration during suspension feeding in Oligometra serripinna (Echinodermata: Crinoidea)

Suspension feeding by the crinod Oligometra serripinna was studied at Lizard Island, Australia, in 1986. Video recordings were made of 90-m particles interacting with the filter of the crinoid in a laboratory flow chamber. A complete census of particles was possible because both the capture event and the filter area could be defined unequivocally. Also, because O. serripinna is a passive suspension feeder, a census of partcles could be made at different ambient current speeds without interference due to active pumping by the crinoid. Experiments were run at seven current speeds from 0.9 to 13.3 cm s^-1. Particles approaching the filter: (1) were captured, (2) passed through the filter without triggering a capture event, (3) passed through the filter after escaping from an unsuccessful capture event, or (4) were deflected around the filter. With increasing current speed, the proportion of deflections declined and the proportion of particles passing through rose: these results could be partially explained by the progressive widening of the spaces within the filter due to distortion of filter parts by the current. The proportion of captures (normalized to approaches) was comparatively low at 0.9 cm s^-1, rose to a relatively constant maximum from 1.7 to 6.4 cm s^-1, and then declined progressively at 9.5 and 13.3 cm s^-1. These proportions were translated into capture rates for whole crinoids by taking into consideration both the encounters with particles and the reduction of filter area by distortion of body parts at higher speeds. When plotted against current speed, capture rate peaked at 6.4 cm s^-1, which was close to the mean current speed that we measured on the reef in the microhabitat of O. serripinna.     

Crinoid phylogeny: a preliminary analysis (Echinodermata: Crinoidea)

We describe the first molecular and morphological analysis of extant crinoid high-level inter-relationships. Nuclear and mitochondrial gene sequences and a cladistically coded matrix of 30 morphological characters are presented, and analysed by phylogenetic methods. The molecular data were compiled from concatenated nuclear-encoded 18S rDNA, internal transcribed spacer 1, 5.8S rDNA, and internal transcribed spacer 2, together with part of mitochondrial 16S rDNA, and comprised 3,593 sites, of which 313 were parsimony-informative. The molecular and morphological analyses include data from the bourgueticrinid Bathycrinus; the antedonid comatulids Dorometra and Florometra; the cyrtocrinids Cyathidium, Gymnocrinus, and Holopus; the isocrinids Endoxocrinus, and two species of Metacrinus; as well as from Guillecrinus and Caledonicrinus, whose ordinal relationships are uncertain, together with morphological data from Proisocrinus. Because the molecular data include indel-rich regions, special attention was given to alignment procedure, and it was found that relatively low, gene-specific, gap penalties gave alignments from which congruent phylogenetic information was obtained from both well-aligned, indel-poor and potentially misaligned, indel-rich regions. The different sequence data partitions also gave essentially congruent results. The overall direction of evolution in the gene trees remains uncertain: an asteroid outgroup places the root on the branch adjacent to the slowly evolving isocrinids (consistent with palaeontological order of first appearances), but maximum likelihood analysis with a molecular clock places it elsewhere. Despite lineage-specific rate differences, the clock model was not excluded by a likelihood ratio test. Morphological analyses were unrooted. All analyses identified three clades, two of them generally well-supported. One well-supported clade (BCG) unites Bathycrinus and Guillecrinus with the representative (chimaeric) comatulid in a derived position, suggesting that comatulids originated from a sessile, stalked ancestor. In this connection it is noted that because the comatulid centrodorsal ossicle originates ontogenetically from the column, it is not strictly correct to describe comatulids as unstalked crinoids. A second, uniformly well-supported clade contains members of the Isocrinida, while the third clade contains Gymnocrinus, a well-established member of the Cyrtocrinida, together with the problematic taxon Caledonicrinus, currently classified as a bourgueticrinid. Another cyrtocrinid, Holopus, joins this clade with only weak molecular, but strong morphological support. In one morphological analysis Proisocrinus is weakly attached to the isocrinid clade. Only an unusual, divergent 18S rDNA sequence was obtained from the morphologically strange cyrtocrinid Cyathidium. Although not analysed in detail, features of this sequence suggested that it may be a PCR artefact, so that the apparently basal position of this taxon requires confirmation. If not an artefact, Cyathidium either diverged from the crinoid stem much earlier than has been recognised hitherto (i.e., it may be a Palaeozoic relic), or it has an atypically high rate of molecular evolution.Electronic Supplementary Material Supplementary material is available in the online version of this article at Communicated by J.P. Thorpe, Port Erin     

Form and feeding mechanism of a living Planctosphaera pelagica (phylum Hemichordata)

We describe aspects of the anatomy and suspension-feeding mechanism of a single Planctosphaera pelagica captured from the plankton in June 1992 off Bermuda in the western Atlantic. We also describe several unusual features of the larva, including its occurrence in surface waters, unusually large size, and limited swimming ability. Our account of the form and feeding behavior of P. pelagica is the first based on observations of a specimen captured and observed alive. Our limited observations suggest that the planctosphaera may use a suspension-feeding mechanism much like that of the other feeding deuterostome larvae (the pluteus and bipinnaria larvae of echinoderms and the tornaria larva of enteropneust hemichordates) known to capture food particles using a single ciliated band. Although we could not observe cilia directly, the movement of dye streams and food particles and the structure of the ciliated band suggest that some particles may be captured at the ciliated band by the reversal of ciliary beat. The planctosphaera possesses many prominent mucous glands near the food grooves. This suggests an important role of mucus in the biology of the larva, but we were not able to observe directly any role of mucus in particle capture.     

Effect of low salinity on the activity,feeding, growth and absorption efficiency of Luidia clathrata (Echinodermata: Asteroidea)

Exposure of Luidia clathrata (Say) to low salinity (17 S) results in a decrease in activity and rate of feeding, but has little effect on the absorption efficiency. Growth, as indicated by changes in body size and energy content of the body wall and pyloric caeca, is reduced in low salinity due to a decrease in feeding rate (energy consumption) and to a decrease in efficiency of utilization of material and energy absorbed. The low efficiency indicates that either additional energy is required for maintenance or energy is used inefficiently in low salinity. Thus, L. clathrata is limited energetically in low salinities, although it lives and reproduces there.     

Cuvierian tubules of the holothuroid Holothuria forskali (Echinodermata): a morphofunctional study

Quiescent Cuvierian tubules of Holothuria forskali (Delle Chiaje, 1823) have a pseudostratified mesothelium made of ciliated cells that cover elongated cells containing lipoproteie granules. Together these cells form conspicuous transversal folds that penetrate the underlaying connective tissue. Circular and longitudinal muscle cells occur under the tips of the mesothelial folds. These cells are presumably myoepithelial cells; they divide the connective tissue into a thin outer layer (where collagen fibers are directed perpendicularly to the tubule long axis) and a thick inner layer (where collagen fibers are arranged in helices parallel to the tubular long axis). Nerve processes are associated with the longitudinal muscles; they also occur between the spirally arranged collagen fibers. A spiral nerve runs along the tubules; it innervates the circular muscles. The tubule lumen is narrow with a highly convoluted limiting epithelium. Epithelial cells are not ciliated; they have basal processes that contain enlarged spherules including mucosubstances and proteins. While having the same diameter as quiescent tubules, elongated tubules have a much thiner wall surrounding an enlarged cylindrical lumen. The mesothelium has no adluminal cells and consists of unfolded granular cells. In contact with a solid surface, granules become a sticky secretion. Longitudinal muscle fibers disintegrate and circular fibers form conspicuous rings along the tubules. Collagen helices still occur, but are considerably elongated and flattened. Inner epithelial cells dissociate from each other and typically lack basal processes and spherules, the latter being secreted into the lumen of elongating tubules. Discharge of Cuvierian tubules results from tubule expulsion and elongation. Tubule expulsion is triggered by the opening of the anus of a contracted holothuroid and results from the rupture of the cloaca with subsequent expulsion of coelomic fluid. Tubule elongation results both from the mechanical stimulation of the tubule sphincter by hydrostatic pressure and the entry of water into the tubule. Mechanical stimulation of the sphincter results in a rapid contraction of the circular muscles that causes the disintegration of adluminal cells, the unfolding of granular cells and the stretching of inner epithelial cells. Entry of water immediately follows sphincter stimulation and complete tubule elongation. Water pressure causes the irreversible elongation of collagen helices, which results both in a considerable thinning of the tubule wall and the formation of enlarged water-filled lumen. It is suggested that slippage of collagen fibers in elongating tubules is nervously mediated.     

Diverticulum sand in a miniature sand dollar Sinaechinocyamus mai (Echinodermata: Echinoidea)

Sinaechinocyamus mai (Wang) were collected from the low intertidal zone at Tunghsiao, western Taiwan, periodically from July 1990 to July 1991 and May 1993. The mean body length was 7.3±1.01 mm from 146 juveniles and adults. All individuals contained sand grains in their intestinal diverticula. The densities of sand dollars ranged from 1.2 to 2.5 mg cm^-3 and had an inverse linear relationship to the body length. The percentage of sand weight in the diverticulum to the wet body weight is inversely correlated to the body length, indicating that juveniles contain a higher proportion of sand than adults. The ratio of sand weight to body length did not change significantly during the study period. 74% of the diverticulum sand was 0.075 to 0.125 mm in diameter, whereas only 0.1% of the sand in the substrate was this size. The sand in both the diverticulum and the substratum consisted of feldspars and quartz (88.4%) and iron oxide (11.6%). The sand grains of the diverticulum were eliminated from the anus.     

Comparative study of sub-cuticular bacteria in brittlestars (Echinodermata: Ophiuroidea)

Arm tissues from species of brittlestars from the British Isles and North America were examined by light and electron microscopy for the presence of sub-cuticular bacteria (SCB) which were recorded in 17 of the 19 species studied. Three major groups of SCB could be distinguished on the basis of their morphology. The bacterial morphology was not correlated with the host ecology but did appear to be related to the phylogeny of the hosts. Ophiuroids of the same genera had morphologically similar SCB and this was also generally true of species from the same family. This indicates the possibility of co-evolution between the SCB and their hosts. Estimates of SCB load were made for 9 of the species by direct counting and by quantifying the amount of bacterial endotoxin present in the host tissues. SCB numbers varied interspecifically from 3.7×10⁸ to 4.6×10⁹ SCB per gram of ash-free brittlestar arm tissue. Endotoxin values ranged from 5.97 to 285 g g^–1 ash-free arm tissue. Calculations suggest that SCB form at least 0.1 to 1% of the total biomass of the arm tissues. There was considerable intraspecific variation in SCB load. The possible role and significance of SCB is discussed.     

Observations on the food of Antedon bifida (Echinodermata: Crinoidea)

The gut contents of specimens of the temperate crinoid Antedon bifida (Pennant) were collected from Dalkey, County Dublin, at monthly intervals for 1 yr, and occasionally from other areas around the Irish coast. Quantitative analysis showed the main components to be detritus (65%), plankton (18%) and inorganic particles (17%). This composition was remarkably constant throughout the year and at all locations, the main variation being in the plankton which was at a minimum in February (4%) and reached a maximum in August (36%). Food particle collection appeared to be nonselective within the appropriate size group, the essential feature of a particle being that it would fit into the ambulacral groove. Fragile planktonic diatoms and dinoflagellates, which occurred in blooms in summer and autumn, were digested by A. bifida, but more robust diatoms passed intact through the gut. Histochemical investigations indicate that the bulk of the detritus is refractory, and it is suggested that its associated micro-flora and micro-fauna may be a major source of nutriment for this crinoid.     

“Glandular pockets” of the integument and feeding mechanism inPagurus bernhardus (Crustacea: Anomura)

The benthic anomuran crabPagurus bernhardus (L) were collected from the North Sea near Helgoland, West Germany, during the years 1986–1987. The histological study of the integument ofPagurus bernhardus reveals a double structure with dorsal and ventral cuticular layers and with two epithelial cell layers. Additional structures have been developed within the integument to trap micro food organisms. The structure and function of the cupshaped glandular pockets of the integument is described. The cells which secrete mucus are also described. Histological and histochemical methods have been employed to study the chemical nature of various cells of the integument and the secretions of the glandular pockets. The ecological significance of the sensory hairs, glandular pockets, cuticular layers and the supra-branchial groove is discussed with reference to the crab's feeding mechanism.     

Reproductive biology of a deep-sea brittle star Amphiura carchara (Echinodermata: Ophiuroidea)

 New information on the brooding reproduction of Amphiura carchara, and previous studies of several deep-sea congeners, contradict the prevailing notion that direct development is exceptional among deep-sea echinoderms. Over 500 specimens of A. carchara from 2,850 to 4,100-m depths off the coast of California, USA, were studied. The species was found to be gonochoric, although most brooding species of ophiuroids are hermaphroditic. Females each brooded up to 72 embryos at a time, with up to 10 in a single bursa. The embryos of individual adults were often at different stages of development, but those brooded in a single bursa tended to be at the same stage. Thus, the species has characteristics that breach the distinctions between sequential and simultaneous brooding exhibited by shallow-water ophiuroids. The embryos developed from yolky eggs that are large for an ophiuroid, with the mean largest oocytes 0.45 mm, and ranging to 1.28 mm in diameter. Almost all late-stage embryos were positioned with their mouth and arms pressed against the wall of the bursa, possibly to facilitate the uptake of nutrients from the parent. Thus, A. carchara may be matrotrophic. The largest embryos examined had a rudimentary disk skeleton, and arms with four joints and a terminal plate. Emerging juveniles probably differ in disk diameter. The species appears to brood year round, although differences in gonad size, the incidence of brooding, and the relative numbers of early developmental stages in summer and winter samples indicated that there are seasonal trends in reproduction. Received: 14 February 2000 / Accepted: 3 July 2000     

Reproductive cycle of the sea urchin Holopneustes purpurascens (Temnopleuridae: Echinodermata)

This study documents the annual reproductive cycle of the Temnopleurid echinoid Holopneustes purpurascens near Sydney. H. purpurascens reached sexual maturity between 11 and 26 mm diameter and was gonochoristic. The sequence of oogenesis was similar to previously described echinoids. However, the proportion of eggs at each stage showed no temporal pattern in abundance, suggesting that vitellogenesis is continuous throughout the year. Spermatogenesis was also similar to other echinoids and showed a significant increase in the proportion of partially spawned testes in spring, followed by a similar increase in the proportion of partially spawned testes in late spring and summer. Gonad indices showed a peak in weight from late winter to mid-spring (9.10ǃ.47 for females; 6.28ǂ.43 for males; mean-SE), then a decline for both sexes. Although spawning was variable over time, there was a peak in the proportion of spawning from late winter to early summer that correlated with the observed peaks in gonad indices and gametogenic cycles. The demographic implications of this reproductive pattern are that new recruits can enter the population through synchronous spawning during the breeding period, and smaller haphazard spawning events at other times of the year.