Free-swimming Nauplius Research Articles

Cadmium and zinc reversibly arrest development of Artemia larvae.

Despite the widespread distribution of heavy metals such as cadmium and zinc in the environment and their well-known cytotoxicity and embryotoxicity in mammals, comparatively little is known about their effect on aquatic organisms, particularly invertebrates. Post-gastrula and early larval development of the brine shrimp, Artemia, present some useful advantages for studies of developmental aspects of environmental toxicology. Dormant encysted gastrulae, erroneously called brine shrimp eggs, can be obtained commercially and raised in the laboratory under completely defined conditions. Following a period of post-gastrula development within the cyst, pre-nauplius larvae emerge through a crack in the cyst shell. A few hours later, free-swimming nauplius larvae hatch. Cadmium is acutely toxic to both adults and nauplius larvae of Artemia, but the reported LC50s are as high as 10 mM, depending on larval age. In this paper the authors show that pre-nauplius larvae prior to hatching are much more sensitive to cadmium than are hatched nauplius larvae. At 0.1 ..mu..m, cadmium retards development and hatching of larvae; higher concentrations block hatching almost completely and thus are lethal. However, the larvae arrested at the emergence stage survive for 24 hours or more before succumbing to the effects of cadmium, and during this period themore » potentially lethal effect is reversible if the larvae are placed in cadmium-free medium. The effects of zinc parallel those of cadmium, although zinc is somewhat less toxic than cadmium at equal concentrations.« less

Sibling species of Doridicola (Copepoda: Lichomolgidae) from California sea anemones: biology and host specificity

Copepods living in association with various intertidal, Californian sea anemones were studied, both in the field and in the laboratory. The copepods all belong to the genus Doridicola and four new species were recently described. Copepods were found on the sea anemones Anthopleura artemisia (Pickering in Dana), A. elegantissima (Brandt), A. xanthogrammica (Brandt), Epiactis prolifera Verrill, Tealia coriacea (Cuvier), T. crassicornis (Müller), T. lofotensis (Danielssen) and T. piscivora Sebens & Laakso, where they live on the column and tentacles, probably feeding on host tissue. The copepods show quite high host-specificity, and spend their entire life on their host except for the free-swimming nauplius stages. They have a high fecundity and a short lifespan with many generations per year.

Some observations on the swimming and feeding of the nauplius larvae of Lepas pectinata (Cirripedia: Crustacea)

Limb movements of restrained stage VI nauplii of Lepas pectinata were studied by cine-photography. Outline drawings were made of successive limb positions in both swimming and grooming activity. The antennae appeared to act as leaky paddles performing both propulsion and food gathering. Free-swimming nauplii averaged 120 limb beats min-1 and a speed of c. 4 mm s-1. Grooming occurred every 7–20 beats. It was concluded that lack of streamlining favours filtration at the expense of propulsion. The grooming sequence differs from that of balanid nauplii and is one method of transferring food to the vicinity of the mouth, where sorting and rejection take place prior to ingestion. Fine- and coarse-mesh filters presumably exploit different plankton types. The overall behaviour pattern is well-designed for exploitation of scarce food in the oligotrophic conditions of the ocean-surface habitat.

Some observations of hatching of electron-irradiated Artemia eggs under a scanning electron microscope.

Encysted dry eggs of Artemia sauna are observed under a scanning electron microscope, after irradiation with electrons for 5min. At 18-hr-incubation in 2% NaCl solution at 27°C, the egg shells crack open, and embryos emerge from the shells. At 24- hr-incubation, the embryos hatch out into free-swimming nauplii. Exposure of the eggs shows a linear decrease of hatchability with an increase of irradiation time.

Physical properties of Artemia salina ribosomes

Eukaryotic ribosomes were isolated from the cryptobiotic embryos and from the further-developed free-swimming nauplii of the brine shrimp Artemia salina. Analytical boundary sedimentation and photon correlation spectroscopy yielded, respectively, the standard sedimentation and diffusion coefficients at infinite dilution, s degrees 20,w = 81 +/- 1 S and D degrees 20,w = (1.41 +/- 0.02) x 10(-7) cm2/s, for the unfixed and formaldehyde-fixed ribosomes from different developmental stages and for ribosomes attached to a messenger RNA fragment. Also, the density increment was determined, from which the partial specific volume was derived (0.63 +/- 0.01 cm3/g). Combination of the different measured parameters gives accurate values for the molecular weight (3.8 +/- 0.1) x 106 and for size and solvation parameters. These results are compared with their counterparts for the smaller ribosomes from the prokaryote Escherichia coli.

DNA-Dependent RNA Polymerases from Artemia salina: Decreasing Polymerase Activities and Number of Polymerase II Molecules in Developing Larvae

Embryos and larvae of the brine shrimp, Artemia salina, provide a useful biological system for biochemical studies of animal development. Dormant encysted embryos can be cultured readily in the laboratory to provide large quantities of free-swimming nauplius larvae. The rate of synthesis of all classes of RNA in swimming larvae declines markedly between 24 and 72 h after immersion of dormant embryos in sea water. Nuclei were isolated from 24-72 h larvae and RNA polymerase activity was measured under conditions in which the nuclei remained intact. Total RNA polymerase activity of isolated nuclei decreased in parallel with RNA synthesis in vivo. RNA polymerases were solubilized from nuclei and fractionated by chromatography on DEAE-cellulose. The levels of both RNA polymerases I and II also decreased in parallel with RNA synthesis in vivo. The specific activity of highly purified RNA polymerase II was determined by comparison of enzyme activity with the mass of RNA polymerase II subunits displayed on SDS gels. The specific activities of RNA polymerase II preparations from 24 and 72 h larvae were identical. The number of polymerase II molecules was estimated from the mass of the subunits. The number of molecules per nucleus declined from 20,000 at 24 h to 3500 at 72 h.

DNA-Dependent RNA Polymerases from Artemia salina: IV. Appearance of Nuclear RNA Polymerase Activity during Pre-Emergence Development of Encysted Embryos

Dessicated and encysted gastrulae of the brine shrimp Artemia salina remain metabolically dormant until they are rehydrated. At this time development resumes, culminating in the hatching of free swimming nauplius larvae. The resumption of embryogenesis provides a convenient system for studying biochemical events which accompany development of a eukaryotic organism, and in particular Artemia has proven useful for studies of the transcriptional regulation of gene expression. Encysted gastrulae of Artemia yielded only trace amounts of DNA-dependent RNA polymerase activity when crude nuclear pellets were subjected to sonication at high ionic strength. Furthermore, when crude nuclear pellets from encysted gastrulae and developing nauplius larvae were mixed prior to sonication, subsequent solubilization of proteins from the mixture did not yield RNA polymerase activity; sonication of the pellet from nauplii alone resulted in the solubilization of large quantities of RNA polymerases I and II as we have previously found [1]. RNA polymerases I and II were detectable in sonicates of crude nuclear pellets after 1-h incubation of Artemia cysts in sea water. This presents the possibility that dormant gastrulae of the brine shrimp contain RNA polymerase which is inactive, and that the rapid appearance of nuclear enzymatic activity which accompanies the resumption of development may not require de novo synthesis of the polymerase.

Free-Swimming Copepod Nauplii of Narragansett Bay with a Key to Their Identification

Zooplankton surface samples were taken with a number 12 silk bolting cloth net towed by a Clark-Bumpus quantitative plankton sampler in Narragansett Bay for 12 months. The samples were collected twice weekly, except during December, January, and February, at night at one position in the West Passage of Narragansett Bay. Ten calanoid, three cyclopoid, and one harpacticoid species of free-swimming copepod nauplii were collected from July 1957 through June 1958. The structure and arrangement of elements of the caudal armatures of these copepod nauplii showed certain differences which were utilized to develop a key.

VIII. On the embryclogy of a mysid crustacean, Hemimysis lamornæ

The study of the embryology of Hemimysis Lamornæ , of which the following pages contain an account, was first undertaken with a view of tracing the later development of the mesoderm, and the formation of the heart and segmental excretory organs. The later embryological stages of the Malacostraca have not been investigated in much detail, and usually with poor fixation of the material. In view of the recent work of Cannon (1924 and 1927) on the development of Estheria and Chirocephalus , where the presence of segmental cœlomic cavities in the mesoderm and their relation to the heart formation has been demonstrated, it became highly desirable that some Malacostracan should be examined with similar care. A Mysid, although it is not liberated as a freeswimming nauplius, can be taken as one of the least specialised Malacostraca, possessing a long tubular heart, simple antennal gland and most of the external features of the caridoid facies. For these reasons, and for the fact that abundant material is available, the type selected was Hemimysis Lamornæ . However, it became evident that an examination of the earliest stages was equally necessary, and the development from segmentation stages onwards has been followed. In spite of abundant literature on Malacostracan germ-layer formation, the accounts are incomplete and often inaccurate, owing chiefly to inferior technique. In the Peracarida the origin of the germ layers and the formation and closure of the blastoporal area have not been satisfactorily worked out in any one type. Among the Decapod a the recent work of Sollaud (1923) on the Palæmoninæ is the most complete and careful account so far produced. Very little is known of the development of the Hoplocarida apart from the complicated metamorphosis. The embryology of the Syncarida is unknown. The literature contains much that is contradictory, especially concerning the Peracarida, so that a thorough account of the early development of any one form, and particularly of one of the Mysidacea which occupy a central position in the Peracarida, seems called for. Such a study would be useless unless a new technique was found.

Papers read to the Society, February 28, 1901.

I. “The New Star in Perseus.—Preliminary Note.” By Sir Norman Lockyer, K.C.B., F. R. S. II. “On the Structure and Affinities of Fossil Plants from the Palaeozoic Rocks. IV.—The Seed-like Fructification of Lepidocarpon , a Genus of Lycopodiaceous Cones from the Carboniferous Formation.” By Dr. D. H. Scott, F. R. S. III. “A Preliminary Account of the Development of the Free-swimming Nauplius of Leptodon hyalina (Lillj.).” By Dr. E. Warren. IV. “On the Result of Chilling Copper-Tin Alloys.” By C. T. Heycock, F. R. S., and F. H. Neville, F. R. S. V. “On the Theory of Consistence of Logical Class-frequencies, and its Geometrical Representation.” By G. Udny Yule.

A preliminary account of the development of the free-swimming nauplius of Leptodora hyalina (Lillj.)

Leptodora appears to be a primitive daphnid in retaining a long, markedly segmented abdomen, and for this reason it seemed likely that an investigation on the development of the winter-generation might throw some light on the vexed (questions in Crustacean development. It was more particularly desired to ascertain whether any vestige of a cœlom occurred, and that if so, whether any remnant of it persists in the adult. With this object in view, it was necessary to inquire into the origin of the genital cells and of the antennary and maxillary glands.

Societies and Academies

LONDON. Royal Society, February 28.—“A Preliminary Account of the Development of the Free-swimming Nauplius of Leptodora Hyalina (Lillj.).” By Ernest Warren, D.Sc. Communicated by Prof. Weldon, F.R.S.