Psalitrus yamatensis Hoshina & Sato , 2005

Minoshima, Yusuke N., 2019, First known larva of omicrine genus Psalitrus d'Orchymont (Coleoptera, Hydrophilidae), Deutsche Entomologische Zeitschrift 66 (1), pp. 107-118 : 108-113

Psalitrus yamatensis Hoshina & Sato, 2005 Figs 1, 2, 3, 4

Material examined.

1 presumably first instar larva; see Table 1.

Diagnosis of larva.

See generic diagnosis.

Description of presumably first instar larva.

General morphology. Length 1.2 mm in the specimen fixed by ethanol; head width 0.2 mm. Body (Fig. 1A) maggot-like in shape, widest between abdominal segments 3-6. Colour. Head capsule and thoracic sclerites yellowish, membranous parts milky white.

Head. Head capsule subquadrate (Fig. 2A); cervical sclerites undetectable. Frontal lines U-shaped at base, then divergent laterally, ending behind outer margin of antennal socket; coronal line absent. Surface of head capsule smooth; stemmata present on each anterolateral portion of head capsule; number of stemmata unclear but two (groups of) stemmata detectable: posterior one oval; anterior one wider than posterior one. Posterior tentorial pits present, on midlength of and close to submental sulcus. Clypeolabrum symmetrical in shape (Fig. 3C) but asymmetrical in arrangements of setae (see description of chaetotaxy). Nasale distinctly projecting, with four large teeth; all teeth almost similar in size and equidistant. Asymmetrical median projection absent. One pair of presumably egg-bursters present behind median two teeth of nasale. Epistomal lobe absent (Fig. 3C); lateral part of epistome almost straight.

Antenna (Fig. 4A) three-segmented, short and stout; surface of antenna smooth. Antennomere 1 widest, distinctly wider than antennomere 2; antennomere 3 narrowest. Antennomeres 2 slightly shorter than antennomere 1; antennomere 3 slightly shorter than antennomere 2. Antennal sensorium present, as long as antennomere 3.

Mandibles (Fig. 4B) stout, distinctly widened in basal part, almost symmetrical; median part with two inner teeth; incisor area and basal margin of inner teeth weakly serrate.

Maxilla (Fig. 4C) six-segmented, stout, longer than antenna, asymmetrical. Cardo irregularly triangular. Stipes widest and longest, shorter than palpomeres 1-4 combined; maximum length of stipes as long as maximum width. Maxillary palpus somewhat stout, four-segmented; palpomeres 1-3 wider than long, 4 longer than wide. Approximate ratios of length of palpomeres 1-4 as follows: 1:0.6:0.6:0.7. Palpomere 1 widest and longest, completely cylindrically sclerotised; inner process small, sclerotised. Palpomere 2 shorter and narrower than palpomere 1, as long as palpomere 4. Palpomere 3 shortest, narrower than palpomere 2. Palpomere 4 narrowest.

Labium (Fig. 4D) developed. Submentum subpentagonal, transverse, fused with head capsule; submental sulcus present. Submentum without large lateral extension, i.e., not fused with associate sclerites of cardo. Mentum subquadrate from ventral view; sclerite of dorsal face very deeply emarginated medially, narrowly and very strongly projected posteriorly at midwidth; border of sclerotised and membranous portions indistinct. Prementum subquadrate, transverse; median part of dorsal surface membranous. Ligula apparently absent or reduced to a minute membranous projection between palpomeres. Labial palpus moderately long, palpomere 1 wide, palpomere 2 narrower and distinctly longer than palpomere 1.

Thorax. Thoracic segments bearing microtrichiae, which may catch and securely keep the dirt on its integument, except for ventral area between legs; this area bare and not bearing dust as other parts. Prothorax slightly wider than head capsule (Fig. 1A). Proscutum formed by one large plate bearing several very long setae, subdivided by fine sagittal line, anterior and posterior margins weakly sclerotised. Prosternal sclerite transverse, not clearly detectable in the specimen. Mesothoracic spiracles forming small tubercle. Legs short, reduced to four segments, well sclerotised (Figs 1B, 2C). Trochanter and femur fused into a segment or trochanter reduced; coxa, tibiotarsus and claw (pretarsus) well defined.

Abdomen 10-segmented, widest in anterior half, then tapering posteriad (Fig. 1A). Membranous part densely bearing microtrichiae, covered with dirt. One pair of spiracles on lateral part of dorsal surface, weakly tuberculate. Spiracular atrium (Fig. 1C): segment 8 with oval dorsal sclerite bearing sparse microtrichiae and setae. Segment 9 trilobed, bearing long microtrichiae except for dorsal surface; median lobe of spiracular atrium with median emargination posteriorly. A pair of sclerotised urogomphi short, conical, bearing extremely long seta, fused basally, thus, outline of urogomphi looks to be V-shaped.

Primary chaetotaxy of head. Frontale (Fig. 3A, C). Rather long seta FR1 situated mesally at midlength of frontale. FR2 absent. FR3 short seta, anterior and slightly mesal to FR1. FR4-6 located behind inner margin of antennal socket; FR4 pore-like, slightly elongate, anterior to FR5 and FR6; rather long seta FR5 and long seta FR6 very closely situated, FR5 mesal to FR6. FR7 on inner margin of antennal socket. Two sensilla close to inner margin of antennal socket; pore-like sensillum FR14 mesal to antennal socket, rather short seta FR ”9/10?” behind FR14. FR13 absent. Pore-like sensillum FR11 between FR14 and gFR1; left FR11 situated more anteriorly on than right one. Two short, stout setae (FR12 and additional seta) present between FR11 and FR14 (both marked as “12?” in Fig. 3C) on left; these absent on right. Pair of pore-like sensilla FR15 behind median two setae of gFR1. Six sensilla (gFR1) present on anterior margin of nasale; mesal four short, stout setae; character state of lateral ones unclear.

Parietale (Fig. 3A, B). Dorsal surface with a group of five sensilla (PA1-5) forming irregular longitudinal row in posterior part; PA1-2 and 4-5 may be short setae, PA3 pore-like. Minute additional pore present between PA4 and PA5. PA6 absent. Probable PA7 situated anterolaterally to PA5; PA7 may be a seta which is missing in the specimen. Very long seta PA8 and pore-like sensillum (probable PA10) anterior to PA7; PA8 close to frontal line; PA10 between PA7 and PA8. Two rather short additional setae close and mesal to PA8. Group of three long to very long setae lateral to PA8 and PA10; homology of them unclear (probably PA12-14); PA11 likely absent. Pore-like sensilla PA15 situated laterally at anterior two-fifths. Long seta PA9 posterolateral to antennal socket. PA19-22 situated dorsolaterally on anterior corner of head capsule; PA19 pore-like, dorsal to PA20-22; PA20-22 assumed very long to long setae, very closely aggregated; PA20 anterior to PA21; PA22 ventral to PA20 and PA21. Pore-like sensilla PA23-25 lateroventral, close to ventral mandibular articulation; PA23 lateral to PA24; PA24 and PA25 closely situated; PA24 posterolateral to PA25. Pore-like sensilla PA17 situated lateroventrally on anterior fourth of head capsule. Two very long setae (PA16 and PA18) posterior to PA17, precise homology of respective sensilla unclear. Very long seta PA26 close and mesal to PA17. PA27 and PA28 situated on median part of parietale, slightly anterior to midlength of head capsule; PA27 pore-like, anterior to PA28, PA28 seta. PA29 pore-like, posteromesal to PA28. Pore-like sensillum PA30 laterally on midlength of ventral surface.

Head appendages. Antenna (Fig. 4A). Antennomere 1 with five pore-like sensilla (AN1-5). AN1 situated dorsally on midlength of dorsal surface of sclerite. AN2 anterolateral to AN1, close to borderline between sclerite and membrane. AN3 and AN4 apically on intersegmental membrane or borderline between sclerite and membrane; AN3 on inner face, AN4 lateral face. AN5 apically on ventral surface. Antennomere 2 with seven sensilla. AN6 dorsally on subapical part of sclerite. One small additional or secondary pore-like sensillum on basal margin of sclerite. Minute setae AN7 and AN8, long seta AN10, short seta AN11, and sensorium SE1 on intersegmental membrane between antennomeres 2 and 3. AN7 and AN8 dorsally on lateral part, behind SE1. AN9 absent. AN10 and AN11 on lateral face. SE1 situated on outer face, slender and long, as long as antennomere 3, partly sclerotised. Antennomere 3 with group of apical sensilla (gAN) in apical membranous area. One ventral seta of gAN situated posterior to remaining sensilla; although borderline between membrane and sclerite hardly visible and almost undetectable, the seta seems to be on the borderline based on examination of very fine line indicated borderline.

Mandibles (Fig. 4B). Five sensilla (MN1-5) on anterior one-third to two-fifths; MN1 and MN5 short setae, MN2-4 pore-like sensilla. MN1 on anterior to midlength of mandible. MN2 mesal to MN1. MN4 anterior to MN2, between MN2 and MN5. MN3 lateral to MN2 and MN4. MN5 anterior to MN4. MN6 undetectable; three sensilla-like structures present on subapical part of mandible.

Maxilla (Fig. 4C). Cardo with one ventral seta (MX1). Inner face of stipes with irregular longitudinal row of five rather short setae (MX7-11); MX7 at base, slenderer than others; MX8-11 stout. Pore-like sensilla MX2 and MX3 situated ventrally on median part, MX2 posterolateral to MX3. Pore-like sensilla MX4, rather long seta MX5, and long seta MX6 situated subapically and ventrally on lateral face. MX6 lateral to MX4, MX5 posterior to MX4. Rather long seta MX16 basally on inner face of palpomere 1. Pore-like sensillum MX12 and rather long seta MX13 situated subapically on lateral face; MX12 anterior to MX13. MX14 ventrally and subbasally on inner part of sclerite. Pore-like sensillum MX15 ventrally on membrane behind inner appendage; MX17 absent. Inner appendage with few short apical setae of variable length (gAPP). Palpomere 2 with pore-like sensillum MX18 and minute seta MX27 on sclerite. MX18 lateroventral ly at midlength; MX27 basally on lateral face. Pore-like sensillum PA19 on inner face of intersegmental membrane between palpomeres 2 and 3. Palpomere 3 with two pore-like sensilla (MX20 and MX22), and two setae (MX21 and MX23). MX23 and MX20 on subapical part of sclerite; MX23 dorsal, MX20 lateral. MX21 apically on lateroventral part. MX22 on posteroventral part of inner face. Palpomere 4 with three sensilla (MX24-26) on sclerite. MX24 seta on inner face; digitiform (MX25) and pore-like (MX26) sensilla on lateral face, MX25 dorsal, MX26 ventral. Apical membranous area of palpomere 4 with several minute setae (gMX).

Labium (Fig. 4D). Submentum with two pairs of setae (LA1 and LA2); LA1 trichoid, situated mesally to LA2; LA2 short, leaf-like, on lateral part. Mentum with one pair of very long setae (LA3) and pore-like sensilla (LA4) on lateroventral face; LA4 at base, LA3 anterior to LA4. Prementum with 5 pairs of sensilla (LA5-8, LA10). LA5-7 situated laterally on ventral face; minute seta LA5 at base; long seta LA6 and pore-like sensillum LA7 on apical part of sclerite; LA7 lateral to LA6. LA8 pore-like, dorsally on median part. Stout short seta LA10 anterolateral to LA8. LA9, LA11, and LA12 absent. Labial palpomere 1 with minute seta LA13 lateroventrally at base. Pore-like sensillum (LA14) dorsally on intersegmental membrane between palpomeres 1 and 2. Palpomere 2 with one pore-like sensillum (LA15) situated subbasally on outer face; several minute sensilla of variable shape and length (gLA) on apical membranous area.

Biology.

Adults and the larva were collected from leaf litter (for the photograph of collecting locality, see Minoshima 2018: fig. 1H). They were collected together with adults and larvae of Peratogonus reversus ( Omicrini ), Cercyon sp., and Armostus ohyamatensis Hoshina & Satô, 2006 (both Megasternini ).