Glossary - Freshwater Algae: Identification, Enumeration and Use as Bioindicators - page 257

Pennate Diatoms that are bilaterally symmetrical
about the apical axis

Raphe ribs Longitudinal ribs running alongside
the raphe

Perforation With holes or spaces between the
cells

Reniform Kidney-shaped

Reticulate Like a net in its arrangement

Periplast Cell membrane of euglenoids, or other
bounding membrane

Rhomboid A parallelogram with oblique angles
and adjacent sides unequal

Phycocyanin The blue-green pigment in the cells
of Cyanophyta

Ribbon-like Large numbers of elongate cells
joined by their sides to form a filament-like struc-
ture. In transverse section, however, a ribbon is never
circular (see Fragilaria crotonensis )

Polar nodule A body on the inner wall at the end
(pole) of some diatoms and other algae

Rostrate Narrowing or ending in a beak

Polar septum A partition or cross wall near the end
of the cell

Scalariform Ladder-like

Posterior The rear or back end of an organism

Segment-shaped Shaped like the segment of an
orange

Prostrate Creeping or growing over a substrate and
being closely adhering to it

SEM Scanning electron microscope

Pseudocilium A flagellum-like structure but not an
organ of locomotion, found in the Tetrasporales

Semicell One half of a desmid cell

Septum A cross partition either completely or
partly across a diatom cell dividing it into chambers
(pleural Septa).

Pseudoparenchymatous Appearing like paren-
chyma but in reality is made up of closely packed
filaments

Seta A hair-like growth arising from a cell

Pseudoraphe Afalserapheindiatoms.Acleararea
between makings on the valve surface which forms
an area in the position of a true raphe but no canal,
visible as a line, is present

Setiferous Bearing setae or hairs

Sheath A covering envelope, sometimes thin cov-
ering a filament or group of cells

Punctate Small dots or pores on the surface of
a diatom frustule usually forming a characteristic
pattern

Sickle-shaped Acutely curved or crescent-shaped

Sigmoid Shaped like an S

Siliceous wall A cell wall impregnated with silica
in diatoms and often bearing distinctive markings.
Its presence can be detected by digesting the organic
matter with an oxidizing agent leaving the silica wall
behind. Diatoms have distinctive silica cell walls but
some other algae have small silica scales on the out-
side of the cell wall, e.g. in some members of the
Chrysophyta

Pyrenoid A protein body in the cell associated with
the chloroplast which may or may not have a sheath
of starch (depending on genus). If starch is the storage
product the pyrenoid will stain darkly with iodine

Pyriform Pear-shaped, with a wider base than top

Quadrate Square or rectangular in shape

Raphe A longitudinal canal (visible as a line on the
surface) in the wall of some diatoms. Some genera
have a raphe on one valve some on both and others
no raphe at all. The raphe is associated with gliding
movements in some genera

Sinus A deep furrow between the semicells of a
desmid

Siphonaceous Atubularorilamentous-likethallus
having no cross walls, e.g. in Vaucheria