Contributions to Zoology, 78 (3) - 2009
Diversity in the maxillipede dentition of Mecistocephalus centipedes (Chilopoda, Mecistocephalidae), with the description of a new species with unusually elongate denticles
Lucio Bonato1,3, Alessandro Minelli2,4
Keywords: Chilopoda, functional morphology, Geophilomorpha, maxillipede, Mecistocephalus, Mecistocephalus megalodon n. sp., Predation
Centipedes (Chilopoda) are important predators in most soil communities throughout the world and, among centipedes, geophilomorphs are especially adapted to creep in the interstices of litter and soil. Common to all centipedes is the unique functional specialisation of the first pair of trunk appendages as poisonous, stinging maxillipedes (also called forcipules or prehensors), which are used to catch prey as well as to keep enemies at distance. Maxillipedes project forwards from below the head, and are used in grasping, poisoning and manipulating other arthropods, earthworms, and probably a larger array of soil animals (Lewis, 1981; Edgecombe and Giribet, 2007).
Out of more than two hundred known genera of geophilomorph centipedes, Mecistocephalus Newport, 1843 is one of the richest, comprising more than 130 named species, but many other species still await description or are expected to be discovered after further field research (Bonato et al., 2003). Mecistocephalus represents a well-defined clade, clearly diagnosed by many peculiar morphological traits, including a very broad maxillipede segment and especially the remarkably elongated maxillipedes (Fig. 1), which distinctly overreach the anterior margin of the head. Mecistocephalus species occur almost exclusively in the tropical and subtropical regions of Africa, Asia and Oceania, where they are often dominant in the centipede communities of forest soils. Recent taxonomic and faunistic investigations contribute to a more adequate understanding of the morphological diversity in the genus (Bonato and Minelli, 2004; Bonato et al., 2004; Uliana et al., 2007).
Despite the ecological impact of Mecistocephalus centipedes as predators in many soil communities, our knowledge is fully speculative with respect to their dietary spectrum, their predatory behaviour and other biological aspects of their trophic role, as well as with respect to possible differences between species. Indeed, the interspecific variation in morphological traits that are clearly related to the feeding behaviour has not been adequately explored and documented. Among these traits is the pattern of the sclerotised projections on the mesal side of the maxillipede articles (Fig. 1). All these projections are here referred to as denticles, irrespective of their shape or size, but have been variously called teeth, tubercles, nodes or nodules. Due to the particular position of the condyles between the articles, the maxillipedes perform adduction and abduction on a sub-horizontal plane only and, as a consequence, their mesal denticles are directly involved in the grasping mechanics. Therefore, variation in the pattern of denticles is expected to affect prey selection and efficiency in holding prey.
Even though the maxillipedes of all known Mecistocephalus species share a common ground structure and a quite conserved overall shape, preliminary observations have disclosed some interspecific variation in the arrangement, shape and size of the denticles. Published information on such diversity is fragmentary and heterogeneous in quality, because only some authors recognised the interspecific diagnostic value of the pattern of maxillipede denticles (e.g., Crabill, 1970) and therefore their aspect has been hitherto described and illustrated adequately only for a small number of species.
In this paper, we explore the diversity in the arrangement, size and shape of the maxillipede denticles within the genus Mecistocephalus after comparatively examining a significant percentage of the species, as well as integrating all available published information for all known species. Within this comparative analysis, we also document a remarkable array of unusually elongate denticles in a species recently discovered in the Seychelles, which is described here as new.
Material and methods
For the circumscription and species composition of the genus Mecistocephalus, we refer to the most recent comprehensive treatments (mainly Minelli, 2006; updated by Uliana et al., 2007, and Bonato and Minelli, in press). Accordingly, Mecistocephalus is considered here to include Brachyptyx Chamberlin, 1920, Dasyptyx Chamberlin, 1920, Ectoptyx Chamberlin, 1920, Formosocephalus Verhoeff, 1937, Fusichila Chamberlin, 1953 and Megalacrus Attems, 1953; the identity of all these nominal genus-group taxa has been already discussed (Bonato et al., 2003, 2004; Uliana et al. 2007). We took into account all species currently considered valid within Mecistocephalus (following Minelli, 2006, and subsequent papers). However, we excluded the nominal species Mecistocephalus pilosus Wood, 1862, because its inclusion in the genus Mecistocephalus is uncertain.
Intraspecific variation in the pattern of maxillipede denticles, particularly with respect to changes during growth and inter-individual variation, was tested in two species for which large series of specimens of different body length were available to study, namely M. karasawai Uliana, Bonato and Minelli, 2007 (82 specimens, body length 11-55 mm, from Kyushu and Ryukyu islands; collections NSMT and MB; see below for abbreviations) and M. diversisternus (Silvestri, 1919) (37 specimens, body length 20-55 mm, from Honshu, Ryukyu islands, and Taiwan; collections HWC, MB, TT).
Interspecific variation in the pattern of maxillipede denticles was assessed by comparing 32 species. Species were selected in order to represent all different morphologically recognizable groups or clades within Mecistocephalus, based on previous phylogenetic and taxonomic studies (Bonato et al., 2003; Bonato and Minelli, 2004; Uliana et al., 2007). A total of 1 to 5 specimens were examined for each species. As far as possible, in order to control for possible allometric effects and other changes during growth, we selected specimens with body length in the range of 3-5 cm and maxillipede coxosternum width in the range of 1.2-2.0 mm (values found in adult specimens of most species of Mecistocephalus). Furthermore, in order to check for possible sexual dimorphism, we examined both males and females for each species, whenever available.
Maxillipedes were examined through light microscopy, after removing the head. Specimens were cleared under ethylene glycol and mounted on temporary slides, in ventral view, following standard procedures for geophilomorphs (Pereira, 2000; Foddai et al., 2002). Photographs were taken for each specimen by means of a digital camera applied to a microscope Leica DMLB, after standardizing the position of the specimen and the photographic conditions; for each specimen, a series of 4 to 8 photographs taken at different focal planes was assembled using the software CombineZM (Hadley, 2008). Profiles of the mesal margin of the maxillipedes were drawn based on the photographs obtained, and superimposed according to alternative criteria; lack of obvious landmarks along the profile did not allow applying quantitative morphometric approaches.
A complete survey of the literature on Mecistocephalus was also performed, in order to retrieve all published information on the pattern of maxillipede denticles of different species, through either descriptions or illustrations of representative specimens. Information based on specimens overtly misidentified (often under the names M. punctifrons, M. maxillaris or M. insularis; see Bonato and Minelli, 2004) was considered after emendating the identification whenever possible.
The evolution of major features in the pattern of maxillipede denticles in the family Mecistocephalidae was inferred by optimizing selected characters on the only available phylogenetic tree of the family (Bonato et al., 2003), following the parsimony criterion and applying both AccTran and DelTran options.
For descriptive purposes, we followed the traditional morphological terminology (as illustrated in Fig. 1), even though it rests on possibly unwarranted assumptions on the homology between the articles of the maxillipedes and those of the walking legs.
Abbreviations for collections: BM = Bishop Museum, Honolulu; CAS = California Academy of Sciences, San Francisco; HLD = Hessisches Landesmuseum, Darmstadt; HWC = H.-W. Chang, National Sun Yat-Sen University, Kaohsiung, Taiwan; LD = L. Deharveng, Univ. P. Sabatier, Toulouse; MB = A. Minelli and L. Bonato, Univ. Padova; MVR = Museo civico di Storia naturale di Verona; NHML = Natural History Museum, London; NSMT = National Science Museum, Tokyo; PB = P. Beron, Bulgarian Academy of Sciences, Sofia; SI = Smithsonian Institution, National Museum of Natural History, Washington; SM = Senckenberg Museum, Frankfurt am Main; TT = T. Tanabe, Kumamoto University, Kumamoto; VD = K. Van Damme, Ghent Univ.; ZMC = Zoological Museum, Copenhagen Univ.
Results and discussion
The basic pattern of maxillipede denticles
Common to most species of Mecistocephalus is an array of denticles on the mesal side of each maxillipede, comprising (Fig. 1):
- two denticles on the trochanteroprefemur, one distal to the other; the basal denticle emerges proximal to a weak furrow that runs transversally on the mesal side of the trochanteroprefemur (such furrow was hypothesised to correspond to a putative ancestral articulation between two distinct articles; Crabill, 1970); the distal denticle emerges just proximal to the distal end of the trochanteroprefemur;
- a single denticle on each of the two intermediate articles;
- two denticles close to the basis of the tarsungulum, one dorsal to the other.
Of all these denticles, those on the trochanteroprefemur are the largest, those on the tarsungulum the smallest; of the trochanteroprefemoral denticles, the distal one is usually more conspicuous then the basal one; in the same way, of the denticles of the intermediate articles, the distal one is usually larger than the basal one.
With respect to the resting position of the maxillipedes, all denticles are projecting antero-mesally.
In addition to the denticles along the appendages, two paired denticles emerge on the anterior margin of the coxosternum, from a shallow sinus between the maxillipedes (Fig. 1).
Examination of conspecific specimens of different body size of two representative species of Mecistocephalus showed that number, arrangement and shape of the denticles do not change significantly during growth. Instead, the relative size of the basal trochanteroprefemoral denticle increases slightly with respect to the other denticles and the maxillipede as a whole, at least in M. karasawai. A comparable allometry was already found in M. tahitiensis by Silvestri (1919). Independent from body size, we found only minor inter-individual variation in the size of denticles within each of the species examined.
Our observations suggest that the pattern of maxillipede denticles in Mecistocephalus species is indeed affected by some intraspecific variation, but this can be regarded as negligible compared to interspecific differences. Published information for other species is consistent with this assumption. However, as the relative size of the denticles may actually change with growth, we performed our comparison between species after controlling, as far as possible, for the body size of the specimens examined (see Material and methods).
Sex-related differences were not found in any of the species examined. More generally, sexual dimorphism in Mecistocephalus is very slight in the external morphology, but for the genital region: consistent differences between sexes have to date only been detected in the maximum body size (females growing slightly larger than males) and the elongation of antennae (these are slightly more elongate in males than in females) (Bonato and Minelli, 2004). Furthermore, no case of sexual differences in the external morphology of maxillipedes has been reported for any geophilomorph species.
Fig. 2. Diversity in the maxillipede denticles between Mecistocephalus species: microscopic photographs of the right maxillipede, ventral view, of representative specimens. Species are illustrated according to the alphabetic order. Data on specimens are given in Appendix 2.
Interspecific diversity and the unusual pattern of maxillipede denticles in M. megalodon n. sp.
Direct examination of 32 representative species of Mecistocephalus (Fig. 2) and study of all published information for all species in the genus revealed interspecific diversity in the following features.
The denticles on the anterior margin of coxosternum are always present, but variable in relative size (from almost inconspicuous, e.g., in M. angusticeps, to very large, e.g., in M. affinis), shape (from stout and rounded, e.g., in M. tahitiensis, to sharply pointed, e.g., in M. silvestrii and M. megalodon n. sp.), and degree of forward projection from the coxosternal margin (from not distinctly projecting because emerging from inside a deep concavity, e.g., in M. glabridorsalis, to conspicuously projecting, e.g., in M. affinis).
The denticles on the trochanteroprefemur are variable in relative size with respect to the article (from very tiny, e.g., in M. zygethus, to much larger, e.g., in M. karasawai), general shape (for example, stout with rounded tip, in M. waikaneus; stout with flattened tip and thus with an angulated profile, e.g., in M. japonicus; long with pointed tip, e.g., in M. marmoratus), especially in the orientation (usually projecting straight in mesal-anterior direction, e.g., in M. rubriceps, but sometimes distinctly bending mesally, e.g., in M. glabridorsalis, or instead straight projecting anteriorly, e.g., in M. megalodon n. sp.) and aspect of the mesal profile (from concave, e.g., in M. togensis, to almost straight, e.g., in M. pallidus, or convex, e.g., in M. megalodon n. sp.; sometimes peculiarly sinuous, e.g., in M. punctifrons) (see also Fig. 3 for a direct comparison of profiles).
Fig. 3. Diversity in the denticles of the trochanteroprefemur in Mecistocephalus species: superimposed profiles of the mesal margin of the right trochanteroprefemur in representative specimens of 32 species, taken from the microscopic photographs in fig. 2. Alternative superimpositions have been obtained selecting different landmarks (empty circles, indicated by arrows): (a) the distal bases of the two denticles; (b) the distal basis of the basal denticle and distal end of the mesal margin of the trochanteroprefemur. The profile of M. megalodon n. sp. is indicated by a thicker line.
According to the literature, the basal denticle of the trochanteroprefemur is apparently so inconspicuous in some species that it has been described and illustrated as virtually absent in M. conspicuus Attems, 1938 (Attems, 1938; Lewis, 1991), M. manazurensis Shinohara, 1961 (Shinohara, 1961: fig. 5), and M. satumensis Takakuwa, 1938 (Takakuwa, 1938: fig. 4). Peculiar conditions are reported for a few other species: both denticles are illustrated as unusually very slender in M. momotoriensis Takakuwa, 1938 (Takakuwa, 1938: fig. 2); the distal denticle is illustrated as remarkably expanded in M. insularis (Lucas, 1863) (Brölemann, 1926: fig. 167); both denticles are distinctly curved backwards and thus appearing hook-like in M. uncifer (Silvestri, 1919) (Silvestri, 1919).
Fig. 5. Evolution of the pattern of maxillipede denticles in the Mecistocephalidae. Presence of denticles (dent.) in different positions is scored for each clade (when variability is present within a clades, the most probable ancestral condition for the clade is considered): black-filled = present; grey-filled = uncertain; empty = absent. Transitions reconstructed under AccTran (A) or DelTran (D) options are marked on the tree by different symbols (empty for reversal). Sources: phylogeny from Bonato et al. (2003); ancestral characters states for Adesmata and Scolopendromorpha mainly based on Foddai and Minelli (2000), Edgecombe and Giribet (2004, 2007), and Koch et al. (2009).
Also the denticles on the intermediate articles are always present but variable in relative size with respect to the maxillipedes (from very tiny, e.g., in M. japonicus, to much larger, e.g., in M. heteropus and M. megalodon n. sp.), general shape (usually stout with rounded tip, e.g., in M. microporus, but sometimes more swollen and projecting, e.g., in M. waikaneus, or stout with flattened tip, e.g., in M. lohmanderi). As a rule, size and shape of these denticles correlate with those of the denticles on the trochanteroprefemur.
The denticles at the basis of the tarsungulum are variable in relative size with respect to the maxillipede, but also in their apparent number (from two distinct denticles, e.g., in M. marmoratus, to a single shallow bulge, e.g., in M. tahitiensis). Additional projections on the tarsungulum are known for one species only, M. aethelabis Bonato and Minelli, 2004: in the single known specimen, each tarsungulum bears a peculiar shallow projection at about the mid-length of the internal margin (Bonato and Minelli, 2004).
A new species recently discovered in the Seychelles, described below as M. megalodon n. sp. (Appendix 1; fig. 6), is remarkable in its pattern of maxillipede denticles. With respect to the diversity hitherto known and here comparatively assessed for the whole genus Mecistocephalus, M. megalodon n. sp. appears exceptional in the relative elongation, and therefore the overall size, of the whole set of denticles (Fig. 4). Particularly unusual are also the profile, and thus the overall shape, of the denticles of the trochanteroprefemur (Figs 3, 4): the profile of the basal denticle appears approximately ‘securiform’ (axe-shaped), whereas that of the distal one appears more‘lanceolate’ (lance-shaped). Out of all known species of Mecistocephalus, these profiles resemble in some respect those found in another species only (still undescribed, Fig. 2), but in the latter species the denticles are much smaller than in M. megalodon n. sp.
The evolutionary differentiation of a species with very elongated maxillipede denticles within a clade characterised by moderately elongated denticles, as observed in the case of M. megalodon n. sp., probably parallels similar evolutionary transitions that have occurred in a few other lineages of geophilomorphs, distantly related to each other. An example is provided by Schendyla armata Brölemann, 1901 (Schendylidae), which is characterised by a very elongated sub-conic denticle emerging at the distal end of the trochanteroprefemur (Brolemann, 1930), as opposed to the less conspicuous denticles in all other species in the genus Schendyla Bergsøe and Meinert, 1866.
Evolution of maxillipede denticles in the mecistocephalids
An analysis of the evolutionary changes that gave rise to the diversity currently observed in Mecistocephalus is hindered by the lack of resolution of the internal phylogeny of the genus obtained by Bonato et al. (2003). Instead, the evolutionary origin of the general pattern of maxillipede denticles that is common to all extant species of Mecistocephalidae, and therefore most probably ancestral to the genus, may be traced back by extending the comparative analysis to all major clades recognised in the family Mecistocephalidae, as well as to the most closely related lineages, namely the Adesmata and the Scolopendromorpha, and exploiting the available genus-level phylogeny of the family (Fig. 5).
Common to all mecistocephalids, and therefore featuring as the ancestral condition of the family, is the presence of a pair of denticles on the coxosternal margin and a denticle on the trochanteroprefemur that corresponds to the distal one of the two present in Mecistocephalus. This condition could be a plesiomorphic trait, as possibly homologous sclerotised projections are present in the same position in different Adesmata and Scolopendromorpha, but this remains uncertain as a large variation occurs within both these two groups and their internal phylogeny remains broadly unresolved (Edgecombe and Giribet, 2004, 2007; Koch et al., 2009).
Also the presence of denticles on the intermediate articles could be ancestral to the whole family Mecistocephalidae, but the variation observed within different genera suggests that those intermediate denticles could have undergone multiple evolutionary losses and gains. Even less clear is whether a basal denticle on the tarsungulum is ancestral to the whole family and went lost in some clades, or has been repeatedly acquired by different clades (Fig. 5).
Most probably, the basal denticle on the trochanteroprefemur originated at the root of the Mecistocephalus clade. It is lacking in all other mecistocephalids, even though a shallow bulge in a few species of Arrup (Uliana et al., 2007) could be interpreted as corresponding in position to the basal denticle of Mecistocephalus, however not affecting our evolutionary inference. If confirmed, the putative lack of this basal denticle in a few species of Mecistocephalus could be explained by secondary loss, as at least one of these species (M. conspicuus) came out nested within many other congeneric species in the phylogenetic analysis by Bonato et al. (2003). Worth noting is that a similar basal trochanteroprefemoral denticle is present in some other lineages of Adesmata, e.g., within the Aphilodontidae and the Geophilidae, which however are only distantly related to Mecistocephalidae (Edgecombe and Giribet, 2004, 2007) and therefore an independent origin may be assumed.
The presence of a pair of basal denticles, instead of a single one, at the basis of each tarsungulum originated at the root of either Mecistocephalus or a subclade of this genus. Indeed, a pair of distinct denticles were detected in another mecistocephalid species, Anarrup flavipes (Attems, 1930) (Bonato et al., 2003) and could be a common feature of the small, very distinct genus Anarrup Chamberlin, 1920. However, this is most probably due to evolutionary convergence, as Anarrup is only distantly related to Mecistocephalus, whereas the most closely related genera Takashimaia Miyosi, 1955 and Krateraspis Lignau, 1929 have only a shallow bulge at the basis of the tarsungulum.
We are grateful to J. Gerlach, who allowed us to study the geophilomorphs collected in the Seychelles within the Indian Ocean Biodiversity project, and thus to discover the new species described here. We are also grateful to all persons who collected specimens and provided an unprecedented sample of species. We thank Christiane Beidatsch (Hessisches Landesmuseum Darmstadt), Hieronymus Dastych (Zoologisches Museum der Universität Hamburg), Stefan Friedrich (Zoologische Staatssammlung, München), Charles E. Griswold (California Academy of Science, San Francisco), Jochen Martens (Johannes Gutenberg Universität, Mainz), Sabina Swift and Gordon Nishida (formerly at the Bishop Museum, Honolulu), who allowed us to examine important specimens in their respective museum collections. Two anonymous reviewers provided useful comments. This research was supported by the University of Padova (CPDA081134/08).
Received: 11 March 2009
Accepted: 8 July 2009
Published online: 7 October 2009
Editor: M. Schilthuizen
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Description of Mecistocephalus megalodon n. sp.
Holotype: ♀, adult, 45 mm long; from Aride (Seychelles islands), 0 m a.s.l., II-1999, J. Cadbury leg.. coll. NHML.
Other material examined: 3 ♂♂ and 3 ♀♀, sub-adults to adults, 24 to 37 mm long, from Aride (Seychelles islands), 0 m, II-1999, J. Cadbury leg.; 1 ♀, sub-adult, 26 mm long, from Aride (Seychelles islands), XI-2000; 1 ♂, sub-adult, 23 mm long, from Aride (Seychelles islands), 20-III-2002; 1 ♂, adult, 30 mm long, from Cousine (Seychelles island), 0 m, 13-III-1998, J. Kelly leg.; coll. MB.
Diagnosis: a Mecistocephalus species with invariantly 49 leg-bearing segments; head and most anterior trunk segments reddish brown, contrasting with the paler yellow remaining trunk; areolate part of the clypeus without non-areolate insulae; clypeus with about three pairs of setae on the areolate part, arranged in an almost transverse row, and a pair of setae in the plagulae, close to the mid-longitudinal areolate stripe, at about 1/3 of medial length of the stripe; buccae with setae on the posterior half only; maxillipede cerrus absent; denticles on the anterior margin of the maxillipede coxosternum and on the mesal side of the maxillipedes very elongate, pointed and projecting forwards; each tarsungulum with two distinct basal denticles; sternal mid-longitudinal sulcus anteriorly furcate, with an obtuse angle; sternum of the last leg-bearing segment sub-triangular, wider than long, with a distinct medial posterior projection.
Description of the holotype (see also Fig. 6).
Condition of the specimen. Body in four pieces: head without maxillae; maxillary complex; anterior part of the trunk (including the most anterior 35 leg-bearing segments); posterior part of the trunk (including the most posterior 14 leg-bearing segments). Some legs lacking, including the distal part of the right leg of the last pair.
Color (in alcohol): head and most anterior trunk segments reddish brown, gradually but distinctly changing into yellow in the remaining body, without dark patches.
Cephalic capsule. Head plate 1.6 times as long as wide; frontal line rounded. Antennae 3.3 times as long as the head width. Apical sensilla about 10 µm long, with a distinct transverse crown-like projection at about 1/3 of the length. Club-like sensilla on the external sides of antennal articles VII-XIV of both antennae, and on the internal sides of antennal articles IX-XIV of the right antenna and XI-XIV of the left antenna. Clypeus about 2.5 times as wide as long; areolate part without smooth insulae; mid-longitudinal extent of the plagulae about half of the clypeus; three pairs of setae approximately aligned inside the areolate part, and another pair flanking closely the areolate mid-longitudinal stripe at about 1/3 of medial length of the stripe; no evident sensilla or pores on the clypeus. Labrum: anterior ala subtriangular, medially reduced to a point; posterior ala with medial margins convergent posteriorly, their postero-medial corners slightly projecting; posterior margin of each side-piece uniformly slightly convex, without crenulation and without hair-like projections. Spicula distinctly bent medially; each bucca with eight setae, in the posterior half only.
Mandibles. Each mandible with 12 well-developed lamellae; first lamella with six teeth; average intermediate lamella with about 30 teeth; basal tooth of the mandible rounded, not overreaching the first tooth of the first lamella, with margin only sparsely scalloped.
First maxillae. Coxosternum with 4 paramedian pairs of setae, and a few other setae close to the anterior margin; antero-external corners slightly projecting. Each medial projection about 2.0 times as long as wide, with eight-nine setae on the basal part, and distal lobe almost uniformly narrow. Each telopodite about 3.4 times as long as wide, slightly sinuate along the external margin, with two setae on the basal part, the distal part almost uniformly narrow.
Second maxillae. Coxosternum about 1.4 times as wide as long; total length about 2.0 times the mid-longitudinal length; wide medial band and posterior marginal band uniformly areolate, without non-areolate areas; many scattered setae on the posterior half. First article of telopodite about 4.9 times as long as wide; with two-three setae. Third article about 2.4 times as long as wide, with many setae; apical claw well developed.
Maxillipede segment. Tergum about 1.3 times as wide as long, its exposed part about 1.4 times as wide as long, with a distinct mid-longitudinal groove. Pleurites with a well sclerotised dorsal ridge, the anterior tip not particularly elongate. Exposed part of coxosternum about 1.2 times as wide as long; cerrus absent; no condylar projections; anterior margin with a pair of elongate, pointed denticles. Trochanteroprefemur about 1.4 times as long as wide, with two well developed denticles, the basal one only slightly smaller and its margin less convex than the distal one; each of the intermediate articles with a well developed denticle, that on the third article larger than the other, both distinctly smaller than those of trochanteroprefemur; tarsungulum with two subconic basal denticles, the dorsal one more projecting than the other. Poison calyx reaching about 0.6 of the length of trochanteroprefemur.
Leg-bearing trunk. A total of 49 leg-bearing segments. Sternal sulcus furcate, anterior angle between the branches from about rectangular on a few most anterior segments to about 120° wide on the other segments. Length of leg I about half of that of leg II.
Last leg-bearing segment. Tergum subrectangular, about 1.7 times as a long as wide. Sternum subtriangular, about 1.2 times as wide a long; the lateral margin strongly converging backwards, almost straight, only slightly sinuous; a distinct medial posterior rounded projection; dense setae on the posterior half. Each coxopleuron about 1.8 times as long as the sternum, covered with tens of scattered pores of various size. Telopodite about 2.0 times as long as that of the preceding leg, with a tiny sub-apical spine.
Posterior tip of the trunk. Gonopods well developed, subtriangular, bi-articulate, almost touching each other at the basis. A pair of anal pores.
Description of a male (30 mm long, from Cousine; collection data given above).
Differing from the female holotype only in the posterior tip of the trunk: gonopods bi-articulate, slender, with a rounded tip, well separated from each other by a sub-conic genital projection in between.
Etymology: from ancient Greek’μεγας’ (big) and ̔οδους, οδοντος’ (tooth); referring to the unusually large size of the maxillipede denticles.
Specimens illustrated in Fig. 2.
M. cf. affinis Lawrence, 1960: ♂, 32 mm, 49 leg pairs, from Madagascar, III-1969, W.L. Brown leg., coll. SI
M. angusticeps (Ribaut, 1914): ♀, 15 mm, 47 leg pairs, from Picard Island, Seychelles, 9-IX-2005, K. Mach & O. Maurel leg., coll. MB
M. changi Uliana, Bonato and Minelli, 2007: ♀, 50 mm, 49 leg pairs, from Yungan, Taiwan, date unknown, H.W. Chang leg., coll. MB
M. diversisternus (Silvestri, 1919): ♀, 40 mm, 57 leg pairs, from Aono, Minami-izu-machi, Japan, 26-VIII-1978, K. Ishii leg., coll. MB
M. glabridorsalis Attems, 1901: ♀, 32 mm, 49 leg pairs, from Mont Plaisir, Silhouette, Seychelles, 11-VIII-2000, J. Gerlach leg., coll. MB
M. guildingii Newport, 1843: ♂, 24 mm, 49 leg pairs, from Smith’s, Bermuda, 2-IV-1976, collector unknown, coll. NHML
M. cf. heteropus Humbert, 1865: ♀, 26 mm, 49 leg pairs, from Dambula, Sri Lanka, 25-XII-1984, P. Beron & S. Andreev leg., coll. PB
M. japonicus Meinert, 1886: ♀, 68 mm, 63 leg pairs, from Odamiyama, Japan, 19-VI-1996, E. Yamamoto leg., coll. MB
M. karasawai Uliana, Bonato and Minelli, 2007: ♀, 30 mm, 49 leg pairs, from Mt. Nishime, Japan, 13-XI-2001, S. Karasawa leg., coll. MB
M. leonensis (Cook, 1896): ♂, 38 mm, 49 leg pairs, from Ribeira Seca, Santiago Id, Cabo Verde, 26-I-1988, P.T. Bailey leg., coll. ZMC
M. lohmanderi Verhoeff, 1939: ♀, 29 mm, 49 leg pairs, from La Passe, Silhouette, Seychelles, 16-VII-2000, collector unknown, coll. MB
M. longiceps Lawrence, 1960: ♂, 50 mm, 49 leg pairs, from Majakatompo, Madagascar, 25-XI-1959, E.S. Ross leg., coll. CAS
M. marmoratus Verhoeff, 1934: ♂, 50 mm, 49 leg pairs, from Beililungshan, Taiwan, date unknown, collector unknown, coll. MB
M. cf. mauritianus Verhoeff, 1939: ♀, 52 mm, 49 leg pairs, from Petrin, Mauritius Is., 31-III-1969, W.L. Brown leg., coll. SI
M. ̔maxillaris’ sensu Silvestri (1919): ♀, 38 mm, 49 leg pairs, from Haiku, Maui, Hawaii Ids, 20-III-1967, N.L.H. Krauss leg., coll. BM
M. megalodon n. sp.: ♀, 45 mm, 49 leg pairs, from Aride, Seychelles, II-1999, J. Cadbury leg., coll. NHML.
M. microporus Haase, 1887: ♀, 52 mm, 93 leg pairs, from Cebu, Philippines, 31-I-1980, V. Cottarelli leg., coll. MVR
M. mikado Attems, 1928: ♀, 37 mm, 49 leg pairs, from Shiauliouchiou, Taiwan, date unknown, H.W. Chang leg., coll. MB
M. cf. modestus (Silvestri, 1919): ♀, 32 mm, 49 leg pairs, from Kuper-Range, Wau, Papua New Guinea, 10-X-1992, A. Riedel leg., coll. CAS
M. nannocornis Chamberlin, 1920: ♀, 40 mm, 45 leg pairs, from San Jose, Mindoro, Philippines, III-1945, E.S. Ross leg., coll. CAS
M. nilgirinus Chamberlin 1920: ♀, 55 mm, 49 leg pairs, from Koraput, India, 2-II-1962, E.S. Ross & D.Q. Cavagnaro leg., coll. MB
M. pallidus (Silvestri 1919): ♂, 40 mm, 49 leg pairs, from Netarhåt, India, 11-XI-1961, E.S. Ross & D.Q. Cavagnaro, coll. MB
M. punctifrons Newport, 1843: ♂, 50 mm, 49 leg pairs, from 8 mi. NE of Tuni, India, 5-II-1962, E.S. Ross & D.Q. Cavagnaro leg., coll. MB
M. rubriceps Wood, 1862: ♂, 41 mm, 49 leg pairs, from Chichijima, Ogasawara, Japan, 18-I-1996, K. Ishii leg., coll. MB
M. silvestrii Bonato and Minelli, 2004: ♀, 50 mm, 49 leg pairs, from Kåthgodåm, India, 30-XI-1961, E.S. Ross & D.Q. Cavagnaro leg., coll. MB
M. sp. indet.: ♀, 47 mm, 51 leg pairs, from Abd al Kuri, Yemen, 17-18-II-1999, K. van Damme leg., coll. VD
M. spissus Wood, 1862: ♂, 42 mm, 45 leg pairs, from Necker, Hawaii Islands, VI-1923, E.H. Bryan leg., coll. BM
M. subgigas (Silvestri, 1919): ♀, 75 mm, 49 leg pairs, from Finschhafen, Papua New Guinea, 10-V-1944, E.S. Ross leg., coll. CAS
M. tahitiensis Wood, 1862: ♀, 48 mm, 47 leg pairs, from Puerto Princesa, Philippines, 4-II-1981, G.B. Osella & V. Cottarelli leg., coll. MVR
M. togensis (Cook, 1896): ♀, 36 mm, 49 leg pairs, from 56 km N of Matadi, Democratic Republic of the Congo, 28-VII-1957, E.S. Ross & R.E. Leech leg., coll. CAS
M. waikaneus Chamberlin, 1953: ♂, 23 mm, 49 leg pairs, from Hawaii, Hawaii Ids, 22-I-1974, J. Jacobi leg., coll. BM
M. cf. zygethus Chamberlin, 1939: ♀, 36 mm, 51 leg pairs, from Batu Lubang, Halmahera, Indonesia, 24-VII-1988, L. Deharveng & A. Bedos leg., coll. LD