Thrinoxethus verhoeffi ( Kraus, 1956 )

Golovatch, S. I. & Korotaeva, A. M., 2023, A new, montane record of the millipede, Thrinoxethus verhoeffi (Kraus, 1956) from the Andes of Peru (Diplopoda: Polydesmida: Aphelidesmidae), Russian Entomological Journal 32 (2), pp. 243-251 : 246-248

publication ID	https://doi.org/ 10.15298/rusentj.32.2.16
persistent identifier	https://treatment.plazi.org/id/03B0878E-3834-FFB6-4016-5C76A4BAFDB2
treatment provided by	Felipe
scientific name	Thrinoxethus verhoeffi ( Kraus, 1956 )
status

Treatment

Thrinoxethus verhoeffi ( Kraus, 1956) View in CoL

Figs 1–27 View Figs 1–5 View Figs 6–9 View Figs 10–14 View Figs 15–21 View Figs 22–24 View Figs 25–27 , Map.

Pycnotropis (Cyclotropis) verhoeffi Kraus, 1956: 146 View in CoL , pl. 19, figs 28–29 (original description).

Thrinoxethus verhoeffi View in CoL — Jeekel, 1963: 72 (listing); Vohland, 1998: 140, 141, figs 63–70 (taxonomic comments on the holotype and a new record).

MATERIAL. 3 ♂♂, 1 ♀, several juveniles (nearly all fragment- ed) ( ZMUM), Peru, Pasco Region, Oxapampa Prov., ca 5 km W of Santa Rosa, Selva Alta , 1550 m a.s.l., S 10°00´23´´, W 75°27´36´´, 22–29.XI.2016, I. Melnik leg. GoogleMaps

DESCRIPTION. Body length of complete adults ca 55– 57 mm, width of midbody pro- and metazonae 5.0–5.2 and 7.5–8.0 mm, respectively (♂, ♀).

Colouration in alcohol only occasionally brown ( Figs 1– 5 View Figs 1–5 ), but mostly dark chocolate brown or dark red-brown to nearly black-brown, largely with contrasting yellowish paraterga ( Figs 6–14 View Figs 6–9 View Figs 10–14 ). Antennae and legs usually dark red-brown ( Figs 6–14 View Figs 6–9 View Figs 10–14 ), but sometimes light yellow-brown ( Figs 1–5 View Figs 1–5 ), usually infuscate distally. Adult body with 20 segments.

Tegument mostly smooth and shining. Head with squarish genae, three central teeth at anterior margin of labrum and a distinct/deep epicranial suture; setae usually compound (= arranged in bundles of individual hairs): 6–9 + 6–9 labral, 2– 3 + 2–3 supra-labral, and 1–3 + 1–3 facial ( Figs 3 View Figs 1–5 , 7 View Figs 6–9 ); vertex bare. Genal convexities in front of antennal sockets very distinct. Antennae short and robust, in situ extending past middle of ring 2 when stretched dorsally (♂, ♀); in length, antennomeres 6>2=3=4=5>1=7, with four apical cones on antennomere 8. Antennomeres 5–7 especially densely setose. Interantennal isthmus about half as large as diameter of antennal socket ( Figs 1–3 View Figs 1–5 , 6–7 View Figs 6–9 , 10–12 View Figs 10–14 ).

In width, head << collum <3=15 <ring 2; starting with ring 15, body gradually tapering towards telson ( Figs 1–14 View Figs 1–5 View Figs 6–9 View Figs 10–14 ). Paraterga very strongly developed, broad and wing-shaped, clearly and increasingly arcuate, set low (at about half of midbody height), starting with collum, dorsum strongly and regularly convex; paraterga in lateral view like thin (poreless rings) or thicker (pore-bearing rings) ridges. Paraterga on collum acute triangular to subrectangular, narrowly rounded caudolaterally ( Fig. 4 View Figs 1–5 ). Anterior shoulders of postcollum paraterga infuscate, narrowly bordered and arcuate, laterally turning into strong drop-shaped calluses, increasingly well produced and directed caudolaterad towards telson, narrowly rounded to increasingly pointed; starting with ring 7 or 8, caudolateral corner of paraterga increasingly acute and clearly extending past rear tergal margin, especially well so on rings 16–18, only on ring 19 rather finger-shaped and round- ed; caudal margin of paraterga slightly bordered, microdenticulate and increasingly concave ( Figs 1–14 View Figs 1–5 View Figs 6–9 View Figs 10–14 ). Dorsal surface above paraterga very finely areate, areations being polygonal, arranged in three transverse rows, growing more distinct towards and extending onto base of lateral callus, up to nearly or fully obliterate mid-dorsally, each with a traceable insertion point of a seta. Pore formula normal (5, 7, 9, 10, 12, 13, 15–19), ozopores inconspicuous, but quite visible, lateral in position, often traceable dorsally in rings of caudal body half due to lateral margin being slightly sinuate near middle. Stricture between pro- and metazona narrow, shallow and very faintly striolate longitudinally both dorsally and dorsolaterally. Limbus thin and entire, very finely beaded immediately at place of contact to metazonite proper. Pleurosternal carinae traceable only on rings 2–4 as very low subtransverse and denticulate ridges with a roughly granulate surface around ( Figs 7 View Figs 6–9 , 12 View Figs 10–14 ). Epiproct spade-shaped, very broad and flat, rounded and sparsely setose at caudal margin, setae again being mostly arranged in bundles of individual hairs ( Figs 9 View Figs 6–9 , 14 View Figs 10–14 ). Each paraproct with two bundles of setae borne on distinct tubercles. Hypoproct semi-circular, high and regulasarly rounded at caudal margin, there with 1+1 bundles of setae, both being well separated.

Sterna basically unmodified, bare or nearly so, only sometimes with traces of a minute knob near each coxa ( Figs 3 View Figs 1–5 , 7 View Figs 6–9 , 12 View Figs 10–14 ), cross-impressions very distinct, especially so transverse ones; only sternites between ♂ legs 7 considerably broader and slightly excavate to accommodate tips of gonopods ( Fig. 7 View Figs 6–9 ). Each coxa 2 with a small tubercle, round, low and either perforated and bearing a gonopore (♂, Fig. 7 View Figs 6–9 ) or blunt, slightly elongate and directed ventrocaudally (♀, Fig. 12 View Figs 10–14 ). Legs robust, setose rather sparsely and mostly ventrally, ca 1.4–1.5 (♂) or 1.2–1.3 times (♀) as long as midbody height; claws simple, slender, slightly curved ventrad, ca 1/3 as long as tarsus ( Fig. 15 View Figs 15–21 ). Many setae on podomeres unusually strong and long (= macrosetae). In length, femur ≥ tarsus> prefemur = postfemur = tibia> coxa ( Figs 3 View Figs 1–5 , 7 View Figs 6–9 , 12 View Figs 10–14 , 15 View Figs 15–21 ).

Gonopod aperture transversely oval, simple, its caudal rim slightly elevated ( Fig. 18 View Figs 15–21 ). Gonopods ( Figs 3 View Figs 1–5 , 7 View Figs 6–9 , 15–27 View Figs 15–21 View Figs 22–24 View Figs 25–27 ) with long subcylindrical coxites, both closely adjacent and fused medially at base through a small, central, rudimentary, sternal sclerite; coxites unusually densely setose, setae (= macrosetae) also being unusually long and strong; each coxite with a short, small, simple and unciform cannula, as usual. Telopodites elongate, about twice as long as coxites, simple, directed cephalad and slightly crossing only terminally, each telopodite clearly and deeply bipartite, well delimited against acropodite only laterally; prefemorite (= densely setose part, pf) ca 1/3 as long as acropodite, with an inconspicuous vesicle-like structure (v) apicomesally at base of solenomere branch (sl), the latter the longest and strongest of the two, and a strong, sigmoid, somewhat shorter, more slender, apically acuminate, prefemoral process (pfp); sl unciform, strongly, but regularly curved mesad, protected by pfp on ventral side, branching subapically into a shorter ventral spine and a longer, curved, acuminate, flagelliform solenomere proper. Seminal groove (sg) first running mesally on pf to twist thereafter ventrolaterally on pf before moving through v onto sl.

REMARKS. Despite as many as five of the congeners being known only from ♀ holotypes [ Chamberlin [1941], thus clearly jeopardizing the identity of the younger name verhoeffi , we are quite confident that the samples described and illustrated by Kraus [1956] and Vohland [1998] from two lowland parts of Peruvian Amazonia are conspecific. The only size of older material that was published was that of the ♂ holotype: length 60 mm, width 8.3 mm [ Kraus, 1956]. This agrees very closely with our data: length 55–57 mm, width 7.5–8.0 mm. The colour was described as uniformly light yellow-brown with orange-yellow calluses on paraterga. One of our ♂♂ also matches this description quite well ( Figs 1–5 View Figs 1–5 ), although most of our samples are dark chocolate brown to dark red-brown with contrasting yellow calluses ( Figs 6–14 View Figs 6–9 View Figs 10–14 ). Minor differences can also be noted in the presence of a small ventral knob near each of coxae 3–6 [ Kraus, 1956].

The decisive evidence of conspecificity, however, comes> from the gonopodal structure which agrees in every detail, including not only the conformation of the gonotelopodite, but also the abundant macrosetae located on the gonocoxites ( Figs 22–24 View Figs 22–24 ). This latter character, according to the late R.L. Hoffman, is deemed to represent a symplesiomorphy shared, so far as known, only with T. siolii (see Vohland [1998]). All minor variations in size, colour, peripheral and gonopodal characters etc. can be regarded as only infraspecific, especially inasmuch as the distribution of T. verhoeffi appears to be quite vast (Map).

Now that T. verhoeffi has become recorded in a mountainous part of northeastern Peru, the following biogeographic scenario can readily be suggested. The Andean Selva Alta, both the highest montane and the westernmost record, may have served as a source area whence a downstream dispersal into the Ucayali Basin of Amazonia could have occurred, at least as far east as Alexander von Humboldt National Park in Loreto (Map) .

Molecular analyses must definitely be applied to clarify and stabilize the taxonomy of Aphelidesmidae , Thrinoxethus included.

Acknowkedgements. Special thanks go to Igor V. Melnik, the collector, and Kirill V. Makarov (both Moscow,

Russia) who so skillfully took the pictures. Pavel Nefediev (Barnaul, Russia) kindly helped in generating the map. The first author was partly supported by the Presidium of the Russian Academy of Sciences, Programme No. 41 “Biodiversity of Natural Systems and Biological Resources of Russia ”.

Competing interests. The authors declare no competing interests.