Riotintobolus Wesener & Enghoff & Sierwald 2009, gen. n.

Riotintobolus Wesener, gen. n.

urn:lsid:zoobank.org:act: 2D3A99A5-E680-4E8D-BFD4-B10BD 240636 D

Type species: Riotintobolus mandenensis sp. n.

Other species included :

R. minutus sp. n.

R. aridus sp. n.

R. anomalus sp. n.

Diagnosis: only Malagasy Spirobolida genus where males in some species still have apodous rings in front of the telson. Body rings dorsally with a very wide stripe of flashy colour (Figs 24A, 40A), a unique feature, although slim stripes occur in several genera of Spirobolida. The posterior gonopods differ from other Spirobolida in the presence of a unique, finger-shaped process located laterally on the telopodite (Fig. 26M, x, y), and the presence of a large, very thin membrane located apically like a flag (Fig. 26M, z). Anal valves with extraordinary thick lips (absent in R. anomalus sp. n., Figs 26B, 27G), a unique character for this genus. Living specimens of Riotintobolus mandenensis sp. n. and R. minu- tus sp. n. often remain stiff like a stick instead of rolling into a spiral when disturbed, a unique behaviour for Spirobolida. Telson with a well-developed, sharp-edged preanal process (absent in R. anomalus sp. n., Figs 26B, 27G, 28A), a feature only shared with Pseudocentrobolus gen. n. and Granitobolus gen. n. Collum not greatly enlarged, similar to Spiromimus and other small-bodied genera of Spirobolida. Gnathochilarium with a subdivided mentum and a single sclerotized ledge on each stipites (Figs 26F, G, 27C), like in Flagellobolus, Pseudocentrobolus gen. n., Granitobolus gen. n., Caprobolus gen. n., Alluviobo- lus gen. n., Ostinobolus gen. n. Vulva simple, bivalve-like, similar to all other small-bodied genera of Spirobolida from Madagascar. Posterior plate apically overlapping anterior one. Anterior gonopods of a very general shape (Fig. 26K), similar to those of numerous other, probably not closely related genera, like Aphistogoniulus Silvestri, 1897 (Wesener et al. in press). Telopodite of posterior gonopod with a torsion: the sperm canal runs basally along the mesal margin, but is apically rotated, so that the opening is located at the lateral margin (Fig. 26M). A torsion also exists in Zehntnerobolus and Alluviobolus gen. n.

Distribution and ecology : two species, Riotintobolus mandenensis sp. n. and R. minutus sp. n. were collected in the littoral rainforest. The two other species occur in the spiny forest. R. aridus sp. n. was recorded from the spiny forest of Angavo, circa 20 km East of Antanimora, as well as Antafoky (Fig. 25), while R. anomalus sp. n. is recorded from the driest parts of Madagascar (Battistini 1972, Moat & Smith 2007), the Mahafaly plateau and the Cap Sainte Marie (Fig. 25). The genus Riotintobolus is the first example of a relationship between spiny forest and littoral rainforest species (Fig. 25). R. mandenensis sp. n. and R. minutus sp. n. are microendemic, R. mandenensis is most probably restricted to the littoral rainforest of Mandena, while R. minutus could only be found in Sainte Luce (Fig. 25). Both species from the littoral forest were collected inside the wet leaf litter, mainly on the bottom of the thin layer of leaves slightly above the root horizon. In both species the eyes are partly reduced, featuring only 12–20 fused ocelli (Figs 26A, C, 27E). Legs are also shorter than in the other two congeneric species (reaching only 0.7 times the diameter of body rings, Fig. 27D). No explanation can be given for the unique and highly unusual defence behaviour of R. mandenensis and R. minutus. Both species turn stiff and motionless like a stick and rarely curl into a spiral like most other species of the Spirobolida.

Description. Males: length up to 45 mm, diameter up to 4.3 mm. 38–45 podous and up to two additional apodous rings. Females: length up to 51 mm, diameter up to 4.6 mm. 39–45 podous and up to two additional apodous rings.

Colour highly species-specific, ventrally always with a distinct wide stripe, see species for accurate descriptions.

Head: each eye either with circa 28–34 (R. aridus and R. anomalus), or 12–20 (R. mandenensis and R. minutus) partly fused ocelli arranged in 3–5 vertical rows (Figs 26C, 27E). Labrum with standard three irregular teeth and a row of 10–12 stout marginal setae. Clypeus with two (rarely three) setiferous foveolae on each side (Fig. 26D). Antennae short or of medium length, reaching back to ring 2 or 5 (Figs 26A, 27B). Relative lengths of antennomeres: 1<<2>3=4=5<6 (Figs 26A, 28B, 29B). Terminal antennomere with four large sensory cones located together inside a membranous area. Antennomere 5 latero-apically with a field of four rows, antennomere 6 with a field of two rows of sensilla basiconica.

Gnathochilarium unusual (Fig. 26F). Lamellae linguales each with two standard setae located behind one another. Stipites each with three apical setae (Fig. 26F). Mentum basally subdivided by a wide suture (Figs 26G, 27C). Stipites each towards mentum with a large sclerotized ledge (Fig. 26G) Palpi of gnathochilarium with numerous sensilla. Hypopharyngeal crest with a field of spine-like structures. Central pads of endochilarium separated by a step into two levels, each carrying sensory cones, number of cones not counted.

Mandible: external tooth simple, rounded; mesal tooth with three shallow cusps (Fig. 26H). Four or five pectinate lamellae. Molar plate with few (five) transverse furrows, anterior two furrows enlarged, posterior furrows minute.

Collum: smooth, laterally not protruding as far as ring 2 (Fig. 26A).

Body rings: dorsally and laterally smooth, meso- and metazona ventrally with numerous transverse impressions. Ozopores starting at ring 6, touching suture between mesozona and metazona (Fig. 27B).

Telson: preanal process protruding, sharp-edged (except for R. anomalus sp. n.). Anal valves with well-visible lips and micropunctation (Fig. 26B). Deep groove present anteriorly to sharp-edged lips in R. mandenensis sp. n. and R. minutus sp. n. (Figs 26B, 27G).

Legs: coxae 1 and 2 elongated and fused with sternum, podomeres from prefemur to tarsus in both sexes each with 4–10 ventral/mesal setae. Length of midbody legs species-specific (Figs 27D, 28C, 29C). Each podomere with an apical ventral seta. Coxae 3 and beyond of cylindrical shape (Figs 28C, 29C). Tarsus with a stout dorso-apical seta and three pairs of ventral setae. Tibia short, half as long as tarsus (Figs 28C, 29C).

Male sexual characters: male legs in some species with tarsal pads. Male coxae 3–7 unmodified (Fig. 27F).

Anterior gonopods: median sternal projection triangular, broadly rounded (Fig. 26I). Sternite longer than coxite, but slightly shorter than mesal process of coxite (Fig. 26I). Process of coxite long, but shorter than telopodite (Fig. 26I). Telopodite always with a large, triangular retrorse process. Retrorse process laterally and apically extending beyond telopodite and coxite (Fig. 26K).

Posterior gonopods coxite and telopodite clearly separated (Figs 26J, M). Sternite sclerotized and well-visible (Fig. 26M). Coxite mesally with a single groove, coxite protruding into a short stem towards telopodite. Telopodite slightly shorter than coxite (Fig. 26M). Sperm canal discharging apically and laterally instead of mesally because of a torsion (Figs 26J, M). Telopodites laterally always with a fingershaped process (Fig. 26M, x, y), apically with a large, thin membrane (Fig. 26M, z). Width of membrane apically larger than basally. Sperm canal first running along inner margin of coxite and sternite, than apically running through the telopodite before discharging laterally on finger-shaped process and often also apically into thin membrane (Fig. 26M).

Female sexual characters: vulva simple, with a small, poorly sclerotized operculum at base, bivalve-like. Posterior valve apically overlapping anterior valve. Both valves smooth, lacking sensory cones. Towards opening basally on each valve with two or three rows of setae.

Etymology: Riotintobolus, masculine, refers to the mining company Rio Tintoº. Rio Tinto’s subsidiary, Qit Madgascar Minearlsº, now owns the littoral rainforests of Mandena and Sainte Luce (Vincelette et al. 2003). This encompasses all the remaining distribution area of Riotintobolus mandenensis sp. n., which only occurs in Mandena, and of R. minutus sp. n., a species only recorded from Sainte Luce. Conservation zones will be the only remaining natural habitat after a large-scale mining action is undertaken by Riotinto in the coming years (Ganzhorn et al. 2003, Bollen and Donati 2006). These conservation zones will be directly managed by Qit Madagascar Minerals in order to conserve the biodiversity of the forests. The proposed conservation zones are 160 ha (but divided by a swamp) for the littoral forest of Mandena, and Riotintobolus mandenensis sp. n. The conservation zone for R. minutus sp. n., the S9 fragment of Sainte Luce is circa 200 ha large. The area between both forests is already degraded to pseudosteppe (Fig. 24B). The conservation zones, at least of the Sainte Luce fragment, are still under human pressure (Fig. 24C). Since Rio Tintoº owns and is responsible for the only remaining habitat where two Riotintobolus gen. n. species exist, the whole genus is named after the company. The author hopes that this move will increase the probability of the survival of R. mandenensis sp. n. and R. minutus sp. n.