Crustaceans

Crustaceans

As many of you may know already, crustaceans are classified within the phylum, Arthopoda. They share this classification with 3 other groups, which includes hexapods, myriapods, and chelicerates. In general, hexapods refer to insects; myriapods refer to millipedes and centipedes, and chelicerates refer to horseshoe crabs and arachnids.

Qualities of Arthropods

Though arthropods are the most diverse group of animals with regards to number of species, they still retain some common characteristics that are listed up on the screen. These include the presence of rigid exoskeletons that provide the animal with support for walking and some protection against predators, as well as segmented bodies, jointed limbs, and muscle attachment inside the exoskeleton that allow the animal to perform complex movements.

Crustaceans Rundown

As a taxon, crustaceans are a diverse group of approximately 52,000 species featuring familiar animals such as crabs, shrimp, lobsters, krill, and barnacles, some of which are depicted here. Like other arthropods, crustaceans have segmented bodies, jointed limbs, and an exoskeleton, which they must molt in order to grow. Yet, on the other hand, they are distinguishable from other arthropods in three main ways. These include a nauplius larval stage, biramous appendages, and a cephalon. Unlike other arthropods, most crustaceans go through a series of larval stages, the first being the nauplius larva, in which only a few limbs are present, near the front of the body. Other limbs do not show up until later in development. Secondly, crustaceans exhibit limbs or appendages that are split in two, usually as two segmented branches, one internal (known as an endopod) and one external (known as an exopod); hence, two-part or biramous. Lastly, crustaceans have a unique five-segmented head (known as a cephalon), followed by a long trunk typically regionalized into a thorax and abdomen.

Copepods

And now I’m going to isolate two particular crustacean groups. The first is copepods. Copepods are a group of small crustaceans that are found in the sea as well as nearly every freshwater habitat. Some species are planktonic (drifting in sea waters), some are benthic (living on the ocean floor), and some are continental that live in other wet terrestrial places, such as swamps, bogs and springs. However, one type holds a particular interest for humans. The marine benthic copepod, Robertsonia propinqua, is currently being studied as a bioindicator of sediment-associated contaminants. In the lab, scientists at Lincoln University in New Zealand are determining the effect that particular contaminants such as atrazine and zinc sulfate have on its life cycle by injecting them into the copepod and observing the results.

Barnacles

The second crustacean group I would like to focus on is barnacles. Barnacles are a group of arthropods that are exclusively marine and tend to live in shallow, tidal waters. They are sessile (non-motile) filter feeders that obtain food by straining and suspending food particles from the water. At first glance, it might be hard to believe that barnacles are classified as arthropods. Though segmentation is usually indistinct, their bodies do possess unequal divisions of a head, thorax, and abdomen. Adult barnacles have few appendages on the head, with only a single pair of antennae. They also have six pairs of thoracic limbs, referred to as “cirri”, which are long, feathery appendages that are used to filter feed. Barnacles were originally thought be mollusks because of their apparent possession of a shell, but they are actually crustaceans with their nearest relatives being shrimp and lobsters. The barnacles depicted on the slide, Chamaesipho tasmanica, are known as honeycomb barnacles because they form dense covers of hundreds or even thousands of barnacles over rock surfaces in tidal waters.

 

Biology Terms 3

lichen An organism resulting from the symbiotic association of a true fungus and either a cyanobacterium or a unicellular alga.

mutualism The type of symbiosis, such as that exhibited by fungi and algae or cyanobacteria in forming lichens, in which both species profit from the association.

mycorrhiza An association of the root of a plant with the mycelium of a fungus.

parasite An organism that attacks and consumes parts of an organism much larger than itself. Parasites sometimes, but not always, kill their host.

symbiosis The living together of two or more species in a prolonged and intimate ecological relationship.

cell wall A relatively rigid structure that encloses cells of plants, fungi, many protists, and most prokaryotes. Gives these cells their shape and limits their expansion in hypotonic media.

centriole A paired organelle that helps organize the microtubules in animal and protist cells during nuclear division.

chloroplast An organelle bounded by a double membrane containing the enzymes and pigments that perform photosynthesis. Chloroplasts occur only in eukaryotes.

cilium Hairlike organelle used for locomotion by many unicellular organisms and for moving water and mucus by many multicellular organisms. Generally shorter than a flagellum.

collagen A fibrous protein found extensively in bone and connective tissue.

cytoplasm The contents of the cell, excluding the nucleus.

cytoskeleton The network of microtubules and microfilaments that gives a eukaryotic cell its shape and its capacity to arrange its organelles and to move.

cytosol The fluid portion of the cytoplasm, excluding organelles and other solids.

endomembrane system Endoplasmic reticulum plus Golgi apparatus; also lysosomes, when present. A system of membranes that exchange material with one another.

endoplasmic reticulum (ER) A system of membranous tubes and flattened sacs found in the cytoplasm of eukaryotes. Exists in two forms: rough ER, studded with ribosomes; and smooth ER, lacking ribosomes.

endosymbiosis Two species living together, with one living inside the body (or even the cells) of the other.

endosymbiotic theory The theory that the eukaryotic cell evolved via the engulfing of one prokaryotic cell by another.

eukaryotes Organisms made up of one or more complex cells in which the genetic material is contained in nuclei.

extracellular matrix In animal tissues, a material of heterogeneous composition surrounding cells and performing many functions including adhesion of cells.

Golgi apparatus A system of concentrically folded membranes found in the cytoplasm of eukaryotic cells; functions in secretion from cell by exocytosis.

intermediate filaments Cytoskeletal component with diameters between the larger microtubules and smaller microfilaments.

lysosome A membrane-enclosed organelle found in eukaryotic cells (other than plants). Lysosomes contain a mixture of enzymes that can digest most of the macromolecules found in the rest of the cell.

microfilament Minute fibrous structure generally composed of actin found in the cytoplasm of eukaryotic cells. They play a role in the motion of cells.

microtubules Minute tubular structures found in centrioles, spindle apparatus, cilia, flagella, and cytoskeleton of eukaryotic cells. These tubules play roles in the motion and maintenance of shape of eukaryotic cells.

mitochondrion An organelle in eukaryotic cells that contains the enzymes of the citric acid cycle, the respiratory chain, and oxidative phosphorylation.

nuclear envelope The surface, consisting of two layers of membrane, that encloses the nucleus of eukaryotic cells.

nucleoid The region that harbors the chromosomes of a prokaryotic cell. Unlike the eukaryotic nucleus, it is not bounded by a membrane.

nucleolus A small, generally spherical body found within the nucleus of eukaryotic cells. The site of synthesis of ribosomal RNA.

nucleus In cells, the centrally located compartment of eukaryotic cells that is bounded by a double membrane and contains the chromosomes.

organelles Organized structures found in or on eukaryotic cells. Examples include ribosomes, nuclei, mitochrondria, chloroplasts, cilia, and contractile vacuoles.

plasma membrane The membrane that surrounds the cell, regulating the entry and exit of molecules and ions. Every cell has a plasma membrane.

prokaryotes] Organisms whose genetic material is not contained within a nucleus: the bacteria and archaea. Considered an earlier stage in the evolution of life than the eukaryotes.

ribosome A small organelle that is the site of protein synthesis.

vacuole A liquid-filled, membrane-enclosed compartment in cytoplasm; may function as digestive chambers, storage chambers, waste bins.

Biology Terms Continued

oil A triglyceride that is liquid at room temperature.

oligosaccharide A polymer containing a small number of monosaccharides.

optical isomers Two isomers that are mirror images of each other.

pentose A sugar containing five carbon atoms.

peptide linkage The bond between amino acids in a protein. Formed between a carboxyl group and amino group (CO—NH) with the loss of water molecules.

phosphodiester linkage The connection in a nucleic acid strand, formed by linking two nucleotides.

phospholipids Lipids containing a phosphate group; important constituents of cellular membranes.

polymer A large molecule made up of similar or identical subunits called monomers.

polysaccharide A macromolecule composed of many monosaccharides (simple sugars). Common examples are cellulose and starch.

primary structure The specific sequence of amino acids in a protein.

protein One of the most fundamental building substances of living organisms. A long-chain polymer of amino acids with twenty different common side chains. Occurs with its polymer chain extended in fibrous proteins, or coiled into a compact macromolecule in enzymes and other globular proteins.

purine One of the types of nitrogenous bases. The purines adenine and guanine are found in nucleic acids.

pyrimidine A type of nitrogenous base. The pyrimidines cytosine, thymine, and uracil are found in nucleic acids.

quaternary structure The specific three dimensional arrangement of protein subunits.

R group The distinguishing group of atoms of a particular amino acid.

ribose A five-carbon sugar in nucleotides and RNA.

ribozyme An RNA molecule with catalytic activity.

RNA (ribonucleic acid) An often single stranded nucleic acid whose nucleotides use ribose rather than deoxyribose and in which the base uracil replaces thymine found in DNA. Serves as genome from some viruses.

saturated fatty acid A fatty acid usually containing from 12 to 18 carbon atoms and no double bonds.

secondary structure Of a protein, localized regularities of structure, such as the α helix and the beta pleated sheet.

starch A polymer of glucose; used by plants to store energy.

structural isomers Molecules made up of the same kinds and numbers of atoms, in which the atoms are bonded differently.

tertiary structure In reference to a protein, the relative locations in three-dimensional space of all the atoms in the molecule. The overall shape of a protein.

triglyceride A simple lipid in which three fatty acids are combined with one molecule of glycerol.

unsaturated hydrocarbon A compound containing only carbon and hydrogen atoms, with one or more pairs of carbon atoms that are connected by double bonds.

vitamins Organic compounds that an organism cannot synthesize, but nevertheless requires in small quantity for normal growth and metabolism.

 

binary fission Reproduction by cell division of a single-celled organism.

biofilm A community of microorganisms embedded in a polysaccharide matrix, forming a highly resistant coating on almost any moist surface.

bioluminescence The production of light by biochemical processes in an organism.

cyanobacteria (Cyanobacteria) A group of unicellular, colonial, or filamentous bacteria that conduct photosynthesis using chlorophyll

decomposers Organisms that metabolize organic compounds in debris and dead organisms, releasing inorganic material; found among the bacteria, protists, and fungi.

flagellum Long, whiplike appendage that propels cells. Prokaryotic flagella differ sharply from those found in eukaryotes.

Koch’s postulates A set of rules for establishing that a particular microorganism causes a particular disease.

lateral gene transfer The transfer of genes from one species to another, common among bacteria and archaea.

pathogen An organism that causes disease.

peptidoglycan The cell wall material of many bacteria, consisting of a single enormous molecule that surrounds the entire cell.

spore Any asexual reproductive cell capable of developing into an adult organism without gametic fusion. In plants, haploid spores develop into gametophytes, diploid spores into sporophytes. In prokaryotes, a resistant cell capable of surviving unfavorable periods.

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Biology Important Definitions

alpha (α) helix A prevalent type of secondary protein structure; a right-handed spiral.

amino acid Organic compounds containing both NH2 and COOH groups. Proteins are polymers of amino acids.

base (1) A substance that can accept a hydrogen ion in solution. (2) In nucleic acids, the purine or pyrimidine that is attached to each sugar in the backbone.

beta (β) pleated sheet Type of protein secondary structure; results from hydrogen bonding between polypeptide regions running anti-parallel to each other.

carbohydrates Organic compounds containing carbon, hydrogen, and oxygen in the ratio 1:2:1 (i.e., with the general formula CnH2nOn). Common examples are sugars, starch, and cellulose.

cellulose (sell´ you lowss) A straight-chain polymer of glucose molecules, used by plants as a structural supporting material.

chemical evolution The theory that life originated through the chemical transformation of inanimate substances.

complementary base pairing The AT (or AU), TA (or UA), CG, and GC pairing of bases in double-stranded DNA, in transcription, and between tRNA and mRNA.

condensation reaction A reaction in which two molecules become connected by a covalent bond and a molecule of water is released. (AH + BOH → AB + H2O.)

denaturation Loss of activity of an enzyme or nucleic acid molecule as a result of structural changes induced by heat or other means.

deoxyribose A five-carbon sugar found in nucleotides and DNA.

disaccharide A carbohydrate made up of two monosaccharides (simple sugars).

disulfide bridge The covalent bond between twosulfur atoms (–S—S–) linking to molecules or remote parts of the same molecule.

DNA (deoxyribonucleic acid) The fundamental hereditary material of all living organisms. In eukaryotes, stored primarily in the cell nucleus. A nucleic acid using deoxyribose rather than ribose.

double helix In DNA, the natural, right-handed coil configuration of two complementary, antiparallel strands.

ester linkage A condensation (water-releasing) reaction in which the carboxyl group of a fatty acid reacts with the hydroxyl group of an alcohol. Lipids are formed in this way.

fat A triglyceride that is solid at room temperature.

fatty acid A molecule with a long hydrocarbon tail and a carboxyl group at the other end. Found in many lipids.

functional group A characteristic combination of atoms that contribute specific properties when attached to larger molecules.

glucose The most common monosaccharide; the monomer of the polysaccharides starch, glycogen, and cellulose.

glycerol A three-carbon alcohol with three hydroxyl groups; a component of phospholipids and triglycerides.

glycogen An energy storage polysaccharide found in animals and fungi; a branched-chain polymer of glucose, similar to starch.

glycosidic linkage Bond between carbohydrate (sugar) molecules through an intervening oxygen atom (–O–).

hexose [Gk. hex: six] A sugar containing six carbon atoms.

hydrolysis A chemical reaction that breaks a bond by inserting the components of water: AB + H2O → AH + BOH.

isomers Molecules consisting of the same numbers and kinds of atoms, but differing in the bonding patterns by which the atoms are held together.

ligand Any molecule that binds to a receptor site of another (usually larger) molecule.

lipids Substances in a cell which are easily extracted by organic solvents; fats, oils, waxes, steroids, and other large organic molecules, including those which, with proteins, make up the cell membranes.

macromolecule A giant polymeric molecule. The macromolecules are proteins, polysaccharides, and nucleic acids.

monomer A small molecule, two or more of which can be combined to form oligomers (consisting of a few monomers) or polymers (consisting of many monomers).

monosaccharide A simple sugar. Oligosaccharides and polysaccharides are made up of monosaccharides.

nucleic acid A long-chain alternating polymer of deoxyribose or ribose and phosphate groups, with nitrogenous bases—adenine, thymine, uracil, guanine, or cytosine (A, T, U, G, or C)—as side chains. DNA and RNA are nucleic acids.

nucleotide The basic chemical unit in a nucleic acid. A nucleotide in RNA consists of one of four nitrogenous bases linked to ribose, which in turn is linked to phosphate. In DNA, deoxyribose is present instead of ribose.

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