Palaeos		Glossary
Metazoa		Glossary D-G

Invertebrate Glossary D-G

LIFE
|--Eubacteria
`--+--Archaea
   `--Eukarya
      |--Chlorobionta
      `--+--Fungi
         `--METAZOA  
            |--Choanoflagellata  
            `--Porifera 
               |--Radiata
               `--+--Cnidaria 
                  `--Bilateria
                     |--Deuterostomia
                     `--Protostomia
                        |--Ecdysozoa
                        `--Spiralia

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

D

decapentaplegic: a gene (dpp), a transcriptional regulator associated with formation of viscera.  See Hox Genes.

Deformed: a gene, abbreviated dfd, a hox4 homologue of arthropods. See Hox Genes.

desmosome: a portion of a cell membrane specialized for contact with other cells.  This is an important structure shared by all Eumetazoa.  Wikipedia has an excellent short discussion. More information ans electron micrographs of vertebrate desmosomes may be found here. 

deuterocerebrum: same as deutocerebrum.

deutocerebrum: (arthropod anatomy; also called deuterocerebrum) the portion of the arthropod brain in the segment 1 (acron =  #0).  In Crustacea, it is associated with chemosensation and olfaction through the antennules.

dfd: abbreviation for Deformed, a hox4 homologue of arthropods. See Hox Genes.

diactine: (sponge anatomy) a spicule or spicule axis with two rays.  See Spicule Terms.

diagenetic: in paleontology, used to describe a change in chemical composition or crystalline structure which occurs during fossilization.

diaxon: (sponge anatomy) a spicule with two axes.  See Spicule Terms.

diploblast: an animal having only two fundamental embryonic layers, i.e., lacking mesoderm. 

dispherula: (sponge embryology) the characteristic larva of the Halisarcida, consisting of two balls of cells, one inside the other.  Both are lined with ciliated cells. The cilia of the outer layer face outward.  Those of the inner ball, outward.  The dispherula arises from a process which looks very much like classical eumetazoan gastrulation, i.e. by invagiation of ectodermal cells at one point (emboly).

dissepiment: "dissepiment: 'partition'; a horizontal, or nearly horizontal, plate of tissue supporting a tabula in an archaeocyathan or coral skeleton; a connecting structure in the rhabdosome of a dendroid graptolite." Benton & Harper (1997).

distalless: a gene (dll), a transcriptional regulator associated with formation of appendages.  See Hox Genes.

dll: see distalless.  

dmbx: a class of homeobox transcription factor genes found only in cnidarians and deuterostomes.  During development, it is expressed at the anterior limit of hox expression.  See Hox Genes. 

dolomite: (geology) calcium magnesium carbonate, CaMg(CO₃)₂.  In practice, calcium carbonates fall in a continuum from pure calcite, with no magnesium, through high-magnesium calcite, to dolomite (50% magnesium), and even to magnesite (magnesium carbonate).  The substitution of magnesium for calcium ions in calcite skeletons can occur diagenetically (after death).  This process is called dolomitization. 

dorsal: (bivalve anatomy) on the edge, or in the direction of the edge, bearing the hinge ligament and (usually) the curved peaks of the umbos. If the

Doushantuo Fm: (geology) "The ... Doushantuo Formation is of early [Ediacaran] age, ~590 Ma at its base to ~565 Ma at its top. It is represented by a phosphate-dolostone sequence in Wengan, where it is 33 to 55 m thick and consists mainly of dark phosphate, cherty phosphate, chert, and gray dolomite. ... About 15 km west of the county town of Wengan on Beidaoshan, the Doushantuo Formation consists of three units: the Lower Phosphate unit (20 m thick), the Middle Dolostone unit (3.7 m) and the Upper phosphate unit (15 m)." Li et al. (1998).

dpp: see decapentaplegic. 

E

element: a segment of a segmented appendage. 

emboly: (embryology) gastrulation by invagination of cells at a particular point. 

en: abbreviation for engrailed. 

endite: In Crustacean anatomy, usually an appendage element projecting downwards or inwards from the protopodium.  See image at protopod.  See Dr. Joel Martin's Crustacea Glossary for details and exceptions. 

endo-: 1) In anatomy, a prefix suggesting that the structure lies, grows, or points below or within the root structure (e.g. endoderm). 2) In crustacean appendages, it suggests that a limb element grows ventrally or ventrolaterally, generally as an outgrowth of the protopod (e.g. endite, endopod).   

endopod: See image at protopod. The crustacean appendage is often described as "biramous."  The idea is that the crustacean appendage splits, distal to the protopod, into two axes, the exopod and the endopod.  The endopod is usually conceived to be a continuation of the main axis.  The assumed evolutionary scenario is that the endopod was a swimming appendage, while the exopod was a gill.  Many crustacean appendages don't actually look like this, and the actual evolution of their structure may have been quite different and various.  However, this is the ground-plan which carcinologists almost always have had in mind when they describe the details of an appendage. We must learn this frame of reference or remain befuddled by terminology which makes sense (if at all) only as an expression of this particular "anatomical philosophy," to borrow Janvier's (1996) useful phrase.  On the other hand, we must also be careful to understand that the "biramous appendage" is, at most, only a conceptual tool among other tools.  The problem with having a good hammer is that we may come to approach all problems as nails.  The problem with the "biramous appendage" is that we may go beyond using it as morphological shorthand and begin to accept its unstated assumptions about evolution, development, and homology as proven fact.  See Dr. Joel Martin's Crustacea Glossary for details and exceptions. 

engrailed: a homeobox gene associated with segment formation in crustaceans and some insects, abbreviated en. 

epi-: 1) In anatomy, a prefix suggesting that the structure lies, grows, or points above or out from the root structure (e.g. epidermis). 2) In crustacean appendages, it suggests that a limb element grows dorsally or dorsolaterally, generally as an outgrowth of the protopod (e.g. epipod).  3) In development or evolution, a prefix suggesting that a structure, form, or process is a later addition to, or elaboration of, the root structure, form, or process (e.g. epigenetic, epimere). 

epifauna: the animal community living on the sea bottom -- not in, under, or above the bottom.  Epifauna walk on, or are attached to, the bottom, but with the bulk of their bodies in the water column. 

euryhaline: tolerating a broad range of salinities

even-skipped: a Drosophila homeobox gene of the evx class associated with segment formation.

evo-devo: evolutionary developmental biology.  For an explanation, see Why we care. 

evx: a class of homeobox genes.  Evx genes are associated with segment formation in some arthropods.

exo- or exi-: 1) In anatomy, a prefix suggesting that the structure lies, grows, or points out from the root structure. 2) In crustacean appendages, it suggests that a limb element grows laterally, generally as an outgrowth of the protopod. 

exopod: In crustacean anatomy, the structure conceived of as the dorsal branch (from the protopod) of the original biramous limb.  See endopod for explanation and complaints.  The exopod typically consists of several elements (segments).  See image at protopod.  See Dr. Joel Martin's Crustacea Glossary for details and exceptions. 

F

flagellum: (pl. flagella) A eukaryotic flagellum is a bundle of nine fused pairs of microtubules called "doublets" surrounding two central single microtubules (the so-called 9+1 structure of paired microtubules; also called the "axoneme"). At the base of a eukaryotic flagellum is a microtubule organizing center about 500 nm long, called the basal body or kinetosome. The flagellum is encased within the cell's plasma membrane, so that the interior of the flagellum is accessible to the cell's cytoplasm. This is necessary because the flagellum's flexing is driven by the protein dynein bridging the microtubules all along its length and forcing them to slide relative to each other, and ATP must be transported to them for them to function. This extension of the cytoplasm is called the axosome.  Important note: The eukaryotic flagellum is completely different from the prokaryote flagella in structure and in evolutionary origin. The only thing that the bacterial, archaeal, and eukaryotic flagella have in common is that they stick outside of the cell and wiggle to produce propulsion.  From Flagellum - Wikipedia.  Image: O'Kelly et al. (1999).

G

galectin: a lectin which binds galactose.  See excellent short discussion at Galectin.

gamete: haploid sex cell, i.e. egg or sperm cell.

gastrulation: (embryology) Actually, there is no iron-clad definition of gastrulation.  Classically, it is the series of moves an embryo makes to form a gut.

glyconectin: a family of glycoproteins, each member of which is capable of tight, specific adhesion to other copies of the same protein.  Glyconectins are the basis for cell-cell adhesion in at least some sponges.

gonochoric: having two distinct sexes, dioecious. 

guild: in ecology, a group of organisms having a similar morphology, and exploiting the same food resources, living the same life-style and in the same environment, but which are not necessary related. Because no two types of organisms can occupy the same ecological niche (one will inevitably outcompete the other, and push it aside), comparable guilds have to be separated by geographical or chronological distance.  A good example of the same guild is the Crocodilian today, and the phytosaurian thecodont (parasuchia) of the late Triassic. Both are astonishingly similar in size, appearance, and life-style, and indeed modern crocodiles only appeared after the phytosaurs had become extinct. But they are only distantly related (both are archosaurian reptiles, but their common ancestor lived millions of years before the first phytosaur appeared).  MAK010510.     

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