Ricinoides atewa, Naskrecki, Piotr, 2008

Naskrecki, Piotr, 2008, A new ricinuleid of the genus Ricinoides Ewing (Arachnida, Ricinulei) from Ghana, Zootaxa 1698, pp. 57-64 : 58-63

Ricinoides atewa n. sp.

( Figures 1–13 , 20–25 , 27–28 )

Differential diagnosis. This species can be easily recognized by the combination of its large size (body length up to 11 mm in the male; see Table 1 ), the enlarged femur II and the presence of a short spur on tibia II in the male, a strongly elongated, thin and sickle-shaped apical lobe c of the tarsal process, and the presence of 6–7 genital sacks in the female. From R. afzelii (Thorell, 1892) it can be distinguished by the overall shape of the tarsal process, in particular the extreme elongation of the apical lobe c (lobe c much shorter and wider in R. afzelii ; figs. 14–17), the proportions of the lamina cyathiformis (lc) on tarsus III of the male (in R. atewa lc is about as long as the basal part of tarsomere 2 (tt2) and about twice as long as wide; in R. afzelii lc is about 0.8 times as long as the basal part of tt2 and lc is only about 1.6 times as long as wide), and the development of the tibia on leg II (the spur in R. afzelii is much larger, slightly longer than the width of the tibia, whereas in R. atewa the spur is only as long as half the width of the tibia). From R. feae (Hansen) it differs in its larger size, shorter and stouter palpal tibia, and the shape of the tarsal process, especially the size and shape of the lateral lobe (lb). It can be distinguished from all other African Ricinulei by its large size and the strong sexual dimorphism in the development of the leg II.

Description. Male. Body large for the genus, robust and stout ( Tables 1 and 2 ); legs relatively thick.

Prosoma. Cucullus about 1.5 times wider than long (fig. 3); anteromedian knob ( Legg 1978b) absent. Cephalothorax slightly wider than long, ratio width/length 1.1, dorsally with distinct median furrow and two oblique lateral depressions about half way back from front; no ocelli present; dorsal surface densely covered with rounded tubercles (density 34–39 tubercles/ 1 mm 2) (fig. 12); posterior margin of cephalothorax broadly rounded, with distinct, long furrow, parallel to posterior edge (fig. 1). Sternal region with coxa I not meeting tritosternum; coxa II longest, meeting coxa III along their posterior 3/4; coxa IV about as long as coxa III, but distinctly wider distally and directed posteriad (fig. 2). Ventral surface of coxae covered mostly with short navicular setae and few, scattered tubercles (greatest concentration of tubercles on posterior edge of coxa III).

Opisthosoma. About 1.4 times as long as wide, its margins nearly parallel (fig. 1). Tergites 11–13 large, rectangular; ratio of widths of median portions of tergites 11–13: 1/0.83/0.64; tergite 10 very wide and short, 1.8 times wider than tergite 13. Surface of tergites covered with tubercles similar in size and density to those on cephalothorax. Sternites 11–13 also covered with tubercles, their density slightly higher than on tergites (about 40 tubercles/ 1 mm 2); sternites 11–13 with pair of shallow depressions near anterior margin of sternite. Basal segment of telson (sternite 14) with small dorsal notch (fig. 13).

Appendages. Basal part of chelicera robust, nearly as thick as long (fig. 5); cheliceral fixed digit with 5 large, rounded denticles; proximal denticles about 1/3 size of distal denticles; movable cheliceral digit strongly sickle-shaped and with 8–9 shallow denticles (denticles appear to be worn off in older individuals), about 2.5 times as long as fixed digit; base of movable digit with 15–18 setae (setal formula 1+ 14 to 1 + 17; figs. 4–6). Palpal femur short and stout, distinctly bent, at base nearly twice as thick as at apex; ratio length/ maximum width 1.7; ventral surface of femur with distinct groove devoid of setae or tubercles. Palpal tibia long and straight, with parallel edges; ratio length/width 6.1 (length measured from base to tip of movable digit). Leg I short and stout; all podomeres densely covered with tubercles but relatively few setae (except for densely setose tarsus); femur without well developed dorsal groove; basitarsus grooved dorsally, tarsus consisting of single teleomere. Leg II greatly enlarged, robust; femur strongly thickened, nearly 3 times as thick as femur of legs III and IV, ratio length/maximum width 1.81 (figs. 1–2); not grooved dorsally. Tibia of leg II with large, internal tooth about half as long as tibia’s width (fig. 25). Basitarsus II and 3 basal teleomeres with distinct dorsal groove devoid of setae or tubercles. Leg III slender, with reproductive modifications of tarsus typical of all male Ricinulei ; femur grooved dorsally; lamina cyathiformis (lc) on 2nd tarsomere (tt2) about twice as long as wide, and about as long as basal portion of tt2 (fig. 24); 4th tarsomere (tt4) about twice as long as 3rd tarsomere (tt3). Tarsal process with large, wide, lateral lobe (lb); apical lobe c strongly developed, long and sickle-shaped when seen laterally (figs. 20–23); lobe c clearly extends beyond proximal edge of lamina cyathiformis even when tarsal process is folded (fig. 24). Leg IV slender, unmodified; femur, tibia, basitarsus and 4 basal teleomeres with distinct groove dorsally.

Female. Similar to male in size, but opisthosoma shorter and wider, ratio length/maximum width 1.3 (fig. 8). Legs not enlarged; leg I with distinct dorsal groove only on basitarsus; legs II–IV with distinct dorsal grooves on all podomeres except patella and terminal teleomeres. Anterior genital lip (sternite VIII) of genital opening 0.76 mm wide; posterior genital lip (sternite IX) 1.03 mm wide (fig. 10); posterior genital sacks (possibly functioning as spermathecae [ Legg 1976]) tubular, arranged in 2 groups on both sides of midline; each group with 6–7 sacks; outermost sacks longest, 130–150 µm long (fig. 11); accessory spermathecae (as) (as defined by Harvey [1984]) well developed, 340–350 µm long.

Coloration. General coloration of adult animals gray-brown, body often covered with soil and mud, obscuring underlying body coloration; freshly molted adults reddish; as in most Ricinulei , the larvae and nymphs are orange-red to red, with opisthosomal tergites darker than surrounding membrane (fig. 28).

Material examined. GHANA: Eastern Region, Atewa Range Forest Reserve, Asiakwa (6°15'43.9''N, 0°33'16.5”W), elev. 827 m, 8.XII.2007 (leg. P. Naskrecki, V. Awotwe-Pratt and N. Jengre) – holotype male ( AMNH), 1 male (paratype), 2 female (paratypes), 1 deutonymph, 2 tritonymphs ( MCZ, AMNH); same locality, 11–16.VI.2006 (leg. P. Naskrecki) – 1 female (paratype), 1 deutonymph, 1 tritonymph ( MCZ); Asiakwa, along main reserve road (6°15'.7''N, 0°33'53.7''W), elev. 817 m, 7–11.XII.2007 (leg. P. Naskrecki, V. Awotwe- Pratt and N. Jengre) – 4 males, 2 females (paratypes), 3 deutonymphs, 6 tritonymphs ( MCZ, AMNH); Ajenjua Bepo Forest Reserve (6°22'2.3''N, 1°1'58''W), elev. 300–330 m, 26–30.VIII.2006 (leg. P. Naskrecki) – 3 males, 4 females (paratypes), 1 protonymph, 1 deutonymph, 2 tritonymphs ( MCZ, AMNH).

Etymology. The specific epithet refers to the type locality of the new species, the Atewa Range Forest Reserve, one of the last remaining sites of the Upland Evergreen Forest in West Africa. The Atewa forests are threatened by mining, logging, and bushmeat hunting, and their preservation is vital for the survival of many species, including this new Ricinoides .

Natural history. Although searches were conducted in both the rainy and dry seasons, seasonality appeared to have no effect on the abundance of this species, perhaps because of the nearly constant high humidity of the soil in the closed canopy forest. Their abundance was relatively low, and a three-person team usually managed to collect only 2–3 individuals in an hour of searching. Their distribution in the forest appeared to be patchy, and restricted only to undisturbed, shady parts of the forest, with little or no undergrowth but well developed leaf litter. R. atewa shows a degree of association with termites, and individuals were often collected near termite colonies (mostly nasutitermites) and small colonies of ants. Nymphs were frequently encountered in old, abandoned mounds of Cubitermes sp., both in the soil under the nest and inside empty chambers of the nest. While such nests had no active termite colonies, small colonies of ants were always present there, providing a potential source of food for the ricinuleids. In captivity individuals of R. atewa were observed feeding both on nymphs and workers of termites, and larvae of ants. The density of individuals in abandoned termite mounds was usually high, reaching up to 8 individuals per nest (not all nymphal specimens were collected). However, only single individuals were found in individual chambers, whereas multiple individuals could be found sitting close together under logs and rocks (both nymphs and adults). While ricinuleids show nocturnal activity, on one occasion a single nymph was found during the day walking on the surface of leaf litter.

Figures

FIGURES 1 – 7. Ricinoides atewa sp. n. 1, male, dorsal view; 2, male, ventral view; 3, male cucullus, dorsal view; 4 – 6, female left chelicera, ventral, lateral, and dorsal views; 7, penis.

FIGURES 8 – 13. Ricinoides atewa sp. n.: 8, female, dorsal view; 9, ventral view; 10, female posterior genital lip, showing genital sacks (spermathecae), internal view; 11, close-up of female posterior genital lip, showing genital sacks (spermathecae) and accessory spermathecae (a. s.); 12, tubercles and navicular setae on opisthosomal tergite; 13, female telson.

FIGURES 20 – 25. R. atewa n. sp.: 20 – 23, tarsal process, frontal, lateral, posterior, and dorsal views; 24, male tarsus III, posterior view (bt – basitarsus; bp – basitarsal process; lc – lamina cyathiformis; tt 1 – tt 4 – tarsomeres); 25, male tibia III.

FIGURES 26 – 28. Ricinoides atewa sp. n. and habitat. 26, an old, abandoned mound of soil termites Cubitermes sp., a typical habitat of R. atewa in the Upland Evergreen Forest of Ghana; 27, female R. atewa; 28, tritonymph of R. atewa, note the reddish coloration typical of larval and nymphal stages of Ricinulei.

Tables

TABLE 1. Body measurements of R. atewa n. sp.

	Body	Cucullus width	Cephalothorax width	Cephalothorax length	Opisthosoma width	Opisthosoma length
Male	10.0–11.0	3.1	3.8	3.4	4.0–4.2	6.2–6.4
Female	9.7	3.1	3.6	3.2	4.5	6.1

TABLE 2. Leg measurements of R. atewa n. sp. (number above – male; number below – female).

	Basifemur	Femur	Patella	Tibia	Basitarsus	Tarsus
Palp	–	1.70 1.50	–	2.48 2.50	–	–
Leg I	–	2.39 2.15	1.54 1.51	1.93 1.89	2.13 1.96	0.83 0.81
Leg II	–	3.97 3.40	2.17 1.80	3.06 2.90	3.13 2.60	2.67 2.05
Leg III	1.24 1.06	2.93 2.45	1.62 1.50	2.01 1.89	1.40 1.78	2.51 1.51
Leg IV	0.95 1.00	2.90 2.73	1.62 1.28	2.06 1.96	1.85 1.80	1.86 1.74