MYRIAPODOLOGICA

Viiginia Museum of Natural History

Vol. 4, No. 12 ISSN 0163*5395 April 1 5, 1997

A NEW PSAPHODESMINE GENUS FROM NEW GUINEA
(POLYDESMIDA: PLATYRHACIDAE)
by Richard L Hofftnan

ABSTRACT

Petalorhacus is proposed as a new genus to accomodate the type species P. morohe, from
Morobe District, Papua New Guinea. This species is similar to Psafjfwdesmus and
Parazodesmus in having five telopodite processes and enlarged, penicillate coxal setae, but
differs from these and other psaphodesmine taxa in having processes a, b, and c
originating from a very short common stem, all three widely separated and c laminately
enlarged; apex of d expanded and lobed.

INTRODUCTION

Resumption of a long-deferred revision of the Papuan milliped group Psaphodesmini has
recently produced treatments of the genera Parazodesmus ("Steenstrupia", in press) and
Ozor/vacus (in MS). Progress toward definition of psaphodesmine genera has been
accomplished by adoption of fairly exclusive criteria involving the number, shape, and
position of projections on the gonopod telopodite, which vary from one to five, following
establishment of serial homologies of these processes among the various genera of
Platyrhacidae. A detailed account of this situation is provided in my forthcoming revision of
Parazodesmus. While the resulting species groups appear to be defensible monophyletic units,
inhabiting cohesive ranges, their relative evolutionary status has not yet been adequately
ascertained. It has so far been difficult to identify numbers of processes lower than five as
incomplete derivatory stages, or as the results of reduction from an original number of five.
Both addition and loss events could be operational concurrendy within this single tribe. As
the Indonesian platyrhacid fauna becomes better known, resolution of such questions will
become feasible.

I am much indebted to my friend and colleague Jurgen Gruber, Naturhistorisches
Museum, Vienna, for the loan of the specimens upon which the new species is based.

Scanned with permission by Virginia Tech Insect Systematics Group 2014 (www.jointedlegs.org)

102

Myriapodologica

Petalorhacus morobe, n. sp. Fig. 1. Left side of coUum, dorsal aspect Fig. 2, Left paranota
of segments 1 0 and 1 1 , dorsal aspect, showing marginal position of p>eritreme. Fig. 3. Left
side of segments 18 and 19, and epiproct

Hoffman: PetdIor?uicus

103

TAXONOMY
Tribe Psaphodesmini

Psaphodesmin: (as subfamily) Cook, 1896, Brandtia, no. 1, p. 4.— Hof¥man, 1980,

Classification of the Diplopoda, p. 180.

Diagnosis: Apical processes of gonotelopodite variable, ranging from two to five, but all
clearly derivable from basic parazodesmine pattern (five unmodified subsimilar processes) by
loss or modification in shape and location of, the four subtending the solenomere. Body
form variable, typically small, to moderate in size Qength 40-60 mm long), dorsum relatively
convex in most species with metaterga coarsely granular and ornamented with transverse
series of rounded tubercles; paranota typically small and declivent, oiopores located on or
near the lateral edge; sterna normally unspined; epipioct broadly rounded.

Components: Parazodesmus Pocock, PsapKodesmus Cook, T^esmus Pocock, Pleorluictts
Attems, Ozorhacus Attems, Erythrkacus Hofiman, PetalorhacuSt n. gen.

Range: Papuan region from Luzon and Sulawesi east to the Pelieu and Solomon islands
(thus east of Wallace's Line), with the greatest diversity occurring on New Guinea.

Petalorhacus, new genus

Type species: P. morobe, new species.

Name: A neologism composed of the Greek elements petalon (leafi + -rkacus, a
combining stem commonly used in the formation of generic names in this family; suggested
by the somewhat leaf-like form of the (a+b+c) structure on the gonopod tclopodite.
Masculine.

Diagnosis: The single species referred to this genus differs from all known
psaphodesmine taxa by the configuration of telopodite processes, of which c is so enlarged
as to dominate the common (a+b+c) stem and displace a and b from their usual position;
process e is present; process d is large, extending beyond the end of (a+b+c), and subapically
lobed instead of simply acuminate, Gonocoxae widK a small field of peniciUate macrosetae on
the dorsal side.

Range: Known only from the type locality of the type species.

Remarks: All five telopodite processes are present in only two other genera of
Psaphodesmini, Parazodesmus (Pocock, 1897) and Psapliodesmus (Cook, 1897). Enlarged
penicillate coxal setae also occur in both these genera, to which comparisons may be
restricted.

In both genera mentioned, processes a, b, and c are localized at the end of a long
common stalk, with c by far the smallest of the three. In PsapKodesmus (Fig. 7) process e is
small and located at the base of the (a,b,c) common stem, d originates at the same level as e
on the lateral side of the telopodite. In Parazodesmus (Fig. 6) process e is as large as d and
the two are not basally syntopic. Of the two, Psaphodesmus appears more similar to
PetalorKacus in gonopod structure, but neither has anything remotely approaching the
(a+b+c) shape of the latter.

A revision of Parazodesmus (eight species in the Solomons and New Britain) in currently
in press; a similar treatment of PsapKodesmus (four nominal species in the Moluccas) is in
preparation. The gonopods of a representative of each genus are illustrated here to illustrate
the several details discussed in the preceeding paragraph. The point is clearly made that
simply the presence of particular processes per se does not constitute a species-group; it is
the size and location of the processes that is important, as die drawings demonstrate.

104

M3friaf)odoiogiax

Petalorkacus morobe, n. sp. Fig. 4- Left gonopod, mesal aspect, showing shorted and
broadened common stalk of processes a. b, and c, reduced process e, and elongated,
dislocated process d typical of this genus. Fig, 5, The same gonopod, apical half of
telopodite, lateral aspect, enlarged, with apex of process d shown in another aspect.

Petalorkacus morobe, new species
Figures 1-5

Material: Male holotype (Naturh. Mus. Wien), labeled "Nova Guinea: zwisch. Poyu a
Tawa (Poyu 10 m. Aseki, Tawa 13 m. von Kaintiba), 27-IX-1972, J. Eiseltdon." Poyu and
Tawa are too small to appear on any map; Aseki (7®2TS, 146ol2'E) and Kaintiba (7^30'S,
146«02'E) are located 65-70 km west of Wau, Morobe District, Papua New Guinea.

Diagnosis: With the characters of the genus.

Holotype: Adult male, broken and curved, approximately 48 mm long; maximum vridth

Hoffman: Petalorhacus

105

7.8 mm at segment 8; widdi of collum, 5,3 mm, of 2nd segment, 7.0 mm; of 6di segment,
7.6 mm, of 10di-15th segments, 7.7 mm; of 16th segment, 7.6 mm, of 18th segment, 6.9
mm. L/W ratio «* 16%. Original coloration altered by alcohol, at present generally light
brown with prozona a litde darker, legs and sterna lighter.

Head evenly granulose, unmodified, genal impressions very shallow. Collum relatively
narrow, laterally declivent, of the form shown in Fig. 1 , with distinct anterior and posterior
marginal rows of rounded tubercles, and two irregular tows across disk. Second segment with
paranota much broader than collum, also strongly declivent; metazona of segments 2-16
subsimilar, surface dense set with two sizes of granules and three transverse series of large
rounded tubercles, all about equally prominent, becoming smaller on posteriormost terga.
Paranota relatively small and continuing slope of dorsum, thus imparting a distinctly convex
facies to the body form, width/height ratio 70% at segment 10; shape on most segments as
shown in Fig. 2, anterior and posterior edges smooth, lateral edge with 4-5 small dentations
between corners; ozopores located on lateral edge. Paranota of last several segments
triangularly produced posteriad, somewhat more strongly tuberculate than at midbody (Fig.
3); epipTOCt broadly rounded, not constricted basad.

Fig. 6. Parazodesmus sc/iwtogon Chamberlin, left gonopod, mesal aspect, showing subequal
processes d and e, enlarged b and unmodified coxal setae typical of this genus. Fig. 7.
PsapKodesmus annectens (Humbert DeSaussure), left gonopod, mesal aspect, showing
clustering of processes a, b, and c, at the end of a long common stalk; also the elongated
process d, reduced process e and enlarged penicillate coxal setae typical of this genus.

106

Myrwfxxloiogica

Paraprocts and hypoproct of normal platyrhacid form; stEma relatively narrow (1 .6 mm
near midbody), about equal to length of a femur, medially depressed, setose, elevated at base
of coxae but not produced into spines. Legs short, uniformly set with short, curved, laciniate
setae as well as with much longer, straight setae dispersed on ventral surfaces. Sides of
metaiona finely granulate with a small projection above posterior coxae; stigmata large and
auriculate, almost in contact, ihe posterior extending slighdy ferther dorsad.

Gonopod aperture rounded-oval, edges elevated adjacent to coxae of 8th legs. Gonopods
as described under the generic heading and illustrated (Figs. 4, 5), notable for modification of
the (a+b+c) common stem.

Address of Author:

Virginia Museum of Natural History
Martinsville, VA 24112