Stylocellus Westwood, 1874
Schwendinger, Peter, Giribet, Gonzalo & Steiner, Helmut, 2004, A remarkable new cave-dwelling Stylocellus (Opiliones, Cyphophthalmi) from peninsular Malaysia, with a discussion on taxonomic characters in the family Stylocellidae, Journal of Natural History 38 (11), pp. 1421-1435: 1423-1434
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|Stylocellus Westwood, 1874|
Synonymy and diagnosis. See Giribet (2002).
Type species. Stylocellus sumatranus Westwood, 1874 .
Species account and distribution. Twenty-six valid species (including the new species described here) are known from peninsular Malaysia and from most large islands in the Malay Archipelago, i.e. Singapore, Sumatra, Borneo, Java, Sulawesi and the Philippine island of Palawan ( Shear, 1979, 1980; Giribet, 2000, 2002). Undescribed species were additionally found in Irian Jaya (the Indonesian part of New Guinea), in Thailand, and in the Riau and Lingga Archipelagos ( Indonesia; off the tip of the Malay Peninsula).
Types. Malaysia (peninsula), Perak, Gunung (~ Mount) Lanno, south of Ipoh : male holotype from Gua (~ cave) Gereja Hujan (04 ‡ 31.244’N, 101 ‡ 08.311’E), 9 November 2001, leg. H. Steiner ( MHNG 444 View Materials /01); seven paratypes: one female from Gua Gereja Hujan, 21 November 2001, leg. H. Steiner ( MHNG 357 View Materials /01-1); one female from Gua Kong Fook Ngam (04 ‡ 31.058’N, 101 ‡ 08.365’E), 8 November 2001, leg. J. Segl ( MHNG 346 View Materials /01); one male from Gua Angin (04 ‡ 30.994’N, 101 ‡ 08.431’E), 10 November 2001, leg. L. Price ( MHNG 477 View Materials /01); one male from Gua Monophyllaea (04 ‡ 31.303’N, 101 ‡ 08.587’E), 13 November 2001, leg. H. Steiner ( MCZ 44691 View Materials ) ; one female from Gua Gatsch (04 ‡ 31.216’N, 101 ‡ 09.204’E), leg. H. Steiner, 15 November 2001 ( MCZ 44692 View Materials ) ; two males from Gua Puncak (04 ‡ 31.536’N, 101 ‡ 09.000’E), 21 November 2001, leg. J. Segl ( MHNG 356 View Materials /01; MCZ 44693 View Materials ) .
Etymology. Latin adjective: globosus ~ globular, round. The specific epithet refers to the general body shape of the animal.
Diagnosis. Troglobiomorphic styllocellid with broad and strongly arched dorsal scutum ( figures 1–4 View FIGS View FIGS ), long and slender legs ( figures 12, 13 View FIGS ) and reduced eyes without cornea ( figure 10 View FIGS ). Similar to S. gryllospecus Shear , distinguished by: proximal article of chelicerae with ventral process (processus inferior exterior sensu Hansen and Sørensen, 1904; second ventral process sensu Giribet and Boyer, 2002) smaller than and anterior to the dorsal process; second cheliceral article almost completely ornamented between both joints ( figure 14 View FIGS ); adenostyle long and narrow, located distally on tarsus IV, at about two-thirds of tarsus length ( figure 21 View FIGS ); anal plate of male with a smooth longitudinal carina; distal margin of tergite VIII of male with an anal gland pore; tergite IX narrowing in the midline anterior to the anal gland pore ( figure 7 View FIGS ); penis with setal formula 3, 8, 8/8 (8/7); median ventral seta situated more distally than the other two ventral setae; dorsal setae not fused basally; lobus medialis with a smooth lateral process on each side ( figures 24–28 View FIGS ).
Description. Total length of male holotype (female paratype MHNG 346/01 in parentheses) 4.88 (5.10), width across ozophores 2.47 (2.44), greatest width 3.13 (3.18); length–width ratio 1.56 (1.60). Body dark reddish brown (in alcohol) with most of the dorsal surface and legs showing a tuberculate-granulate microstructure as illustrated for Siro exilis Hoffman, 1963 (see Murphree, 1988). Anterior margin of dorsal scutum without lateral projections; prosomal region trapezoidal. Eyes inconspicuous, visible as more or less distinct pale spots shining through the cuticle, variable in size [measuring 145 µm in maximum diameter (vertical) in the female examined with SEM], located anterior to the ozophores. Cornea absent, eye cuticle similar to the surrounding cuticle ( figure 10 View FIGS ). Ozophores conical, with a structure in the shape of protruding lips rising from inside the ozopore ( figure 9 View FIGS ). Transverse prosomal sulcus distinct but not conspicuous. Transverse opisthosomal sulci distinct in lacking granulation; middorsal, longitudinal opisthosomal sulcus absent. Dorsal scutum arched high like the carapace of a tortoise ( figures 1, 2 View FIGS ); its opisthosomal region fairly wide, reaching its maximum width at segment II.
Coxae of leg I movable, coxae of the remaining legs fused. Ventral prosomal complex of males ( figures 3 View FIGS , 5 View FIGS ) typical of stylocellids, with left and right coxae II and IV meeting in the midline, but coxae III not so; coxae IV partly separated along the posterior midline for a distance longer than the gonostome length. Pores of coxal glands clearly visible at inner corners of coxae III. Gonostome semicircular, wider than long. Lateral walls formed by elevated posteroproximal processes of leg coxae IV; these processes being smaller in the female. Gonostome posteriorly bordered by a well-developed, more or less rectangular first opisthosomal sternite forming a short genital operculum. Ventral prosomal complex of females ( figures 4 View FIGS , 6 View FIGS ) with only coxae II meeting in the midline; left and right coxae IV completely separated by the gonostome. The latter forming a
‘tube’ inclined at about 45 ‡ with regard to the surface of the animal.
Spiracles in the shape of a pronounced letter ‘C’ ( figures 1–4 View FIGS View FIGS ). Sternites VIII and IX and tergite IX free, not forming a complete corona analis ( figures 7, 8 View FIGS ). Anal gland pore (g.p.) present medially on the posterior margin of tergite VIII (situated on the ventral side of the body), measuring 37 µm in diameter. Tergite IX constricted in its middle portion next to the anal gland pore. Anal plate with a slightly elevated longitudinal carina (l.c.) free of any granulation ( figure 7 View FIGS ), the anal plate measuring 0.64X 0.40 in the male and female examined with SEM. Cuticle with granular surface in all ventral areas including coxae and anal plate (except for its carina).
Chelicerae ( figure 14 View FIGS ) relatively short and strong, furnished with numerous long setae. Proximal article with granular surface, carrying a transversal dorsal crest and
a single short ventral process equivalent to the anteroventral process of other stylocellids (e.g. Fangensis leclerci and Stylocellus ramblae Giribet, 2002 ). Second article fairly robust, almost completely ornamented with small granules between base and joint of distal article (movable finger). Proximal article of male paratype (female paratype in parentheses) 1.88 (1.85) long, 0.35 (0.49) wide, second article 2.05 (2.03) long, 0.37 (0.30) wide, movable finger 0.76 (0.79) long, 0.12 (0.22) wide, 37% (39%) of second article length. Dentition uniform and similar on both
cheliceral fingers, with about 15 denticles ( figure 15 View FIGS ).
Palps ( figures 11 View FIGS , 16, 17 View FIGS ) without a ventral process on trochanter. Length/width [length–width ratio in square brackets] of palpal articles from trochanter to tarsus of male holotype (of female paratype in parentheses): 0.67/0.18 [3.7] (0.67/0.22 [3.0]); 1.24/0.24 [5.2] (1.30/0.24 [5.4]); 0.75/0.20 [3.8] (0.75/0.24 [3.1]); 0.87/0.18 [4.8] (0.93/0.18 [5.2]); 0.89/0.16 [5.6] (0.95/0.18 [5.3]); total length 4.42 (4.60). Palpal claw 0.12 (0.14) long.
Legs ( figures 12, 13 View FIGS , 18–23 View FIGS ) with all claws smooth, long and hook-like, without dentition or lateral pegs. Surface of all articles, including the base and the dorsal surface of tarsus I, clearly ornamented with granules. Ventral side of tarsus I with a concentration of short sensory hairs occupying about three-quarters of the total tarsal length but not forming a distinct solea ( figure 18 View FIGS ). Tarsus I and II with a pronounced longitudinal dorsal groove (less distinctly developed on other tarsi) longer than half the tarsus ( figure 23 View FIGS ). Tarsus IV of male ( figure 21 View FIGS ) entire, carrying a short adenostyle tipped with a tuft of setae ( figure 22 View FIGS ); position of adenostyle at about 70% of the tarsal length; no ovoid plate or other cuticular structures discernible. Tarsus IV of female without modifications. Leg measurements, see table 1.
Penis ( figures 24–28 View FIGS ) short, typical of stylocellids. Setal formula 3, 8, 8/8 (7/ 8 in the second male dissected). Ventral side ornamented with tiny denticles along distolateral and distal margins. Three ventral setae set back from distal margin, their bases separated by about two to three times their diameter; the median seta situated anterior to the other two setae. Broadly rounded distal margin of penis with eight apical setae; their bases not ornamented with denticles ( figures 25, 26 View FIGS ). Dorsal side of penis with a group of eight (seven) long setae on each side; their bases not fused ( figure 24 View FIGS ). Gonopore complex ( figures 27, 28 View FIGS ) with lacinia dorsalis (l.d.) broadly rounded distally; lobuli laterales (l.l.) quite long and thick, densely set with short, acute fimbriae; lobus medialis (l.m.) carrying curved, pointed protuberances along its distal and distolateral margins, a pronounced pair of distolateral digiti (d.) reaching the apical margin of penis, and a pair of smooth, sausage-like proximolateral processes (l.p.).
Ovipositor ( figure 29 View FIG ) long, composed of two apical lobes and 43 circular articles, each of the latter furnished with eight equally long setae. Apical lobes carrying several setae (increasing in length towards the tip); a long subterminal seta (s.s.) rising from a small socket just below the terminal edge of each lobe. Sensitive processes (s.p.) carrying a group of about 8–10 bifurcate setae interspersed with unbranched setae. Receptacula seminis situated in an elongate chamber in the proximal two-thirds of each apical lobe, composed of long and winding tubes with a more strongly sclerotized scoop-shaped section close to the orifice.
Variation. Range of measurements: male, N ~ 5 (female, N ~ 3, in parentheses): dorsal scutum length 4.81–4.88 (5.06–5.12), width across ozophores 2.41–2.47 (2.35–2.41), maximal width 3.00–3.15 (3.06–3.18). Eyes are indiscernible in one male and one female, distinct in another male, discernible as small light spots in all other specimens. One female has all tarsal claws much shorter than in the other specimens examined, blunt and only slightly bent, presumably worn ( figure 23 View FIGS ). The area between the free sternites VII–IX may be more or less depressed ( figures 1, 2 View FIGS ), depending on whether the specimen is well-fed or not.
Apart from a minor variation in the number of dorsal setae (eight plus seven versus eight plus eight), there is no marked difference between both penes examined ( figures 24–28 View FIGS ).
Relationships. Stylocellus globosus n. sp. obviously belongs to the family Stylocellidae , although its relationships with other members of the family are not completely clear. The presence of anal glands suggests a relationship with Fangensis , as does the absence of an eye lens (the eyes are visible through the transparent cuticle). However, several species of small stylocellids from Thailand available to us also possess anal glands in males. The chelicerae of S. globosus n. sp. resemble those of S. silhavyi , of an undescribed Stylocellus sp. from Gunung Mulu (deposited in the James Cokendolpher collection), of Fangensis leclerci , and of three other undescribed stylocellids (at least two of them clearly belonging to Fangensis ) from Thailand in having a broad second segment. The granulation of this segment is extensive in all these species as well. The penis of S. globosus n. sp. is most similar to that of S. gryllospecus in that both species possess a gonopore complex with well-developed lobuli laterales, long digiti and pointed protuberances on lobus medialis (distally rounded, finger-like in all other Stylocellus spp. illustrated in the literature). This suggests a putative relationship between these seven species of mostly troglobiomorphic stylocellids. A modified anal region as present in the male of S. globosus n. sp. has not previously been described in the literature, but a re-examination of the male type specimen of Stylocellus sumatranus Westwood, 1874 has shown a similar modification, i.e. a smooth longitudinal stripe on the anal plate (presumably homologous with the carina of S. globosus n. sp.) and an anal pore on the posterior margin of tergite VIII. However, the body shape of S. globosus n. sp. does not correspond to any other stylocellids studied so far.
The uniqueness of S. globosus n. sp., due to the presence of anal glands, of a modified anal plate, of reduced eyes without cornea and of a distinctly rounded body, may be considered as a sufficient base for generic separation. However, as we doubt that the genera Miopsalis and Fangensis are truly distinct from Stylocellus ( S. globosus n. sp. may represent a link between the latter two genera), we prefer not to establish yet another monotypic new genus until further closely related species have been discovered and a robust phylogenetic hypothesis for the stylocellid genera is available.
Distribution and habitat. The new species is known from inside six caves (maximum interdistance 1.65 km) in Gunung Lanno ( figure 30 View FIG ), a limestone hill on the Malay Peninsula. No connections between these caves are known, but it is possible that a system of tiny interconnecting channels exists which would enable exchange of small arthropods.
Gua Gereja Hujan is a dry cave with a total length of 135 m, which consists basically of one large chamber without longer side passages. The single entrance is rather high up on the slope; the cave harbours a colony of insectivorous bats. Gua Kong Fook Ngam (also spelled Kwong Fook Nhan) is a maze of narrow tunnels and small chambers behind a Chinese temple of the same name. The temple was built in 1884 into the entrance chamber; the tunnels are currently enlarged and
equipped with electric lights to serve as a show cave. The total length of the cave is 792 m. Gua Angin is a cave of approximately 385 m, with two levels and two entrances. It is rich in invertebrates. Gua Monophyllaea has a total length of 569 m and consists mainly of a single room with one side passage. The single entrance is quite high up on the cliff face. The cave is inhabited by insectivorous bats; the skull of a Hipposideros diadema (Geoffroy, 1813) ( Chiroptera , Hipposideridae ) specimen was found there. Gua Gatsch is a tunnel of 517 m, previously used to pump water through an extension of the hill. It partly follows natural tunnels and cuts into some
larger chambers. Water in the cave is stagnant or only slowly moving, the bottom of the first half is covered with very soft and deep mud. Wider sections in the middle of the tunnel house a colony of insectivorous bats and an abundance of invertebrates. This is the only wet cave where Stylocellus globosus n. sp. was found. Gua Puncak is a natural cave of 1584 m length, parts of which have been mined for tin. It contains a foggy and dusty chamber, which is one of the largest in peninsular Malaysia. Two pools are present in the cave; its single entrance is on ground level. Further specimens were seen (but not collected) in two other caves in the same hill, i.e. Gua Kera Mati and Gua Tanah Merah.
The typical fauna of these caves consists of cave crickets of the genus Diestrammena ( Rhaphidophoridae ), millipedes [which probably belong to the genus Plusioglyphiulus ( Cambalopsidae )] and an assortment of Araneae, Coleoptera, Diptera and Hymenoptera. In the two caves with larger bat colonies, i.e. Gua Gereja Hujan and Gua Gatsch, larvae and adults of the tineid moth Tinea porphyropa Meyrick, 1893 were found.
The S. globosus n. sp. specimens examined were collected from the cave walls, bedrock and dry speleothem, in areas of permanent darkness, where they were seen slowly walking about in the open. They seem to be absent from the entrance areas and the twilight zones, and from caves with multiple entrances and several openings. A few specimens were covered with a fine dust of tiny calcium crystals, giving them a shiny, velvety appearance.
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