Tisamenus irenoliti, Hennemann, 2025

Hennemann, Frank H., 2025, A taxonomic review of Philippine Obrimini stick insects: The genus Tisamenus Stål, 1875 (Insecta: Phasmatodea: Heteropterygidae: Obriminae), Faunitaxys 13 (24), pp. 1-85 : 45-47

Tisamenus irenoliti n. sp.

( Fig. 25-26)

ZooBank: https://zoobank.org/ 547D2412-D268-45D1-B07D-DBBEA288EA56

HT, ♀: Coll.R.I.Sc.N.B., Coll.I.R.Sc.N.B., Philippines, Marinduque,2010,local collector [ RBINS] .

PT, ♂: Coll.I.R.Sc.N.B., Philippines, Marinduque,2010,local collector [ RBINS] .

PT, ♂: Coll.R.I.Sc.N.B., Philippines, Marinduque, II.2014, local collector, I. Lumawig [ RBINS] .

PT, ♀ (penultimate instar): Philippinen, Marinduque Island, Boac Municipality, Cawit, leg. Eric Oria III.2009 [ FH, No. 1518-1] .

Differentiation. – This species most closely resembles T. lachesis ( Rehn & Rehn, 1939) and T.polillo ( Rehn & Rehn, 1939) but is only known from the island of Marinduque, whereas the other two species are distributed on Luzon and the Polillo Islands. The ♂ is easily separable from lachesis by the much smaller size (body length in lachesis > 42.5 mm), slightly stockier overall shape ( Fig. 26 A-D), more trapezoidal and gradually broadening mesothorax, lack of an enlarged anterior spine on the two carinae of the triangular mesonotal area, notably more incrassate metafemora and more numerous, distinct and acute ventral teeth of the metatibiae ( Fig. 26E). From polillo this ♂ is readily distinguished by the much more pronounced meso- and metapleural spines, conically raised posterior portion of the meso- and metanotum ( Fig. 26C, I, J) which bears a low pair of inter-posterior meso- and metanotals, smaller triangular area of the mesonotum, which covers notably less than half the length of this segment, more incrassate metafemora ( Fig. 26E) and distinct, triangular ventral teeth of the metatibiae (only 2-3 small dentate nodes in polillo ). The ♀ differs from that of lachesis by the having the anterolateral mesopleural much smaller than the following and rather sub-obsolete (distinct and spinose in lachesis ), the arched margins of the triangular mesonotal area, which lacks an anterior spine (more or less straight and with a spinose anterolateral projection in lachesis ), more distinct praeopercular organ ( Fig. 25G), more broadly and evenly rounded posterior margin of the anal segment ( Fig. 25F), as well as the larger teeth of the posterodorsal carina of the profemora and more distinctly dentate ventral carinae of the metatibiae. From polillo this ♀ is distinguishable by the slightly stockier form, having four instead of three mesopleural laterals,shorter triangular mesonotal area that does not attain the middle of the segment ( Fig. 25H; notably more than half as long as mesonotum in polillo ), lack of the anterolateral spinose projection of the carinae of that area seen in polillo , presence of two distinct metapleurals (lacking in polillo ), larger teeth of the posterodorsal carina of the profemora and more distinctly dentate ventral carinae of the metatibiae.Moreover, the ♀ holotype of irenoliti n. sp. readily differs from both species by the remarkably blunt and peg-like, not truly spinose meso- and metapleural laterals, andgenerallyless pointed elementsof head and body armature,but as stated below this might be an individual trait of the holotype with these elements of thoracic armature actually showing noteworthy intraspecific variability.

Etymology. – This new species is named after Ireno L. Lit jr., assistant professor at the Department of Forest Biological Sciences and entomological curator at the UPLB, Los Baños, Philippines, for his efforts in the biodiversity study of Philippine Phasmatodea among which, he has described three species of Tisamenus and also presented a list of species in the genus (Lit & Eusebio, 2010).

Description

♀ ( Fig. 25)

Form and colouration. – Size average for the genus (body length 54.7 mm); general form moderately slender and elongate, legs slender and with distinct armature; elements of armature moderately developed with the meso- and metapleural spines in the unique holotype remarkably blunt and rather peg-like than spinose, which is unique within the genus but may underlie intraspecific variability as an immature ♀ suggest (see remarks below). General colour of the holotype ( Fig. 25 A-D) varying from mid to dark brown to drab with the raised medio-longitudinal keel of meso- and metanotum orangey ochre; mesosternum greyish buff, the metasternum rather chestnut brown with the lateral longitudinal carinae of mesonotum marked by three washed dark grey spots. Limbs unevenly flecked with ochre. Antennae drab with the terminal five joints yellow to buff.

Head. – Rectangular, longer than wide with the genae roughly parallel-sided and almost 1.3x longer than wide. Frons with an obtuse swelling between the eyes. Supra-orbitals moderately prominent, bluntly conical and with a small, tubercle anteriorly and posteriorly; occipitals low and obtusely conical; lateral and median coronals rather small, tubercular and more acute than occipitals. Genae with a gular ridge that is supplied with a about three obtuse nodes and some scattered granules in lower portion ( Fig. 25H). Eyes fairly small, almost hemispherical and their diameter corresponding to scarcely more than half the length of gena.Antennae comparatively long and slender, with all joints except IV and V notably longer than wide and consistingof 26 joints; scapus weakly trapezoidal in dorsal aspect withinterior carina rounded apically, pedicellus a little more than half as long as scapus and almost cylindrical; III slightly longer than pedicellus, IV much shorter and

A. Dorsal view of HT [USNM © Paul D. Brock]. B. Dorsolateral view [USNM © Paul D. Brock]. C. Ventral view [USNM © Paul D. Brock]. D. Dorsal view [FH 1263-2]. E. Dorsolateral view [FH 1263-2]. F. Anteroventral view of left hind leg [FH 1263-2]. G. Closeup of head, pro- and mesonotum [FH 1263-2. H. Terminalia in lateral view [FH 1263-5]. I. Terminalia in dorsal view [FH 1263-5]. J. Terminalia in ventral view [FH 1263-5]. K. Live couple San Fernando, Romblon, Mount Guiting Natural Park, Sibuyan [© Albert Kang https://inaturalist.ca/observations/62277997]

joints up to XII slightly increasing in length, then somewhat gradually decreasing with the terminal antennomere elongated and almost as long as preceding two joints taken together. Scapus and pedicellus each with an ochre, extero-basal swelling.

Thorax. – Pronotum rectangular; triangular area narrow and quite well indicated with margins tubercular and anterolaterally with a fairly strong but bluntly conical bifid spine ( Fig. 25H), pre-sulcal area somewhat gibbose; posterior pronotals low, conical. Mesothorax gradually widening towards the posterior and 2.45x longer than prothorax with posterior portion some 1.3x wider than anterior margin. Mesonotum sub-rectangular with a gentle median constriction and almost 2.1x longer than width at anterior margin; triangular area not reaching middle of notum ( Fig. 25H), somewhat longer than wide, disk shallowly concave and the margins weakly arched and minutely tuberculate with the anterolateral angles protruded into an only very indistinctly enlarged obtuse tubercle; posterior portion of mesonotum with a distinct and unevenly granular medio-longitudinal bulge, that is faintly indicated in the posterior section of the triangular area by a few low granules; posteromedian portion of mesonotum conically raised and shallowly bi-tuberculate. Mesopleurae notably expanding towards the posterior and armed with four laterals, the antero-lateral small and sub-obsolete, the second to fourth one short but strong, (in the holotype) remarkably blunt, peg-like and roughly uniform in size; mesopleural basically like the three large mesopleurals; supra-coxal small, tubercular. Metanotum somewhat wider than long, with a slight narrowing pre-medially and the antero-lateral portions distinctly lowered; otherwise with the same medio-longitudinal bulge and obtuse, bi-tuberculate pre-posterior swelling seen onmesonotum.Metapleurae with two short and bluntly conical laterals; metapleural larger, tubercular and the supra-coxal angle with a small, obtuse spine that is accompanied by a small tubercle posteriorly. Mesosternum distinctly tri-carinate, the medio-longitudinal carina in particular strongly developed; metasternum with a shallower medio-longitudinal carina, densely but unevenly granular and with a few faint indications of metasternals laterally ( Fig. 25I).

Abdomen. – Median segment transverse with anterior margin broadly rounded, shallowly carinate and granulate medio-longitudinally. Segments II-VII broadly transverse and all terga with a slight trace of two closely spaced medio-longitudinalcarinae; II about 2.3x and VII only about2x wider than long; all gradually narrowing; with VII distinctly trapezoidal in outline. Terga II-VI with second paired posteriorsrepresentedby spiniform tubercles, that are most prominent on II and notably decrease in size towards VI; on VII merely represented by low tubercles; postero-lateral small and tubercular. Sterna II-VII destitute of anynoteworthyarmature;praeopercular organ on VII formed by a somewhat raised posterior margin in the median portion, that bears a low, transverse tubercular swelling at each lateral end ( Fig. 25G). Tergum IX obtusely tectate bi-carinate medio-longitudinally and with a moderate conical swelling posteromedially ( Fig. 25E); at anterior margin supplied with four nodose anteriors ( Fig. 25F). Anal segment strongly declining with the lateral margins very obliquely convergent in posterior half and with a fairly well developed medio-longitudinal carina; close to anterior margin with two pairs of nodes and posterior margin very broadly rounded ( Fig. 25F).Epiproct shallowly tectate longitudinally with an indication of a medio-longitudinal carina, the lateral margins weakly and obliquely convergent and the posterior margin rounded with a small median swelling ( Fig. 25F). Subgenital plate fairly elongate, notably projecting beyond epiproct, navicular, distinctly carinate in posterior half and the apex narrowly triangular and acute ( Fig. 25G).

Legs. – All slender and elongate for the genus; the femoral teeth comparatively small but pointed and the ventral teeth more pronounced than dorsal ones. Profemora as long as mesothorax, metafemora reaching about one-third the way along abdominal segment V and metatibiae slightly projecting beyond tip of abdomen. Posterodorsal carina of profemora with five distinct and acute spiniform teeth in basal half;the one or two apical teeth much smaller to sub-obsolete. Dorsal carinae of meso- and metafemora with seven teeth, the two outer ventral carinae of mesofemora with five teeth that notably decrease towards base of femur; in metafemora these teeth are all comparatively more pronouncedandthe large apical one isaccompanied bya second much smaller tooth. Metatibiae smooth dorsally and with 8-10 unequally sized triangular teeth ventrally. Tarsi comparatively long; basitarsi almost as long as following three tarsomeres combined.

Measurementsof holotype [mm]. – Body54.7, pronotum 4.1, mesonotum 10.9, metanotum 5.2, median segment 2.8, profemora 10.7, mesofemora 9.6, metafemora 12.8, protibiae 10.8, mesotibiae 9.7, metatibiae 14.1, antennae 20.4.

♂ ( Fig. 26)

Form and colouration. – Size rather small for the genus (body length 39.0 mm); general form slender and elongate, legs fairly strong with the metafemora strongly incrassate; elements of armature moderately developed with short but strong meso- and metapleural spines and a distinct conical posteromedian swelling of meso- and metanotum. General colour mid brown to buff with the raised medio-longitudinal keel of meso- and metanotum and most of abdomen ochre (in one of the paratypes more distinct than in the other); meso- and metasternum straw coloured with the lateral regions exterior to the lateral longitudinal carinae densely flecked with drab. Antennae buff and gradually becoming lighter in colour in their apical one-third.

Head. – Essentially as in ♀. Inter-ocular swelling of frons with a Cshaped, transverse impression behind, which comprises four low granules ( Fig. 26J). Genae with gular ridge just shallow and unevenly granular ( Fig. 26 I-J). Eyes fairly small, hemispherical and their diameter corresponding to scarcely more than 0.4x length of gena. Antennae similar to ♀, but only with 24 joints; the terminal antennomere somewhat more elongated and as long as preceding two joints taken together.

Thorax. – Pronotum essentially as in ♀ rectangular, but the bifid anterior spine of triangular area much larger and acutely pointed with the second spike slightly higher than the anterior one ( Fig. 26 I-J). Armature of meso- and metathorax more developed and acute than in ♀. Mesothorax elongate, gradually widening towards the posterior and about 2.6x longer than prothorax with posterior portion 1.5x wider thananterior margin. Mesonotum sub-rectangular with a moderate median constriction and about 2.5x longer than width at anterior margin; triangular area not reaching middle of notum ( Fig. 26 I-J), somewhat longer than wide, disk shallowly concave and the margins minutely tuberculate with the anterolateral angles protruded into a somewhat enlarged obtusely conicaltubercle;posterior portion of mesonotum with a distinct and shallowlygranulate medio-longitudinal bulge, that is faintly indicated in the triangular area by a few low granules; posteromedian portion of mesonotum strongly conically raised and obtusely bi-tuberculate (notably more pronounced than in ♀, Fig. 26 I-J). Mesopleurae notably expanding towards the posterior and armed with four laterals, the antero-lateral small and sub-obsolete, the second to fourth one short but strong, spinose and just weakly sub-uniform in size (size somewhat variable); mesopleural a prominent conical spine; supra-coxal small, tubercular. Metanotum longer than wide with a narrowing pre-medially and the antero-lateral portions distinctly lowered; otherwise with the same medio-longitudinal bulge and conical, bi-tuberculate pre-posterior swelling. Metapleurae with two short and conical laterals; metapleuralsmall, tubercular and the supra-coxal anglewitha strong spine that isaccompanied by a smalltubercle posteriorly.Mesosternum distinctly tri-carinate, anteriorly the lateral carinae are connected by a distinct, widely V-shaped transverse carina; metasternum like in ♀.

Abdomen. – Median segment transverse with anterior margin broadly rounded and shallowly carinate medio-longitudinally. Segment II trapezoidal, III-VII almost uniform in width and very slightlydecreasing in length;all sub-quadrate. Terga II-VII with very faintly indicated medio-longitudinal carina; II-IV with lowtubercular paired secondposteriors (just represented as minute nodes on V-VI). Sterna II-VII with a fine medio-longitudinal carina. Terga VIII and IX with the medio-longitudinal carina much more pronounced than on preceding segment and somewhat raised posteriorly; VIII trapezoidal and widening towards posterior, IX transverse. Anal segment longer than IX, somewhat cucullate in lateral aspect, narrowed posteriorly with the lateral margins angular andthe dorsalsurface with a fine but lowmedio-longitudinal carina;posterior margin witha deep, concave medianexcavation and the outer angles triangular ( Fig. 26G). Epiproct distinct, shield-shaped, almost semi-circular in shape and a little projecting beyond anal segment ( Fig. 26G). Vomer broad, transverse withafairly longand strong,terminalhook,thatis about 30° dextral-directed. Poculum rather small, roundly cup-shaped ( Fig. 26F) witha large and verybroad, weakly labiate and angularflange of the free upper margin that is straight posteriorly and reaches slightly less than halfway along anal segment ( Fig. 26F, H).

Legs. – Allstocky with the femora weakly and the metafemora strongly incrassate; the femoral teeth however comparatively small with the ventral teeth more pronounced than dorsal ones. Profemora slightly longer and mesofemora a little shorter than mesothorax, metafemora reaching toposterior of abdominal segment V and metatibiae almost reaching to tip of abdomen. Ventro-basalswellingof metafemora smallbutdistinct, gibbose and smooth; all four outer carinae with six teeth, those on dorsal carinae weakly increasing in size towards base of femur, the two apical ventral teeth prominent and somewhat spiniform. Metatibiae smooth dorsally and with about eight unequally sized triangular teeth ventrally. Tarsi comparatively long; basitarsi about as long as following three tarsomeres combined.

Measurements of paratypes [mm]. – Body 38.7-39.0, pronotum 3.0, mesonotum 7.6-7.7, metanotum 3.9, median segment 2.1, profemora 7.3-7.5, mesofemora 6.8-7.0, metafemora 8.9-9.3, protibiae 7.7–8.0, mesotibiae 6.7-7.2, metatibiae 8.0-9.0, antennae 15.5-16.7.

Remarks. – The immature ♀ inthe author’s collection, which appears to be in the penultimate instar,hasall the elements of the body armature much more developed than in the adult ♀ holotype, acutely pointed and spinose. This suggests the shape and size of the meso- andmetapleurals in particular to underlie considerable intraspecific variability,similar like in e. g. T. polillo ( Rehn & Rehn, 1939) . However, more examples are needed to prove or dismiss this assumption. Egg unknown. Body length of penultimate instar ♀ paratype 45.0 mm.

Distribution. – Marinduque, endemic [RBINS – type locality].