Larval morphology of Thermonectus succinctus (Aubé 1838) (Coleoptera: Dytiscidae: Dytiscinae), with biological notes and chaetotaxic analysis.

The three larval instars of Thermonectus succinctus (Aubé 1838) are described and illustrated for the first time, emphasizing the morphometry and chaetotaxy. Biological notes are included. Thermonectus Dejean is distinguished from other Aciliini genera by its slightly bifid median process of the prementum, which bears two spine-like setae (LA8). First instars of T. succinctus differ from those of Acilius Leach and Graphoderus Dejean in the lower number of additional anterodistal setae on the femur. The shape of seta TA1 and the presence of an additional posterior pore on the tibia separate first instars of Graphoderus from those of Acilius and T. succinctus . Regarding the mature larva, T. succinctus differs from T. alfredi Griffini 1898 in its smaller size, from T. basillaris (Harris 1829) in the lack of a row of minute hairs along the internal margin of the galea, and from T. nigrofasciatus ornaticollis (Aubé 1838) in the shorter length of seta LA8. [ABSTRACT FROM AUTHOR]