On Melchisedec, a New Genus of the Spider Family Oonopidae (Araneae, Dysderoidea)

ABSTRACT A new genus, Melchisedec, is established for two new Afrotropical species, M. thevenot (type species) and M. birni. These spiders are unique among oonopids in having a crest on the ventral pedicel sclerite, and in having very short, scepterlike setae on the distal metatarsi I and II. The male of M. thevenot has a long, inward-curved embolus-conductor complex and a sternal pouch. The embolus-conductor complex resembles that of the Australian genus Grymeus Harvey, but differs in important details. The genital system of the female is highly complex, and includes two uterine sclerites, two winglike lateral apodemes and a receptaculum with a globular appendix. The receptaculum is much larger than in most other Oonopidae and has an unusual, strongly folded surface.


INTRODUCTION
Oonopidae are very small (1-3 mm), haplogyne spiders that occur throughout the temperate and tropical regions of the world (Ubick, 2005). They are found in a wide variety of habitats, ranging from deserts and grasslands to mangroves and rain forests (e.g., Baehr et ah, 2010;Grismado, 2010). The majority are leaf-litter dwellers, but some are arboreal, while others live in caves (Fannes et al., 2008;Harvey and Edward, 2007).
Until relatively recently, the Oonopidae were considered to be a fairly small family How¬ ever, the Goblin Spider Planetary Biodiversity Inventory (PBI) project (http://research.amnh. org/oonopidae/index.php) has shown that oonopids are extremely diverse, in terms of both species richness and morphological disparity (e.g., Duperre, 2009, 2010). More than 2000 species are now estimated to exist worldwide (Ubick and Griswold, in press).
Recently, while sorting the oonopid collection of the Royal Museum for Central Africa (Tervuren), I discovered two species with a strangely modified pedicel. These species could not be assigned to any of the existing oonopid genera. Hence, a new genus, Melchisedec, is estab¬ lished to accommodate them. M. thevenot, the type species, is described and illustrated in detail, with particular attention being devoted to the pedicel sclerites and the internal female genitalia. Some comments on the morphology and affinities of Melchisedec are provided.

MATERIAL AND METHODS
Specimens were examined under a Zeiss KL 2500 stereomicroscope. The descriptions were generated automatically from the Species Descriptive Database of the PBI project. Habitus images were produced using a Leica MZ125 stereomicroscope, a DFC 500 camera and Leica Application Suite (LAS) software. Specimens were immersed in K-Y® brand jelly and a Z-stack of 15-20 images was generated. The Z-stack was subsequently merged into a single montaged image that was processed further in Adobe Photoshop. Montaged images also served as a basis for the drawings.
Measurements were taken from a lateral (tibia I length and diameter) or dorsal (other measure¬ ments) point of view. The width of the carapace and dorsal scutum was recorded at the widest point while their length was measured along the midline. Total length is the sum of carapace length and dorsal scutum length. Measurements are given in millimeters unless noted otherwise.
For SEM, specimens were dehydrated in 95% ethanol and hexamethyldisilazane (Brown, 1993;Nation, 1983) and mounted on a strip of copper tape itself fixed to an SEM stub. After sputter coating with gold for 70 seconds, the specimens were examined under a JEOL 6480 scanning electron microscope. Given the few available specimens of Melchisedec thevenot, a single female abdomen was used to study both the external morphology of the scuta and the internal genitalia.  (6), 20 pm (7, 8), 80 pm (9, 10). SIGMA P3292 Pancreatin, following Alvarez-Padilla and Hormiga (2008). After digestion, the ventral abdomen was rinsed in water and processed for SEM as described above. In order to examine less accessible internal structures, the ventral abdomen was repeatedly removed from the copper tape, dissected further with a small piece of razor blade and remounted. To study palpal morphology in detail, the right palp of the single male known was removed and prepared for SEM.  Harvey, 1987 (see Discussion); ECC terminology therefore largely follows Harvey (1987) and Burger (2010). Terminology of the female genitalia mostly follows Burger (2010). An exception is made for the sclerites in the walls of the uterus externus, which are here called the anterior and posterior uterine sclerite. NO  oval, wider than long, PME oval, longer than wide, PLE oval, longer than wide, posterior eye row recurved from above; ALE separated by less than their diameter, ALE-PLE separated by less than ALE radius, PME-PME touching or almost touching, PLE-PME separated by less than PME radius (figs. 3-5); just outside each ALE a medially projecting seta, no setae between ALE, between each PME and PLE a medially projecting seta (     Distribution: Known from Guinea-Bissau, Ivory Coast, Nigeria, Cameroon, and Ethio¬ pia ( fig. 1).
Note: The specimens from Guinea-Bissau, Ivory Coast, and Ethiopia are tentatively assigned to M. thevenot. These specimens, all females, strongly resemble the female holotype from Cameroon. However, given the large geographical distances involved ( fig. 1), it is possible that some of them do not belong to M. thevenot. The specific status of these specimens will remain uncertain until males have been collected from the same localities. in life, they are situated partly in the pedicel tube and partly in the anterior abdomen. The ventral pedicel sclerite covers the ventral and lateral sides of the pedicel (figs. 59, 62-67); ante-riorly the sclerite is fused to the prosoma. In none of the examined species did the ventral sclerite exhibit a crestlike elevation. In most oonopids, the ventral surface of the sclerite is rather featureless (e.g., Antoonops corbulo Fannes and Jocque,figs. 62,63). However, in some species the sclerite exhibits a ridge. For example, in the two Opopaea species that were exam¬ ined, a low but distinct ridge transverses the sclerite (figs. 64, 65). The members of an unde¬ scribed genus were also found to exhibit a ridge, but in this case the ridge is much more Immediately above the ropelike ridge there is a layer of closely packed papillae (Pa, fig. 72).
The papillae are almost perfectly round, with a diameter of approximately 5 pm, and are sepa¬ rated from each other by narrow cuticular ridges (figs. 72, 73). They lack mushroomlike caps, one of the most distinguishing features of papillae (Burger, 2010), but this could be an artifact of the digestion procedure. and could thus function as a stridulatory file. It may be argued that this is unlikely given the fact that the crest is as well developed in females as in males; usually, female spiders have either no or much-reduced stridulatory organs (e.g., Jocque, 2005;Maddison and Stratton, 1988).
Presumably, entelegyne spiders use these setae to monitor the distance between the coxae dur¬ ing locomotion (Barth, 2001;Eckweiler et al. 1989). The smooth setae observed in Melchisedec may serve a similar function.
The scepterlike setae are situated on the distal metatarsi of legs I and II (figs. 42, 43). They occur either as a single seta or as a closely spaced pair of setae ( fig. 43). Scepterlike setae have never been reported from other oonopids and may be unique to Melchisedec. Interestingly, some species of Grymeus have closely spaced pairs of densely barbed setae on their distal metatarsi I (Fannes, personal obs.); these paired setae may be homologous to the scepterlike setae of Melchisedec.
The aberrant morphology of the receptaculum raises many questions. Is the large size of the receptaculum an adaptation to allow for the storage of more sperm? If so, does this mean that females of Melchisedec store the ejaculate of more than one male? What is the functional significance of the folds? Do they simply add mechanical strength to the voluminous recep¬ taculum? Or do they allow the receptaculum to expand? To answer these and other questions, additional histological and ethological studies are needed.
Affinities of Melchisedec: Melchisedec may be closely related to the Australian genus Grymeus. The two genera have many features in common, including a large globular appendix (figs. 72, 77;Burger, 2010), a sternal pouch ( fig. 9; Harvey, 1987), a prominent conductor (figs. 48-50;Burger, 2010;Harvey, 1987), and a densely grooved embolus that ends in two equally long flanges (figs. 48-52;Burger, 2010;Harvey, 1987). Furthermore, both species of Melchisedec and at least some species of Grymeus have closely spaced pairs of setae on the distal metatarsi (see above). However, it must be noted that there are also many differences between the two genera. For example, in Melchisedec the embolus and conductor are positioned close together, especially basally ( fig. 48), whereas in Grymeus they are relatively well separated (see, e.g., Burger, 2010, fig. 7B). Also, in Melchisedec the conductor splits into a dorsal and a ventral branch (figs. 50, 52) while no such bifurcation is apparent in Grymeus (Burger, 2010;Harvey, 1987;Fannes, personal obs.).
Other possible relatives of Melchisedec are Gamasomorpha Karsch and Diblemma O.P.-Cambridge. Judging from the available drawings, these genera have genitalia similar to those of Melchisedec (e.g., Saaristo, 2001). Unfortunately, Gamasomorpha and Diblemma have not yet been studied by SEM, precluding any detailed comparison. The genera Silhouettella, Myrmopo¬ paea, and Lionneta may also be related to Melchisedec. As noted above, their female genital system is broadly similar to that of M. thevenot (Burger, 2007(Burger, , 2010Burger et al., 2006).
Members of the PBI project are currently revising the genera Grymeus, Gamasomorpha, and Silhouettella. The results of these studies will help to determine whether Melchisedec is related to these genera. que, Darrell Ubick, and an anonymous referee provided valuable comments on earlier draffs of this paper.