Early Postlarval Development Research Articles

Early life cycle description and effects of microalgal diets on larval and post‐larval development of the mangrove cockleAnadara tuberculosa(Sowerby, 1833)

Natural populations of the edible mangrove cockle (Anadara tuberculosa) are threatened by overexploitation and environmental degradation due to anthropogenic activities. The indoor production of larvae and early spat of mangrove cockles requires knowledge regarding the evolutionary characteristics of their larval morphology, associated with the appropriate use of microalgae. Therefore, we describe the larval and early post-larval development of A. tuberculosa raised in the laboratory and the effect of six microalgae on its growth and survival. Additionally, microalgae ingestion–digestion was determined using epifluorescence microscopy, and the fatty acid profile of the microalgae was analysed. Microscopic observations indicated the presence of D veliger larvae 18 h post fertilization, and the first batch of spat was obtained after 45 days of culture. The spat reached a manoeuvrable size at 90 days post fertilization (3 mm). Best shell lengths of oculated larvae (157.62 and 172.47 µm), daily growth rates (4.77 and 4.52 µm/day), survivals (30% and 23%) and settlement rates (23% and 11%) were obtained with the diatoms Chaetoceros gracilis and Chaetoceros muelleri respectively. Diets Tetraselmis chuii, Thalassiosira sp. and Pavlova lutheri, despite being ingested–digested, did not result in oculated larvae, which possibly indicates an inadequate lipid content for A. tuberculosa larvae culture. Larvae seem to have a high nutritional requirement for myristic acid, palmitoleic acid, hexadecadienoic acid, stearic acid and eicosapentaenoic acid. Our findings show the feasibility of producing spat in captivity, which contributes to promoting its production and thereby developing ecological restoration plans and/or diversifying aquaculture in Ecuador.

Juvenile eucladid crinoid from the Middle Devonian of Turkey

A microcrinoid-sized eucladid crinoid (Eucladida Wright, 2017) is described from the Yığınlı Formation (Devonian, Famennian) in the Büyük Zap Anticline in the Hakkari region of SE Turkey. Compared to other eucladids of similar size, the Yığınlı Formation specimen is at a quite advanced morphological stage with arms present through at least the secundibrachials. Early post-larval development is a key for understanding homologies among crinoid clades; however Paleozoic crinoids in the microcrinoid range (≤ 2.0 mm) are very rare. This specimen is either at a very advanced developmental stage for its size, or typical microcrinoids are neotenic.

Trophic cues as possible triggers of mussel larval settlement in southeastern Brazil

Oligotrophic conditions may impose a nutritional challenge for the larval and early post-larval development of bivalves during the search for a suitable benthic habitat. Here we investigated what settlement cues might be important for mytilid populations in southeastern Brazil. Our results point to a trophic trigger mediating larval settlement that may include an effect of saturated fatty acids, probably linked to organic detritus and bacterial production deriving from terrestrial inputs. The prevalence of drifting in this population suggests it may be a strategy for individuals to delay final settlement until encountering favorable trophic environmental conditions.

A post-larval stage-based model of hard clam Mercenaria mercenaria development in response to multiple stressors: temperature and acidification severity

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 558:35-49 (2016) - DOI: https://doi.org/10.3354/meps11882 A post-larval stage-based model of hard clam Mercenaria mercenaria development in response to multiple stressors: temperature and acidification severity Cale A. Miller1,*, George G. Waldbusser2 1Huxley College of the Environment, Western Washington University, 516 E. College Way, Bellingham, WA 98225, USA 2College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, 104 COAS Administration Building, Corvallis, OR 97331, USA *Corresponding author: mille454@students.wwu.edu ABSTRACT: Complex biogeochemical processes in the coastal oceans lead to highly variable carbonate chemistry that is further modified by the shifting baseline of pCO2 caused by ocean acidification. Unfavorable carbonate chemistry, which is pervasive in near-shore, shallow-water deposits, due to high rates of organic matter remineralization and the oxidation of reduced metabolites, has been shown to negatively affect benthic calcifying organisms. For settling infaunal bivalve larvae, such as the hard clam Mercenaria mercenaria, pore waters high in CO2 exert a physiological stress on early post-larval development and homeostasis. The effects of acidification have been shown to increase mortality and reduce calcification for ‘just settled’ juvenile M. mercenaria, a life stage that heavily affects adult clam abundance. To better understand the effects of acidification and temperature on this sensitive life stage, we constructed a post-larval stage-based development model that investigated how varying degrees of aragonite saturation state affect post-settlement survival of juvenile M. mercenaria. Initial model simulations predict a similar consistency and trend to field experiments that examined the survival of juvenile Mya arenaria residing in buffered and unbuffered sediments. According to our model, the magnitude of acidification had a large effect on post-larval stage duration, which translated to a 60% decrease in total survivors under high variability compared to low variability saturation state scenarios. By modifying temperature-dependent growth rates, we were able to progress juveniles out of the more sensitive life stages faster and, therefore, determined scenarios in which faster growth can reduce exposure to acidification during more sensitive stages. KEY WORDS: Ocean acidification · Stage-based model · Juvenile clam · Mercenaria mercenaria · Temperature-dependent growth · Post-larval development Full text in pdf format PreviousNextCite this article as: Miller CA, Waldbusser GG (2016) A post-larval stage-based model of hard clam Mercenaria mercenaria development in response to multiple stressors: temperature and acidification severity. Mar Ecol Prog Ser 558:35-49. https://doi.org/10.3354/meps11882 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 558. Online publication date: October 25, 2016 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2016 Inter-Research.

Heterochronies in the formation of the nervous and digestive systems in early postlarval development of opisthobranch mollusks: Organization of major organ systems of the arctic dorid Cadlina laevis

For the first time using laser confocal microscopy and histochemical and immunocytochemical methods (detection of F-actine, catecholamines, acetylcholintransferase, substances of P and FM RFamide) in combination with classical histological methods and electron microscopy of total preparations, the general structure and regularities of formation of the main organs and the nervous, muscular, and digestive systems in early postlarval development (2 to 4 months) in the opistobranch mollusk Cadlina laevis were studied. Heterochronies manifested in positive allometry of the sensory organs, ganglia of the central nervous system, and the pharyngeal region of the digestive system in relation to general body sizes in juvenile individuals compared to adult animals were detected.

Revision of the Bivalvia from the Upper Jurassic Reuchenette Formation, Northwest Switzerland--Ostreoidea.

The current work is the first part of a taxonomic revision of the highly diverse Kimmeridgian bivalve fauna of the Reuchenette Formation of northwestern Switzerland (Canton Jura). It provides a taxonomic, paleoecologic and bibliographic review of the eight oyster species characterizing the northern Helvetic shelf: Circunula n. gen. cotyledon (Contejean, 1859) (Gryphaeidae, ?Pycnodonteinae), Nanogyra (Nanogyra) nana (J. Sowerby, 1822), Nanogyra (Palaeogyra) reniformis (Goldfuss, 1833), Nanogyra (Palaeogyra) virgula (Deshayes, 1831) (Gryphaeidae, Exogyrinae), Helvetostrea n. gen. sequana (Thurmann & Etallon, 1862) (Flemingostreidae, Crassostreinae), Praeexogyra dubiensis (Contejean, 1859), Praeexogyra monsbeliardensis (Contejean, 1859) (Flemingostreidae, Liostreinae), and Actinostreon gregareum (J. Sowerby, 1815) (Arctostreidae, Palaeolophinae).The paper proposes two new genera: Circunula and Helvetostrea. Palaeogyra Mirkamalov, 1963, is considered a subgenus of Nanogyra Beurlen, 1958. Lectotypes are designated for six species: C. cotyledon, Praeexogyra acuminata, P. dubiensis, P. monsbeliardensis, H. caprina, H. sequana. The figured types of H. oxfordiana (Rollier, 1917) and N. auricularis (Münster in Goldfuss, 1833) are considered holotypes by monotypy. All types are refigured in drawings and/or photographs. Early phases of shell ontogeny in general and the generic characters of Praeexogyra are revisited. Larval shells or their internal moulds are shown for six species: N. nana, N. reniformis, N. virgula, N. cf. auricularis, Praeexogyra cf. sandalinoides (de Loriol, 1901), and Actinostreon marshii (J. Sowerby, 1814). All of them are "Crassostrea"-like suggesting a planktic-planktotrophic mode of development. Circunula n. gen. shows a relatively high incidence of prosogyry (up to ca. 20% of studied specimens) during very early postlarval development. To a lesser extent, prosogyry has also been observed in species of Catinula, Praeexogyra and Pernostrea. Chomata are typical of early ontogenetic stages of Circunula n. gen., but they disappear during later growth stages. Circunula n. gen. cotyledon is a typical early settler on hardgrounds but occurs also in subtidal soft-bottom environments attached to large shells. Nanogyra (N.) nana attached itself to all kinds of biogenous hard and soft substrates including algal stems and thalli. It is regularly found in calm to moderately energetic shallow marine paleoenvironments. Nanogyra (P.) reniformis frequently settled on the interior of empty bivalve shells. Nanogyra (P.) virgula was esentially a secondary soft-bottom dweller of shallow marine marls and lime muds. The species is often found concentrated in widely distributed (par)autochthonous lumachelles ("virgula marls" of authors) in the Upper Oxfordian, Upper Kimmeridgian and Tithonian. Praeexogyra dubiensis and P. monsbeliardensis occur in marly, shallow marine paleoenvironments. Praeexogyra dubiensis appears to have preferred attachment to small objects in a moderately energetic facies. In the study area it is also associated with algal meadows. Praeexogyra monsbeliardensis was preferentially gregarious in somewhat deeper and calmer paleoenvironments. The strongly chambered and probably fast growing Helvetostrea n. gen. sequana was adapted to moderate to high energetic shallow marine, marly habitats. It is frequently associated with corals and forms ostreoliths or small oyster buildups. Actinostreon gregareum usually lived gregariously but was also able to attach itself to algae on soft substrates. The species is known from calm marly to higher energetic coralline paleoenvironments.

Effect of darkness on the early postlarval development of Haliotis corrugata abalone fed different diatom densities

Four-day-old postlarvae of the abalone Haliotis corrugata were exposed to different diatom densities (Navicula incerta, 0 to 8000 cells mm–2) under two illumination conditions: constant light (19–21 µmol quanta m–2 s–1) and darkness. The effect of these two factors on postlarval grazing rate, survival, and growth was evaluated. The experiment was conducted for 14 days in 10-mL sterile wells following a split-plot experimental design with three replicates per treatment. The highest grazing rate was observed in the 2000 cells mm–2 density treatment and it was higher in darkness (196 ± 67 cells pl–1 h–1) than in constant light (139 ± 36 cells pl–1 h–1). Mean survival was also higher in darkness (59%) than under constant light (44%), as was mean growth rate (20 and 14 µm d–1, respectively). Growth rate at the end of the experimental period tended to decrease with the increase in diatom density. Higher grazing and growth rates in darkness reinforce the hypothesis that the nocturnal habits of abalone develop soon after metamorphosis and not at juvenile stages as usually considered.

Early post-larval development of the endoparasitic platyhelminthMesocestoides corti: Trypsin provokes reversible tegumental damage leading to serum-induced cell proliferation and growth

Mesocestoides corti is a suitable in vitro model for studying the development of human endoparasitic platyhelminthes. Treatment with trypsin, supplemented with fetal bovine serum (FBS), induces M. corti development from larvae (tetrathyridia) to segmented adult worm; however, the role of this protease and of FBS in post-larval development induction remains unknown. To characterize the participation of trypsin enzymatic activity and of FBS in the induction of tetrathyridia growth and development, both stimuli were added to the larvae either together or sequentially. Additionally, specific inhibition of trypsin activity was also monitored. Finally, the effect of the enzyme on the parasite tegument as well as the proliferative activity and location of proliferating cells after induction of tetrathyridia development were also studied. We conclude that trypsin-induced tetrathyridia development to adult worm is FBS-dependent and that the effect of serum factors is dependent upon a previous trypsin-induced reversible damage to the larva tegument. In dividing and non-dividing tetrathyridia, proliferative activity of cells is mainly located within the apical massif in the anterior region and nerve cords of larvae, respectively. In tetrathyridia stimulated to develop to adult worms, an intense proliferative activity is evident along the nerve cords. Our results suggest that in natural infections the tetrathyridia tegument is temporally made permeable to growth factors by proteolytic enzyme activity in the intestine juice of the definitive host, thus leading to development to adult worms.

Effect of artificial and natural diets on energy allocation in Litopenaeus setiferus (Linnaeus, 1767) and Litopenaeus vannamei (Boone, 1931) early postlarvae

The amounts of energy channeled into growth ( P), maintenance ( R), excretion ( U) and exuviae ( E v) were quantified in six dietary treatments during early postlarval development in Litopenaeus setiferus and Litopenaeus vannamei reared at 28±1 °C and 35±1‰ salinity. The six diet combinations were: (1) freshly hatched Artemia nauplii, (2) freshly hatched Artemia nauplii supplemented with algae, (3) microparticulate commercial diet (MCD), (4) MCD supplemented with algae, (5) Artemia nauplii partially substituted (50%) by MCD and (6) Artemia nauplii partially substituted (50%) by MCD supplemented with algae. Oxygen consumption, ammonia excretion and dry weight were measured from postlarvae day 1 (PL 1) to PL 10 (1 to 10 days after metamorphosis). Energy distribution in both species was affected by diet with significantly higher proportion of energy allocated into production (1.49 J day −1 for L. setiferus and 1.77 J day −1 for L. vannamei) when animals were fed a mixed diet. The proportion of assimilated energy channeled into production ( P/As) was greater when both species were fed mixed diet and was lower when fed on MCD alone or MCD plus algae. On the contrary, the proportion of assimilated energy used in respiration ( R/A) was higher for both species when fed on MCD alone or MCD plus algae, with the lowest values in animals fed on the mixed diet. Low values of net growth efficiency ( K 2) were found in both species when the main food was MCD (alone or supplemented with algae), with the highest K 2 when animals were fed the mixed diet. Results show that divergences between these two species during early postlarval stages only appear when animals were in a poor physiological condition due to an inefficient diet. Artemia nauplii, partially substituted by MCD with a supplement of algae, integrated a high-quality diet for both species producing high net growth efficiency.

Ontogenetic changes in biochemical composition during larval and early postlarval development of Lepidophthalmuslouisianensis, a ghost shrimp with abbreviated development

Changes in growth and biochemical composition during the transition from egg through zoea to decapodid in the ghost shrimp, Lepidophthalmus louisianensis (Schmitt, 1935), were documented in terms of dry weight, lipid classes, fatty acid composition, and carbon to nitrogen (C:N) ratios. Larvae of the ghost shrimp were mass-reared in the laboratory (28°C; 20‰ S) from hatching to the decapodid stage. Iatroscan lipid class analysis revealed that major lipid classes in recently produced eggs were phospholipids (80.8±1.3%) and triglycerides (16.0±1.1%), which decreased during the incubation period. Polar lipids (zoea I: 77.4±1.7%; zoea II: 77.5±2.1%; decapodid: 80.0±1.7%) and neutral lipids, of which free fatty acids (zoea I: 10.5±2.7%; zoea II: 13.1±5.2%; decapodid: 7.8±2.1%) were dominant, represented the major lipid classes in the zoeal and decapodid stages. Triglycerides were present in small amounts. The predominant fatty acids of L. louisianensis eggs, zoeae and decapodids were palmitic (16:0), stearic (18:0), eicosapentaenoic (20:5ω3), oleic (18:1ω9), and arachidonic (20:4ω6). Elemental composition of eggs, larvae, and the decapodid stage revealed conspicuous changes in the C:N ratio, with N being relatively stable during larval development but C decreasing during the decapodid stage. These data suggest independence of newly hatched L. louisianensis on external energy resources. This combined with the ability to incorporate saturated fatty acids into polar lipids provides a selective advantage for fast development of new tissue and growth, characteristic of decapod crustacean larvae with lecithotrophic development.

Nutritional effects on body composition, energy content and trypsin activity of Penaeus japonicus during early postlarval development

The growth, elemental (C, N, H) and biochemical (lipid, protein) composition, energy content and trypsin activity of Penaeus japonicus early postlarvae (PL 1–PL 20, as days after metamorphosis) fed under a commercial hatchery regime were measured. From PL 1 to PL 4, freshly hatched Artemia nauplii were used, followed by enriched Artemia nauplii (PL 5–PL 9), and a prepared diet from PL 10 to PL 20. Survival for the total experimental period was 80% and daily gain in absolute values of dry weight, energy and elemental composition was observed. Significant increment ( P<0.05) of relative values of carbon, hydrogen and energy was verified from PL 1 to PL 3 as well as increases in protein and lipid content from PL 1 to PL 5. In the period PL 10–PL 20, carbon, hydrogen and energy content decreased significantly ( P<0.05). This may have been due to the poor quality of diet supplied after PL 5, which possibly caused malnutrition. During this period, lipid was a major source of energy for the postlarvae. Body protein of postlarvae as determined by nitrogen content (N×6.25) was overestimated after PL 5, which indicates to a possible role of the non-protein nitrogen fraction under poor feeding conditions. Protein-specific trypsin activity showed significant increment ( P<0.05) at periods PL 1–PL 5 and PL 15–PL 20, which may indicate a possible influence of diet composition. It is concluded that this type of approach may be useful as a tool to assess the nutritional condition of cultivated shrimp, during postlarval stages.

Comparative Larval Development in Two Species of the Burrowing Ghost Shrimp Genus Lepidophthalmus (Decapoda: Callianassidae)

ABSTRACT The early life history is described and compared in the estuarine callianassid shrimp species Lepidophthalmus sinuensis from the Caribbean coast of Colombia and L. louisianensis from the northern Gulf of Mexico, on the basis of laboratory larval cultures and wild plankton collections. Both species have an abbreviated larval development of 2 zoeal stages usually transcended within 3-4 days, with that of L. sinuensis being the shorter and exhibiting greater advancement in the zoeal stages. Development in both species is markedly shorter and morphologically more advanced than in comparable callianassid species for which stages have been described, including most of those known to have only 2 zoeal stages. Larval duration in Lepidophthalmus is nearest that of the ecologically comparable Callianassa s.l. kraussi from southern Africa and suggests possible convergence in early developmental strategies. On the basis of presently known larval histories, genera allied to Lepidophthalmus within the Callichirinae appear to either have long larval histories of 5 zoeal stages, or, if of 2 stages, to bear a morphological resemblance as zoeae to comparable stages in some of the non-Callichirinae. The decapodid (first postlarval) stage is imaginal in form and exhibits burrowing behavior, though appendage development is far short of adult form. Successive early postlarval development and behavior beyond this stage remains unknown. Detailed illustrations of zoeal and decapodid stages are provided to support comparative discussions and for use in larval identifications.

Ontogenetic Changes in Enzyme Distribution and Midgut Function in Developmental Stages of Penaeus setiferus (Crustacea, Decapoda, Penaeidae).

Ultrastructure and histochemical distribution of enzymes were examined in the midgut of larval and postlarval stages of Penaeus setiferus. Acid phosphatase and esterase activities were present in all gut tissues at all stages. Protease activity was present in the anterior and lateral midgut caeca, as well as in the anterior portion of the midgut trunk (MGT) of larvae and early postlarvae (PL1-PL4). Amylase activity could not be detected histochemically in larvae or early postlarvae, even though it was detected in assays of whole-animal homogenates. In later postlarvae, both protease and amylase activities were present in the hepatopancreas and anterior MGT, but were absent from the anterior midgut diverticulum. In larvae, alkaline phosphatase activity is present throughout the midgut, suggesting that absorption is widespread. In juveniles, activity is restricted to the hepatopancreas and regions of the MGT within the cephalothorax. The abdominal MGT (or "intestine") is no longer absorptive by the time the hepatopancreas has attained its adult form. Although epithelial cells of the MGT synthesize protein and produce electron-dense secretory vesicles, they are substantially different in ultrastructure from those cells in the hepatopancreas responsible for digestive enzyme synthesis and secretion. Epithelial cells of the larval anterior and lateral midgut caeca are structurally and functionally similar to cells of the postlarval hepatopancreas. However, the lateral midgut caeca retain these features as they transform into the hepatopancreas, while the anterior midgut caeca lose these functions as they degenerate into the anterior diverticulum and change in ultrastructure during early postlarval development. The anterior and posterior midgut diverticula of postlarvae are similar ultrastructurally even though they differ in ontogenetic history.

The Larval and Post-Larval Development of Pennant's Swimming Crab, Portumnus La Tipes (Pennant) (Brachyura, Portunidae), Reared in the Laboratory

Pennant's Swimming Crab, Portumnus latipes (Pennant, 1777) has been recorded from the North Sea and British Isles to the Azores Islands and the Mediterranean (see Monod, 1956; Zariquiey-Alvarez, 1968; Ingle, 1980). Lebour (1928, 1944) described the zoeal stages, megalopa and early crab stages, but her descriptions are too brief to allow comparisons with recently described larvae of other Portunidae. In January 1986 an ovigerous female o? Portumnus latipes was trawled in Ria Formosa, South Portugal, by Mr. C. Sousa Reis. The hatched larvae were reared to the second crab stage and provided sufficient material to give a des cription of the complete larval and early post-larval development.

Post-Larval Development of the Tellinacean Bivalves Abra Alba, Tellina Fabula and Donax Vittatus (Mollusca: Bivalvia), With Reference to the Late Larva

The post-larval shell and hinge development of the bivalves Abra alba (Wood), Tellina fabula Gmelin and Donax vittatus (da Costa) from the recently metamorphosed size to a juvenile size of 1·2–1·4 mm shell length has been examined using scanning electron microscopy. Early post-larval development in the stages up to 1·0–1·2 mm size can involve considerable morphogenetic change and requires careful description with photographic developmental series. The form of the pediveliger larva is present in the early post-larval shell and confirms the identity of the larvae of A. alba and T. fabula. The veliger and pediveliger larvae of A. alba are described. The similar larval form of the tellinacean bivalves is modified by differential margin growth early in post-larval development. Comparison of these bivalves with allied species reveals that the post-larvae are distinguishable at even the smallest sizes by the shell and hinge form. The metamorphic size of A. alba ranges from 0·26 to 0·31 mm, of T. fabula from 0·25 to 0·28 mm and of D. vittatus from 0·25 to 0·35 mm. The bivalve post-larvae were collected from the shallow sublittoral of Oxwich Bay, Bristol Channel, U.K., and the larvae from the overlying waters, during the years 1980–2.

Larval and Early Postlarval Development of Lepidopa benedicti Schmitt, 1935 (Anomura: Albuneidae) Reared in the Laboratory

Larval and Early Postlarval Development of Lepidopa benedicti Schmitt, 1935 (Anomura: Albuneidae) Reared in the Laboratory

Post-larval development of the common north-west European brittle stars Ophiura ophiura, O. albida and Acrocnida brachiata (Echinodermata: Ophiuroidea)

The post-larval skeletal plate ontogeny of the ophiuroids Ophiura ophiura (Linnaeus) and Acrocnida brachiata (Montagu) from the recently metamorphosed 0.3 mm disc diameter size to a juvenile size of 2.0 mm disc diameter has been examined using scanning electron microscopy. Post-larval development of O. albida Forbes is briefly described for sizes between 1.0 and 2.0 mm disc diameter. Early post-larval development in the 0.2 to 1.0 mm discsize range involves considerable morphogenetic change and necessitates the use of a developmental series in the identification of newly settled ophiuroids. Comparison of these ophiuroids with other closely related species reveals that the post-larvae are readily distinguishable at even the smallest sizes by their transient post-larval morphologies. Abbreviated larval development in A. brachiata is suggested from the egg size and post-larval form. The ophiuroid post-larvae were collected from the shallow sublittoral of Oxwich Bay, Bristol Channel, UK, during the years 1980 to 1982.

Larval and Early Post-Larval Development of Arctica Islandica

Mature eggs were stripped from ripe adult specimens of Arctica islandica and exposed to a dilute solution of ammonium hydroxide for various lengths of time before addition of stripped sperm. Larval and early post-larval stages were cultured under experimental laboratory conditions using standard bivalve rearing techniques. Larval cultures were maintained at various controlled temperatures ranging from 8·5 to 14·5 °C. Minimum time to settlement was 32 days at a temperature of approximately 13 °C; at temperatures between 8·5 and 10·0 °C, settlement was not observed until approximately 55 days after fertilization. Larval growth rates were significantly faster at temperatures between 11·0 and 145 °C than at temperatures between 8°C. Morphometry of the larval shell and morphology of the larval hinge apparatus were independent of larval growth rates and experimental culture conditions.

Larval and Early Post-Larval Development of Arctica Islandica

Mature eggs were stripped from ripe adult specimens of Arctica islandica and exposed to a dilute solution of ammonium hydroxide for various lengths of time before addition of stripped sperm. Larval and early post-larval stages were cultured under experimental laboratory conditions using standard bivalve rearing techniques. Larval cultures were maintained at various controlled temperatures ranging from 8·5 to 14·5 °C. Minimum time to settlement was 32 days at a temperature of approximately 13 °C; at temperatures between 8·5 and 10·0 °C, settlement was not observed until approximately 55 days after fertilization. Larval growth rates were significantly faster at temperatures between 11·0 and 145 °C than at temperatures between 8°C. Morphometry of the larval shell and morphology of the larval hinge apparatus were independent of larval growth rates and experimental culture conditions.

A Contribution To Knowledge of the Larval Development of Macrobrachium Olfersii (Wiegmann, 1836) (Decapoda, Palaemonidae)

Species of genus Macrobrachium are widely distributed in fresh and brackish waters mainly in subtropical and tropical parts of world. In past fifteen years interest in these shrimps, many of which reach large size, has increased greatly, largely due to possibility of commercial culture of some of them. Among studies that have been carried out in this period have been a number dealing with larval and early postlarval development of various species. Thus Ling & Merican (1961), Ling (1969), and Uno & Kwon (1969) studied Macro brachium rosenbergii (De Man, 1879) Lewis & Ward (1965) and Choudhury (1971) worked on M. carcinus (L., 1758), Kwon & Uno (1969) investigated M. nipponense (De Haan, 1849), Fielder (1970) M. australiense Holthuis, 1950, and Choudhury (1970) and Dobkin (1971) M. acanlhurus (Wiegmann, 1836). Other works dealing with larval development of species of this genus in a somewhat less complete fashion were those of Henderson & Matthai (1910) and Rajyalakshmi (1961) on AL lamarrei (H. Milne Edwards, 1837), Sollaud (1923) on M. borellii (Nobili, 1896), M. potiuna (M?ller, 1880) M. iheringi (Ortmann, 1897), and M. pilimanus (De Man, 1879), and Boschi (1961) on M. borellii (Nobili, 1896). Species of Macrobrachium thus far discovered in Florida are M. acanthurus (Wiegmann), M. carcinus (L.), M. faustinum (De Saussure, 1857), M. hetero chirus (Wiegmann, 1836), M. ohione (Smith, 1874), and M. olfersii (Wieg mann). The latter species, object of this study, shows a rather peculiar distri bution. Holthuis (1952) reported it from Central and South America from Mexico to southern Brazil, with a single record of its occurrence in northern Florida at St. Augustine. Holthuis & Provenzano (1970) found species just south of Miami and state that the Florida finds of M. olfersii are so eccentric that it has been suggested that species was introduced into Florida waters with