Gigaxytes Srisonchai, Enghoff & Panha, 2018

Srisonchai, Ruttapon, Enghoff, Henrik, Likhitrakarn, Natdanai & Panha, Somsak, 2018, A revision of dragon millipedes III: the new genus Gigaxytes gen. nov., with the description of three new species (Diplopoda, Polydesmida, Paradoxosomatidae), European Journal of Taxonomy 463, pp. 1-43 : 4-9

Genus Gigaxytes Srisonchai, Enghoff & Panha gen. nov.

urn:lsid:zoobank.org:act:71FC419F-3CB9-4F01-BB57-461E8DD2D771

Type species

Desmoxytes gigas Golovatch & Enghoff, 1994 .

Diagnosis

The genus Gigaxytes is characterized by:

1. Paraterga subspiniform, long.

2. Metaterga with three regular rows of tubercles/cones/spines.

3. Metaterga 2–17 with a long caudolateral spine on each side.

4. Male femora 5, 6 or 5, 6, 7 with an apophysis (except. G. gigas comb. nov. without apophyses).

5. Postfemur of gonopod absent (mesal and lateral sulci poorly developed).

6. Lamina lateralis (ll) indistinctly demarcated from lamina medialis (lm).

7. Lamina lateralis (ll) larger and longer than lamina medialis (lm).

Etymology

The name is a combination of the species epithet of the type species, ‘ gigas ’ from Latin, refers to the larger size of all species (30–40 mm in length); ‘- xytes ’ ensures harmony with Desmoxytes (and its synonym Pteroxytes Jeekel, 1980 ).

Included species (4)

- Gigaxytes fusca gen. et sp. nov.

- Gigaxytes gigas ( Golovatch & Enghoff, 1994) gen. et comb. nov.

- Gigaxytes parvoterga gen. et sp. nov.

- Gigaxytes suratensis gen. et sp. nov.

Remarks

The new genus exhibits great morphological similarity with Nagaxytes Srisonchai, Enghoff & Panha, (2018a) (= the ‘ acantherpestes ’ group) with which it shares subspiniform paraterga, but also resembles Hylomus Cook & Loomis, 1924 by having Orthomorpha -like gonopods.

General description of Gigaxytes gen. nov.

The description applies to adult males and females, except for the gonopods or when ‘male’ is specified ( Figs 1 , 2 ). The general description of gonopods is based mainly on G. gigas ( Golovatch & Enghoff, 1994) gen. et comb. nov. ( Fig. 3 ).

SIZE. Body length 30–40 mm (male) 34–40 mm (female), width ca. 2.8–3.0 mm (male) 3.5–3.7 mm (female), varies between species, usually female wider and longer than male.

COLOUR ( Figs 4 A–C, 9A–E, 14A, B, 19A–E). Most species pinkish brown/brownish pink in life, some species brown. Colour in alcohol: all specimens partly faded to pale brown after 4 year’s preservation in alcohol; specimens kept in darkness faded more slowly.

ANTENNAE. Long and slender, covered by delicate setation, usually reaching backwards to body ring 5–7 (male) and 4–6 (female) when stretched dorsally. Antennomere 2 = 3 = 4> 5> 6> 1> 7> 8.

HEAD ( Fig. 2I ). Delicately setose; vertex, labrum and genae delicately setose; epicranial suture conspicuous as a long and deep, brown or black stripe.

COLLUM ( Fig. 2A, C ). With three regular rows of setiferous cones/spines; number of cones/spines in each row varies between species. Paraterga of collum subspiniform, usually elevated at ca. 20º–50º, directed caudolaterad, with two conspicuous notches at lateral margin.

TEGUMENT ( Fig. 2 A–G, K–L, N). Dull; collum, metaterga, surface below paraterga and base of paraterga finely microgranulate; prozona finely shagreened; paraterga, epiproct and sterna smooth. Stricture between prozona and metazona wide; often deep, sometimes shallow.

METATERGA ( Fig. 2A, D, G ). With three transverse rows of setiferous cones and spines; number of cones/ spines in each row varies between species. Caudolateral spine on ring 2–17 very long. Suture (transverse sulcus) on metaterga quite deep, conspicuous on body rings 5–17 in all species. Mid-dorsal (axial) line missing.

PLEUROSTERNAL CARINAE ( Fig. 2B ). Forming a complete, tooth-like crest on ring 2, a long or short ridge on ring 3 and/or 4, missing on remaining body rings.

PARATERGA ( Fig. 2 A–B, D–E, G–H). Subspiniform, long, extremely elevated at ca. 40º–70º (male) 30º–60º (female), directed caudolaterad on rings 2–16 or 2–17, directed increasingly caudad on rings 17–19 or 18–19. Callus and shoulder poorly developed, inconspicuous. Anterior margin with two distinct notches; on body rings 9–10, 12–13, 15–19 with a denticle at lateral margin, near tip. Degree of elevation of paraterga in male usually higher than in female. Posterior angle concave; tip pointed and sharp. Ozopore visible from lateral view, round, small, slightly inconspicuous.

TELSON ( Fig. 2 F–G, L, N). Epiproct quite short, flattened dorsoventrally, tip usually subtruncate, sometimes slightly emarginate; lateral setiferous tubercles conspicuous, long, digitiform; apical tubercles conspicuous, sometimes inconspicuous; epiproct apically with four spinnerets at the corners of a square, not in a depression, anterior pair close to apical tubercles. Paraprocts convex. Hypoproct usually subtrapeziform, sometimes subrectangular, sometimes subsemicircular; caudal margin often subtruncate, sometimes round, with two conspicuous or inconspicuous setiferous tubercles.

STERNA ( Fig. 2K ). Delicately setose, cross-impressions quite shallow. On body ring 5 with a swollen lobe, subtrapeziform; base swollen; tip subtruncate; with one pore seen in posterior view.

LEGS ( Fig. 2J ). Very long and slender. Relative lengths of podomere: femur> tarsus> tibia> postfemur> prefemur> coxa> claw. Male femora 5, 6 or 5, 6, 7 with a ventral apophysis in most species, without modification in G. gigas gen. et comb. nov.

GONOPODS ( Fig. 3 ). Orthomorpha -like. Coxa longer than prefemoral part, subequal in length to femorite, with a distoanterior group of seta. Cannula mostly rather short, sometimes quite long. Telopodite curved (falcate). Prefemoral part ca. ¾ as long as femorite. Femorite long and curved. Seminal groove running entirely on mesal surface of femorite. Mesal sulcus and lateral sulcus poorly developed. Solenophore sheath-like, curved: lamina lateralis lamella-like, thin, longer and wider than lamina medialis: lamina medialis indistinctly demarcated from lamina lateralis, tip in situ directed ventrad/mesoventrad. Solenomere long, slender, supported by solenophore.

Distribution and habitat

No sympatry between species of Gigaxytes gen. nov. has been found in this study; each species has a narrow distribution range. The four species (re)described here appear to be endemic to limestone habitats. The specimens were usually found living exclusively on the ground with leaf litter and hiding under dead leaves. Currently, Gigaxytes gen. nov. is distributed only in South Thailand and South Myanmar: Thailand – Krabi (Ao Luek, Muaeng Krabi, Plai Phraya), Nakhon Si Thammarat (Nopphitam, Thung Song), Phatthalung (Khuan Khanun, Kongra, Si Banphot, Srinagarinda), Songkhla (Rattaphum), Surat Thani (Ban Ta Khun, Khirirat Nikhom, Phanom) and Trang Provinces (Hui Yot, Na Yong, Palian, Ratsada); Myanmar – Thanintharyi Region.

Figures

Fig. 1. Gigaxytes fusca Srisonchai, Enghoff & Panha gen. et sp. nov., Ƌ paratype. Watercolour by Photchana Kriatpraprai.

Fig. 2. General body characters of Gigaxytes gen. nov. (G. fusca Srisonchai, Enghoff & Panha gen. et sp. nov., Ƌ paratype) – SEM images. A–B. Anterior body part (arrowheads point to pleurosternal carinae). C. Collum. D. Body rings 9–10. E. Body rings 8–10. F. Telson. G. Posteriormost rings and telson. H. Body ring 10. I. Mouthparts, ventral view. J. Ƌ leg 13. K. Sternal lobe between Ƌ coxae 4. L, N. Tip of epiproct. M. Tip of tarsus and claw of leg 13.

Fig. 3. SEM images of right gonopod of Gigaxytes Srisonchai, Enghoff & Panha gen. nov. – Gigaxytes gigas (Golovatch & Enghoff, 1994) gen. et comb. nov., ³, specimen from Wat Tham Sue (Tiger Cave). A. Lateral view. B. Mesal view. C. Dorsal view. D. Ventral view. Colours: red = lamina medialis, yellow = solenomere, green = lamina lateralis, purple = seminal groove.

Fig. 4. A–C. Photographs of live Gigaxytes fusca Srisonchai, Enghoff & Panha gen. et sp. nov. A. Ƌ paratype, specimen from Phitsadarn Cave. B. Ƌ paratype, specimen from Phrayarhtan Cave (Buddha Cave). C. ♀ paratype, specimen from Phitsadarn Cave. D–E. Phoretic histiostomatid mites. F. Habitat.