biovulate a. [L. bis, two; ovum, egg] Having two ovules.
biparasitic a. [L. bis, two; parasitus, one who eats at the table of another] Being a parasite upon or in a parasite.
biparental a. [L. bis, two; parentalis, parent] Pertaining to or derived from two parents.
biparietal a. [L. bis, two; paries, wall] Provided with two paries.
biparous a. [L. bis, two; parere, to beget] Producing two young at a time.
bipartite a. [L. bis, two; partitus, divided] Having two distinct parts; bifid.
bipartite uterus A uterus with paired, tubular uteri that fuse at the point of junction with the vagina.
bipectinate a. [L. bis, two; pecten, comb] Having branches on two sides like the teeth of a comb.
bipectunculate a. [L. bis, two; pectunculus, small scallop] Minutely pectinate.
bipennate a. [L. bis, two; penna, feather] Twice pinnate. bi-penniform a.
bipinnaria larva (ECHINOD: Asteroidea) The free-swimming, bilaterally symmetrical larva; characterized by ciliated pre-oral and postoral bands and extending onto lobes projecting from the body; dipleurula larva. see brachiolaria.
biplicate a. [L. bis, two; plicatus, fold] Twice plaited or folded.
bipocillus n. [L. bis, two; poculum, cup] (PORIF) A spicule (mi-crosclere) with a curved shaft and cup-shaped expansion at either end; in Iophon , one discoid end and one pointed or forked end.
bipod a. [L. bis, two; Gr. pous, foot] Having one pair of legs. bipody n. see tetrapod.
bipolar a. [L. bis, two; polus, pole] 1. Having two poles or processes. 2. Pertaining to the polar regions.
bipolarity n. [L. bis, two; polus, pole] 1. Being bipolar. 2. Pertaining to the polar regions, as comparing the flora and fauna between the northern regions and the southern regions, and with that in between. 3. Nerves having processes at both ends.
biprostatic a. [L. bis, two; pro, before; stare, to stand] Having two prostates.
bipupillate a. [L. bis, two; pupilla, pupil of the eye] 1. Having two pupils. 2. Having two ocelli or spots that resemble two pupils.
biradial cleavage Cleavage in which the tiers of blastomeres are symmetrical with regard to the first cleavage plane.
biradial symmetry A type of symmetry in which an organism consists of radially arranged parts, equally arranged on each side of a median longitudinal plane.
biradiate a. [L. bis, two; radiatus, rayed] Having two rays or spokes. see diactinal, diaxon.
biramous a. [L. bis, two; ramus, branch] Consisting of two branches.
biramous appendage (ARTHRO: Crustacea) An appendage with two rami; also antennule or antenna with two flagellar elements; not all appendages of a crustacean are bira-mous.
biramous parapodium (ANN) A parapodium having bundles of setae on both noto- and neuropodium.
birefringent a. [L. bis, two; refringens, refractive] Having double refraction, high or low according to the difference between the refractive indices.
birostrate a. [L. bis, two; rostrum, beak] Having two beak-like processes.
birotulate spicules (PORIF) A spicule having a disc or series of radial, umbrella-like spokes at both ends; amphidiscs.
birth pore Uterine pore; birth opening.
bisegment n. [L. bis, two; segmentum, piece] One of two equal segments of a line.
biseptate a. [L. bis, two; septum, partition] Having two partitions.
biserial a. [L. bis, two; series, row] Arranged in two rows, or subdivided into two series.
biserial crochets (ARTHRO: Insecta) Crochets of larvae with proximal ends arranged in two, usually concentric rows. see serial crochets.
biserrate a. [L. bis, two; serra, saw] Having two notched or saw-teeth.
bisetose a. [L. bis, two; seta, bristle] Having two bristle-like appendages.
bisexual a. [L. bis, two; sexus, sex] 1. Of or pertaining to both sexes. 2. A population composed of functional males and females. 3. An individual possessing functional male and female reproductive organs; hermaphrodite.
bisinuate a. [L. bis, two; sinuare, to bend] Twice winding or bending; having two sinuations or notches.
bistrate a. [L. bis, two; stratum, layer] Having two layers of tissues.
bisulcate a. [L. bis, two; sulcus, groove] Of or pertaining to twice scored or grooved.
bithecal a. [L. bis, two; theke, case] 1. Having two thecae. 2. (ANN) Having two spermathecae.
bituberculate a. [L. bis, two; tuberculum, swelling] Having two tubercles or swellings.
biuncinate a. [L. bis, two; uncus, hook] Having two hooks.
bivalent a. [L. bis, two; valens, strong] 1. Having two completely or partially homologous chromosomes pairing during the first meiotic division. see univalent. 2. Double or joined in pairs; pertaining to an articulation permitting le-vator and depressor movements.
bivalve a. [L. bis, two; valvae, a folding door] Having two valves or parts; clamlike.
Bivalvia, bivalves n., n.pl. [L. bis, two; valvae, a folding door] A class of marine, estuarine or freshwater bivalve mollusks, in which the body is enclosed within two calcareous valves, or shells; other names for this class are Acephala, Conchifera, Pelecypoda, Conchophora, Dithra, Lamellibranchia, Lamellibranchiata, Elatobranchiata, Cormopoda, Tropipoda, Aglossa, Elatocephala, Anodontoda and Lipocephala.
bivittate a. [L. bis, two; vitta, band] Having two broad longitudinal stripes or vittae.
bivium n. [L. bivius, two-way] (ECHINOD: Asteroidea) Collectively, the two rays of a sea star, between which lies the madreporite. see trivium.
bivoltine a. [L. bis, two; It. volta, time] Having two sets of offspring a year. see polyvoltine.
bivulvar a. [L. bis, two; vulva, vulva] Having two vulvae in a single female.
bladder n. [A.S. blaeddre, bag] Any membranous sac or vesicle filled with air or fluid.
blade n. [A.S. blaed, leaf] 1. Any elongate, flattened, usually stiff structure shaped like a leaf, sword or knife. 2. (AR-THRO: Insecta) The lacinia or galea. 3. (nemata) see lamina.
blastaea n. [Gr. blastos, bud] Hypothetical animal ancestral to all metazoans; inferred from the blastula as a common stage in the development of higher invertebrate animals.
blastema n.; pl. -temata [Gr. blastema, bud] 1. Undifferentiated cells that later develop into an organ or structure. a. The part of an organism that gives rise to a new organism, as in asexual reproduction. b. That which often gives rise to regeneration of a lost part or appendage. see anlage.
blastocephalon n. [Gr. blastos, bud; kephale, head] (ARTHRO: Insecta) The head of an embryo.
blastocheme n. [Gr. blastos, bud; ochema, vehicle] (CNID) A reproductive bud in certain medusae.
blastochyle n. [Gr. blastos, bud; chylos, juice] Fluid contained in a blastocoel.
blastocoel(e) n. [Gr. blastos, bud; koilos, hollow] The primary cavity formed during the embryological development of animals; segmentation cavity; the subgerminal cavity.
blastocyst n. [Gr. blastos, bud; kystis, bladder] (PLATY: Cestoda) In Trypanorhynca, a posterior bladder of the metacestode into which the body is withdrawn.
blastocyte n. [Gr. blastos, bud; kytos, container] An embryonic cell before differentiation.
blastoderm n. [Gr. blastos, bud; derma, skin] The primary epithelium formed in early embryonic development of many invertebrates; germinal membrane.
blastogenesis n. [Gr. blastos, bud; genesis, beginning] 1. Development by asexual reproduction, or of an organ or part from a blastema. 2. The transmission of inherited characters by germ plasm. see embryogenesis.
blastogenic a. [Gr. blastos, bud; genos, birth] Originating in germ cells.
Blastoidea, blastoids n., n.pl. [Gr. blastos, bud; eidos, form] A class of extinct echinoderms of the former Subphylum Pelmatoza; Ordovician to Permian.
blastokinesis n. [Gr. blastos, bud; kinesis, movement] Displacements, rotations and revolutions of an embryo within an egg.
blastomere n. [Gr. blastos, bud; meros, part] Cells formed during primary cleavage of an egg, before the formation of a distinct gastrula stage.
blastophore n. [Gr. blastos, bud; phorein, to bear] 1. The external opening of the enteron of a gastrula. 2. (ANN) The endodermal cells brought into an internal position in the embryo during the mitotic division.
blastopore n. [Gr. blastos, bud; poros, passage] The mouth like opening from the archenteron to the exterior during the gastrula stage of development.
blastostyle n. [Gr. blastos, bud; stylos, pillar] (CNID: Hydro-zoa) The living axial portion of a modified gonangium, from which numerous medusae are budded.
blastozooid n. [Gr. blastos, bud; zoion, animal; eidos, form] A zooid or individual produced by asexual reproduction. see oozooid.
blastula n., pl. -lae [Gr. dim. blastos, bud] A stage near the end of cleavage, in the form of a hollow sphere bounded by a single layer of cells.
blister n. [A.S. blastr, a swelling] Any vesicle or raised spot on the surface of an organism.
Blochmann's body (ARTHRO) Any intracellular organisms in the egg; mainly bacteria; thought to be symbiotic.
blood n. [A.S. blod, blood] The variously colored or colorless fluid circulating in the vascular system or body cavity of animals, usually containing respiratory pigments, and carrying oxygen, food-materials, excretions, etc.
blood cells Cellular elements of the blood; hemocytes; plas-matocytes.
blood channel (ARTHRO: Insecta) In predacious larvae, a channel, either internal (duct or tube) or external (excavation or groove), usually extending the full length of the inner margin of the mandible.
blood gills (ARTHRO: Insecta) Thin walled respiratory or osmoregulatory evaginations continuous with the hemocoel and filled with blood, occurring in, but not confined to aquatic larvae.
blood rooms (ARTHRO: Crustacea) In Conchostraca, a network of anastomosing cavities in the body that function in blood circulation.
blood sinus (MOLL: Bivalvia) A blood vessel which is irregular in shape without specialized walls.
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