Ozopore

Abstract: The morphology of the scent glands of Trogulus tricarinatus (Linnaeus 1767) (Trogulidae), a small, soil-dwelling opilionid species, was investigated by means of serial histological semi thin-sections. The glands constitute paired prosomal glandular sacs that open to the body surface via one pore (ozopore) on either side of the body, dorsally adjacent to coxae I. Consistent with the generally recognized organization of scent glands in Opiliones, an anterior non-secretory region of the reservoir could be distinguished from a posterior secretory area, the latter characterized by a thick vacuolated epithelium. However, there are several unusual scent gland features in T. tricarinatus. First, the ozopores are hidden, with each being surrounded by a kind of external secretion atrium formed by a dorso-lateral integumental fold (dorsal limitation), coxa I (ventral limitation), and a wall of projecting cuticular papillae (outer lateral limitation). A horizontal slit (''secondary opening'') between the top of this wall and the dorsal integumental fold is externally visible. Secondly, no fluid, but solid spherical structures that may represent condensed secretion are found in the reservoirs. Thus, the secretion must pass through the external atrium before reaching the outside, perhaps as a gas produced by slow sublimation of solid secretion boli. Scent gland organization in T. tricarinatus, especially the findings of an external atrium around the ozopores, is not consistent with use in chemical defence, as is generally assumed for scent glands of Opiliones, but indicates a possibly non- defensive role.

Abstract: Arachnids of the order Opiliones (harvestmen), which includes around 6000 species, have a pair of scent glands that open at the sides of the body, producing substances used as defence. Several types of behavioural, morphological and chemical defensive mechanisms have been identified in the order as a whole, although some of these tactics were restricted to particular groups. Only around 60 species have been studied from this perspective so far, more than half of which belong to the largest harvestman family within the order Laniatores, the Gonyleptidae, and have only recently been studied in an evolutionary perspective, showing the usefulness of defensive characters in taxonomy and evolutionary biology. Within Laniatores, the Grassatores clade includes the Gonyleptidae and 20 additional families, mostly poorly or not previously studied. We describe the morphology of the structures involved in fluid displacement during chemical defence in 15 of these families (data on two additional families are available from the literature) and discuss the evolution of such traits based on an available phylogenetic hypothesis of relationships within Grassatores, using the representatives of Triaenonychidae (a non-Grassatores family of Laniatores) for comparison. We conclude that most non-gonyleptoid Grassatores share (maybe plesiomorphically) a series of characteristics, mostly strongly different from what is observed within the gonyleptoids, and that smaller groups seem to share diagnostic features related to chemical defence, as is the case of stygnids, cosmetids and triaenonychines, and especially of manaosbiids and cranaids, whose defensive morphologies largely resemble those of derived gonyleptids. The following main synapomorphies were detected: (a) Grassatores: the presence of a deep and well-defined descending channel; (b) Samooidea+Zalmoxoidea+Assamioidea+Gonyleptoidea: lateral pegs along the lateral channel; (c) Samooidea+Zalmoxoidea: deep channels forming an H on the dorsal scute; (d) Gonyleptoidea: ozopore cutting dorsally (reversing in Agoristenidae and Stygnidae to a laterally placed oval ozopore), a wide and smooth lateral channel, reversing to a lateral channel whose bottom is covered with either small plates (Agoristenidae) or high tubercles (Stygnidae), and apophyses of coxa II close to or covering the ozopore. Zusammenfassung Die etwa 6 000 Arten der Opiliones (Weberknechte) besitzen ein Paar Stinkdrusen, die sich an den beiden Korperseiten offnen und Sekrete zur Verteidigung abgeben. Verschiedene ethologische, morphologische und chemische Verteidigungsmechanismen sind in der gesamten Gruppe verbreitet, andere sind auf einzelne Teilgruppen beschrankt. Bisher sind unter diesen Gesichtspunkten nur etwa 60 Arten untersucht worden, von denen mehr als die Halfte zur grosten Familie innerhalb der Laniatores gehoren, den Gonyleptidae. Sie sind erst kurzlich studiert worden, um die Verwendbarkeit derartiger Schutzmechanismen fur Taxonomie und Evolutionsbiologie zu zeigen. Innerhalb der Laniatores enthalt der Kladus der Grassatores die Gonyleptidae und 20 weitere Familien, die zumeist nur wenig oder bisher uberhaupt noch nicht studiert wurden. Wir beschreiben die Morphologie der Strukturen, die in die Sekretabgabe bei der chemischen Verteidigung involviert sind, fur 15 dieser Familien (Daten von zwei weiteren Familien stammen aus der Literatur) und diskutieren ihre Evolution auf der Grundlage von vorhandenen Verwandtschaftshypothesen der Grassatores. Als Vergleich dienen Vertreter der Traenonychidae, einer nicht zu den Grassatores gehorenden Familie der Laniatores. Wir schliesen daraus, dass die meisten nicht-gonyleptoiden Grassatores eine Reihe von Merkmalen – vielleicht als Plesiomorphien – miteinander teilen. Sie unterscheiden sich meist stark von denen, die man bei den Gonyleptoiden findet. Kleinere Gruppen stimmen wohl in diagnostischen Abwehrstrukturen uberein, was fur die Stygniden, Cosmetiden und Triaenonychiden, besonders aber fur die Manaosbiiden und die Cranaiden zutrifft, deren Strukturen stark denen der abgeleiteten Gonyleptidae ahneln. Folgende Apomorphien wurden festgestellt: (a) Grassatores: tiefer, deutlicher Ausleitungskanal; (b) Samooidae + Zalmoxoidea + Assaioidea + Gonyleptoidea: seitliche Stifte entlang des seitlichen Kanals; (c) Samooidea + Zalmoxoidea: tiefe Kanale, die ein H auf dem dorsalen Scutum bilden; (d) Gonyleptoidea: dorsal eingelassener Drusenporus (dagegen ein lateraler ovaler Porus bei Agoristenidae und Stygnidae), ein breiter und glatter lateraler Kanal im Gegensatz zu einem Kanal, dessen Boden entweder mit kleinen Plattchen (Agoristidae) oder Hockern (Stygnidae) bedeckt ist, und Apophysen an der Coxa II, die nahe am Porus stehen oder diesen bedecken.

Abstract: Harvestmen have a pair of scent glands that open through ozopores. The literature suggests a link between the morphology of the ozopore area and the emission of a defensive secretion. A previous study on a species that aggregates in open areas, where individuals are probably more easily spotted by predators, showed that this defensive secretion causes conspecifics to flee. However, it is unknown whether this behavior occurs in species that aggregate in sheltered areas, where prey are harder to find. Herein, we describe the morphology of the ozopore area, the mode of emission of the defensive secretion, and its chemical composition in the harvestman Discocyrtus pectinifemur. We also tested if the defensive secretion is used as an alarm pheromone. We found that D. pectinifemur releases the defensive secretion in different ways, one of them being as a jet. Emission as a jet contrasts with that known for all congeners previously studied, and is in accord with the expected morphology of the ozopore. We found that the defensive secretion of D. pectinifemur does not function as an alarm pheromone. The composition of the defensive secretion, a mixture of quinones, is congruent with those already described for the clade that includes Discocyrtus. Our results support the link between the morphology of the scent glands area and the emission behavior of the defensive secretion, and they suggest that the alarm pheromone function in harvestmen may be dependent on ecological factors.

Abstract: Most species descriptions of harvestmen from Central America that belong to the suborder Eupnoi are based on characters such as total body length, relative size of leg segments, coloration of the body and legs, and armature of the eye mound and dorsal scutum. Characters based on reproductive morphology and microanatomical structures are generally absent from most taxonomic works. Not surprisingly, the taxonomy of these harvestmen from this region requires extensive revision. In an effort to identify novel characters, we used scanning electron microscopy to compare the morphology of somatic and reproductive structures of Prionostemma vittatum (Roewer, 1910), Metopilio niger (Goodnight and Goodnight, 1942), and Metopilio ornatipes (Banks, 1909). Specifically, we investigated the morphology of the ocularium, ozopore, dorsal scutum, genital plate, pedipalp, spiracular opening on tibia II, ovipositor, and penis. We compared the morphology of these Neotropical taxa with that of a temperate sclerosomatid species, Leiobunum formosum (Wood, 1870). In general, we observed interspecific variation in the surface texture of the cuticle and the distribution of setae on the body and appendages. Potentially informative characters include cuticular structures associated with the ocularium, anterior propeltidium, meso- and metapeltidium, dorsal scutum, genital plate, pedipalp, and penis. We also observed intersexual variation with respect to morphology of Spicer's tarsal organ and the claw of the pedipalp.