Hylophthirus Durden, Beati, Greiman & Abramov, 2024

Durden, Lance A., Beati, Lorenza, Greiman, Stephen E. & Abramov, Alexei V., 2024, A new genus and new species of sucking louse (Phthiraptera: Anoplura: Enderleinellidae) from the particoloured flying squirrel (Hylopetes alboniger) in Laos, and an updated identification key to enderleinellid genera, Zootaxa 5405 (4), pp. 545-561 : 547

Hylophthirus Durden, Beati, Greiman & Abramov , new genus

Type species: Hylophthirus spinosus new species

Diagnosis. Morphologically, Hylophthirus differs from all other enderleinellid genera by several unique features. In the head, Hylophthirus lacks large, ventral protuberances (present in Microphthirus ). The antennae of Hylophthirus are 5-segmented (4-segmented in Phthirunculus ) and have an elongate, slightly bulbous terminal segment (shorter and parallel-sided in all other enderlenellid genera). The small mesothoracic spiracles of Hylophthirus are each uniquely borne on a dorsal thoracic protuberance. The thoracic sternal plate is well developed and very broad in Hylophthirus (absent in Atopophthirus ), whereas this structure is typically longer than broad in other enderleinellids. On the abdomen of Hylophthirus , there are no paired accessory sternal plates on segment two (which are diagnostic for members of the genus Enderleinellus ) or on any other abdominal segments. The presence of paratergal plates on each side of abdominal segments 2, 3, 4, 7 and 8 in Hylophthirus is unique. Phthirunculus lacks paratergal plates and members of the other enderleinellid genera have paratergal plates on other abdominal segments. Males and females of Hylophthirus have distinct abdominal sternites and broad tergites (sternites and tergites are absent in Werneckia ) and the sternites have massive lateral spines (modified setae) in both sexes, which is unique within the Enderleinellidae . The male genitalia of Hylophthirus have uniquely very narrow, curved parameres posterior to a broad basal apodeme. The female genitalia in Hylophthirus have unique gonopods that are extremely large, especially gonopods IX, that extend well beyond the apex of the abdomen.

Description: Very small size (body length of adults, ~ 0.450 –0.585 mm). Head longer than wide with broadly rounded anterior and lateral margins; distinct dorsal head suture present; antennae 5-segmented with slightly bulbous terminal segment; no sexually dimorphic antennal segments ( Fig. 1 ). Thorax wider than long, lacking notal pit; thoracic sternal plate broad (Figs, 3B, 4B); mesothoracic spiracles small, each borne on protuberance; forelegs and midlegs small, each with small acuminate tibiotarsal claw; hindlegs much larger with massive tibiotarsal claw ( Figs 3–4 ). Abdomen wider than thorax with five paratergal plates on each side—borne on abdominal segments 2, 3, 4, 7 and 8; paratergal plate I small, lacking spiracle and with pair of short paratergal setae (PrS); paratergal plate II with small spiracle and pair of slightly longer PrS; paratergal plate III with small spiracle and pair of long PrS; paratergal plate IV lacking spiracle and with pair of long PrS; paratergal plate V lacking spiracle and with pair of extremely long PrS; small lateral spiracles present on each of abdominal segments 5 and 6 ( Figs 2–4 ); Tergites broad and relatively unmodified; sternites present—some anterior sternites with unique massive lateral spines (modified setae). No sternal accessory plates on segment two or on other abdominal segments ( Figs 3–4 ). Male genitalia highly modified with very narrow parameres, which are shorter than basal apodeme ( Fig. 3D ). Female genitalia highly modified with small subcircular subgenital plate, flanked on each side by broad accessory plate; gonopods, especially gonopods IX, very large and extending well beyond apex of abdomen ( Fig. 4D ).

Host distribution: Only known from the particoloured flying squirrel, Hylopetes alboniger (Hodgson) ( Rodentia : Sciuridae ).

Geographical range: Currently, the new louse genus is only known from Laos.

Etymology. The new genus name is derived from the first four letters of the host genus and appended by phthirus from phtheir, Greek for louse. Gender masculine.

Figures

FIGURE 1. Hylophthirus spinosus n. gen., n. sp. Cleared, slide-mounted specimens. A. Male. B. Female.

FIGURE 2. Hylophthirus spinosus n. gen., n. sp. Scanning electron micrographs of adults. A. Dorsal male. B. Ventral female (with hind tibiotarsal claw grasping host underfur hair). Numbers refer to abdominal tergites 1 through 9. (gIX = gonopod IX, hh = host hair, sp = spiracles, vs = ventral abdominal spine).

FIGURE 3. Hylophthirus spinosus n. gen., n. sp. line drawings of male. A. Dorsoventral views (dorsal view on left of midline; ventral view on right of midline). B. Thoracic sternal plate. C. Paratergal plates and adjacent sections of ventral sternites showing spines. D. Genitalia (ae = aedeagus, ba = basal apodeme, pa = paramere, ps = pseudopenis; sgp = subgenital plate; sp = spiracles).

FIGURE 4. Hylophthirus spinosus n. gen., n. sp. line drawings of female. A. Dorsoventral views (dorsal view on left of midline; ventral view on right of midline). B. Thoracic sternal plate. C. Paratergal plates and adjacent sections of ventral sternites showing spines. D. Genitalia and adjacent structures (gVIII = gonopod VIII, gIX = gonopod IX, sgp = subgenital plate, sp = spiracles).