In sea anemones, a thread armed with nematocysts and extruded from the mouth or through a pore in the body wall.
Adductor muscle
In bivalve mollusks, a muscle that draws the two valves together, enclosing the soft parts.
Alternation of Generations
In life cycle, alternation of a generation having sexual reproduction with a generation having asexual reproduction. The sexually and asexually reproducing forms are often very different from each other. Occurs among animals in hydroids, jelly fish, tapeworms; in these both generations are diploid. In plants seen most clearly in ferns where the two generations are independent. The fern plant is a diploid sporophyte and reproduces asexually by the formation of haploid spores following meiosis. Germination of the spores initiates the gametophyte generation, a small prothallus, which reproduces sexually. Male and female gametes fuse together to form a zygote which develops into a new fern plant.
Ambulacral groove
A groove containing rows of tube feet on the lower surface of a sea star or brittle star.
Antenna (Antennae)
A sensory appendage on the head of an arthropod or annelid.
Antennal scale
The bladelike outer member of the 2nd antenna of a higher crustacean.
Aperture
The opening of the body whorl of a snail or tusk shell through which the foot and head of the animal protrude.
Apical organ
An organ sensitive to gravity, located at the end opposite the mouth in a ctenophore, and consisting of a capsule containing heavy granules that tumble in response to gravity as the animal's position changes, stimulating the animal to right itself.
Aristotle's lantern
The chewing mechanism of a sea urchin, consisting of 5 teeth operated by a complex system of levers and muscles.
Asymmetrical
When divided, the two sides do not form identical halves.
Atrium
In cephalochordates and tunicates, a chamber around the pharynx through which water flows from the pharyngeal gill slits to the outside, via the excurrent siphon.
Autonomy
The capacity of some animals to shed a part of the body or to break into several pieces, in the absence of external force.
Avicularium
See Pincher
Axis
The straight line with respect to which a body is symmetrical.
Basal body
See Centriole.
Bilateral Symmetry
A body plan in which paired body parts lie on wither side of a midline, so that each side is a mirror image of the other.
Binary Fission
Reproduction by splitting into two equal parts. Binary fission occurs in many unicellular organisms, and some multicellular ones like coral.
Bioluminescence
Light produced by a living organism through a biochemical reaction.
Blepharoplast
See Centriole.
Body Whorl
The last whorl of a snail's shell, ending at the aperture and containing the bulk of the animal.
Brackish
Containing some salt, but less than seawater.
Budding
Reproduction by splitting into several equal parts, each being a smaller version of the mature form. Budding occurs in many unicellular organisms, and some multicellular ones like coral.
Byssal threads, or Byssus
Tough, silken threads secreted by certain bivalve mollusks s a means of attachment to a substrate.
Carapace
That part of the exoskeleton of a horseshoe crab or higher crustacean extending over the head and thorax, but not the abdomen.
Centriole
Minute rod-shaped body, 300-500 nm long and 150 nm diameter, present in many resting cells, just outside the nuclear membrane. Cylindrical, containing nine short, parallel, peripheral fibrils, each fibril consisting of one to three sub-fibrils. Doubles during or after mitosis, and at the beginning of the next mitosis the two centrioles move apart and form the poles of the spindle, and the centers of the asters when present. Absent in higher plants.
Cephalothorax
The fused head and thorax of a crustacean.
Chela
See Pincer.
Cilium (Cilia)
A microscopic, hairlike projection on the free border of epithelial cells that beats with others in coordinated waves.
Cirrus (Cirri)
A tactile projection that varies in shape according to the phylum; may be tentaclelike, fingerlike, or hairlike.
Cnidocyte
In cnidarians, a cell containing a nematocyst, or stinging capsule.
Coatis
Coelenterata
Phylum of animals (coelenterates) containing hydroids, jellyfish, sea anemones, corals, and comb jellies. All aquatic, and most marine. Body built more or less radially symmetrical; of jelly-like consistency; gut, or coelenteron, has one opening only (a mouth, no anus); nervous system diffuse; no excretory system; no blood system.
Coelenteron
The digestive cavity of a cnidarian.
Coelom
A body cavity lying entirely within tissues of mesodermal origin.
Collar cell
A cell in the lining of the cavity of a sponge, bearing a trumpetlike collar surrounding a flagellum.
Columella
That part of the spiral shell of a snail surrounding the axis, about which the shell coils.
Comb plate
A comblike membrane of used cilia in a ctenophore; a ctena.
Commensal
(Of members of different species) living in close association, such as in the same burrow, shell, or coral reef, without much mutual influence, not symbiotic.
Conies
See Pika
Corallum
The skeleton of a calcium carbonate deposited by the base of a stony coral.
Creodonts
Ctena (Ctenae)
One of the comblike flaps of fused cilia found in rows on the body of a ctenophore, and used in locomotion.
Cytoplasm
All the protoplasm of a cell excluding the nucleus. It is usually a transparent slightly viscous fluid with inclusions of various sizes ranging from microscopically visible plastids and Golgi apparatus to invisible ribosomes. Differentiated externally as a plasma membrane.
Detritus
Particles worn off a solid body.
Dextral
In snails, having the aperture in the right-hand side of the columella.
Diatom
A microscopic, unicellular plant living either attached to a solid or as plankton, and capable of photosynthesis.
Dinoflagellate
A microscopic, unicellular planktonic organism with two flagella, sometimes capable of photosynthesis.
Dioecious
Having separate sexes.
Diploid
(Of a nucleus) having the chromosomes in pairs, the members of each pair being homologous so that twice the haploid number is present. Characteristic of almost all animal cells except the gametes; of the zygotes of many green algae and of many fungi; which undergo meiosis so that later stages are haploid; and of the sporophyte of other algae, Bryophyta and vascular plants.
Ectoderm
Endoderm
Ephyra (ephyrae)
Epidermis
Outermost layer of cells of a plant or animal. In plants one cell-layer thick, covered in aerial parts by a non-cellular protective cuticle. In vertebrates there is no non-cellular cuticle, and epidermis is several layers thick; outermost ones being dead and horny in land-living vertebrates. In vertebrates the epidermis is only one cell-layer thick and often secretes a cuticle.
Epithelio-muscular cell
Epithelium (Epithelia)
Exoskeleton
Eyra
Fauna
Flagellum (Flagella)
Fine long thread about a quarter of a micrometer thick and up to several hundred micrometers long having lashing or undulating movement, projecting from a cell. Has an external structure consisting of an outer membrane continuous with plasma membrane and enclosing a matrix in which eleven fibrils (microtubules) are arranged longitudinally, a central pair of single fibrils being surrounded by nine double fibrils near the periphery. Anchored in cytoplasm on cylindrical body similar in structure to centriole known variously as basal body, blepharoplast, kinetoplast, and kinetosome. Some bear exceedingly fine lateral projections (mastigonemes) along their length, or a delicate undulating membrane. Characteristic of one group of unicellular organisms (Flagellata), present in most motile gametes, in zoospores, and in some metazoan cells, like endodermal cells of Hydra. Usually only one or a few per cell, although some Protozoa have many. Motion of most flagella consists of waves traveling along them. Flagella are responsible for movement of those unicellular organisms and reproductive sells which bear them; and they move water through body of sponges. Flagella are also found in many bacteria, but are very much simpler in structure, consisting of a single fibril.
Gamete
Reproductive cell. Also referred to as sperm and ovum, or egg. Some animal and plant species produce cells, which are also gametes, like female gametes of the same or related organism, but which develops into a new individual without fertilization. In plants, the sperm is also called pollen.
Gametophyte
Phase of life cycle of plants, which has haploid nuclei; during it the sex cells are produced. It arises from a spore produced by meiosis from a sporophyte.
Gape
A region of incomplete closure between the two valves of a bivalve mollusk.
Gastrodermis
Lining of gastrointestinal system.
Gemmule
Of sponges, a bud formed internally as a group of cells, which may become free by decay of parent and subsequently form a new individual. Freshwater sponges over-winter in this way.
Genus
Girdle
Gonad
Organ of animals which produces gametes. In some animals produces hormones, too.
Gonophore
Gonotheca (Gonothecae)
Growth line
Haploid
Having a single set of unpaired chromosomes in each nucleus. Characteristic of gametes; of some Sporozoa; of somatic nuclei of parthenogenetically (Ova fertilize spontaneously in the absence of males) produced males of some animals like bees; and of gametophytes and many spores of algae, fungi, Bryophyta, and vascular plants.
Hermaphroditic
Holdfast
Hydranth
Hydroids
Member of one of the orders of Hydrozoa. Colonial animals forming tuft-like growths on seaweeds, etc.
Hypostome
Inner lip
Kinetoplast
See Centriole.
Kinetosome
See Centriole.
Ligament
Lip, or Outer lip
Madreporite
See Sieve plate.
Mantle
Mantle cavity
Manubrium
A fleshy stalk on the underside of a cnidarian medusa, bearing the mouth.
Margin
Marsupium
Mastigonemes
Maxilla
Maxilliped
Medusa
Meiosis
Mesentery
Mesoderm
Mesoglea
Microtubules
Mitosis
Monoecious
See Hermaphroditic.
Mucus
Muscle scar
Mutualism
Nematocyst
Nephridium (nephridia)
Ocellus (Ocelli)
Operculum
Opisthosoma
Oral arm
Oral disk
Oral lobe
Osculum (Oscula)
Ostium (Ostia)
Oviparous
Egg-laying; a term applied to animals whose eggs are released from the body of the female before undergoing embryonic development.
Ovoviviparous
Pallial line
Palp
Papilla (Papillae)
Parapodium (Parapodia)
Parasite
Parenchyma
Undifferentiated tissue filling the space not occupied by organs in the body of a flatworm or nemertean worm.
