Acentetaphyllium, Cumming & Le Tirant, 2022

Cumming, Royce T. & Le Tirant, Ste ́ phane, 2022, Three new genera and one new species of leaf insect from Melanesia (Phasmatodea, Phylliidae), ZooKeys 1110, pp. 151-200 : 151

Acentetaphyllium gen. nov.

Type species.

Phyllium brevipennis Größer, 1992: 164, herein designated.

Taxonomic hierarchy.

This clade, based upon molecular analyses, was recovered as sister to the Nanophyllium a placement which is supported by the linked morphological features of the wider than long prescutum, two lobed posteromedial tubercle, and similar antennae morphology ( Bank et al. 2021). Therefore, this new genus is included within the tribe Nanophylliini Zompro & Größer, 2003 along with its sister genus Nanophyllium .

Discussion.

The selected type species for this new genus is Phyllium brevipennis Größer, 1992 (= Acentetaphyllium brevipenne ( Größer, 1992), comb. nov.) as this was the first species described from this group and is represented by a good condition holotype female with detailed collection data so little confusion surrounds the type species. Additionally, this species has been sequenced and included in molecular phylogenies ( Bank et al. 2021) while the other species are still lacking.

Again, the uniqueness of this clade was recognized by Hennemann et al. (2009), with their designation of the Acentetaphyllium brevipenne species group, and they even recognized this clade as closely related to the Nanophyllium (which as the time were still considered the Phyllium (Pulchriphyllium) frondosum species group, not the opposite sex of the Nanophyllium yet which would not be until a decade later in Cumming et al. 2020a).

Within the phylliid-wide phylogeny of Bank et al. (2021) Acentetaphyllium brevipenne comb. nov. was recovered as sister to all sampled Nanophyllium species with high support. Despite the drastic morphological differences between this new genus (Fig. 13A ) and the Nanophyllium sensu stricto (Fig. 13B ), there are still several morphological features which help to link these two genera. Most notably the two lobed posteromedial tubercle of the head capsule and the similar mesothorax morphology, which is notably wider than long, immediately link these two genera.

Little is known about the Acentetaphyllium gen. nov. ecology except for labels included with two females from within the BPBM collection noting their host plant as " Eucalyptus " (Fig. 14 ). Several other genera/species are known to accept Eucalyptus spp. as a host within captivity (pers. comm. Tomas Stijnts (Belgium; Flanders)). Additionally, these BPBM specimens also note an elevation of collection at 750 meters, whereas a specimen in the Coll SLT from Wau, Morobe Province was collected at 1,200 meters, suggesting this species is not restricted to a limited elevation range.

Within the Nanophyllium the association of opposite sexes has always been problematic due to limited material and notable age of many specimens not allowing molecular comparison. Only recently was the confusion surrounding the “missing” Nanophyllium females for the most part been resolved ( Cumming et al. 2020a). However, even within that work it was recognized that there were two distinct clades known for the males (noted within Cumming et al. 2020a as the pygmaeum species group and the Acentetaphyllium stellae species group, see therein figures and side-by-side morphological comparisons) but females were only confirmed for the pygmaeum species group. The Acentetaphyllium stellae species group was recognized as having numerous morphological similarities and differences to the pygmaeum species group but no tentative female had been linked with clarity. Now with the molecular results of Bank et al. (2021) recovering Acentetaphyllium brevipenne as sister to the Nanophyllium , the males of the Acentetaphyllium stellae species group can with higher confidence be associated with these morphologically unique females (see Fig. 13 for a side by side of these two clades). Although not yet confirmed by breeding or from molecular comparison, the numerous shared morphological features of the males of the Acentetaphyllium stellae species group and Acentetaphyllium brevipenne strongly suggest these are opposite sexes of the same clade (Fig. 13A, C ).

For detailed discussion and figures of the non " Acentetaphyllium brevipenne " Acentetaphyllium gen. nov. species which were originally placed within Nanophyllium , see the recent work of Cumming et al. (2020a) as these species ( Acentetaphyllium larssoni (Cumming, 2017), comb. nov.; Acentetaphyllium miyashitai (Cumming et al., 2020), comb. nov.; and Acentetaphyllium stellae (Cumming, 2016), comb. nov.) are not discussed below as no additional information can be added at this time to supplement the recent publication and their original descriptions.

Morphological differentiation from Nanophyllium sensu stricto.

Features which link these two genera are their antennae morphology (in females), thorax shape and spination (both sexes), and genitalia (both sexes). There are several notable differences between the genera, for female Acentetaphyllium gen. nov. the tegmina are highly sclerotized and rudimentary (Fig. 15D ), at most reaching onto the anterior of abdominal segment II leaving the dorsal of the abdomen fully exposed versus tegmina which are fully developed and covering most of the abdomen in Nanophyllium . For male Acentetaphyllium gen. nov. the shape of the femoral lobes differentiates them as the profemoral interior lobes are rounded without a sharp angle and the mesofemoral interior lobes have a large rounded triangular lobe, reaching from end to end and lacking prominent spination (versus Nanophyllium which have profemoral interior lobes which are angular and mesofemoral interior lobes which are heavily weighted towards the distal end and are marked by distinct serrate teeth on the distal half). Also, the alae of the male Acentetaphyllium gen. nov. allow differentiation as the media anterior and the media posterior do not fuse, instead they both run to the wing margin, and the cubitus after splitting from the first anterior anal fuses with the media posterior near the wing margin and they run fused to the wing apex (versus Nanophyllium which have the media posterior fusing to the media anterior and then they run fused to the wing margin without fusing with other veins (see Cumming et al. 2020a: figs. 10-13 for side by side comparisons)).

Autapomorphic features.

For females the tegmina are highly sclerotized and rudimentary, no longer than the anterior of abdominal segment II (Fig. 14 ), whereas all other phylliids have well-developed tegmina which at least reach halfway onto the abdomen and in most cases cover most of the abdomen. For males the alae venation is autapomorphic as the media anterior and the media posterior do not fuse, instead the media anterior runs alone to the wing margin and the cubitus (after splitting from the first anterior anal) fuses with the media posterior near the wing margin and then they run fused to the wing apex as one (see Cumming et al. 2020a: fig. 13B for an illustration of this venation pattern).

Generic characteristics.

The Acentetaphyllium gen. nov. have females that for phylliids are average length (ca. 80 mm) and males which are on the smaller end (ca. 40 mm), which gives a male to female length ratio of ca. 1.0:2.0 between the sexes for this genus which is the most extreme known in the family (Fig. 13A, C ) as typically a male to female ratio of 1.0:1.2 to 1.0:1.6 is common. Interestingly for Acentetaphyllium gen. nov. coloration, males are only known to have brown forms but within females brown, green, and yellow are all known to exist. Hopefully as more males are located it will become apparent if males are exclusively brown or also come in different color forms.

Antennae. Females have antennae with nine segments with segments IV through VIII which are uniform in length, disk-like, marked with granulation, and the terminal segment is stout and densely covered in setae (Fig. 15B ). Males have antennae with 21 to 22 segments which are relatively flat, and most segments are covered by setae which are longer than the segment is wide.

Head capsule. Males have well-developed ocelli and females lack ocelli. Males have compound eyes which are strongly protruding and occupy ca. 2/5 of the head capsule lateral margins versus females which have compound eyes which are notably smaller, only occupying ca. ¼ of the head capsule lateral margins and which to not strongly protrude from the capsule (Fig. 15A ). Both sexes have head capsules which are marked throughout by distinct but somewhat irregularly sized granulation which is relatively evenly spaced (Fig. 15A ).

Thorax. In both sexes the prescutum can be two to three times wider on the anterior than long with lateral margins that are granular, and a prescutum surface which is only slightly granular, lacking a prominent anterior rim or sagittal crest (Fig. 15D ). In both sexes the mesopleurae begin notably wider than the prescutum anterior rim and weakly diverge gradually and can be marked with a single anterior tubercle or by as many as nine warty tubercles (Fig. 15D ).

Legs. Both sexes have interior protibial lobes which span the full length in a broadly rounded triangle, lack lobes on the protibial exterior, and the meso-, metatibiae are simple, lacking both interior and exterior lobes. In both sexes the profemoral interior lobe is notably smaller than the exterior lobe and is rounded without a strong angle and marked by two to four dulled weakly formed teeth (Fig. 15C ). The profemoral exterior lobe is somewhat variable in males (being roundly obtuse or with a slight recurve giving the lobe a boxier appearance) but in females it appears to be more stable as it is notably recurving posteriorly and marked with a strongly serrate posterior margin and a smoothly arcing anterior margin (Fig. 15C ). Both sexes have the interior meso-, and metafemoral lobes ca. 1.5 to 2.0 times as broad as the exterior lobes, with both arcing smoothly, giving the meso-, and metafemora smooth, pointed leaflet-like appearances which tuck in nicely to the anterior of the abdomen helping to give the habitus a full ovoid appearance (Fig. 14 ).

Wings. In both sexes the tegmina are highly reduced and heavily sclerotized, with a maximum length of reaching the anterior margin of abdominal segment II, but mostly shorter, only reaching the metanotum (Fig. 15D ). Females lack alae but in males the alae are fully developed, reaching onto abdominal segment IX or X. Male alae have a costal vein running along the anterior margin; a subcostal vein which runs alongside the costal vein for most of its length until it fuses with the costal vein near the wing margin; the radial vein is bifurcate, splitting into the first radial and radial sector near the distal third of the alae and these run to the wing margin without fusing to other veins or each other; the media splits early on into the media anterior and media posterior which run parallel to the wing apex, with the media anterior arriving alone, but the media posterior has the cubitus fuse to it near the distal 1/8 of the wing apex; the cubitus is fused with the first anterior anal for ca. half of the wing length until the first anterior anal splits and runs to the wing margin and the cubitus fuses with the media posterior; the anal veins are split into two groups, the anterior anals and the posterior anals (with seven anterior anals and six posterior anals).

Abdomen. Abdominal shapes are somewhat variable; females are often perfectly spade-shaped (Fig. 14B ) but in some forms the abdominal segments can have slightly undulating margins, giving them a wavy appearance (Fig. 14A ); males have similar appearances as they can be smoothly spade-shaped (Fig. 14C ) or can have abdomen which are strongly undulating (see Acentetaphyllium larssoni comb. nov., for an example of a strongly undulating abdomen in males). Female subgenital plate is short and stout with the apex only reaching halfway onto abdominal segment IX and ending in a fine point; gonapophyses VIII are long and slender, but not quite reaching to the apex of the terminal abdominal segment; gonapophyses IX are located to either side of the gonapophyses VIII and have broad bases for ca. ½ their length which taper quickly to slender points; the cerci are relatively flat and rounded, with a slightly wrinkled surface (Fig. 15E ). Males have a narrow, triangular vomer which is ca. two times longer than the greatest width and terminates in a single hook. Male cerci are notably marked with granulation and distinct setae along the margins.

Egg. Egg morphology is not yet known for this rare genus.

Etymology.

Acentetaphyllium meaning "flawless leaf". This generic epithet is a compound of the Latinized name Phyllium the type genus for the family (from Greek φυλλον, -ου (phyllon, - oy) + -um; Poitout 2007), coupled with the Latin prefix acenteta meaning “flawless”. One of the most remarkable features of this genus is how the abdomen and legs are shaped so that when the legs are at rest the habitus is a perfect oval, giving this genus a flawless leaf-like shape (Fig. 14B ). This new genus is neuter in gender, following Phyllium .

Distribution.

At present only known from a handful of records as this appears to be a rarely collected genus. However, it appears as though this genus is found throughout the island of New Guinea as an undescribed Acentetaphyllium gen. nov. is known to us from Fak Fak, Indonesia, there are multiple records from northern New Guinea from the Cyclops Mountains (Indonesia side) and Bewani Mountains (Papua New Guinea side), and multiple records from Morobe Province, Papua New Guinea. See Suppl. material 1 for details on known records.

Figures

Figure 13. Dorsal habitus of adult Acentetaphyllium gen. nov. and Nanophyllium to help illustrate the morphological differences / similarities between these two genera. Images scaled to relative size; scale bar associated with all images A Acentetaphyllium brevipenne female (Coll TM) B Nanophyllium chitoniscoides (Groesser, 1992) female (Coll TM) C Acentetaphyllium stellae comb. nov. holotype male (SDNHM) D Nanophyllium rentzi holotype male (NHMUK) A, B photographs by Rene Limoges (IMQC) C photograph by first author D photograph by Paul Brock (NHMUK).

Figure 14. Examples of abdominal variation observed within Acentetaphyllium brevipenne comb. nov. adult females from within the BPBM collection, dorsal habitus, with their associated data labels to the right of each specimen. Photographs by Miho Maeda, Jerilynn Chun, and James Boone, 2020 (BPBM) A brown form with distinct eye spots on three of the abdominal segments, and a notably lobed abdomen B green form female with eye spots on a single abdominal segment and an abdominal shape which has smoother margins.

Figure 15. Acentetaphyllium brevipenne comb. nov. adult female details A, B, E from Coll SLT C, D from Coll TM Photographs by Rene Limoges (IMQC) A details of head, dorsal B details of antennae, dorsal C details of protibiae and profemora, dorsal D details of head through thorax, dorsal E details of genitalia, ventral.