Cylichnogaster lawrencei Verhoeff 1937

Shear, William A., 2016, Redescription of the South African millipede Cylichnogaster lawrencei Verhoeff, 1937 and notes on the family Siphonotidae (Diplopoda, Polyzoniida), Zootaxa 4079 (1), pp. 119-128 : 120-125

Cylichnogaster lawrencei Verhoeff 1937

Figs. 1–12

C. lawrencei Verhoeff 1937a , 85; 1937b, 118. C. lawrencei, Schubart 1966 , 200.

C. lawrencei, Lawrence 1984 , 116–118. C. lawrencei, Hamer 1998 , 21.

Types. Fifty-eight male and female cotypes from Sir Drummond Chaplin’s estate, Noordhoek, Western Cape, South Africa (34.1°S, 18.367°E), collected May 1928 by E. L. Gill, deposited in the entomology collection of the Iziko Museum of South Africa (formerly the South African Museum), Cape Town, South Africa; examined 2015.

Verhoeff (1937b) gives the type locality as “…one of the valleys of the mountain slopes near Chapman’s Peak, Cape Peninsula.” I was not able to exactly locate the Drummond Chaplin estate, but Sir Drummond Chaplin was an important South African and Rhodesian official who owned property called De Gooede Hoop near Chapman’s Peak; this tallies with latitude and longitude data added at some later date to the locality labels. Verhoeff (1937b) implies that R. F. Lawrence, who transmitted the specimens to him, was the collector, but the labels with the specimens attribute the collection to E. L. Gill. Verhoeff also mentions three males and “numerous” females in the collection, but the cotype collection includes at least a dozen males. Some confusion is introduced in the German version of the species description ( Verhoeff 1937a) where the type locality is given as “… am Abhange des Tafelberges …(slope of Table Mountain).” Table Mountain is some 20 km NNE of Chapman’s Peak and curiously is closer to the locality of the newly collected specimens. However, the type locality proper should be considered as given on the the labels of the cotypes.

The new specimens (5 males, 9 females and several juveniles) on which the following redescription is based were collected in Kirstenbosch National Botanical Garden at Skeleton Gorge by Gonzalo Giribet on April 9, 2001. Skeleton Gorge is a part of Table Mountain National Park. A trail to the summit of Table Mountain follows the gorge, passing through moist indigenous forest. The specimens were collected by sifting leaf litter near the start of the trail. This site (S 33° 58’ 58", E 18° 25’ 28", elevation 214 m asl) is only about 13 km from the type locality near Chapman’s Peak.

Description of male from Skeleton Gorge, South Africa. Length, about 3 mm, greatest width 1.6 mm (measured dorsally across trunk ring 8). Color light creamy brown, faintly mottled darker; antennae heavily mottled dark purplish brown, eyes prominently black. Body ( Fig. 1 ) fusiform, tapering sharply to width of 0.8 mm at penultimate ring. Head (as in female, Fig. 3 ) triangular in frontal view, with two prominent, pigmented ocelli obliquely situated on either side, posterior ocellus the larger; two prominent setae between eyerows. Head transversely depressed between antennal sockets. Opening to preoral chamber small, nearly rectangular, between lateral elements of gnathochilarium (Figs, 6, 7). Plate of gnathochilarium truncated-quadrangular, lateral elements meeting anteriorly in midline, each with two prominent setae, numerous peg sensilla ( Fig. 7 ). Antennae about half again as long as head, stout, somewhat clavate; antennomeres 2–5 subequal in length, antennomere 5 widest, with small dorsoapical sensory area bearing two or more sensilla; antennomere 6 about twice as long as 5, also with few accessory sensilla. Antennomeres 7 and 8 much reduced, entirely withdrawn into 6, eighth with usual four sensory cones ( Fig. 4 ).

Trunk (Fig, 1) with 20 segments, including collum, and terminal segments (all 5 males in collection with 20 trunk segments). Collum hood-like, completely covering head in dorsal view of partially enrolled animal; head probably partially exposed in fully extended animal. Diplotergites increasing in width and length to tergite 8, then decreasing in width, but not length, to terminal segment (epiproct). Diplotergites with distinct lateral marginations, smoothly overlapping, posterior edges not raised. Ozopores beginning on tergite 5, distinctly rimmed, directed slightly posteriorly, distant from lateral margins of tergites. Terminal segment broadly rounded posteriorly, with four prominent long setae on posterior margin; forming complete ring around strongly margined, hemispherical anal valves ( Fig. 5 ). Sternites narrow, pair of long setae between coxae, coxae nearly touching in midline. Spiracles prominently rimmed, slightly raised. Pleurites 3–5 times wider than long, four prominent setae on laterodistal margin of each. Legs short, stout, prefemora and femora subequal, tarsus abruptly narrower than tibia, about equal to tibia in length. Claw prominent, curved, subtended by slightly sigmoid accessory claw 2–3 times its length. Eversible coxal glands begin on legpair 3.

Second legpair with coxae drawn out into long apophyses, vas deferentia open at their tips. Anterior gonopods ( Figs. 8, 9 ) with 7 podomeres, seventh podomere drawn out into long, sigmoidally curved spine, hollow with pore at tip ( Fig. 9 ). Posterior gonopods ( Figs. 8–10 ) with 7 podomeres; coxae separated by slightly more than their width; gonopods curve first mesally, then posteriorly. Seventh (terminal) podomere modified as tarsungulum, sharply curved ventrally, two or three setae on ventral surface with bases close together in large sockets. Ventrolaterally, seventh podomere with deep groove which receives terminal podomere of anterior gonopod.

Description of female from Skeleton Gorge, South Africa. Length, 3.3 mm, greatest width, 1.65 mm. Trunk ( Fig. 2 ) with 23 segments (all other females in collection with 21 or 22 segments). Other nonsexual characters as in male. Coxae of second legpair enlarged, extended posteriomesally. Cyphopods mesal to coxae, evidently with mesal valves only, lacking lateral valves and opercula; mesal valves with pair of setae ( Fig. 11 ).

Distribution. Now known from two localities in the Western Cape, about 13 km apart.

Notes. Comparisons with original description and cotypes. Verhoeff’s (1937b) English description of C. lawrencei was prepared with optical microscopes, while the description above is based on both optical and scanning electron micrography.

Presumably, Verhoeff (1937b) studied the 58 cotype specimens and gives the trunk segment numbers of both sexes as 20–26, with males from 3.75–5.0 mm in length, and females 3.75–5.25 mm. I was able to confirm those counts. The largest females in the cotype collection have 26 trunk segments; all the males, however, have 20. In the Giribet collection, all 4 males had 20 trunk segments and were close to 3.0 mm long, while 9 females were somewhat longer, but none more than 4.0 mm, with 21–23 trunk segments. I found it difficult to accurately count segments under a dissecting microscope at 60X, but with SEM the figures of 20 and 23 were verified for the specimens used. The length differences are due to the fact that the cotypes are inflated and extended by whatever manner of original preservation was used, while the new specimens have retained their live appearance. Verhoeff described the color as “dark brown,” in contrast to the light pigmentation of the new specimens, but the cotypes are now pale creamy white and largely transparent. Verhoeff counted 7 podomeres in both the anterior and posterior gonopods, as did I. Schubart (1966) clearly illustrates 6 podomeres in the anterior gonopods of C. nigricornis , but seems unclear about the posterior gonopods; 7 podomeres are illustrated on the right posterior gonopod and only 6 on the left. In very small animals, this character is hard to observe without at least removing the gonopods and mounting them on a slide for examination at high magnification with a compound microscope. The number of podomeres in the gonopods has been a contentious issue as regards its taxonomic significance in polyzoniidans. While Attems (1928) reported 7 podomeres in both pairs of gonopods of Burinia, Mauriès & Silva (1971) show no more than 5 in their detailed illustrations of Chilean species of Siphonotus . Yet Hoffman (1977) and Golovatch (2014) considered the Chilean species to belong to Burinia .

Cylichnogaster nigricornis . Cylichnogaster nigricornis Schubart, 1966 is almost certainly a distinct species, based on the gonopod illustrations published with the original description ( Schubart 1966). The type locality (Stormsrivierpiek, Eastern Cape) is 505 km east of the known localities for C. lawrencei , in quite a different climatic regime. The tarsungulum of the posterior gonopod of C. lawrencei has a broad, spatulate terminus, while that of C. nigricornis ends in a long, attenuate filament. The anterior gonopods of the two species are essentially the same, though in both anterior and posterior gonopods of C. nigricornis, Schubart illustrates fewer distinct podomeres than probably actually exist, likely due to the small size of the appendages and his use of an optical microscope to draw them. Cylichnogaster nigricornis is also described as larger (males from 3.5–4.0 mm long, females from 4.0– 4.5 mm long) and with more trunk segments (two males with 31 and 34, four females ranging from 29–33).

The smallest colobognathan? Cylichnogaster lawrencei might take the title of the smallest known colobognathan; its congener is similar in size, and two recently described species (both polyzoniidans) are challengers. Nepalozonium trimaculatum Shelley, 1996 was described from two males collected in Nepal that measured 3.7 and 4.3 mm long, with 22 and 27 trunk segments respectively. Octoglena claraqua Shelley, Richart & Bogan, 2010 is known only from the holotype male, taken in Idaho, USA; that specimen is 4.0 mm long with 28 trunk segments. However it must be kept in mind that colobognathans do not have fixed numbers of trunk segments and continue to molt and add segments after maturity at an early instar, thus individuals of C. nigricornis , N. trimaculatum and O. claraqua may represent young males which could have grown larger with time. In particular, all of the other species of Octoglena are larger and have more segments in the largest, and presumably oldest, specimens ( Shelley 1995).

Volvation. Golovatch (2003) reviewed volvation in the millipede order Polydesmida. As with the Colobognatha, only a small number of species of polydesmidans are capable of volvation. Due to the differences in the adaptations that make polydesmidan volvation possible , and the distribution of volvatory forms in several unrelated families, Golovatch concluded that the habit had evolved in parallel several times among them. The morphological changes allowing volvation were summarized as follows: small, cryptic species with relatively few body segments (a little more than 20 at the most), declined paraterga, at least one much enlarged postcollum tergite (often the second), reduced collum, relatively short legs with their bases close together, short antennae, and a reduced terminal segment. Golovatch also pointed to a few features that often, but not always, accompany volvation: mimetic coloration, hardened cuticle, and reduced ozopores.

Cylichnogaster lawrencei , while capable of volvation, has few of these adaptations. It is a small, cryptic species with a reduced number of segments. The tergites are highly arched, almost a half-circle in outline, and their lateral parts (similar to paranota in polydesmidans) are nearly vertical. But none of the postcollum tergites is conspicuously enlarged. Instead the trunk behind the collum broadens sharply to the sixth or seventh tergite, which in dorsal view is the widest; behind these tergites the trunk tapers sharply to a width of less than half that of the sixth tergite. The terminal segment is not reduced, but the legs are short and set close together. Compared to confamilial forms (Chilean specimens of Siphonotus ), the antennae are of the usual length. For the auxiliary features, mimetic coloration does not appear to be present and the ozopores are quite conspicuous.

The trunk segments of C. lawrencei , as with those of glomerid millipeds, are much longer dorsally than ventrally, since when volvated much more of the dorsal surface stands to be exposed, while the ventral surface is compressed. Ventrolaterally, the ventrodistal part of each tergite slides under the same part of the preceding tergite and head and antennae tuck in at about the ventral midpoint of the trunk, while the legs are drawn inward and hidden by the overlapping tergites. Thus, as Lawrence (1984) observed, the defensive behavior of C. lawrencei is intermediate between the spiral coil of larger colobognathans and true volvation.

A possible parasite . Unnoticed until the SEM photographs were taken was a segmental anomaly of tergite 10 in one of the newly collected female specimens. The anomaly seems due to an object protruding from between tergites 9 and 10, and possibly between the pleurite and tergite of diplosegment 10. The exact nature of this object ( Fig. 12 ) remains unclear but it appears to have arthropod setae, and may be a parasite.

Figures

FIGURES 1, 2. Cylichnogaster lawrencei. Fig. 1. Partially enrolled male with 20 trunk segments. Fig. 2. Partially extended female with 23 trunk segments.

FIGURES 3 – 5. Cylichnogaster lawrencei. Fig. 3. Head of female, frontoventral view. C, clypeus; co, collum; L, labrum; o, ocellus; P 2 – P 5, pleurites 1 – 5; numerals indicate antennal segments. Fig. 4. Tip of right antenna of the same specimen. 6, antennal segment 6; 7, antennal segment 7; d, antennal disc (segment 8) with sensory cones. Fig. 5. Terminal segment and anal valves of the same specimen, ventral view. av, anal valves; m, membranous region; ts 23, terminal segment (23).

FIGURES 6, 7. Cylichnogaster lawrencei. Fig. 6. Rostrum and gnathochilarium of female, frontal view. L, labrum; op, opening to preoral chamber; stg, stipes of gnathochilarium. Fig. 7. The same, ventral view. L, labrum; ll, laminae linguales; M, mentum; op, opening to preoral chamber; stg, stipes of gnathochilarium.

FIGURES 8 – 10. Cylichnogaster lawrencei, gonopods. Fig. 8. Posterior view. Fig. 9. Right gonopods, posterior view. Fig. 10. Same as Fig. 9, lateral view. Numerals indicate gonopodomere numbers; cx, coxa; tr, trochanter; pf, prefemur; f, femur; psf, postfemur; t, tibia; tu, tarsungulum.

FIGURES 11, 12. Cylichnogaster lawrencei. Fig. 11. Second leg coxae and female genitalia; cx 1, first coxa; cx 2, second coxa; cx 3, third coxa; m, mesal valve; o, opening of oviduct; s, spiracle. Fig. 12. Possible arthropod parasite on female shown in Fig. 2, numerals indicate trunk segment numbers.