Dicellophilus, COOK, 1896

Bonato, Lucio, Dányi, László & Minelli, Alessandro, 2010, Morphology and phylogeny of Dicellophilus, a centipede genus with a highly disjunct distribution (Chilopoda: Mecistocephalidae), Zoological Journal of the Linnean Society 158 (3), pp. 501-532 : 512-516

DICELLOPHILUS COOK, 1896

Main references: Cook, 1896a: 61 (original description); Cook, 1896b: 74 (fixation of type species); Silvestri, 1919: 81 (diagnosis and key); Chamberlin, 1920: 186 (key); Attems, 1926: 356 (key); Attems, 1929: 127 (key), 149 (diagnosis and key); Takakuwa, 1938a: 2032 (key); Takakuwa, 1940: 81 (key); Attems, 1947: 103 (key); Matic, 1972: 65 (diagnosis); Titova, 1975: 46 (key); Koren, 1986: 66 (diagnosis); Shinohara, 1999: 700 (key), 709 (diagnosis); Bonato et al., 2003: 548 (phylogeny); Uliana et al., 2007: 26 (diagnosis and key).

Type species: Mecistocephalus limatus Wood, 1862 , by subsequent designation ( Cook, 1896b: 74).

Included species: Dicellophilus carniolensis (C.L. Koch, 1847) ; D. limatus ( Wood, 1862) ; D. anomalus ( Chamberlin, 1904) ; D. pulcher ( Kishida, 1928) .

Synonyms: None.

Adult morphology: Characters common to adults of all species are described below.

Body: Tapering posteriorly. Length at the complete development of gonopods, 4–5 cm; maximum length, 6–7 cm.

Colour: Leg-bearing trunk pale yellow to orangebrown, uniform, without dark patches. Head and forcipular segment darker than the remaining body. Forcipular hinges, forcipular tubercles, and distal part of tarsungulum brown-black.

Antennae: Tapering towards the distal tip. Ratio of antenna length to head length 2.3–2.5 in adult females, 2.7–2.8 in adult males. Length to width ratio of antennal article IV, 1.3–1.5 ( Fig. 6A ). Ratio of length of antennal article XIV to that of XIII, 1.2–1.7. Distal part of each antennal article areolate, remaining surface not areolate. Antennae covered with long setae, arranged in two girdles on each article, and decreasing in size towards the most distal articles, and with short setae scattered on most of the surface of each article, and increasing in density towards the most distal articles. Rows of spine-like basal sensilla (the ‘sensilla microtrichoidea’ of Ernst, 1983, 1997, 2000) are absent on antennal article VI and X. Sensilla on the antennal tip (‘sensilla brachyconica’ of Ernst, 1981, 2000; ‘spearlike sensilla’ of Bonato et al., 2003) ~10–20-Mm long, tapering from around the midlength, surrounded by some subapical sensilla, which are similar in shape but shorter. Numerous club-like sensilla (‘sensilla basiconica’ of Ernst, 1979, 2000) on both the internal and external sides of the distal part of antennal article XIV ( Fig. 6B ); occasionally, in some specimens, also a few club-like sensilla on the distal part of article XIII. Groups of sensilla on the distal part of antennal articles II, V, IX, and XIII, both on the dorsal side, where they are often arranged transversally, and on the ventro-internal side, where they are often aligned longitudinally; variable in shape and size, from short and conical to similar to the sensilla on the antennal tip. Sensilla shaped as very short spines scattered on both the dorsal and ventral side on most basal antennal articles, more numerous on antennal articles II, V, and IX.

Cephalic plate: Length to width ratio, 1.2–1.6. Frontal line evident, appearing as an areolate narrow band. Paramedian setigerous sulci absent. Setae variable in length, arranged in a somewhat symmetrical pattern. Button-like sensilla and micropores scattered over the whole surface.

Clypeus: Areolate part limited to the antenna-bearing processes, longer along the paraclypeal sutures than on the medial part, with a well-defined posterior margin. Clypeal plagula undivided, without midlongitudinal areolate stripe, and extending over most of the clypeal surface. A group of between three and five setae on each anterolateral corner of the clypeus; 70–150 setae scattered on most of the clypeal plagula, absent on wide bands along the lateral and posterior margins. Several micropores scattered in the setigerous area of the plagula.

Bucca: Stilus well developed. Spiculum absent. Setae lacking. Several micropores scattered on the nonareolate surface.

Labrum: Concave dorsally. Mid-piece relatively narrow, about 3.5–4.5 times as long as wide, posteriorly pointed, with fairly parallel lateral sides. Thickened lines dividing anterior and posterior alae are uniformly curved and concave backwards. Posterior alae almost as long medially as the whole labrum. Posterior alae with longitudinal folds; therefore, striped in appearance. Posterior margin of each side piece evidently concave, with medial corner bearing a small, stout process ( Fig. 6C ). Hair-like projections, variable in length, covering a posterior band of the dorsal surface of the posterior alae, and exposed on the posterior margins of posterior alae, particularly on the intermediate part ( Fig. 6C, D ).

Mandible: Ventral surface covered with dense, short, hair-like projections ( Fig. 6F ). A series of between three and seven pectinate lamellae, followed by few rudimentary lamellae ( Fig. 6F ). First lamella with five or six teeth; intermediate lamellae with between 10 and 15 teeth. Basal tooth pointed, smooth.

First maxillae: Coxosternum divided by a midlongitudinal sulcus, completely non-areolate; width to medial length ratio, ~2.4–3.6; between two and four pairs of anteromedial setae; antero-external corners not projecting; lateral incisures absent. Basal part of each medial projection with between five and ten spinous sensilla along the internal margin, and on the ventral surface. Basal part of each telopodite with between one and three setae.

Second maxillae: Coxosternum undivided; width to medial length ratio, 3.6–3.7; areolation on the isthmus, and along the anterior and posterior margins, without non-areolate insulae; several setae on the isthmus, along the anterior margin and on a longitudinal lateral band. Metameric pore in posterolateral position, foraminal process very elongate backwards, with the groove beginning from the metameric pore pointing to the posterior margin of the coxosternum close to the corner. Telopodite overreaching the telopodite of the first maxillae, with the terminal article as wide as the others, and completely covered with setae. Praetarsus in the shape of a tubercle, bearing tiny spines, and usually also with a larger spine ( Fig. 6G ).

Forcipular segment: Tergum trapezoid, 1.6–1.7 times as wide as long; areolation mainly along two marginal lateral bands and two paramedian posterior areas, gradually fading into the central non-areolate surface; largest setae patterned, with a single pair distinctly anterior to the others; mid-longitudinal sulcus not evident. Pleurite 1.8–2.0 times as long as the tergum; dorsal ridge sclerotized, bearing a row of setae; anterior tip (scapular point) well behind the anterior margin of the coxosternum, and only slightly projecting. Cerrus composed of a group of 10–20 setae on each side of the anterodorsal surface of the coxosternum, but no paramedian rows of setae. Ventrally exposed part of coxosternum 1.2–1.4 times as long as wide, covered with scattered setae; a pair of tiny tubercles on the anterior margin. Forcipular telopodite reaching antennal article I. Forcipular article I (trochanteropraefemur) 1.2–1.5 times as long as wide, bearing a single, distal tubercle, and a sutural trace on the internodorsal side ( Fig. 7A ). Forcipular intermediate articles each with a smaller tubercle, and with the distal one usually larger than the proximal one. Tarsungulum bearing a single basal tubercle, emerging from the internodorsal surface ( Fig. 7B ); internal margin crenulated, bearing a series of tiny spines situated in the notches ( Fig. 7D, E ). Pore of the poison gland in dorsal, subterminal position ( Fig. 7B, C ). Poison calyx uniformly narrow, reaching the distal third of the trochanteropraefemur; digitiform processes from the end of calyx to the base of tarsungulum.

Leg-bearing segments: Terga with paramedian sulci. From segment I to at least segment XVII, each sternum bearing a posterior process (endosternal process), which is tongue-like and reaches about the mid-length of the subsequent sternum on the most anterior segments, however shortening and becoming bifurcate on the subsequent segments. Sternal sulcus not furcate, evident from segment II but fading towards posterior segments. Pore fields absent in both sexes. Leg composed of 6 articles. Claw bearing two basal spines (parungues), antero-ventral and posteroventral respectively, each slightly shorter than half of the main claw; usually an additional tiny spine close to the postero-ventral parunguis. Ratio of length of leg I to leg II 0.7–0.8.

Last leg-bearing segment: Tergum subrectangular, 1.4–1.7 times as long as wide. Sternum subtriangular, 0.8–1.2 times as long as wide, covered with long scattered setae on the anterior half and with short dense setae on the posterior half. Each coxopleuron with about 70–80 pores, variable in size, scattered on most part of the ventral and lateral sides; a distinctly larger pore (macropore) near the centre of the ventral side of the coxopleuron ( Fig. 7F–H ); long setae scattered on the whole surface, a wide band of short dense setae on the ventral side along the interno-posterior margin. Telopodite of the last leg of 6 articles, 1.8–2.0 times as long as the telopodite of the preceding leg, slightly swollen in adult males in respect to females, covered with long scattered setae; short, dense setae on the ventral surface, from trochanter or praefemur to the tip; praetarsus shaped as a tubercle with a few short spines ( Fig. 7J ).

Terminal part of the body: Gonopods of 2 articles, covered with long scattered setae ( Fig. 7G–I ). A pair of simple anal pores ( Fig. 7F–H ).

Sexual dimorphism: Adult males and females differ in maximum body size (males slightly smaller than females), elongation of the antennae (~2.7–2.8 times as long as the cephalic plate in males, ~2.3–2.5 times in females), shape of legs of the last pair (slightly more swollen in males than in females), density of short setae on the legs of the last pair (more dense in males than in females), structure of the genital area (gonopods narrow and well separated from each other, with a subconical projection in between, and sternum and pleurites basal to the gonopods evidently separated by anteriorly converging sutures in the males, Figure 7G ; gonopods wide at base, in contact to each other, without any projection in between, and sternum and pleurites basal to the gonopods apparently fully coalescent without any trace of sutures in the females, Fig. 7H ).

Developmental changes during post-larval growth. As observed in D. carniolensis and D. pulcher , the head becomes more elongate and its relative size in respect to the remaining body decreases; setae increase in number, including those in the clypeus and in the cerrus; only the coxal macropores are present at hatching, whereas additional coxal pores open later and increase in number, but the macropores remain recognizable as the largest ones throughout growth; in the terminal part of the body, the anal pores become less conspicuous, whereas the sternum basal to the gonopods elongates and gonopods and male penis emerge and grow increasingly in relative size ( Fig. 7F–H ).

Differential diagnosis: Differential characters in respect to the other genera of Mecistocephalidae are given in Table 2.

Taxonomy and nomenclature follow that of Bonato et al. (2003).

Notes on taxonomy: The genus Dicellophilus was introduced by Cook, 1896a: 61 to include four nominal species, namely Mecistocephalus limatus Wood, 1862 , Mecistocephalus breviceps Meinert, 1886 , Mecistocephalus melanonotus Wood, 1862 , and Mecistocephalus quadratus Wood, 1867 . In that paper, Cook did not fix the type species, even though he stated explicitly that the genus includes all known species ‘congeneric with Mecistocephalus limatus ’ ( Cook, 1896a: 61) . In a different paper published in the same volume (at the same date, fide Jeekel, 2005), Cook (1896b: 74) indicated explicitly Mecistocephalus limatus Wood, 1862 as the type species of Dicellophilus . Disregarding or ignoring the designation by Cook (1896b), different species were subsequently indicated invalidly as the type species of Dicellophilus , namely Mecistocephalus punctifrons Newport, 1843 by Attems (1903) and Clinopodes carniolensis C.L. Koch, 1847 by Attems (1928), neither of which was anyway eligible for type species fixation.

Since its introduction, Dicellophilus has been maintained as a valid genus. Indeed, it was synonymised under Mecistocephalus Newport, 1843 by Attems (1903) based on his erroneous opinion on the type species (see above), but it was later revalidated as a distinct genus by the same author ( Attems, 1926, 1929).

Among the species originally included in Dicellophilus by Cook (1896a), M. melanonotus Wood, 1862 and M. quadratus Wood, 1867 were later demonstrated not to be congeneric with the type species M. limatus Wood, 1862 , nor to be mecistocephalids at all. Instead, both species belong to Geophilidae , but their generic assignment remains debated ( Chamberlin, 1912; Crabill, 1950; Kevan, 1983). Silvestri (1919) suggested that Tygarrup Chamberlin, 1914 , at the time only imprecisely diagnosed, could be a junior synonym of Dicellophilus Cook, 1896 , and included the type species Tygarrup intermedius Chamberlin, 1914 in Dicellophilus with doubt; however, this opinion was dismissed soon after the identity of Tygarrup as a distinct genus was more adequately understood ( Chamberlin, 1920; see also Table 2).

Distribution: Species in the genus Dicellophilus occur naturally in three isolated areas, in north-western America, central Europe, and Honshu respectively ( Fig. 10 ; see below, under each species).

Notes on distribution: Few specimens of Dicellophilus species have been collected occasionally in localities outside the known range (see below, under each species; Fig. 10 ), but no evidence of established populations is available. Dowdy (1947) reported about ten centipedes collected from near Jefferson City, Missouri, within an ecological survey on soil arthropods, and identified by R.E. Hefner as ‘ Dicellophilus sp. of Cook’; however, lacking further details and considering that, as far as we know, work by R.E. Hefner on chilopods was limited to a single paper ( Williams & Hefner, 1928) and no other specimens were found among centipedes collected in that and surrounding states ( Chamberlin, 1928, 1942; Crabill, 1955a, b), his identification is questionable.

Figures

Figure 6. Dicellophilus carniolensis (A–F) and Dicellophilus pulcher (G). A, antennal article XIV, ventral view. B, club-like sensilla on antennal article XIV. C, medial part of labrum, dorsal view (maxillae and mandibles removed). D, part of the right side piece of the labrum, dorsal view. E, right mandible, anteromedial view (detached from head). F, lamellae of right mandible, medial view. G, tips of telopodites of second maxillae, ventral view. Arrowheads: a, club-like sensillum; b, mid-piece of labrum; c, marginal hair-like projections; d, mandible hair-like projections; e, first pectinate lamella of mandible; f, apical spinous tubercle of telopodite of maxillae II. SEM micrographs: A–D, D. carniolensis, ♀, 51-mm long, from Mara, Romania; E, F, D. carniolensis, ♀, 59-mm long, from Lăpuş Mts, Romania; G, D. pulcher, ♀, 38-mm long, from Shiobara, Japan; the detailed data for the specimens are presented in the Material and methods.

Figure 7. Dicellophilus carniolensis (A, C–J) and Dicellophilus pulcher (B). A, forcipular segment, ventral view (head detached). B, forcipular tarsungula, anterodorsal view. C, poison gland pore of the left forcipular tarsungulum, dorsal view. D, E, margin of forcipular tarsungulum, ventral view. F, terminal segments of a juvenile, ventral view. G, terminal segments of an adult male, ventral view. H, terminal segments of an adult female, ventral view. I, terminal segments of an adult male, lateral view. J, tip of a last pair leg. Arrowheads: a, tarsungulum; b, trochanteropraefemur; c, pore of poison gland; d, macropore; e, anal pore; f, suture between sternum and pleurites basal to the gonopods; g, gonopod; h, spinous tubercle on the tip of a last leg. SEM micrographs: A, I, D. carniolensis, ♂, 46-mm long, from Volovec, Ukraine; B, D. pulcher, ♀, 38-mm long, from Shiobara, Japan; C, D. carniolensis, ♀, 55-mm long, from Volovec, Ukraine; D, E, D. carniolensis, ♀, 55-mm long, from Sighetu Marmaţiei, Romania; F, D. carniolensis, juvenile, 14-mm long, from Mara, Romania; G, J, D. carniolensis, ♂, 45-mm long, from Mara, Romania; H, D. carniolensis, ♀, 51-mm long, from Mara, Romania; the detailed data for the specimens are presented in the Material and methods.

Figure 10. Geographical distribution and phylogenetic relationships of the species of Dicellophilus. The shaded areas indicate the established populations; stars indicate either occasional or dubious records. The dotted line indicates the 40 °N parallel of latitude.