Tylopus helicorthomorphoides, Nguyen & Eguchi, 2022

Nguyen, Anh D. & Eguchi, Katsuyuki, 2022, Mountainous millipedes in Vietnam. II. A conspicuous Tylopus species from Northern Vietnam (Diplopoda, Polydesmida, Paradoxosomatidae), ZooKeys 1091, pp. 1-13 : 1

publication ID	https://dx.doi.org/10.3897/zookeys.1091.80094
publication LSID	lsid:zoobank.org:pub:23342288-0BA9-4356-9E39-E8B85102A7AB
persistent identifier	https://treatment.plazi.org/id/5CD2F36B-E138-490F-B426-ABFDB47D3A96
taxon LSID	lsid:zoobank.org:act:5CD2F36B-E138-490F-B426-ABFDB47D3A96
treatment provided by	ZooKeys by Pensoft
scientific name	Tylopus helicorthomorphoides
status	sp. nov.

Treatment

Tylopus helicorthomorphoides View in CoL sp. nov.

Figs 1 View Figure 1 , 2 View Figure 2 , 3 View Figure 3 , 4 View Figure 4 , 5 View Figure 5

Material examined.

Holotype. Vietnam • 1 male; Vinh Phuc Province, Tam Dao National Park, on the way to Tam Dao 2; 1,100 m a.s.l.; 25 Feb. 2017; Anh D. Nguyen leg.; natural forests; IEBR-Myr 603H.

Paratypes. Vietnam • 2 females; same data as for holotype; IEBR-Myr 603P • 1 male; Vinh Phuc Province, Tam Dao National Park , on way to TV tower; 21.46065°N, 105.64863°E; 1,081 m a.s.l.; 10 Dec. 2019; Hoang Quang Duy leg.; natural forests; IEBR-Myr 876 GoogleMaps .

Non-type. Vietnam • 1 male; Ha Giang Province, Bac Me Natural Reserve, Minh Ngoc commune, Lung Can village ; 22.71814°N, 105.17997°E; 361 m a.s.l.; 12-13 Dec. 2018; Anh D. Nguyen leg.; bushes (IEBR-Myr 809) GoogleMaps .

Diagnosis.

The new species distinctly differs from its congeners in having a three-times spiraled solenophore of the gonopods and postfemoral lamella l present while spine z and process h totally absent. The new species is slightly similar to its congener T. strongylomoides ( Korsórs & Golovatch, 1989), from the same locality (Tam Dao National Park), in having a twisted solenophore and solenomere. However, the new species obviously differs from T. strongylosomoides in having a more strongly coiled solenophore and solenomere (3 × vs 1.5 ×).

Regarding the gonopod conformation, the new species is somewhat similar to species of the genus Helicorthomorpha in the twist of both the solenophore and solenomere. However, the postfemoral region of Helicorthomorpha members is more elaborate, twisted, and carries no additional processes, whereas that of the new species is spiraled or coiled rather than twisted, and has a postfemoral lamella.

Etymology.

The species epithet, helicorthomorphoides, is used to emphasize the similarity of the gonopod solenophore between the new species and those of the genus Helicorthomorpha .

Description.

Body length ~ 14.4 mm (male) and 14.9 mm (female). Width of midbody pro- and metazona ~ 1.2 mm (male), 1.6 mm (female) and 1.6 mm (male), 1.9 mm (female), respectively.

Body generally brownish yellow or darkish yellow except antennomere 7 and metaterga with a darker, median, V-shaped region (or median triangular-shaped area on metaterga) (Figs 2 View Figure 2 - 4 View Figure 4 ).

Head (Fig. 2B, C View Figure 2 ) slightly smaller than collum, labroclypeous region densely setose. Epicranial suture clearly distinct, dividing frons into two equal parts, with 2+2 setae along suture. Frons convex. Antenna (Fig. 2A-C View Figure 2 ) short, reaching to approximately tergum 2 laterally. Antennomere 1=7<2=3=4=5<6; antennomere 6 largest, obviously clavate.

Collum (Fig. 2B View Figure 2 ) oval-shaped, surface smooth, without granulates or tubercles, but with 2+2 setae near anterior margin and 2+2 setae in intermediate area. Paratergum well developed, subtriangular, with broad corner.

Body segments 3<4<2=5-17, thereafter gradually tapering towards telson. Prozonae and metazonae clearly divided by deep, striated waists. Prozonae smooth, shining, yellowish brown, with a median, broad, longitudinal yellow stria (Figs 2B View Figure 2 , 3A View Figure 3 ). Metazonae (Figs 2B View Figure 2 , 3A View Figure 3 ) smooth, shining, with 2+2 setae near anterior margin, two lateral spotted areas, and 2+2 or 3+3 oblong knobs near posterior margin. These knobs more obvious on posterior segments.

Metatergal sulcus starting on segment 4 but clearly present from segment 5, nearly reaching base of paraterga (Fig. 2B View Figure 2 ). Axial line distinct.

Paraterga (Figs 2A, B, D View Figure 2 , 3A-C View Figure 3 ) well developed, wing-shaped, with at least one setiferous incision near anterior, broadly round corner; caudal corner acute, more pointed from mid-body segment onwards, but never reaching following segment. Caudal corner of paraterga 17-19 very pointed, spine-like (Fig. 3C, D View Figure 3 ).

Ozopores located inside round hollows at the caudolateral sides of paraterga 5, 7, 9, 10, 12, 13, and 15-19 (Figs 2A, D View Figure 2 , 3B View Figure 3 ).

Pleurites (Figs 2A, D View Figure 2 , 3B View Figure 3 ) smooth, not granulated. Pleurosternal carinae (Fig. 2A View Figure 2 ) present until segment 8, with a small tubercle-like projection, then gradually reduced or missing on subsequent segments.

Telson (Figs 3C, D View Figure 3 , 4A View Figure 4 ). Epiproct strongly concave, forming two long lateral tubercles. Hypoproct sub-trapeziform, with two separated distolateral setiferous knobs.

Sterna . Cross impression distinct. Sternum 5 with a large rectangular lamina between coxae 4 (Fig. 4B View Figure 4 ).

Leg short, ~ 1.5 × as long as midbody height. Prefemora swollen dorsally. Tarsal brushes present till legs 21, then gradually thinner and absent on subsequent legs. Adenostyles present on postfemora and tibiae, each with a small knob/tubercle (Fig. 4C View Figure 4 ).

Gonopod suberect, simple (Figs 4D View Figure 4 , 5 View Figure 5 , 6 View Figure 6 ). Coxite short, with sparsely setose distoventral part. Telopodite long and erect. Prefemorite densely setose, separated from femorite by an oblique sulcus laterally. Femorite somewhat enlarged distally and slightly twisted, without modifications or additional processes. Postfemoral region consisting of a solenomere and a solenophore, both completely coiled 3 ×; lamina l present, spine z and process h missing. Seminal groove running entirely on mesal side of femorite, then entering flagelliform solenomere completely sheathed by solenophore. Tip of gonopod strongly bifid.

Genetic distance.

The COI Kimura 2-Parameter (K2P) distance between the new species and other Tylopus species was reported in Anh et al. (2021). The distance was from 12.2% to 15.6%. This distance was obviously narrower than the distances between Sphaerobelum species (from 20.2% to 24.4%) ( Zhao et al. 2020), but more likely similar to the distances between Glomeris species (from 11.5% to 17.1%) ( Wesener 2015).

Phylogenetic analysis.

The twenty included samples of Tylopus members were divided into two different lineages (Fig. 7 View Figure 7 ). The first lineage, Tylopus I, consisting of three species, T. hilaroides , T. sapaensis , and Tylopus sp.1, was a sister clade of the genus Oxidus with 95% bootstrap support.

The second lineage, Tylopus II, was clearly separated from the clade Oxidus + Tylopus I with high bootstrap support (97%). The new species, T. helicorthomorphoides sp. nov., was positioned in this lineage and is closely related to Tylopus sp. 4 (IEBR-Myr 509), but with low bootstrap support (49%). In addition, the relationship between Tylopus species in the second lineage was very poorly supported (bootstrap less than 70%), except the clade T. crassipes + T. roseiparaterga , with a bootstrap value of 90%.