General Features of the External Morphology of Marine Planktonic Copepods
Anomalies
Marine calanoids are sometimes observed in which the furcal setae are articulated and divided by successive dichotomies. In harpacticoids it is not uncommon to observe one or more furcal setae becoming bulbous at the base, swollen or spatulate over a variable length.
Bytinski-Salz (1933) reports, in a male of Pleuromamma (a marine calanoid), a symmetrical fifth pair of legs (usually strongly asymmetrical), a brown knob on each side of the thorax (whereas it is normally present on one side only, most often the right), and a slightly swollen prehensile antennule.
It is not uncommon to observe individuals of various species presenting an abnormal, most often reduced, number of appendage segments or deformations of these appendages.
In various forms, anomalies of the fifth leg and the antennules have been reported. In some cases, the fifth thoracic leg, which is normally absent, reappears as a rudiment in the adult of Temora longicornis (Mrazek, 1902; Razouls, 1963; Brylinski, 1984).