Epimetopus mendeli, Fikáček & Barclay & Perkins & Sw, 2011

Fikáček, Martin, Barclay, Maxwell V. L., Perkins, Philip D. & Sw, London, 2011, Two new species of the Epimetopus mendeli species group and notes on its adult and larval morphology (Coleoptera: Hydrophiloidea: Epimetopidae), Acta Entomologica Musei Nationalis Pragae 51 (2), pp. 477-504 : 489-497

Epimetopus mendeli sp. nov.

Larval material examined. 12 first instar larvae found in the egg case carried by the female paratype with the following label data: ‘ PERU: Cuzco / Quince Mil / 28 Jan. 1979 / W. E. Steiner // larvae from the egg case / carried by this specimen / used for description by / Fikáček et al. (2011)’ [one slide-mounted larva and two larvae in glycerine deposited in NMPC, two larvae in glycerine in YMC, three larvae in glycerine in a microvial attached to the specimen and returned to USNM, one gold-coated larva mounted on the label returned to USNM].

General morphology. Body ( Fig. 6 ) elongate, thorax and abdomen combined ca. 8× longer than head, slender, almost parallel-sided. Body length ca. 1.6 mm (measured in partly distorted specimens).

Head ( Figs. 8 , 30–31 ) subquadrate in shape, elongate, ca. 1.5× longer than wide, hyperprognathous, with occipital foramen shifted dorsally. Head width 0.15–0.17 mm (n = 4). Frontal lines U-shaped, arising on outer margin of antennal socket and reaching posterior margin of head capsule, slightly bent mesad at midlength; coronal line indistinct. Antennal sockets situated on the laterodorsal portion of head. Frontoclypeus ( Fig. 32 ) symmetrical; nasale small, in shape of slightly asymmetrical quadrate projections. Epistomal lobes large, symmetrical, largely overlapping nasale, well-sclerotized mesally with few teeth on inner margin between epistomal (gFR2) setae, largely membranous laterally, lateral margin with fine membranous finger-like projections. Dorsal mandibular articulation covered laterally by a projection of parietale ( Fig. 35 ). Stemmata indistinct in examined larvae. Gular suture absent, posterior tentorial pits distinct, situated anteromesally. Cervical sclerites indistinct (probably absent) in examined larvae.

Antenna ( Fig. 36 ) 3-segmented, short and rather stout. Scape ca. half as long as pedicel, flagellum ca. as long as scape. Pedicel with only one sensorium (SE1), sensorium as long as flagellum.

Mandibles ( Fig. 39 ) symmetrical, with falcate apical portion. Retinaculum with two teeth; distal tooth small, bearing a spine-like cuticular projection apically; basal tooth large, anvilshaped, partly underlaying the basal portion of distal tooth, bearing a set of spiny semimembranous projections apically as well as basally ( Fig. 42 ). Basal inner face with several small teeth bearing spines at apices, and with a basal field of fine spine-like cuticular projections.

Maxilla ( Figs. 37–38 ) 6-segmented (including cardo), massive, ca. twice as long as antenna. Cardo large, situated laterally, and associated with two additional sclerites lying between cardo and labium. Stipes the longest and widest, cylindrical, largely sclerotized ventrally, but only partially sclerotized dorsally; sclerotized dorsal portions with fine series of spicules. Maxillary palpus with 4 segments, palpomere 1 ca. half as long as stipes, completely sclerotized; palpomeres 2–3 short, palpomere 4 thin and elongate; inner appendage small, largely membranous. Maxillary articulating area in shape of a membranous lobe bearing fine spines mesally.

Labium ( Figs. 40–41 ) freely articulated with parietale at straight submental line (ventral anterior margin of parietale straight, not excised); submentum large, trapezoidal, rather tightly associated with laterally lying triangular sclerite of maxillary articulating area. Mentum and prementum short, transverse. Labial palpus 2-segmented, with basal palpomere ca. 3× shorter than distal palpomere; ligula absent. Labium largely covered by frontoclypeus in dorsal view.

Thorax. Prothorax wider than head capsule. Proscutum ( Fig. 47 ) formed by a large plate subdivided mesally by a sagittal line. Ventral portion of prothorax ( Fig. 48 ) with a pair of triangular presternal sclerites articulating posterolaterally with a precoxal sclerite connecting the presternum with coxal articulation; remaining parts largely membranous except for very weakly sclerotized laterotergites. Mesonotum with a pair of large subtriangular sclerites meeting mesally in anterior half of mesothorax, posterior portion membranous without clear sclerites. Metathorax membranous, without distinct sclerotized areas. Legs moderately long, clearly visible in dorsal view, all pairs similar in shape; prothoracic legs slightly shorter than meso- and metathoracic ones. Leg 5-segmented ( Figs. 49–50 ); procoxae nearly contiguous mesally, meso- and metacoxae well separated from each other; trochanter ca. as long as femur, rather firmly joined to each other; tibiotarsus slender, slightly shorter than trochanter and femur combined. Claw slightly shorter than tibiotarsus, apically slightly bent ventrad.

Abdomen with 9 well developed membranous segments. Segments 2–8 each subdivided into shorter anterior fold and longer posterior fold ( Figs. 51–52 ; af, pf). Segment 1 bare ventrally, ventral portions of segments 2–7 each with a transverse mound bearing several transverse rows of fine cuticular spines on anterior part of the posterior fold ( Fig. 52 ), the spines larger laterally, reduced to nearly indistinct mesally. A pair of spiracles situated dorsolaterally on larger fold of each segment, spiracles biforous, but largely reduced in size ( Figs. 51–52 , sp7). Posterior part of segment 8 ( Figs. 9 , 53–54 , abd8) with a low spiracular tubercle dorsolaterally and a long unsegmented finger-like projection laterally on each side. Segment 9 ( Figs. 9–10 , 53–54 ; abd9) with a pair of long membranous projections laterally and a pair of tiny urogomphi dorsally ( Figs. 9–10 , 53 ; ur); ventral portion with a pair or large membranous finger-like projections (‘ventral papillae’, Figs. 9–10 , 53–54 ; vp). Spiracular atrium not developed.

Primary chaetotaxy. Head. Frontale with 46 sensilla ( Figs. 32–33 ). Central part with three pairs of sensilla diverging posteriad, small seta FR1 situated at frontal line, pore FR2 and small seta FR3 close to each other more mesally. Lateral portions posterior to antennal socket each with two small setae and one pore: seta FR5 situated at frontal line, seta FR6 anteromesally of it, and pore FR4 even more anteromesally. Inner part of antennal socket with a small seta FR7, central portion of frontale between antennae with two pairs of small setae (FR8–9) diverging anteriad. Nasale with a group of four moderately long trichoid setae (gFR1) and with a basal pair of pores (FR15). Each epistomal lobe with a group of six setae (gFR2) situated on inner margin, two mesal short and trichoid, four lateral large, flat and with lobate margins ( Fig. 43 ); a long scale-like seta FR10 situated anteromesally of antennal socket, a pore FR14 between the seta and antennal socket; two closely situated pores (FR11 and FR13) situated mesally at base of epistomal lobe, a pore FR 12 in central portion of the lobe.

Parietale with 29 sensilla each ( Figs. 33–35 ). Posterior portion with a row of five short setae (PA1–2, PA4–5 and PA12) and one pore (PA3) at midwidth of dorsal parietale portion, and with a pore (PA6) and a short seta (PA7) at frontal line. Anterior portion at frontal line with a pore (PA10) and a long trichoid seta (PA9). Lateral portion with a pore (PA30) posteriorly, two long setae (PA14 and PA18) situated more anteriorly, two short setae (PA11 and PA16) situated even more anteriorly, and pores PA15 and PA17 situated anteriorly of PA14 and PA16, respectively; anterior part with a long seta PA20, a pore (PA19) situated dorsally of it and a short seta (PA21) situated more ventrally; sensilla PA22 absent. Ventral portion at the mandibular articulation with three closely standing pores (PA23–25) and a longitudinal row of four sensilla: seta PA26 situated anteriorly, pore PA 27 in anterior third, and seta PA28 and pore PA 29 in posterior third.

Antennae each with 14 sensilla ( Fig. 36 ). Scape with two pores (AN1–2) situated dorsally and three pores (AN3–5) situated in intersegmental membrane, pedicel with one pore (AN6) dorsally in sclerotized area, two moderately long setae (AN10–11) situated mesally and two moderately long setae (AN7–8) situated laterally below antennal sensorium. Sclerotized portion of flagellum lacking sensilla, apical group of sensilla (gAN) bearing two long and three short setae ( Fig. 46 ).

Mandible each with 6 sensilla ( Fig. 39 ). A moderately long seta (MN1) situated basally on outer face, two pores (MN2–3) on dorsal surface in basal third, a pore (MN4) and a short seta (MN5) on outer face in distal third and a small pore (MN6) subapically on inner face.

Maxillae ( Figs. 37–38 ) each with one long seta ( MX 1) situated ventrally on cardo. Stipes with five spine-like setae on inner surface: MX 7 situated at very base, MX 8–9 in basal third, one ventrally of the other, MX 10–11 in distal third. Ventral surface with one pore ( MX 3), lateral surface with two pores ( MX 2 and MX 4) and two long setae ( MX 5–6). Palpomere 1 with two moderately long setae situated basally on lateral surface, MX 14 ventrally of MX 16; distal margin ventrally with a seta ( MX 13) and a pore ( MX 12). Base of inner appendage with one pore ventrally ( MX 15) and one dorsally ( MX 17). Inner appendage (gAPP) with two moderately long seta and a long scale-like seta. Palpomere 2 with one tiny seta ( MX 27) basally and one pore ( MX 18) distally. Palpomere 3 with a series of sensilla at distal margin, setae MX 21 and MX 23 laterally, pores MX 20 and MX 22 dorsally or ventrally, respectively. Palpomere 4 with a long basal seta ( MX 24) and a pore MX 26 and a digitiform sensilla situated subapically. Apical membranous area with 9 short to very short sensilla (gMX, Fig. 45 ).

Labium ( Figs. 34 , 40–41 ). Submentum with one pair of long setae (LA1), LA2 absent. Mentum with basal pair of pores (LA4) and distal pair of short setae on ventral surface. Prementum with two pairs of pores (LA5–6) ventrally, one short seta (LA7) laterally on each side, one pair of basal tiny setae (LA8) dorsally and a a group of two setae pairs (LA10–11) and a pair of pores (LA12) between palpal bases. Palpomere 1 with one tiny seta (LA13) basally and one pore (LA14) on intersegmental membrane, palpomere 2 with a subapical pore (LA15). Apical membranous field with two peg-like sensilla laterally, three short setae on long membranous extensions, and two tiny cap-like sensilla (gLA, Fig. 44 ).

Thorax. Proscutum with 15 setae on each half situated in three transverse rows; anterior row with three short trichoid, three long trichoid and one long scale-like setae; irregular series at midlength with four short trichoid setae, posterior row with three short and one long trichoid setae. Ventral portion with one short seta on posterior margin of each presternal sclerite and one long trichoid seta on anteromesal margin of precoxal sclerite. Lateral portion with a pair of trichoid setae (one long, one short) below proscutal margin, and one short seta dorsally of coxal articulation. Meso- and metanotum with a chaetotaxy similar to that of dorsal portion of abdominal segments.

Metathoracic leg. Coxa with three long and one short setae on a ridge anteriorly above trochanter articulation, and with two pores; posterior portion with two tiny setae proximally and one long seta below trochanter articulation. Trochanter with a group of five stout setae and one trichoid seta on anterodistal surface, ventral face with three moderately long setae and one pore; a series of elongate pore-like sensilla on both anterior and posterior surfaces situated across midlength of trochanter. Femur with three stout setae along anterodistal margin and with two long trichoid setae situated posterodistally, anterior surface with one pore. Tibiotarsus with a oblique row of four stout setae on anterior face, dorsal face with one long seta basally, ventral face with one seta distally, distal portion with four stout and two trichoid setae around claw articulation. Claw unisetose.

Abdomen ( Figs. 51–55 ). Each abdominal segment with a transverse row of setae posteriorly, consisting on each side of one long trichoid, two long scale-like and two short trichoid setae dorsally and one long trichoid and one long scale-like setae lateroventrally. One tiny seta situated between the transverse row and the spiracle. Chaetotaxy of segments 8 modified, consisting on each side of one short seta situated mesally and two short setae situated on spiracular tubercle, ventrally with three closely standing setae including one long scale-like seta; lateral projection with one long seta in apical third and one long seta apically. Segment 9 lacking sensilla except for two pairs of tiny setae on its posterior margin; lateral projections each with a pair of basal setae, one long trichoid and one long scale-like setae at midlength and one trichoid seta apically; urogomphus with one seta and two pores apically, and one pore at midlength ( Fig. 55 ). Ventral papillae lacking sensilla.

Comparative notes. The larva of E. mendeli sp. nov. seems to correspond with the Brazilian larvae of ‘ Epimetopus sp. 2 ’ (see below) in the morphology of the head, head appendages, thorax and abdomen (including the presence of two pairs of long projections at the end of the abdomen, but it lacks ventral papillae) as well as in the general pattern on the head chaetotaxy including the presence of the scale-like setae (however, the Brazilian larvae were examined only on temporary slides without any previous treatment). Stemmata are clearly seen on the Brazilian larvae.

Figures

Figs. 6–10. First instar larva of Epimetopus mendeli sp. nov. 6 – general habitus in ventrolateral view; 7 – detail of frontoclypeus; 8 – head capsule in dorsal view; 9 – abdominal apex in dorsal view; 10 – abdominal apex in dorsolateral view.Abbreviations:abd7–9 – abdominal segments 7–9; app8 – lateral projection of the abdominal segment 8; app9 – lateral projection of the abdominal segment 9; fl – frontal line; ur – urogomphus; vp – ventral papillae.

Figs. 30–32. Head capsule of the first larva of Epimetopus mendeli sp. nov.30–31 – general view of the head capsule: 30 – dorsal view; 31 – ventral view. 32 – detail of frontoclypeus.

Figs. 33–35. Primary chaetotaxy of the head capsule of the first instar larva of Epimetopus mendeli sp.nov. 33 – dorsal view; 34 – ventral view; 35 – lateral view.

Figs. 36–41. Antenna and mouthparts of the first instar larva of Epimetopus mendeli sp. nov. 36 – antenna, dorsal view; 37 – maxilla, dorsal view; 38 – maxilla, ventral view; 39 – mandible, dorsal view; 40 – labium, ventral view; 41 – labium, dorsal view.

Figs. 42–46. Details of the head morphology of the first instar larva of Epimetopus mendeli sp. nov. (redrawn from SEM micrographs). 42 – retinaculum of the mandible, dorsal view; 43 – frontoclypeal setae gFR2, dorsal view; 44 – apical field of labial palpus, lateral view; 45 – apical field of maxillary palpus, apical view; 46 – apical field of antennal flagelum, apical view.

Figs. 47–50. Thorax of the first instar larva of Epimetopus mendeli sp. nov. 47 – proscutum; 48 – ventral portion of prothorax; 49 – metathoracic leg, anterior view; 50 – metathoracic leg, posterior view.Abbreviations: cl – claw; cx – coxa; fe – femur; pcs – precoxal sclerite; pss – presternal sclerite; tr – trochanter; tt – tibiotarsus.

Figs. 51–55. Abdominal morphology of the first instar larva of Epimetopus mendeli sp. nov. 51–52 – abdominal segment 7 (51 – dorsal view; 52 – ventral view); 53–54 – abdominal apex (53 – dorsal view; 54 – ventral view); 55 – detail of urogomphus.Abbreviations: abd8–9 – abdominal segments 8–9; af – anterior fold of abdominal segment; app8–9 – lateral projection of abdominal segments 8–9; pf – posterior fold of abdominal segment; sp7–8 – spiracles on the abdominal segment 7–8; ur – urogomphus; vp – ventral papila.