Tryposoma, Cadena-Castañeda & Hemp, 2024

Cadena-Castaneda, Oscar J. & Hemp, Claudia, 2024, Studies on chevron crickets: Tryposoma gen. nov. (Orthoptera, Anostostomatidae), a new genus from Tanzania, Journal of Orthoptera Research 33 (1), pp. 59-66 : 59

Tryposoma gen. nov.

Type species. -

Tryposoma brachyurum (Karny, 1928) comb. nov.

Generic diagnosis and comparison. -

The new genus described in this study exhibits a morphology that aligns most closely with taxa within the tribe Lutosini . Therefore, we discuss the distinguishing features between Tryposoma gen. nov. and these related taxa. However, given its distribution across the African continent, which harbors several wingless genera of anostostomatids, we also conducted a comparative analysis with these genera. This approach solidifies the differentiation of Tryposoma gen. nov. from other taxa in the same geographic region.

The new genus distinguishes itself from Neotropical Lutosini taxa in several key morphological aspects. Notably, it lacks a plastron and features a notably slender tenth tergite, as opposed to the characteristic division of the last tergite into two plates, a common trait found in Lutosa Walker, 1869, Neolutosa Gorochov, 2001b and Rhumosa Hugel & Desutter-Grandcolas, 2018. Furthermore, certain species of Lutosa and Neolutosa exhibit spiny projections at the apex of the subgenital plate near the base of the styli, a character absent in Tryposoma gen. nov. species. In addition, the paraprocts of the Lutosini are typically slender and narrow, with the epiproct predominantly covering them. In contrast, the species within the new genus possess distinctive paraprocts characterized by a rigid upper section and a ventrally prominent membranous section. The Sp.dl of Tryposoma gen. nov. is notably narrow, resembling a ribbon, whereas in the Lutosini , it takes the form of a plate shaped like a shoulder blade. Furthermore, the ti and TS are more pronounced in the new genus when compared to the taxa of Lutosini .

The newly described genus, Tryposoma gen. nov., differs from African genera: The females of Tryposoma gen. nov. share similarities with those of Libanasa , although they are larger in size. In contrast, the males of Libanasa and Henicus exhibit notable modifications of the mouthparts, distinguishing them from the new genus. Tryposoma gen. nov. can be differentiated from other genera exhibiting sexual modification of the head and mouthparts, such as Borborothis Brunner von Wattenwyl, 1888 and Onosandridus Péringuey, 1916, by the less conspicuous and thick dorsal spines on the hind tibia. Another distinguishing character of the new genus is the absence of a developed horn-like process on the mandibles, which is present in Libanasidus Péringuey, 1916. In contrast to genera without sexual modification of the mouthparts and head, such as Bochus Péringuey, 1916, Onosandridus Péringuey, 1916, and Onosandrus Stål, 1876, Tryposoma gen. nov. stands out due to its larger body size, reaching approximately 30-40 mm. Most species in the previously mentioned genera are of medium size, typically ranging from 15-25 mm. Furthermore, Tryposoma gen. nov. exhibits a conspicuously developed median spur on the hind tibia, extending beyond the first tarsal segment. This is distinct from Bochus , Onosandridus , and Onosandrus , which possess a medium-sized spur similar in size to the dorsal and ventral spurs that does not exceed half of the first tarsal segment. Additional differences between Tryposoma gen. nov. and Bochus include the absence of a rough rostrum in the former, while the latter possesses a cylindrical and inflexible rostrum. Moreover, the paraprocts of Tryposoma gen. nov. are wide, flexible, and flattened, whereas Bochus has protruding cylindrical paraprocts extending toward the front of the terminalia.

Included taxa. -

Tryposoma brachyurum (Karny, 1928) comb. nov. (type species) and Tryposoma kilomeni (Hemp & Johns, 2015) comb. nov.

Etymology. -

From Greek - Trýpes = hole, and - soma = body, Tryposoma = hole inhabiting, since all known Tryposoma species in East Africa stay in earth holes during the daytime and emerge in the evening and night hours only. The gender of the name is being established as neuter.

Description. -

The specimens under study are large in size, measuring between 28 and 40 mm. Coloration in life ranges from yellow to reddish-brown or golden brown, with darker brown pigmentation observed on the posterior margins of the tergites. The hind femora exhibit a bright yellow color that slightly darkens to yellow-brown on the dorsum and apex. Preserved specimens (pinned) display a darker brown coloration (Figs 1 , 4 , 5 ). Head. The head is dorsally and frontally smooth, with the frontal region being higher than wide. Laterally, it appears widened, and the fastigium is twice as broad as the first antennal segment (Figs 2A , 5A ). The eyes are frontally elevated, and the ocelli are conspicuous, with rounded lateral ocelli and an ovoid front ocellus (Figs 2B , 5B ). The scapus and pedicellus are unarmed, and the antennae exceed the length of the body. The mandibles and maxilla exhibit symmetry without any sexual specialization (Figs 2A , 5A ). The ventral process extends beside the base of the labial segment in front of the base of the lacinia. The palpi are thin, elongated, fully pilose, and dilated at the apex (Figs 2B , 5B ). Thorax. The pronotum is slightly wider than it is long (Figs 1A , 5B ) and does not cover the mesonotum (Fig. 1B ). The lateral margin of the pronotum is slightly rounded, and the pronotal disc displays a slight curvature at the anterior and posterior margins (Figs 1B , 5A ). The pronotal lateral lobe has a nearly straight dorsal margin with a slight convexity at the ventral margin. The ventral edge of the mesopleuron forms a weakly projecting rounded flap (Figs 2B , 5B ). The prosternum bears a pair of short cone-like processes. The mesosternum is bispinose, with horizontally compressed spines and slightly backward-bent apices. The metasternum features thorn-like processes with acute backward-bent tips and a broad laterally compressed base. Wings are absent. Legs. The fore coxae is equipped with one prominent lateral spine having a broad and pointed base. The fore and mid femora display several small tubercles from the base to the apex along with two longitudinal parallel carinae at the ventral margin. The fore and mid tibiae possess spines along the dorso- and ventrolateral margins. A tympanum is present on both sides of the fore tibia. The hind femur exhibits 14-16 distinct chevron ridges well-separated by a medial groove that extends from the base to the distal edge of the chevron area (Figs 1A , 5B ). The apical spurs of the hind tibia are fully movable within insertion rings. The dorsal subapical pair is relatively short, the prolateral apical spur is slightly shorter than the metatarsus, and the retrolateral apical spur reaches the midpoint of the second tarsomere. A short ventroapical pair and an even shorter subapical ventral pair are present. Abdomen. Male individuals have minute pegs on the first six abdominal tergites that very likely serve as a stridulatory area (Fig. 2B ). The sternites broaden distally. Tergite 9 exhibits posterior undulations. Tergite 10 is characterized by two well-sclerotized hooks moderately separated by a narrow, medial, and membranous area dorsally (Figs 2C , 5C ). The epiproctus is rounded and has a width equal to its length. The paraprocts lack modifications and are relatively short, with each apex turned dorsal and featuring two very short spinous hooks (Figs 2D , 5C-E ). The cerci are setose, thin, and elongated (Figs 2C-E , 5E ). The subgenital plate is broad at the base, with the corners close to the tergite. It extends as a rounded bulbous plate with a weakly emarginate posterior notch. The styles are short and divergent, emerging before the apex of the subgenital plate (Figs 2E , 5C-E ). Male genitalia: The surface of the dorsal lobe (dl) displays numerous ovoid microstructures (Fig. 3A ). The posterior border of the dl projects toward the anterior margin and tapers into a lingual fold in its last section, curving backward and downward (Fig. 3C ). The titillatory sclerite (TS) and the titillator (ti) form a peduncular system with medium-sized denticulate structures, which are surrounded ventrally and laterally by the lateral folds of the dorsal lobe (ldl) (Fig. 3A ). A thin and ribbon-shaped sclerotized plate (Sp.dl) is present on the dl and forks at the apex (Fig. 3A, C ). The upper folds of the ventral lobe (up.vl) have a rounded distal margin while the lower folds of the ventral lobe (lw.vl) are membranous and possess an angled posterior margin (Fig. 3B ). The ejaculatory duct (ejd) is wide and lacks sclerotic structures, and the ejaculatory vesicles (ejv) are rounded and of medium size (Fig. 3B ). The ventral sclerite (VS) internally covers the TS, and the fore fold of the dorsal lobe (fdl) forms a “U” -shaped fold surrounding the base of the TS (Fig. 3C ).

Female individuals have far fewer and sparser pegs on the stridulatory area. They possess an elongated ovipositor that is as long as the hind femur. The ovipositor exhibits a slight upward curve and has a sharp apex (Figs 2F , 5F ). The cerci are thin and medium-sized, and the subgenital plate is subtriangular with a wavy or acute apex (Figs 2G , 5G ).

Biology. -

All recorded species of the genus Tryposoma gen. nov. in East Africa are nocturnal, living within closed forest from lowland to montane forests. During the day, they hide in holes dug into the ground (Fig. 6A ). At night, they emerge from their shelters and are found on the forest floor among leaf litter or perched on low vegetation (Fig. 6B ). It is noteworthy that all Tryposoma species and populations in this region are seasonal, with adult individuals being observed during the warm period of the year, typically spanning from December to April, the first wet period of the year.

Distribution. -

Africa, Northeast Tanzania, restricted to forest of the montane zone of the North Pare Mountains.

Comments. -

The type specimen of T. brachyurum comb. nov. was initially described based on an immature female specimen (depicted in Fig. 4 ). By comparing it with additional immature and adult specimens that had been previously examined by Johns and Hemp (2015), as well as specimens subsequently collected by C. Hemp from Tanzania, the accurate identification of these specimens was confirmed.

Specimens examined. -

Tryposoma brachyurum comb. nov.: Originally described as Libanasa brachyura Karny, 1928. Holotype ♀ nymph. labelled (1) Libanasa brachyura det Karny Type (in Karny’s hand) (2) Coll. Karny (handwritten) (3) Coll. Karny (printed) (NHMW) Dar es Salaam, Tanzania. There is also a so called “allotype” that is a very small female nymph (NHMW). 2 ♂♂, 1 ♀, 1 ♂ nymph, 1 ♀ nymph, Kazimzumbwi Forest Reserve , Kisarawe District , Tanzania 39°3'E, 6°57'S. Coll. FRONTIER Tanzania, Jan-Feb. 1991 (ZMUC). 1 ♂ nymph, 3 ♀♀ nymphs, Kambai Forest Reserve , Muheza District , (Tanga Region), Tanzania. 4°59'S, 38°41'E. coll. FRONTIER Tanzania, Jan-Feb 1991 (ZMUC). 86 ♂♂ and 75 ♀♀ specimens (and 23 nymphs) of Tryposoma brachyurum coming from the following localities: East Usambara Mts ( Zigi trail, Amani Nature Reserve , Nilo forest reserve, Magoroto Estate ), West Usambara Mts ( Mazumbai , Ndelemai, and Magamba forest reserves), (CCH).

Tryposoma kilomeni comb. nov.: Originally described as Libanasa kilomeni Hemp & Johns, 2015. Holotype ♂. Tanzania, North Pare Mountains , Kindoroko forest reserve, 7°50'44.5"S, 36°53'00.2"E, montane forest, 1750 m, January 2015. Paratypes 4 ♂♂, 9 ♀♀ and 5 nymphs, same locality as holotype .

Figures

Figure 1. Tryposoma brachyurum comb. nov. male. A. Habitus in lateral and dorsal views, respectively.

Figure 2. Tryposoma brachyurum comb. nov. A. Face; B. Detail of male body; C-E. Terminalia in axial, lateral (see paraproct detail), and ventral views, respectively; F. Ovipositor in lateral view; G. Subgenital plate of female.

Figure 3. Tryposoma brachyurum comb. nov. A, B. Male genitalia in dorsal, ventral, and axial views, respectively.

Figure 4. Tryposoma brachyurum comb. nov. Female immature type. A, B. Habitus in lateral and dorsal views. C. Frons. D. Labels. © Natural History Museum Vienna, NOaS Image Collection / H. Bruckner; published with permission.

Figure 5. Tryposoma kilomeni comb. nov. A. Face; B. Detail of male body; C-E. Terminalia in axial, lateral, and ventral views, respectively; F. Ovipositor in lateral view; G. Subgenital plate of female.

Figure 6. Tryposoma brachyurum comb. nov. A. Male specimen from Mazumbai forest reserve, West Usambra, Tanzania, sitting in its hole; B. Same specimen emerging at night.