Responses of ovaries and testes of Lytechinus variegatus (Echinodermata: Echinoidea) to dietary administration of estradiol, progesterone and testosterone

 In many vertebrates, environmental factors influence gamete differentiation and growth of the mature gonad through alteration of sex steroid production or action; however, it is unclear how gamete differentiation and gonadal growth are regulated in echinoids. The purpose of this study was to examine the influence of dietary administration of estradiol (E2), progesterone (P4), testosterone (T) and finasteride (F, a 5α-reductase inhibitor) on the ovaries and testes of mature Lytechinus variegatus (Lamarck) during gonadal growth. Echinoids were fed a formulated diet supplemented with steroids or steroids in combination with finasteride for 36 d. The effects of dietary administration of steroids on L. variegatus were both steroid- and sex-specific. The mean ovary index was 54% greater in individuals fed E2 than from individuals fed the control (C) diet (10.0 ± 1.1 vs 6.5 ± 0.7, respectively; P < 0.05). Individuals fed E2, P4, E2/P4, and P4 in combination with F had significantly smaller oocytes (P < 0.005) than individuals fed C. The volume fraction occupied by nutritive phagocytes in ovarian tubules from individuals fed E2/P4 or P4 were significantly larger than the volume fraction occupied by nutritive phagocytes from individuals fed C, indicating that E2 and 5α-reduced progestins may promote nutrient allocation to nutritive phagocytes. Although oocytes from the individuals fed T alone were significantly smaller than those fed T in combination with F, oocytes from individuals in both treatments were significantly larger compared to oocytes from individuals fed C. These data suggest that upon removal of 5α-reduced androgens, T is able to promote an increase in oocyte diameters. In contrast, the mean testis index was 56% greater in individuals fed P4 than in individuals fed C (8.9 ± 0.6 vs 5.7 ± 0.9, respectively; P < 0.05); the testis index did not increase in individuals fed P4/F, suggesting that 5α-reduced progestins stimulate testicular growth. Testes growth in the presence of 5α-reduced progestins was accomplished by significant increases in the volume fraction occupied by nutritive phagocytes and by a significant reduction in the volume fraction occupied by spermatogenic columns in testicular tubules. These data further indicate that 5α-reduced progestins (or 5α-reduced androgens) may inhibit spermatogenic column formation. In conclusion, E2 stimulated ovarian growth but inhibited oocyte growth, whereas T had no affect on ovarian growth but promoted oocyte growth in L. variegatus. We hypothesize that the E2 (or E2 metabolites) and/or 5α-reduced androgens in combination with T regulate oocyte growth in the echinoid L. variegatus. In addition, 5α-reduced progestins promoted nutrient accumulation in nutritive phagocytes within the ovaries and the testes. Furthermore, 5α-reduced progestins stimulated growth of the testes and inhibited spermatogenic column formation, suggesting that 5α-reduced progestins regulate nutrient accumulation into nutritive phagocytes and spermatogenic column formation in L. variegatus. The differences in estrogen effects between echinoids and asteroids may be related to differences in gonad morphology and, ultimately, the differences in cellular signalling pathways (paracrine vs endocrine). Received: 22 May 1999 / Accepted: 24 May 2000     

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.     

Effects of temperature and salinity acclimation of adults on larval survival,physiology, and early development of Lytechinus variegatus (Echinodermata: Echinoidea)

Larval survival and developmental rates of Lytechinus variegatus (Lamarck) were determined as a function of temperature and salinity in two experiments by: (1) directly transferring fertilized eggs to 35, 30, 27.5, 25, 20, 15, and 10S seawater at 18 and 23°C, and (2) acclimation of adult sea urchins to the conditions described above for 1 to 4 wk prior to spawning. Developmental rates and percent survival of larvae prior to metamorphosis decreased at salinities below 35 (Q₁₀ values for metamorphosis=0.380 to 0.384). Temperature and salinity significantly (P<0.05) affected metabolic rates of L. variegatus plutei. These results show that L. variegatus larvae are stenohaline when compared to larvae of other echinoderm species. LC₅₀ values (S), developmental rates, and survival to metamorphosis indicate that acclimation of adult sea urchins to lower salinity prior to spawing and fertilization does not enhance development or survival of embryos exposed to low salinity.     

Circulation of perivisceral fluid in the sea urchin Lytechinus variegatus

The principal driving mechanism of perivisceral-fluid circulation was investigated in the echinoid Lytechinus variegatus by metal-clad hot-wire anemometry. Analysis of 23 flow profiles from 13 individuals collected from 1 to 3 m water depth at Tarpon Springs and Sarasota, Florida (USA) in 1984 indicates that for this species, the ciliated epithelium is an ineffective driving mechanism for mixing of the perivisceral fluid. Instead, the Aristotle's lantern is the major driving force of circulation of the perivisceral fluid, with velocity fluctuations of 1.5 mm s^-1 amplitude in the cavity center during intermittent periods of activity. These fluctuations rapidly decay as the ciliated surfaces are approached. Spectral analysis of velocity time-series reveals predominant energy-containing velocity fluctuations between 0.007 and 0.05 Hz. The circulation, which can be described as non-turbulent forced mixing, has revealed four different flow patterns which appear to be correlated with specific animal activities. A modified eddydiffusion model predicts that oxygen transport through the cavity over a 2 cm path length requires more than 20 h. Calculation of the oxygen flux to a ripe ovary suggests that supply does not meet ovarian oxygen demand in this case. Alternative pathways of oxygen transport invoking advection in perivisceral-fluid eddies and along the ciliated coelomic surfaces are compatible with the observed flow patterns and lead to much shorter oxygen-transport time scales of the order of 1 to 10 min.     

Factors controlling variation in the seasonal spawning pattern of Lytechinus variegatus

A population of the regular sea urchin Lytechinus variegatus was sampled, and the gonad volume and test diameter recorded at monthly intervals for 10 years. Parameters abstracted from the data included the size and date when the gonads were full and when they were spent, the spawning pattern, and the spawn output. Environmental parameters available were sea temperature and rainfall. Correlations were determined among these. A correlation was also found between the appearance in successive years of a brood of young urchins on the shore and the temperature and rainfall.Contribution No. 1490 from Rosenstiel School of Marine and Atmospheric Science, University of Miami, 10 Rickenbacker Causeway, Miami, Florida 33149, USA. We are indebted to the Federal Water Quality Administration for supporting this work under Grant No. DI WP-01433.     

Frontal ambulacral and peribuccal areas of the spatangoid echinoid Echinocardium cordatum (Echinodermata): a functional entity in feeding mechanism

Echinocardium cordatum (Pennant, 1777) were collected in Normandy, France, in March and November 1985. The grooved frontal ambulacrum of the burrowing echinoid E. cordatum functions in transferring surface sediment from the apex to the mouth of the echinoid. Particles that fall down the burrow's chimney accumulate between the spines of the apical tuft and are taken over by specialized groove spines. Due to the slope of the groove and the type of floor spines it harbours, four successive regions can be recognized, namely the adapical region, the fasciolar region, the ambital region, and the adoral region. As a general rule aboral floor spines (i.e. club-shaped, golf-club-shaped, and isodiametric spines) function in gathering particles while propelling them mouthwards; they simultaneously embed particles in a mucous string. The oral floor spines (i.e. spatulated spines) function in hauling and guiding the mucous string towards the peribuccal area of the echinoid. Once facing the peribuccal area, particles are picked up by the peribuccal tube feet that either transfer them into the esophagus or scrape them out against the peribuccal spines. Spine-retained particles are either sucked up by the pumping action of the esophagus or fall to the burrow's floor where the tube feet may pick them up again. Together the apical tuft, the frontal groove, and the peribuccal area form an efficient food-collecting system that transfers trapped surface particles from the echinoid apex down to the mouth. Compared to that of most other spatangoids the frontal ambulacrum of E. cordatum is highly specialized. Such specialization is related to colonization of fine sediment, as is the occurrence of a chimney linking the burrow to the sediment surface. Actually the burrow's chimney is the only route for oxygen and food supply; it acts as a real ecological umbilical cord for spatangoids buried in fine sediment.     

Moderate stoichiometric homeostasis in the sea urchin Lytechinus variegatus: effects of diet and growth on C:N:P ratios

The influence of dietary elemental contents on consumer stoichiometry was investigated in selected and combined soft tissues (as a proxy of the whole individual) of the omnivorous sea urchin, Lytechinus variegatus. We raised urchins for 4 months in controlled seawater tanks using three different diets with different nutritional contents (from lower to higher: seagrass, red macroalgae, and a formulated diet). Individuals fed the different diets varied an average of 19.7, 19.4, and 38 % in C:N, C:P, and N:P ratios, respectively, with stronger temporal variability for C:P and N:P ratios across tissues and whole individuals. This resulted in homeostasis parameters (1/H) of ?0.45, 0.09, and 0.38, respectively, for C:N, C:P, and N:P, indicative of homeostatic to weakly homeostatic organisms, at least for C:P and N:P ratios. Individuals fed the nutrient-rich formulated diet had higher growth rates (14 ± 0.83 g WW month^?1) than those fed macroalgae or seagrass (9.3 ± 0.57 and 3.4 ± 0.33 g WW month^?1, respectively). However, rapid body increments in more nutritional diets caused both a decrease in the %N and an increase in the %P of soft tissues, which resulted in significant but opposite effects of diet stoichiometry and growth in sea urchin C:N (R = ?0.74 and R = 0.93, for diet and growth effects, respectively) and N:P ratios (R = 0.60 and R = ?0.63, also, respectively, for diet and growth effects). Among potential compensatory mechanisms helping to preserve certain levels of homeostasis, ingestion rates (g WW diet per g WW of urchin) were higher for seagrass and macroalgae diets than for the nutrient-rich formulated diet. In contrast, absorption and growth efficiencies displayed significant negative associations with nutrient contents in diets and did not exhibit nutritional compensation. Overall, our results suggest that resource stoichiometry strongly determines the growth rate of individuals (R = 0.88, P < 0.01), and moderate variability in C:N:P ratios of sea urchins possibly arise from differences in the allocation of proteins and RNA to body components, similarly to what has been proposed by the growth rate hypothesis.     

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.     

Effects of inorganic and organic phosphates on feeding, feeding absorption, nutrient allocation, growth and righting responses of the sea urchin Lytechinus variegatus

The sea urchin Lytechinus variegatus is capable of surviving chronic exposure to sodium phosphate (inorganic phosphate) concentrations as high as 3.2 mg l⁻¹, and triethyl phosphate (organic phosphate) concentrations of 1,000 mg l⁻¹. However, chronic exposure to low (0.8 mg l⁻¹ inorganic and 10 mg l⁻¹ organic phosphate), medium (1.6 mg l⁻¹ inorganic and 100 mg l⁻¹ organic phosphate) or high (3.2 mg l⁻¹ inorganic and 1,000 mg l⁻¹ organic phosphate) sublethal concentrations of these phosphates inhibits feeding, fecal production, nutrient absorption and allocation, growth and righting behavior. Food consumption and fecal production declined significantly in individuals exposed to medium and high concentrations of inorganic phosphates and all levels of organic phosphates. Feeding absorption efficiencies for total organics and carbohydrates decreased significantly in individuals held in the highest concentration of organic phosphate. Feeding absorption efficiencies for lipids were significantly reduced in the highest inorganic phosphate concentration only, while they decreased significantly for protein with increasing phosphate exposure. Carbohydrate and lipid levels in gonad and gut tissues decreased significantly with exposure to increasing phosphate concentrations, potentially impairing both gametogenesis and nutrient storage in the gut. Moreover, gonad indices significantly decreased in individuals exposed to the highest concentrations of either phosphate. Growth rates decreased significantly under the influence of all phosphate concentrations, while increasing in seawater alone. Individuals exposed to increasing phosphate concentrations showed reduced righting responses (a measure of stress) and no acclimation in righting times during chronic exposure to phosphates over a 4 week period. These findings indicate that shallow-water populations of L. variegatus subjected to inorganic and organic phosphate pollutants will exhibit stress and be inhibited in their growth and performance due to reductions in feeding, nutrient absorption and allocation of nutrients to key somatic and reproductive tissues. Received: 10 April 2000 / Accepted: 2 October 2000     

The effects of dietary protein concentration on feeding and growth of small<Emphasis Type="Italic"> Lytechinus variegatus</Emphasis> (Echinodermata: Echinoidea)

Understanding the nutritional requirements of Lytechinus variegatus is essential to define its role in the marine environment and necessary for successful culture of this species. Protein is an essential component for growth, yet the requirements for protein in most marine organisms are not known. Small Lytechinus variegatus (ca. 14 mm diameter, n=160) were collected at St. Joseph Bay, Florida in March 2000. They were held in aquaria and fed ad libitum one of four diets varying in protein concentration (9, 15, 21, or 33% dry weight) for 14 weeks. Diets 21% dry weight protein were sufficient for maximal growth and survivorship. Individuals fed a diet low in protein compensated by consuming higher quantities of food per gram wet weight. However, the protein was insufficient to support maximal growth and survivorship. Total dry matter absorption, protein absorption, and carbohydrate absorption of the prepared feeds were higher than reported for natural diets. Total production and production efficiency was lowest in those fed the low-protein diet. Gonad production occurred in individuals with test diameters smaller than reported previously in field populations and was lowest in those fed the low-protein diet. The acini of both females and males were predominantly composed of nutritive phagocytes, suggesting that growing L. variegatus use the gonad primarily as a nutrient storage organ and not for reproduction. In females the growth rate of oocytes increased with dietary protein. In males, protein concentration 21% resulted in an increase in the volume of germinal epithelium and a decrease in the volume of nutritive phagocytes. The minimal requirement for protein in L. variegatus from approximately 1 g to 15 g total weight is >15% dry weight for the conditions of this experiment. The requirement for a diet >15% protein corroborates with field studies that indicate L. variegatus consumes epibionts and animal tissues preferentially to seagrass, and that the microbial, microfloral, and microfaunal community living on the seagrass may provide the extra protein required for growth and survival of small L. variegatus.Communicated by P.W. Sammarco, Chauvin     

Large-scale estimate of somatic growth in Amphiura filiformis (Echinodermata: Ophiuroidea)

Quantitative data on size structure of the ophiuroid Amphiura filiformis (O.F. Müller) from 35 benthic stations in the Kattegat sampled twice with a 143 d interval, June and October 1991, were used to estimate somatic growth. The material was objectively divided into cohorts, and cohorts, from the two occasions were paired to give estimates of growth. The growth constant, K, in the Von Bertalanffy equation, was estimated from a Ford-Walford plot to 0.54 yr^-1. Results were in agreement with previous estimates from a few single sites, and suggest that the main part of dise growth occurs within the first 5 to 7 yr of living. Size specific growth in oral width was density independent despite high densities of A. filiformis (>3000 ind m^-2) and high total benthic biomass (up to 1000 g wet wt m^-2) in some areas. Growth was uncorrelated with plant pigment concentrations in the sediment and showed weak positive correlation with sediment carbon and nitrogen, as well as water depth. Growth was higher in fine sediments. This is the first attempt to estimate growth in this important species over a large area and to relate growth in the field to environmental factors.     

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.     

Post-metamorphic growth of the arms in Ophiophragmus filograneus (Echinodermata: Ophiuroidea) from Tampa Bay,Florida (USA)

Juveniles of the burrowing amphiurid Ophiophragmus filograneus from Tampa Bay, Florida (USA) exhibit a growth pattern unreported in the ophiuroid literature. Two nonadjacent arms grow at a greater rate than the other three arms. This phenomenon might be a developmental adaptation to avoid salinity and temperature fluctuations in surface waters of the shallow-water environment which O. filograneus inhabits. It is proposed that concentration of growth into 2 of the 5 arms permits earlier descent of the disc into the substratum with continued ability to feed on the surface with the arm tips. Larger specimens show a gradual equalization of arm lengths. Changes in growth rates and cropping of the longer arms by breakage and predation might account for such eventual equalization.     

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.     

Electron microscope study of the digestive system of Strongylocentrotus droebachiensis (Echinodermata: Echinoidea)

The fine structure of esophagus, stomach and intestinal epithelial cells of the sea urchin Strongylocentrotus droebachiensis have been examined. Three types of mucosal cells secreting neutral, acid and sulfated mucopolysaccharides have been found in the esophagus. The modes of origin of different types of mucous granules are described. Storage and zymogen cells have been identified in the stomach epithelium. Storage cells are adapted for intracellular digestion and synthesis of nutritive substance. Zymogen cells are adapted for enzyme synthesis. The columnar cells occur in the intestinal epithelium; they are adapted for nutrient absorption and lipid storage. Digestion in different parts of the digestive tract is considered in context with the ultrastructural and histochemical data obtained. Some problems concerning the relation between intracellular and extracellular digestion are discussed.     

Reproduction and growth of Holothuria atra (Echinodermata: Holothuroidea) at two contrasting sites in southern Taiwan

Reproductive periods and growth of two populations of Holothuria atra Jaeger distinctly different in body size at two sites of southern Taiwan were determined. Individuals examined in the present study were collected between march 1990 and February 1992. At Nanwan (21° 57N, 120° 45E), large individuals (351 to 1400 g wet wt) spawned from June to September. At Wanlitung (22°N, 120° 42E), a small proportion of frequently dividing individuals (<190 g wet wt) have mature gonads in May, June and September, but histological examination revealed no sign of spawning. Sexual recruits, defined as small individuals <5 g wet wt without sign of regeneration, were not found at either site during this 2-yr study. After the peak of fission at Wanlitung, 40% of the population showed signs of external regeneration. At Nanwan, small individuals transferred from Wanlitung grew from 6 g (n=6) to 166±8 g within 8 mo, and from 48±4 g (n=50) to 324±16 g within 1 yr, with a 6.8-fold biomass increase in 1 yr. At Wanlitung, the monthly average body weight of H. atra is between 33 and 62 g, apparently due to frequent fission, and the biomass increased only 2.9-fold in 1 yr. In southern Taiwan, sexual reproduction of H. atra occurs in large individuals. Asexual reproduction, occurring in small individuals, is the chief mechanism for population maintenance and increase, but it may decrease sexual reproductive potential.     

The effect of temperature-salinity combinations on survival and growth of juvenile Patiriella pseudoexigua (Echinodermata: Asteroidea)

Adult Patiriella pseudoexigua were collected in October 1989 from Wanlitung, Taiwan and then induced to spawn in the laboratory. Post-metamorphosed juvenile P. pseudoexigua were reared on a diet of benthic algae Navicula sp. at 25°C and salinity (34). Six weeks after metamorphosis, juvenile P. pseudoexigua at ca. 400 m in radius were reared on a diet of benthic algae Navicula sp. at different combinations of temperatures (20, 25, 30°C) and salinities (26, 30, 34) for 40 d. Both temperature and salinity had a significant effect on juvenile survival and growth. Juveniles survived best (>90%) at 25°C and 34 and grew best (to ca. 750 m in radius) at 30°C and 34. Variation in juvenile size was small immediately after metamorphosis and increased with time.     

Chemical defense in the eggs and embryos of antarctic sea stars (Echinodermata)

Fifteen species of reproductively mature echinoderms (11 sea stars, 3 sea urchins, 1 sea cucumber) were collected from McMurdo Sound, Antarctica, during austral spring and summer of 1985 and 1986; eggs and embryos were obtained, and were tested for ichthyonoxicity using the common marine killifishFundulus grandis as a model predator. Chemical deterrents occurred in the large, yolky eggs of the pelagic lecithotrophic sea starPerknaster fuscus and the planktotrophic sea starPorania antarctica. Brooded embryos of the sea starsDiplasterias brucei andNotasterias armata were also noxious. Significant ichthyonoxicity was not detected in the remaining 7 species of sea stars, 3 sea urchins, and 1 sea cucumber. Chemical deterrents were generally effective at concentrations below a single egg or embryo per agar test-pellet. Although chemicals found in these eggs and embryos are noxious to an allopatric fish, they may not be noxious to sympatric fish.     

The collagenous nature of problematical ligaments in crinoids (Echinodermata)

A major adaptive problem among comatulid crinoids is the need for a system of articulation and muscularization of the skeleton which provides rigidity in the cirri, arms, and pinnules for maintaining position and feeding in moving water masses, and also the ability to undergo occasional rapid flexions. Most skeletal ossicles of comatulids are united by so-called ligament fibers, while arm articulations possess masses of muscle as well as ligament. Light and electron microscopic work shows that the ligament consists primarily of collagen fibers. Similarity of this dual system of crinoid arm musculature to the muscles and collagenous catch apparatus of echinoid spines suggests that the crinoid ligaments may provide the needed rigidity to the crinoid skeleton, in a manner similar to that by which the echinoid catch apparatus can hold the spine tightly to the test in one position.