Phylogenetic placement of pelican spiders (Archaeidae, Araneae), with insight into evolution of the “neck” and predatory behaviours of the superfamily Palpimanoidea

Abstract

Phylogenetic relationships among archaeid spider lineages, as well as the placement of archaeids within the Araneomorphae, present a problem in the systematics of spiders. We investigate these relationships by broadly sampling taxa from the Araneomorphae and superfamily Palpimanoidea, as well as from extant and fossil archaeid lineages. Using parsimony and Bayesian methods we perform a total-evidence analysis that includes 126 morphological characters and over 4000 bases from one mitochondrial and three nuclear molecular markers. Phylogenetic analysis results in a delimitation of the superfamily Palpimanoidea to contain five families: Archaeidae, Mecysmaucheniidae, Stenochilidae, Palpimanidae and Huttoniidae. We also find the extant archaeids, which are restricted to the southern hemisphere, to be monophyletic, with the fossil archaeids paraphyletic. This phylogenetic framework is then used to interpret a novel morphological character, the highly modified and elevated cephalic area and elongated chelicerae (jaws), coupled with prey choice observations in the field and observations of chelicerae movements during predatory attacks. We conclude that the evolution of the elevated cephalic area, which reoriented the chelicerae muscles, led to highly manoeuvrable chelicerae and associated novel prey capture strategies. All members of Palpimanoidea appear to have modifications to the cephalic area, such as a diastema or sclerotization around the chelicerae bases, and furthermore, members appear to have evolved prey specialization.

Evolutionary morphology of the hemolymph vascular system of basal araneomorph spiders (Araneae: Araneomorphae)

“…Although the taxon sampling of basal araneomorphs (i.e. austrochiloids are not included) and Haplogynae is very limited, the results of Griswold et al (2005) and the recent analyses of palpimanoid spiders by Wood et al (2012), suggest that austrochiloids are more closely related to entelegyne spiders (Fig. 1C, dashed lines).…”

A review of the Madagascan pelican spiders of the genera Eriauchenius O. Pickard-Cambridge, 1881 and Madagascarchaea gen. n. (Araneae, Archaeidae)

“…Instead, they are active hunters and they have an unusual modification to their cephalic area that relates to their predatory behaviors: the carapace is extended and tubular in structure, and encircles the cheliceral bases, giving archaeids the appearance of a ‘‘neck’’ and “head”; the chelicerae are also greatly elongated. While most spiders are predatory generalists (Foelix 2011), archaeids are highly specialized and will only prey on other spiders (Legendre 1961; Millot 1948; Wood 2008; Wood et al 2012). The highly modified cephalic area in archaeids is used to employ a novel prey capture strategy that is unique among spiders (see fig.…”

“…The highly modified cephalic area in archaeids is used to employ a novel prey capture strategy that is unique among spiders (see fig. 1 in Wood et al 2007): the modified carapace allows for highly maneuverable and elongated chelicerae that can be extended 90° away from the body to attack spider prey at a distance (Forster and Platnick 1984; Wood et al 2012). There is a diversity of carapace shapes among archaeids, with ‘‘necks’’ of varying degrees of elongation, from long and constricted to short and stout.…”

The Morphology And Phylogeny Of Dionychan Spiders (Araneae: Araneomorphae)

“…COMMENTS: Thaida: the subtegulum-tegulum is a continuous sclerotized band (scored 0). Eriauchenius: embolus base not exposed; Wood et al (2012: fig. 9a) show dramatic distal expansion of the palpal bulb of Eriauchenius, exposing the embolus and other distal sclerites (scored ?).…”

“…Thaida: molts are very common in the field, never found one with genitalia (scored 1). Eriauchenius: immatures have a suture in the cheliceral diastema, to allow molting; the suture is missing in adult females (Wood et al, 2012: figs. 5a, f) (scored 1).…”