Rhagovelia caesius, , Lansbury, 1993

Polhemus, Dan A., 2024, Thirty-four new species of Rhagovelia (Heteroptera: Veliidae) from the East Papua Composite Terrane, far eastern New Guinea, Zootaxa 5400 (1), pp. 1-214 : 179-182

Rhagovelia caesius group

This group was alluded to by J. Polhemus & D. Polhemus (1988), who provided certain diagnostic characters but declined to formally name it, since all the included members were at that time undescribed. Subsequently, Lansbury (1993) described a member of this group, R. caesius , from eastern New Guinea, and on the basis of this D. Polhemus (1995) formally proposed the R. caesius group, also adding another species, R. phoretica , from the Philippines. Two further species from the Philippines, R. lansburyi and R. sallyae , were added to this group by Zettel (1995, 2003), who in the latter paper removed these Philippine taxa from the R. caesius group, placing R. phoretica and R. sallyae in a new R. phoretica group, and re-assigning R. lundbladi to the R. borneensis group as defined by J. Polhemus & D. Polhemus (1988). Two additional species, R. styx and R. salawati , both from the Raja Ampat Islands, immediately west of the Vogelkop Peninsula of western New Guinea, were added by D. Polhemus & J. Polhemus (2011), who also questioned the basis on which Zettel (2003) had separated the R. phoretica group from the R. caesius group, since this seemed to be based on little more than geographic disjunction between species assemblages.

The R. caesius group is characterized by generally ovate body form when viewed from above, with marked sexual dimorphism in size between large females and smaller males (Figs. 297, 298, 303, 304, 310, 311, 316, 317, 321, 322); a tumid and posteriorly bilobate female mesonotum; male genital segments that are small, and partially retracted into the abdomen, with a slender, reduced male paramere (Figs. 300, 306, 313, 319, 327), and a compact male proctiger lacking either basolateral or distolateral lobes, but with the distal cone well developed and coming to an blunt or broadly rounded apex (Figs. 301, 307, 314, 320, 328); relatively slender legs, with the male hind legs bearing few spines or other armature (Figs. 299, 305, 312, 318, 326); paired dorsal abdominal carinae in winged forms that are short, reaching at most onto abdominal tergite II; forewings with 4 closed cells, all in the basal half of the wing, with two long cells basally and two much shorter cells distally ( Fig. 14 ); and a distinctive silvery coloration, typical of Rhagovelia species that inhabit open, unshaded midstream waters.

As noted by D. Polhemus & J. Polhemus (1998, 2011), in general habits and appearance, the members of the R. caesius group are similar to those of the R. diabolica group, endemic to Madagascar (D. Polhemus & Andersen, 2010), and the R. angustipes group, confined to the Neotropical Region (D. Polhemus 1997). However, the basic ground plans of these three groups have noticable differences, so these resemblances are very likely the result of convergent adaptation to life in similar habitats.

Despite the presence of several species in the Philippines and in the Raja Ampat Islands, the clear center of species richness for the R. caesius group is the island of New Guinea. Members of this group may be found on open rivers ( Figs 152 , 315 ) throughout the island, from just above the head of tidal influence upstream to at least 1500 m elevation. Rhagovelia riu and R. woa from the remote Louisiade Archipelago appear to be primitive progenitors of the R. caesius group, indicating that it may have originated on the EPCT and subsequently dispersed to greater New Guinea and the Philippines. The form of the mesonotum in these species is diagnostic for the R. caesius group, but the body form is more elongate (compare Figs. 296 –298, 303, 304 to Figs. 310, 311 , 316, 317 , 321, 324 ), and the intersexual size dimorphism less pronounced.

Overall, the R. caesius group is exhibits many plesiomorphic character states, including a simple male proctiger unmodified by lateral lobes, a small and ovate male paramere, a short pronotum that is not posteriorly prolonged, and slender legs with femora that are not heavily armed or incrassate. The most obvious apomorphic character states in the group are the marked sexual dimorphism in body size, the modification of the male forelegs for grasping the female during phoresy ( Fig. 325 ), and the distinctive silver-grey coloration (Figs. 297, 298, 303, 304, 310, 311, 316, 317, 321, 322).

Within the species of the R. caesius group occurring on the EPCT, two distinct subgroups can be recognized and are noted in the key. The species included in each of these subgroups are as follows:

Rhagovelia woa subgroup: R. woa n. sp. and R. riu n. sp.

Rhagovelia grisea subgroup: R. caesius Lansbury , R. grisea n. sp. and R. cheesmanae n. sp.,

plus the extralimital species R. styx D. Polhemus & J. Polhemus and R. salawati D. Polhemus & J. Polhemus.

Key to wingless forms of the R. caesius group occurring in the EPCT

1. Female connexival margins folded inward and meeting posteriorly, completely covering abdominal tergite VII when viewed from above (Figs. 298, 304); males lacking stiff, erect black setae on abdominal tergites when viewed laterally; Louisiade Islands ( Fig. 309 )..................................................................... R. woa subgroup…2

- Female connexival margins not folded inward, widely separated posteriorly, with all abdominal tergites visible when viewed from above ( Figs. 311 , 317 , 322 ); males bearing stiff, erect black setae on abdominal tergites when viewed laterally; New Guinea ( Fig. 330 )................................................................... R. grisea subgroup…3

2. Female connexival margins parallel basally adjacent to abdominal tergites I and II, then angling sharply inward adjacent to tergites III and IV, then tightly appressed and parallel for remainder of their length (Fig. 298); female abdominal tergite I not tumescent or setiferous; male with abdomen short, length equal to that of head and thorax combined (Fig. 297); Rossel Island.......................................................................................... R. woa n. sp.

- Female connexival margins evenly convergent adjacent to abdominal tergites I–V, then meeting and appressed above tergites VI and VII, lacking a sharp inward inflection adjacent to tergites III and IV ( Fig. 304 ); female abdominal tergite I tumid and setiferous; male with length of abdomen exceeding that of head and thorax combined ( Fig. 303 ); Tagula Island... R. riu n. sp.

3. Antennal segment I short and stout ( Figs. 321, 322 ), length less than twice that of segment II, ratio of length to width 8:1 or less; female mesonotum strongly domed and dorsally convex; pronotum in both sexes bearing numerous appressed silvery setae; male body broadly ovate ( Fig. 321 ), length only 1.8 times maximum width....................... R. cheesmanae n. sp.

- Antennal segment I long and slender ( Figs. 310, 311. 316, 317 ), length twice that of segment II, ratio of length to width 10:1; female mesonotum only gently convex, not strongly domed upward; pronotum in both sexes lacking appressed silvery setae; male body narrower ( Figs. 310 , 316 ), length over 2.1 times maximum width...................................... 4

4. Posterior margin of mesonotum bilobate ( Fig. 317 ), formed into a pair of posteriorly-directed tumescences with rounded apices; posterior apices of these tumescences extending nearly across the length of the metanotum; male connexival margins bearing long, erect black setae................................................................... R. caesius Lansbury

- Posterior margin of female mesonotum truncate ( Fig. 311 ), lacking posteriorly-directed tumescences; male connexival margins lacking long erect black setae................................................................. R. grisea n. sp.

Figures

FIG. 14. Rhagovelia cheesmanae n. sp., forewing, showing the presence of two small distal closed cells of subequal size; specimen from the Udabe River, Owen Stanley Mountains, New Guinea, CL 7247.

FIG. 152. Lower Aleater River, near Kamiali, Morobe Province, Papua New Guinea, CL 7241, habitat for R. caesius Lansbury and R. hirsuta Lansbury.

FIG. 315. Gumini River, west of Alotau, Milne Bay Province, Papua New Guinea, CL 7174, habitat for R. grisea n. sp.

FIG. 296. Rhagovelia woa n. sp., wingless female, dorsal habitus; specimen from Rossel Is., Woa River, CL 7196. Young Sohn illustration.

FIGS. 310–314. Rhagovelia grisea n. sp., structural details; specimens from New Guinea, Muguwe Creek, CL 7169. 310. Wingless male, dorsal habitus. 311. Wingless female, dorsal habitus. 312. Male right hind leg, dorsal view. 313. Male left paramere, outer lateral view. 314. Male proctiger, dorsal view.

FIGS. 316–320. Rhagovelia caesius Lansbury, structural details; specimens from New Guinea, Aleater River, CL 7241. 316. Wingless male, dorsal habitus. 317. Wingless female, dorsal habitus. 318. Male right hind leg, dorsal view. 319. Male left paramere, outer lateral view. 320. Male proctiger, dorsal view.

FIGS. 321–324. Rhagovelia cheesmanae n. sp., structural details; wingless and winged morphs; specimens from New Guinea, Udabe River, CL 7247. 321. Wingless male, dorsal habitus. 322. Wingless female, dorsal habitus. 323. Winged male, dorsal habitus. 324. Winged female, dorsal habitus.

FIGS. 325–328. Rhagovelia cheesmanae n. sp., structural details; specimens from New Guinea, Udabe River, CL 7247. 325. Male left foreleg, dorsal view, showing bowed shape to facilitate phoresy. 326. Male left hind leg, dorsal view. 327. Male left paramere, outer lateral view. 328. Male proctiger, dorsal view.

FIG. 309. Distributions of species in the R. woa subgroup in the Louisiade Islands.

FIG. 330. Distributions of species in the R. grisea subgroup on eastern New Guinea and adjacent islands.

FIGS. 303–307. Rhagovelia riu n. sp., structural details; specimens from the Tagula Island. 303. Wingless male, dorsal habitus. 304. Wingless female, dorsal habitus; 303 and 304 from Kolukolu Creek, CL 7194. 305. Male right hind leg, dorsal view; 306. Male left paramere, outer lateral view. 307. Male proctiger, dorsal view; 276–279 from Kalitau Creek, CL 7190.