This species is cosmopolite
Benthic-periphytic, less frequent in plankton; fresh, brackish and saline waters. Feeding on nannoplankton and detritus
This species is very common, widely cosmopolitan, highly variable and having an extensive Synonymy.
Brachionus quadridentatus is a very common, widely cosmopolitan, highly variable species, having an extensive Synonymy. The variations in different forms of B. quadridentatus are due to initial appearance and subsequent development and elongation of postero-lateral and postero-median spines. The variations are also in the antero-median spines.
Lorica with dorsal and ventral plate, moderately flattened dorso-ventrally, firm, usually stippled or pustulate, occasionally facetted or with regular line patterns. Antero-dorsal margin with six spines; median spines usually longest, curved to lateral or ventral, granulated or serrate; lateral spines longer than intermediate ones. Antero-ventral margin undulate with median notch, flanked by lateral projections. Postero-lateral spines present or absent; subject to great variation in length and shape. Ventro-posterior part of lorica prolonged, forming tubular foot sheath standing at out at angle to ventral plate. Foot opening with large more or less horseshoe-shaped ventral part; dorsally a subquare indentation flanked by spines. Trophi with all characteristics of the genus. Polymorphic species with many variations described.
The lorica of this species is barrel-shaped, swollen at its posterior third, prolonged posteriorly in two stout and parallel lateral spines, their length is usually more than 1/2 the length of the body without spines. Greatest width/length of the body (without spines) ratio = 1. Anterior dorsal margin with six well developed spines, medians longest and bent outwards, laterals slightly divergent. Anterior ventral margin undulate, somewhat elevated toward the center, with a median sinus. The ventro-posterior portion of the lorica forms a typical tubular sheath surrounding the foot opening. Lorica markedly stippled or pustulate.
When viewed from the dorsal side the outline of the animal is trapezoidal, its greatest width being in the lumbar region. It has four occipital spines, the two medians being curved outwards, and having the appearance of antlers; the two outer spines are straight and slightly shorter than the central pair. Between the outer spines on each side a small saw tooth can be seen, and on the corresponding anterior ventral edge are two similar teeth. The posterior spines are long and sharp, and when viewed from the dorsal side make an angle of approximately 30 degrees, with a median line passing lengthwise through the body. Two short recurved spines protect the foot opening. The foot, which is often longer than the animal, is wrinkled, and has the usual two toes.
Lorica length 160‒418 µm, median antero-dorsal spines 21‒72 µm, intermediate antero-dorsal spines 3‒22 µm, lateral antero-dorsal spines 17‒49 µm, postero-lateral spines up to 200 µm.
A large variety sizes was found, and also all stages of cyclomorphic variation.
Total length 176-418 µm ; greatest width 104-265 µm; anterior lateral spines 17-49 µm; anterior intermediate spines 14-72 µm; anterior median spines 28-33; posterior lateral spines 20-156 um.
