Gregory D. EDGECOMBE
Australian Museum, Sydney, Australia
HOMOLOGY OF CEPHALIC SUTURES IN CHILOPODA: THE ANTENNOCELLAR SUTURES OF SCUTIGEROMORPHA
Edgecombe, G.D., 2006. Homology of cephalic sutures in Chilopoda: the antennocellar sutures of Scutigeromorpha. – Tijdschrift voor Entomologie 149: 67-70, figs. 1-7. [issn 0040-7496]. Published 1 June 2006. The cephalic sutures of the centipede orders Lithobiomorpha and Craterostigmomorpha share a common 3-part structure: a transverse suture splits distally into anterior and posterior branches that have the same relationships to the antennal socket and eyes, respectively. Each of these components of the antennocellar sutures is present in the family Scutigerinidae, a group resolved basally in the order Scutigeromorpha based on other morphological characters. The transverse and antennocellar sutures are reinterpreted as general characters for Chilopoda rather than a putative synapomorphy of Lithobiomorpha and Craterostigmomorpha. Correspondence: Gregory D. Edgecombe, Australian Museum, 6 College Street, Sydney, NSW 2010, Australia; e-mail: [email protected] Keywords. – Chilopoda; Scutigeromorpha; Scutigerinidae; cephalic sutures
The striking difference in head morphology be- In lithobiomorphs, a transverse suture spans most of tween Notostigmophora (order Scutigeromorpha) the width of the head plate at about one-third of its and other centipedes complicates some homology length from the front. The transverse suture bifur- statements. The scutigeromorph head is domed, with cates distally into an anterior branch that runs to the the antennae inserting laterally, in contrast to the flat- antennal socket, terminating near to the dorsal articu- tened head with antennae originating frontally in all lar processes, and a posterior branch that runs to the other centipedes, the Pleurostigmophora. The eyes cephalic margin at the rear edge of the ocellus or ocelli and antennae provide essential landmarks for deter- (fig. 7). These anterior and posterior branches were mining homologies of the sutures on the dorsal side called the antennocellar suture by Crabill (1960). of the centipede head capsule or head plate. These A clearly homologous pattern of cephalic sutures is homologies have as yet been imprecisely determined observed in Craterostigmus, the sole member of the across the Chilopoda, principally due to ambigu- order Craterostigmomorpha. As noted by Dohle ity caused by the unique morphology of scutigero- (1990), the transverse suture across the anterior part morphs. of the head plate of Craterostigmus is shared with The cephalic sutures of Scutigeromorpha originate lithobiomorphs. The similarity extends to its distal at the posterolateral margin of the head capsule, run splitting into anterior and posterior branches with the along the inner margin of the compound eye, and same relationships to the antennal base and ocellus then extend anteromedially. In most scutigeromorphs (fig. 7), respectively, as seen in Lithobiomorpha. they terminate in a pair of slender anteriorly directed The antennocellar sutures are lacking in the phylac- projections on each side of a longitudinal median de- tometrian orders Scolopendromorpha and Geophilo- pression (figs. 1, 3). The projection is exceptionally morpha, which are generally regarded as sister taxa (e.g., in Thereuonema) short and triangular (fig. 2). in the clade Epimorpha. Some geophilomorphs have The posterior part of the two projections is connected a transverse suture, called a frontal line or frontal by a transverse suture. sulcus, which is reasonably homologised with the Lithobiomorpha is generally regarded as sister to transverse suture in Lithobiomorpha and Craterostig- all remaining Pleurostigmophora (Edgecombe & momorpha. The positional correspondence of these Giribet 2004 and many earlier morphological stud- sutures on the head plate is matched by a similar ies), the latter grouping being named Phylactometria. functional role of the sutures as ecdysial lines. In the
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lmd
ap
o t
1 2
3 4
lmd a a o
o
t
5 6
Figs. 1-6. Scanning electron micrographs of cephalic sutures in Scutigeromorpha. – 1-3, Scutigeridae; 4-6, Scutigerinidae. – 1, Ballonema gracilipes Verhoeff, 1904; 2, Thereuonema tuberculata (Wood, 1862); 3, Allothereua maculata (Newport, 1844). Detail of anterior projection; 4-6, Scutigerina sp. [Madagascar]. Scales 100 μm except 2, 200 μm, 3, 30 μm. Abbreviations: a, antennal branch of antennocellar suture; ap, anterior projection; lmd, longitudinal median depression; o, ocellar branch of antennocellar suture; t, transverse suture. geophilomorph Strigamia maritima, the ecdysial split been observed along the frontal suture in scutigero- follows the transverse suture (Lewis 1961). This is morphs (Demange 1948). likewise the case for ecdysial rupture in the lithobio- The configuration of head sutures described above morph Lithobius forficatus, with the split following for Scutigeromorpha is applicable to the families the transverse suture and ocellar branch of the anten- Scutigeridae and Pselliodidae, but a significant differ- nocellar suture (Demange 1944) or also extending ence is observed in members of the southern African- along the antennal branch of the antennocellar suture Malagasy family Scutigerinidae. This group consists (Lewis 1981: fig. 55). Ecdysial rupture has likewise of three species belonging to the genera Scutigerina
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Notostigmophora Pleurostigmophora
a ap a a t t o t t o
o o
Scutigerinidae Scutigeridae Lithobiomorpha Phylactometria + Pselliodidae
Fig. 7. Phylogenetic relationships of Chilopoda and homologies of the cephalic sutures. Abbreviations as in figs. 1-6. Ex- emplar species are Scutigerina sp. (Scutigerinidae), Parascutigera latericia (Scutigeridae), Lithobius curtipes (Lithobiomorpha: redrawn from Eason 1964) and Craterostigmus tasmanianus (Phylactometria: Craterostigmomorpha).
Silvestri, 1903, and Madagassophora Verhoeff,± 1936. orders have been grouped together by some workers Scutigerinidae have the posterior (ocellar) branch of (Attems 1928, Hoffman 1982). If Scutigeromorpha the cephalic sutures developed as in other scutigero- lacked these sutures, these characters could serve as morphs, and the transverse branch is clearly identifi- a potential synapomorphy for lithobiomorphs and able, a shallow V-shaped suture with its apex at the Craterostigmus. The interpretation advanced here in- longitudinal median depression (figs. 4-5). Rather stead posits that these sutures are plesiomorphic for than having anterior projections, an anterior suture Pleurostigmophora, inherited from a common ances- splits from the most anterior point of the transverse tor with Scutigeromorpha that possessed the sutures. suture. This anterior branch is slightly curved and gen- The basal chilopod had transverse and antennocellar tly divergent, then curves outwards more strongly in sutures; its anterior part, terminating a short distance from the 2) in retaining the antennal branch of the an- dorsal articular process of the antennal socket (fig. 6). tennocellar suture, Scutigerinidae possess a puta- The three components of the scutigerinid cephalic tive plesiomorphic state that is modified in other sutures can be identified as the homologues of the Scutigeromorpha. This implies that Scutigerinidae is transverse suture and the antennocellar suture of litho- sister to all other scutigeromorphs (Pselliodidae and biomorphs and Craterostigmus (fig. 7). The transverse Scutigeridae), a hypothesis that finds support from suture similarly splits distally into a posterior branch other morphological characters. Scutigerinidae lack that runs to the rear edge of the eye and an anterior particular spine bristles on the second maxillary telo- branch that extends towards the dorsal articular proc- podite that are shared by other scutigeromorphs, they ess of the antennal socket. have relatively pauci-segmented tarsi, they have rela- tively weak longitudinal ridges (carinae) on the legs, they lack the large unpaired spines that are associated Discussion with the spine bristles on the tergites of pselliodids The identification of the antennal branch of the and scutigerids, and the male gonopods of the second antennocellar suture in the scutigeromorph family genital segment are blunt cones rather than elongate Scutigerinidae carries two significant phylogenetic styles (Attems 1928, Lawrence 1960). Each of these implications: character states is presumed to be plesiomorphic in 1) the presence of transverse and antennocellar Scutigerinidae. sutures is not a shared derived character for Litho- The remaining scutigeromorphs share a modifi- biomorpha and Craterostigmomorpha. These two cation of the antennal branch of the antennocellar
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suture. It is uncertain whether the antennal branch Eason, E.H., 1964. Centipedes of the British Isles. is lost or is retained as a component of the anterior – Frederick Warne & Co., London. 294 pp. projection. In either case, the sutures do not have the Edgecombe, G.D. & G. Giribet, 2004. Adding mitochon- drial sequence data (16S rRNA and cytochrome c oxidase relationship to the antennal base that is seen in Scuti- subunit I) to the phylogeny of centipedes (Myriapoda, gerinidae. The disruption of the antennal branch is an Chilopoda): an analysis of morphology and four molecu- additional putative synapomorphy for Psellioididae + lar loci. – Journal of Zoological Systematics and Evolu- Scutigeridae. tionary Research 42: 89-134. Hoffman, R.L., 1982. Chilopoda. – In: S.P. Parker (ed.), Synopsis and classification of living organisms. References – McGraw Hill, New York: 681-688. Lawrence, R.F., 1960. Myriapodes: Chilopodes. – Faune de Attems, C., 1928. The Myriapoda of South Africa. – Annals Madagascar 12: 1-122. – Publications de l’Institute de of the South African Museum 26: 1-431. Recherche Scientifique, Tananarive-Tsimbazaza. Crabill, R.E., Jr., 1960. A new Nuevobius, with a review of Lewis, J.G.E., 1961. The life history and ecology of the litto- the genus (Chilopoda: Lithobiomorpha: Lithobiidae). ral centipede Strigamia (=Scolioplanes) maritima (Leach). – Bulletin of the Brooklyn Entomological Society 55: – Proceedings of the Zoological Society, London 137: 121-133. 221-247. Demange, J.-M., 1944. Quelques mots sur la mue de Litho- Lewis, J.G.E., 1981. The Biology of Centipedes. bius forficatus L. (Myriapodes Chilopodes). – Bulletin du – Cambridge University Press, Cambridge. 476 pp. Muséum National d’Histoire Naturelle, Paris, 2e Série 16: 235-237. Demange, J.-M., 1948. Notes sur la mue, l’autonomie et la regeneration chez un scutigère (Myriapodes-Chilopodes). – Bulletin du Muséum National d’Histoire Naturelle, Paris, 2e Série 20: 165-168. Dohle, W., 1990. Some observations on morphology and affinities of Craterostigmus tasmanianus (Chilopoda). – In: A. Minelli (ed.), Proceedings of the 7th International Received: 19 August 2005 Congress of Myriapodology. – E. J. Brill, Leiden: 69-79. Accepted: 6 February 2006
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