The development of Catenaria anguillulae on the immobilized juveniles of Heterodera cajani was studied. Within 2 h of inoculation, the zoospores of C. anguillulae congregated at the oral openings of juveniles and in 13–15 h the germ-tube passed from the side of the stylet, growing up to the tail region. After 1 h the mycelium became septate at regular intervals and swelling of the sporangia commenced, attaining full size in 40–50 min as it touched the nematode body. At this stage, second septation occurred with rhizoids developing along with growing mycelium. After nearly 5 h of the second stage of septa formation, grouping of fat globules into groups of 4–6 occurred, along with the initiation of discharge-tubes. Precisely within 30 min, 8–12 smaller globules were rearranged in circular forms, followed by half-moon shape 17 min later. Zoospore differentiation, vesicle formation and release of zoospores occurred within 50 min of the half-moon stage.