Pyrgeuma pyrgodesmoides Shear

Shear, William A., 2012, Pyrgeuma pyrgodesmoides, n. gen., n. sp., a new millipede from Malaysia with unusual surface structures (Diplopoda, Chordeumatida, Heterochordeumatidae), Zootaxa 3560, pp. 79-86 : 80-85

Pyrgeuma pyrgodesmoides Shear , new species

Figs. 1–12

Types: Male holotype and four female paratypes collected 2–14 May 2009 by Petr Baňař sifting leaf litter in a shallow ravine near Gunung (Mt.) Perdah (N4°29.2, E101°22.1), 1575 m elevation, Cameron Highlands, Pahang, Malaysia. All specimens deposited in the Zoological Museum of the University of Copenhagen, Copenhagen, Denmark.

Etymology: The species epithet, an adjective, refers to the similarity of this species to polydesmidan millipedes of the family Pyrgodesmidae , with similar depressed paranota, rough cuticle covered in adhering soil, and paramedian elevations of the metazonites.

Description: Male holotype. Length, 8.5 mm, width 2.0–2.2 mm, including paranota. Head typical, smooth, yellowish tan mottled purplish gray to brown. Ocelli 6, in rows of 3, 2, 1. Collum partially covering head ( Fig. 1 ), more than twice as wide as head, with horizontal paranota laterally acute-rounded, markedly elevated posterior ridge, metazonital cuticle with vestiture of minute, curved, spatulate microtrichia averaging about 20 µm in length; marginal microtrichia small, in rows, longer microtrichia along horizontal midline of paranota. On subsequent trunk rings, posterior ridge progressively depressed in midline, forming paramedian elevations becoming more prominent posteriorly ( Figs. 1–3 ). Paranota narrow, not as wide as metazonites, slightly depressed, with anterobasal notch ( Fig. 3 ). Metazonital setae not detectable at magnifications up to 210X, on midbody rings only slightly longer than microtrichia, blunt, with 5–7 prominent ridges (Figs. 4, 5, 12). Epiproct (Figs. 4, 5) rounded, median pair of setae three times as long as usual (ca. 60 µm long), spinnerets prominent, spinneret setae long, anal valves with few long setae. Collum, body rings, epiproct appear dark brown, due to adhering soil. Venter, legs yellowish white.

Gonopods (agp, Figs. 8 , 10, 11 ) fused to coxosternite, to each other at base, complex; erect, not passing laterally, posteriorly to ninth leg coxites (c9, Figs. 8 , 10 ). Ninth leg telopodites one-articled, swollen; ninth leg coxites with long, acute mesal branch, shorter lateral branch tipped with three or four horizontally extending thorns ( Fig. 10 ). Tenth legs ( Fig. 9 ) with coxae slightly enlarged, bearing glands, telopodite reduced to two short articles.

Female with 32 rings; 9.2 mm long, 2.0–2.2 mm wide; similar to male in nonsexual characters.

Notes: The microtrichia of the dorsal surface of the metazonites do not appear to be set in sockets, so instead of setae they are direct outgrowths of the cuticle. They vary in size and distribution; the smallest microtrichia are densely arranged in rows on the anterior and posterior edges of the paranota. Larger microtrichia are found sparsely scattered on the anterior part of the metazonite, and microtrichia of similar size are densely arranged on the elevated parts and along the horizontal midline of each paranotum ( Figs. 3 , 6). The largest and most prominent microtrichia are on the paramedian knobs. While the microtrichia, with their curved, spatulate shapes, appear welladapted for catching and holding soil particles, the particles appear to be held on mostly by a gummy secretion and could only be partially cleaned off using ultrasonics. The mixture of secretion, small soil particles and humic materials appears ropy. Scattered among the microtrichia are very small spherical objects that may represent this secretion, but no glandular pores could be detected even at high magnification under the SEM.

The metazonital setae on midbody rings could be detected with difficulty only under the SEM, and even then were found using magnifications greater than 400X. The median setae are located at the top of the paramedian knobs of the metazonites, the lateral setae at the lateralmost edges of the paranota, and the paramedian seta midway between them near the bases of the paranota. This is the same arrangement seen in Heterochordeuma and Infulathrix species ( Figs. 1 , 16 in Shear 2000), but without the paramedian knobs. Anteriorly, the setae are somewhat larger, and the median setae of the collum can be seen on figure 1. Curiously the median pair on the epiproct are much larger than any others, and can be easily seen with an optical microscope. They may have some special function.

Paranota are winglike extensions from the lateral margins of the metazonites of millipedes and are most commonly found among members of the order Polydesmida (often called “Flat-backed Millipedes”); their absence in members of that taxon is generally taken to be due to secondary reduction. The same may be stated for the unrelated orders Platydemsmida and (some) Siphonophorida. Paranota are rarely found in members of the order Chordeumatida , and the lack of them in basal families of the order suggests that where they have developed they have done so independently. Hoffman (1963), misled by mistaken observations on the gonopods of heterochordeumatids, assumed them to be basal to the order, and their platydesmid-like general appearance led him to draw the conclusion that Chordeumatida and Platydesmida were phylogenetically close. With the exception of the Heterochordeumatidae , each family in which paranota-bearing species occur has the great majority of their species without them. These non-paranotal species often have the lateralmost two metazonital setae of each side set on prominent, horizontally projecting tubercles which give the rings something of a “flat-backed” appearance, and comparison of these with paranotal species suggest that the paranota develop by the extension of the outer part of the tubercles. Functionally, paranota are associated with the “litter-splitting” habit in which the paranota are used as wedges to get into narrow spaces between leaves and other debris in the litter ( Hopkin and Read 1992, p. 38). This is an adaptation to habitat that has very likely arisen independently in Polydesmida, Platydesmida, Siphonophorida and probably several times in Chordeumatida .

The resemblance of Pyrgeuma pyrgodesmoides to species of the polydesmidan family Pyrgodesmidae is remarkable and in the field I doubt the two could be distinguished. Pyrgodesmids are abundant and diverse throughout the tropics, including southeast Asia. Pyrgodesmids also have collum segments that nearly cover the head, prominent, depressed paranota, and many species have notable paramedian swellings that range from humps to long, recurved, hornlike structures. The resemblance is heightened because P. pyrgodesmoides appears to lack the six metazonital setae found in all chordeumatids (they are present but undetectably small). However, close examination would soon reveal differences since pyrgodesmids have 19 or 20 rings compared to 30 or 32 for P. polydesmoides , and on various rings, prominent stalked ozopores project from the paranota of pyrgodesmids (all chordeumatid millipedes lack ozopores). In addition, their adaptations for accumulating soil are different: microtrichia in P. polydesmoides and unusual cuticular vanes comprising a sort of box-work in pyrgodesmids.

Collecting in tropical leaf litter in southeast Asia, the Indonesian archipelago, Borneo and the Philippines has produced more than 35 species of the chordeumatidan genus Metopidiothrix Attems 1907 ( Shear 2002) , many of these species represented by abundant samples. Some narrow geographical regions yield several sympatric species of Metopidiothrix . But heterochordeumatids appear to be much more rare and much less diverse, with only six species known (a seventh, Pocockia sapiens Silvestri 1895 , was described as a heterochordeumatid but is more likely a metopidiotrichid), and each of those from a few specimens at a single locality. Could it be that more Pyrgeuma species are hidden in museums in jars of pyrgodesmids?

Figures

FIGURES 1 – 3. Pyrgeuma pyrgodesmoides, n. sp., male, dorsal views. Fig. 1. Anterior end. Fig. 2. Posterior end. Fig. 3. Rings 8 – 10.

FIGURES 8, 9. Pyrgeuma pyrgodesmoides, n. sp., male. Fig. 8. Gonopods and ninth legs, anterior view. Agp, gonopods; c 9, coxites of ninth legpair; pf 9, prefemora of ninth legpair. Fig. 9. Tenth legpair, anterior view.

FIGURES 10 – 12. Pyrgeuma pyrgodesmoides, n. sp., male. Fig. 10. Coxites of left ninth legpair (c 9) and gonopods (agp), posterior view. Fig. 11. Tip of left gonopod, anterior view. Fig. 12. Lateralmost right metazonital seta of ring 9.