Derovatellus lentus (Wehncke, 1876)

Michat, Mariano C., Alarie, Yves & Benetti, Cesar J., 2024, Description of the mature larva of Derovatellus lentus (Coleoptera: Dytiscidae), Zootaxa 5492 (1), pp. 145-150 : 146

Derovatellus lentus (Wehncke, 1876)

Diagnosis (compare with figures of Vatellus larvae in Michat & Torres 2005): Instar I. Median branch of nasale widening towards spatulate apex ( Fig. 1 ) (parallel-sided in Vatellus ); ratio antennomere 4/antennomere 3> 0.35 ( Fig. 2 ) (<0.35 in Vatellus ); primary seta LA1 absent ( Fig. 3 ) (present in Vatellus ); distal portion of siphon with a pair of long spiniform seta ( Fig. 4 ) (two pairs in Vatellus ).

Instar II. Ratio antennomere 4/antennomere 3> 0.35 (<0.35 in Vatellus ); secondary setae on antennomeres 1 and 2 and maxillary palpomere 1 absent (present in Vatellus ); posterodorsal secondary setae on coxa absent (present in Vatellus ); anterodorsal secondary setae on femur absent (present in Vatellus ).

Instar III. Ratio antennomere 4/antennomere 3> 0.35 ( Fig. 5 ) (<0.35 in Vatellus ); secondary setae on antennomeres 1 and 2 and maxillary palpomere 1 absent (present in Vatellus ); premental seta LA1 absent (present in Vatellus ); anteroventral secondary setae on coxa absent ( Fig. 7 ) (present in Vatellus ); femur with 16–22 spiniform secondary setae ( Figs 7–8 ) (33–55 in Vatellus ); tarsal natatory setae restricted to basal half ( Fig. 8 ) (extending to distal half in Vatellus ); dorsal surface of abdominal segment VIII (excluding siphon) with six spiniform secondary setae ( Fig. 6 ) (more than 15 in Vatellus ).

Description, instar III. As instar II ( Michat & Torres 2011) except for the following features:

Color: Somewhat darker in general, siphon testaceous only on distal tenth.

Body: Measurements and ratios that characterize the body shape are shown in Table 1 .

Head ( Fig. 5 ): Median branch of nasale parallel sided up to spatulate apex, anterior margin with 43–45 spatulate setae (six of them longer) directed downward. Antenna. A2 slightly shorter than A3. Maxilla. MP2 considerably shorter than MP1.

Thorax: Spiracles present on mesothorax. Metatergite with sagittal line.

Abdomen ( Fig. 6 ): Spiracles present on segments I–VII. Sclerite VIII with anterior transverse carina. Siphon extremely long.

Chaetotaxy: Lateral margin of PA with 4–6 spiniform secondary setae; each lateral branch of nasale with 5 secondary setae (3 spiniform, strongly developed, and 2 setiform) ( Fig. 5 ); secondary leg setation detailed in Table 2 and Figs 7–8 .

Habitat. The specimens were taken from a roadside pond at road 40 near Laguna Iberá park ranger office, 28°32’48.65’’S, 57°11’48.02’’W (see Google Earth 2024). The sampling site ( Fig. 9 ) was mostly exposed to insolation, with muddy bottom, relatively high turbidity, and abundant emergent vegetation.

Figures

FIGURE 9. Habitat of Derovatellus lentus: roadside pond near Laguna Iberá park ranger office, Iberá Natural Reserve, Corrientes Province, Argentina (17.2.2018). The photograph at the bottom right corner shows an adult of this species.

FIGURES 1–4. Derovatellus lentus, instar I. (1) nasale, dorsal aspect; (2) antennomeres 3 and 4, dorsal aspect (3) labium, ventral aspect; (4) abdominal segment VIII, dorsal aspect. Scale bars = 0.15 mm.

FIGURES 5–6. Derovatellus lentus, instar III. (5) head, dorsal aspect; (6) abdominal segment VIII and urogomphi, dorsal aspect. AB: abdominal segment VIII; FR: frontoclypeus; PA: parietal; U: urogomphus. Scale bars = 0.40 mm.

FIGURES 7–8. Derovatellus lentus, instar III. (7) left metathoracic leg, anterior aspect; (8) right metathoracic leg, posterior aspect. CO: coxa; FE: femur; PT: pretarsus; TA: tarsus; TI: tibia; TR: trochanter. Scale bar = 0.20 mm.