Corasoides Butler, 1929

Humphrey, Margaret, 2017, A Revision and Cladistic Analysis of the Genus Corasoides Butler (Araneae: Desidae) with Descriptions of Nine New Species, Records of the Australian Museum 69 (1), pp. 15-64 : 17-21

Genus Corasoides Butler, 1929

Corasoides Butler, 1929: 42 ; Neave, 1939: 833; Roewer, 1954: 61; Bonnet, 1956: 1925; Lehtinen, 1967: 225; Forster & Wilton, 1973: 128; Gray, 1981: 797; Main, 1982: 92; Brignoli, 1983: 467, 533; Davies, 1988: 70; Platnick, 1993: 541; Platnick, 1997: 609; Wheeler et al., 2016: 12, 27, 34, 35.

Type species. Corasoides australis Butler, 1929 , by monotypy.

The first inference to a spider of this genus appears to be Rainbow’s (1897) description of a web identified by him as belonging to Agelena labyrinthica, Clerck, 1757 (a European species). From his description, and from the locality given (Sydney, Guildford and Fairfield), it seems that he was referring to what we now call C. australis .

Rainbow’s account was noted by Butler (1929) who questioned Rainbow’s identification and the presence in New South Wales of A. labyrinthica . Butler proceeded to describe the monotypic genus Corasoides and its undescribed type species, Corasoides australis . The only review of Corasoides since that time has been that of Lehtinen (1967) in which he included a New Zealand species, Rubrius mandibularis Bryant, 1935 (later transferred to Mamoea ).

Family affiliations

Butler placed Corasoides in Agelenidae : Ageleninae, probably in part because of its platform web structure and its strong superficial resemblance to Agelena labyrinthica .

Corasoides remained in Agelenidae ( Roewer, 1954; Bonnet, 1956) until Lehtinen (1967) transferred it to the Amaurobiidae : Desinae. Lehtinen removed Corasoides from Agelenidae on account of the unpaired colulus, which is unpaired in all Amaurobiidae, sensu Lehtinen (with one unusual exception) but paired in Agelenidae . The main attribute of Lehtinen’s Amaurobiidae was the presence of a median apophysis in the male palp. Lehtinen acknowledged the absence of the median apophysis in Corasoides (and similarly so in Stiphidion and Porteria which he also placed in Desinae) but he regarded this as a secondary loss. Lehtinen saw a division of his Amaurobiidae into two depending upon the presence or absence of a secondary conductor. Classical characters based on spination, trichobothria, maxillae, eyes etc., he regarded as inconsequential and often associated with overall size ( Lehtinen, 1978). Those subfamilies lacking a secondary conductor included Desinae, Matachiinae and Stiphidiinae .

Forster & Wilton (1973) raised the subfamily Stiphidiinae Dalmas, 1917 to family status within the Amaurobioidea . They placed the New Zealand Cambridgea , Nanocambridgea and Ischalea in Stiphidiidae as well as the Australian Baiami , Procambridgea and Corasoides . Morphologically, Forster & Wilton (1973) restricted the Amaurobiidae to those taxa with a well-developed and strongly sclerotized median apophysis while Stiphidiidae they defined as possessing a simple median apophysis that showed a strong tendency to reduction and eventual loss as in Corasoides .

Stiphidiidae remained in the Amaurobioidea on account of the presence of the median apophysis (or its assumed secondary loss) and the weakly developed and unbranched tracheal system that is confined mainly to the abdomen (Forster & Wilton, 1973).

The position of Corasoides in Lehtinen’s Amaurobiidae , Desinae, is dependent upon the absence, as a secondary loss, of both the median apophysis and the secondary conductor in Corasoides . Members of Lehtinen’s Desinae show a trend towards reduction or loss of the median apophysis.

Griswold et al. (1999) showed that Amaurobiidae (sensu Lehtinen, 1967) is polyphyletic and several of his subfamilies, including Desinae, did not belong in the Amaurobiidae . This confirmed aspects of Forster & Wilton’s (1973) treatment of Lehtinen’s Amaurobiidae , including the raising of the Desinae to family status within the Dictynoidea. While they transferred many of the genera that Lehtinen had placed in the Amaurobiidae to their new family Desidae , based upon the branching structure of the tracheae, they excluded Corasoides . Corasoides cannot be placed in Forster & Wilton’s Desidae because of the absence of a well-developed and sclerotized median apophysis and its simple, unbranched tracheal system.

Forster & Wilton’s (1973) elevation of the Stiphidiinae to family status and the inclusion of Corasoides remained problematic. The colulus of Stiphidiidae is typically a large, hairy, flattened plate, suggesting recent reduction from a cribellum; the colulus of Corasoides (and Cambridgea ) has the form of a small, semicircular flap.

The Stiphidiidae are not adequately separated from the Agelenidae , especially since Forster & Wilton have included within the Agelenidae taxa with a single, undivided colulus and with unelongated posterior spinnerets. The only attribute setting Agelenidae (sensu Forster & Wilton, 1973) apart from other families is the absence of trichobothria on the cymbium. This attribute excludes Corasoides from Agelenidae .

Forster & Wilton (1973) admitted that the structure of the web was the most distinctive feature of the Stiphidiidae . They explained how it could easily have been transformed from the flat, cone-shaped web of Stiphidium (sic, misspelling of Stiphidion ) into the platforms of Cambridgea , Nanocambridgea , Procambridgea and other genera they placed in Stiphidiidae . However, this explanation is dependent upon the spider moving on the under surface of the web and Forster & Wilton mistakenly attributed this behaviour to Corasoides , which moves on the upper surface of the web. There is also an presumption that this is how Stiphidion use their web platform.

The importance of the tracheal system as a taxonomic indicator is also doubtful since it is not consistent even within the classification of Forster & Wilton. In addition, Lehtinen (1978) pointed out that Lamy’s (1902) work showed that the degree of tracheal branching could be dependent upon environmental adaptation, that is, tracheal ramification was often indicative of an active hunting life style.

This leaves no remaining argument from Forster & Wilton (1973) for including Corasoides in their Stiphidiidae . Gray (1981) also questioned the placement of Corasoides within Forster & Wilton’s Stiphidiidae .

Davies (1988) in her discussion of the family placement and relationships of Stiphidion , suggested removal of Ischalea (on account of the presence of lateral teeth on the epigyne and a well-developed median apophysis) and Procambridgea (on account of its marked trochanteral notches, proximal calamistrum and unusually reduced AME) from Stiphidiidae . She, however, retained Corasoides within the Stiphidiidae , along with Baiami , Cambridgea and Nanocambridgea and Stiphidion , as these share a reduced or absent median apophysis, an epigyne without lateral teeth, an extensive conductor and a spiniform embolus.

Wheeler et al. (2016), using results from phylogenetic analyses of markers from mitochondrial and nuclear genomes, transferred Corasoides from Stiphidiidae to Desidae . Similarly, the Australian Baiama and the closely related Cambridgea and Nanocambridgea from New Zealand (all of which run on the under surface of their web) were also transferred from Stipidiidae.

Porteria , retained in Desidae , is well supported as the sister group to Corasodes. Lehtinen(1967) first made the Australian/South American connection, linking Corasoides and Porteria in his Desinae on the basis of their similar abdominal pattern (although a similar pattern can also be found in some Dolomedes ), the absence of a median apophysis and the pattern of pyriform spigots on the anterior lateral spinnerets. Both Corasoides and Porteria also run on the upper surface of their web.

Wheeler’s support for Porteriinae, which contains the above mentioned five genera, was strong, although support for Desidae itself was weak. His Desidae is diverse, including genera both cribellate and ecribellate, with simple to complex tracheae and the spider’s running atop or below the web. Wheeler was inclined to raise the Porteriinae (and several other groupings) to family level but declined to do, so awaiting further study and the inclusion of more genera.

Diagnosis

Within Wheeler’s Porteriinae, Corasoides can be distinguished behaviourally from Nanocambridgea , Cambridgea and Baiami by its web structure and mode of moving on the upper surface of the platform. Morphologically Corasoides can be separated from these genera by the distinct abdominal pattern ( Figs 2a–g, 5a–c, 15d, 30a, 33a): pseudo-feathery hairs ( Fig. 3b, upper right); more retromarginal than promarginal cheliceral teeth; male palp with acutely bent and spine-like retrolateral tibial apophysis and a bristled retroventral apophysis.

Simon’s description of Porteria is inadequate and this genus is currently under study ( Merrill, 2014; unpublished thesis). Wheeler has described Corasoides as appearing as a giant version of Porteria . Until further details are available, Corasoides can be distinguished from Porteria by the presence in most species of three (sometimes two), rather than four tibial processes and the absence of notches on the trochanter.

Description

Small to large (carapace length 2.1–7.9 mm), ecribellate spiders.

Carapace. Longer than wide with discernible head area. Fovea long. Carapace cream to reddish tan to black, darker in head and cheliceral area. Carapace with little pattern or with a pattern consisting of a cream to light tan background with a medial, light brown or tan stripe from ocular quadrangle to pedicel. This is flanked on either side by a brown or tan region extending to the posterior of the carapace but excluding the petiole region and the carapace is bounded by dark edging. Maxillae long, distally enlarged and converging. Labium basally notched. Sternum as long or longer than wide, with distinct posterior point produced between coxae IV. Clypeus broad, often concave in male.

Abdomen. Ovate. Basic pattern, dorsum: central pale stripe or medial area, white/yellow dorsolateral stripes at least to anterior third of abdomen, two rows of white/yellow spots on black background between dorsolateral stripes and central stripe and decreasing in size posteriorly and with first two pairs prominent. In some specimens, the pattern may be less distinct and in some species may be reduced to a vague double row of pale spots on the dorsal surface ( Figs 2, 5, 15d, 30a, 33a). Venter pale, laterally with black striation.

Eyes. Anterior row eyes slightly procurved, posterior row more strongly procurved. AME largest and circular, other eyes slightly smaller and elliptical. All eyes hyaline, surrounded by dark pigment ( Fig. 6f). Tapetum in lateral eyes canoe- shaped.

Chelicerae. Robust and long, extending ventrally well below the level of the sternum. Distinct boss present in most species. Two pairs of prominent frontal bristles present and usually crossing each other in front of chelicerae ( Fig. 6d, 13d). Cheliceral retromargin with more teeth (5–8) than promargin (2–4). Cheliceral teeth may be variable within species ( Fig. 8a–j) and even from left to right in specimens ( Fig. 8f). Cheliceral groove with or without transverse ridges. Fangs with or without serrations.

Legs. Formula 1,4,2,3. Superior claws similar, strongly pectinate, inferior claw with 2–3 teeth. Single row of 4–8 trichobothria on tarsus, decreasing in length proximally. Tarsal organ simple, pyriform, sited apically beyond last trichobothrium. 4th metatarsus longest leg segment. First tibia often longer than 1st metatarsus. Trochanters unnotched.

Hairs. Hair types present include plumose, ciliate and “pseudofeathery”. Pseudofeathery hairs ( Fig.3b, upper right) differ from feathery hairs in having shorter tines which project from more than one plane.

Male palp. Cymbium with long digitiform portion at least twice and up to six times as long as the diameter of the palpal bulb. Single row of 2–7 trichobothria present ( Fig. 3a) decreasing in length proximally. Median apophysis absent. Conductor stalked or T-shaped. Conductor tip sclerotized, spine-like, twisted or bent. Both sides of the conductor may equally form the conductor tip or the ventral side may be dominant. Secondary conductor absent. Embolus long, curved and filiform, arising prolaterally to retrolaterally. Tibia with 2–3 apophyses. Retrolateral tibial apophysis spine-like, tapering, bent or curved. Ventral apophysis, when present, lobe, cup or leaf-like. Retroventral apophysis, when present, finger-like with long, terminal brush of curved bristles. Retrodorsal apophysis, when present, simple and sclerotized.

Epigyne. Strongly sclerotized, paired copulatory openings separated by scape with or without lateral extension. Spermathecae large. Insemination ducts weakly or strongly convoluted. Diverticula often present at junction with spermathecae. Epigynal atria may or may not be plugged. Appearance of external epigyne variable even within species ( Fig. 11a–l).

Spinnerets. Distinct overflow or tail region of small spigots prolaterally on anterior lateral spinnerets in most species ( Fig. 3b). Colulus single, flat, semi-circular, clothed in hairs.

Tracheal system. Four unbranched tubes, confined to the abdomen.

Web. Platform sheet web with labyrinth above and retreat to side through silken funnel, with or without a burrow ( Fig. 7h). Spider runs on top of sheet. Silk is ecribellate and nonsticky. Egg sacs with thick layer of soil or debris hung by thread of silk from roof of burrow. Males may or may not cohabit with penultimate females.