Amastigogonus Broelemann , 1913

Mesibov, Robert, 2017, Iulomorphid millipedes (Diplopoda, Spirostreptida, Iulomorphidae) of Tasmania, Australia, ZooKeys 652, pp. 1-36 : 4-7

Amastigogonus Broelemann, 1913

Amastigogonus Brölemann 1913: 152. Verhoeff 1924: 75, 84; 1932: 1732, 1737; 1944: 36, 41. Jeekel 1971: 107; 1981: 39; 2009: 35. Hoffman 1972: 204; 1980: 91. Mauriès 1987: 198. Mauriès et al. 2001: 585. Korsós and Johns 2009: 3. Edward and Harvey 2010: 5. Korsós and Read 2012: 44.

Euethogonus Chamberlin 1920: 166. Hoffman 1972: 204 (synonymised with Amastigogonus ); 1980: 91.

Type species.

Amastigogonus tasmanianus Brölemann, 1913, by original designation.

Other assigned species.

Amastigogonus danpicola sp. n., Amastigogonus elephas sp. n., Amastigogonus fossuliger Verhoeff, 1944, Amastigogonus hardyi (Chamberlin, 1920), Amastigogonus hellyeri sp. n., Amastigogonus michaelsae sp. n., Amastigogonus orientalis sp. n., Amastigogonus peninsulensis sp. n., Amastigogonus verreauxii (Gervais, 1847).

Diagnosis.

Like Victoriocambala Verhoeff, 1944 in having the coxite process on the anterior gonopod close to the telopodite and nearly as long, forming a chamber resembling a bird’s beak in which the pseudoflagellum is protected. Differences between Amastigogonus / Victoriocambala , as noted by Jeekel (2009: 35), are leg 1 with free/fused tibia and tarsus, posterior gonopod without/with reduced telopodite.

Description.

Living animals usually with black or dark grey rings with annular pale band at rear of each metazonite, often with a greenish tinge (live Amastigogonus fossuliger more consistently green, see species description); head, collum and telson often faintly reddish brown; legs pale. With long storage in alcohol and staining by defensive secretion, animals dull grey with faintly reddish legs.

Observed midbody diameter of larger males 2.5-4.2 mm, 55-71 podous rings. Head smooth, slightly convex, vertigial sulcus reaching to level of dorsalmost ocellar row. Ocellar area of larger males lenticular with ca 25-50 ocelli in 4-6 somewhat irregular horizontal rows. Antennae short, barely reaching past posterior edge of collum when manipulated dorsally; relative antennomere lengths (2=3)>6>(4=5); antennomere 6 widest; 4 apical cones; socket ca 1 socket diameter from lateral margin of head capsule. Gnathochilarium with lateral edges of mentum slightly convex, mentum about as wide as combined lingual plates; mentum-promentum junction slightly concave anteriorly; a prominent pit with small seta anteriorly on each gnathochilarial stipes. Collum convex, laterally narrowing with rounded corner, margins straight. Prozonites only slightly narrower than metazonites; suture weakly defined; fine longitudinal striae on lower portion of metazonite, anterior end of each stria (Fig. 3C; s) bent obliquely upwards towards suture (see Remarks, below); prozonites and metazonites with surface otherwise smooth, free of setae. Ozopores (Fig. 3C; o) small, round, beginning ring 6 at a little over 1/2 ring height, ring 6 ozopore distinctly lower than ring 7 ozopore; each ozopore at ca 1/3 the distance from suture to posterior metazonite margin, and usually absent from apodous rings. Limbus lamellar, undivided. Preanal ring smooth, epiproct broadly rounded, extending slightly over anal valves; hypoproct with slightly convex margin.

Legpair 1 separate on coxosternite, each leg 1 with 5 podomeres without setae, anteroposteriorly somewhat flattened; relative podomere lengths typically femur>tibia>(prefemur=postfemur)>tarsus, relative widths typically prefemur> femur>tibia>postfemur>tarsus (see Remarks, below); no claw. Small brushes of setae on legpair 1 coxosternite anterior to and between legs, and laterally on coxosternite corners. Leg 2 leg-like with large claw and reduced prefemur; penis arising basally on posterior coxal surface, barrel-shaped with a few long setae in apical crown. Leg 7 (and sometimes other legs near gonopod aperture; see Remarks, below) with elongated coxa (Fig. 2). Midbody legs short, ca 2/3 ring diameter when extended; relative podomere lengths prefemur>(femur=tarsus)>(postfemur=tibia). Most prefemora distally with conical prefemoral pad (Fig. 5A, B; pa); pads first appear on ring 8 legs and diminish in size posteriorly; pads small or absent on last 2-4 legpairs (see Remarks, below).

Posterior margin of gonopod aperture raised and thickened on either side, adjoining tips of retracted anterior gonopods. Anterior gonopods (Figs 3A, 3B, 3D, 3E, 6, 8) parallel, closely appressed. Anterior gonopod coxite (Figs 3A, B, D, E; cx) massive, rounded laterally, extending thin, finger-shaped process (Figs 3A, 3B, 3D, 3E, 6, 8; cxp) from anteromedial surface, process slightly concave laterally, thickened medially to ca 2/3 process height (coxite process more complex in Amastigogonus danpicola sp. n., see species description). Telopodite (Figs 3A, 3B, 3D, 3E, 6, 8; te) arising from wide, shallow recess on coxite, paralleling coxite process and slightly longer; thin and slightly concave medially; somewhat thickened distally from near posterior margin to midline near apex, the thickening usually with row of more or less evenly spaced, prominent setae on posterior side and sometimes a separate row or group of setae on anterior side. Posterior surface of telopodite produced basally as rounded flange. Pseudoflagellum (Figs 3C, 6, 8; ps) thinly lamellar, usually arising at ca 1/2 telopodite height, usually supported by setae on distomedial surface of telopodite. Prostatic groove (Figs 3C, 6, 8; pg) running anterodistally from posterobasal corner of telopodite under rounded flange to pseudoflagellum, following anterior side of pseudoflagellum and terminating at pseudoflagellum tip. Posterior gonopod (Fig. 3F) ca 1/3 height of anterior gonopod, subcylindrical with apical recess posterolaterally, a crown of short setae around recess and an arm-like cylindrical process with rounded apex arising at ca 1/2 gonopod height on posterolateral surface and directed distally. In situ, posterior gonopod grips base of anterior gonopod telopodite between arm-like process and body of posterior gonopod, the posterior gonopod apex pressed against prostatic groove: "The rudimentary posterior gonopods (Fig. 3H) appear to be attached like forceps to the wall at the very base of the caudomedian ridges of the anterior gonopods (Fig. 3E)" ( Mauriès, Golovatch and Hoffman 2001: 585).

Female slightly larger in diameter than male with same ring count; leg 1 normally leg-like, claw-bearing; no prefemoral pads on any legs.

Remarks.

Amastigogonus species are closely similar in size, general appearance and habits, and males can only be positively identified by close inspection, and usually dissection, of the anterior gonopods. There is also some variation in non-gonopodal male structures, as noted here and in the species descriptions. The most reliable of these differences are in cardo shape and modifications of near-aperture legs:

Cardo. In Amastigogonus danpicola sp. n. the cardo extends further ventrally in its posterior half than in its anterior half, i.e. the cardo is deeper posteriorly (Fig. 4A). In other Amastigogonus species the ventral edge of the cardo is either evenly convex or is deeper anteriorly (Fig. 4B).

Near-aperture legs. In all Amastigogonus species, leg 7 has an elongated coxa (Fig. 2A, B; arrow). Less elongated coxae are also found on legs 10 and 11 in Amastigogonus hellyeri sp. n. and on legs 6, 10 and 11 in Amastigogonus danpicola sp. n. (Fig. 2C).

Other differences between species do not seem to be large enough or consistent enough to be useful for taxonomic purposes:

Legpair 1. The relative lengths and widths of the leg 1 podomeres vary a little between species (Fig. 4 C–G), between individuals, and sometimes between right and left legs.

Prefemoral pads. There are differences between species in pad length, as shown in Fig. 5A and 5B (pa), but these differences are masked by the anteroposterior size gradient on single individuals as well as by variability from individual to individual.

Metazonal striae. The height reached by the horizontal striae on the metazonites diminishes slightly from anterior to posterior. At ca 2/3 body length, the topmost horizontal stria lies at ca 1/2 or ca 3/4 of the height to the ozopore (Fig. 5C; st), depending on species, but with considerable variation between rings and between individuals.