Mysmenidae COMPARATIVE
Creators: name: Lopardo, Lara
name: Hormiga, Gustavo
Publisher: name: Zenodo
Year: 2015
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Arachnida
Araneae
Mysmenidae

description: MYSMENIDAE COMPARATIVE MORPHOLOGY
Male palp (refer to characters 151–261)
The diversity and sclerite homologies of mysmenid male palps are only superficially understood. Mysmenidae have been recognized and even diagnosed by the generalized shape of the cymbium, described as ‘apically twisted and with lobes’ (Platnick & Shadab, 1978; Brignoli, 1980; Coddington, 1990; Wunderlich, 1995; Griswold et al., 1998; Schütt, 2003). Despite the fact that several relatively modern descriptions of mysmenids have included detailed illustrations of genitalic morphology (e.g. Kraus, 1967; Thaler, 1975, 1995; Saaristo, 1978; Baert & Maelfait, 1983; Baert, 1984a, 1990; Lin & Li, 2008; Miller et al., 2009), most mysmenid species remain poorly described. The details of the palp morphology are also insufficiently studied, especially in terms of explicit hypotheses of homology. For example, it has been suggested that a tegular conductor, median apophysis, and paracymbium are absent (Coddington, 1990; Griswold et al., 1998; Miller et al., 2009); however, a paracymbium had previously been identified in Mysmenidae (Kraus, 1967). The mysmenid male palp appears highly complex and morphologically variable, and in most species it is greatly translucent, so that the cymbium, conductor, and other sclerites are difficult to distinguish and to delineate precisely under light microscopy. In summary, mysmenid male palps have distinct cymbial structures, including a paracymbium, and can also have a tegular conductor. A median apophysis or any other tegular sclerites are lacking, however. As in the details of the different respiratory organs in Mysmenidae, the diversity of palpal structures is great within the family, although each particular arrangement seems characteristic at the genus or sometimes subfamily level (this is simply a consequence of how taxonomists have circumscribed higher taxa in Mysmenidae). In the sections below, we address the large diversity of mysmenid palpal morphology.
Palpal femur, patella and tibia
Mysmenids lack any modifications on the palpal femur and patella. Conversely, and across symphytognathoids, varying shapes of the male palpal tibia can be found. A distally broad tibia (i.e. wider distally, usually more than two times its basal width) may be symplesiomorphic for symphytognathoids, as it also occurs in Theridiidae. Distally broad tibiae occur in Theridiosomatidae, Synaphridae, and most Mysmenidae (Figs 4A, 17D, 28A, 30E, 32E, 38A, 42A, 47B, 63C). Within symphytognathoids, a flat tibia (i.e. flattened from the base, and usually with irregular, not circular, distal section outline) is synapomorphic for the clade comprising Symphytognathidae plus Anapidae (Figs 91F, 95C, D, 102C). Within Mysmenidae, broad male palpal tibiae are widespread, occurring in Trogloneta, Isela, and all Mysmeninae. Moreover, a cylindrical tibia (distal width similar to or less than two times proximal width) is synapomorphic for Maymena, and convergently present in Comaroma and Tasmanapis (Figs 10A, 81D, 98B,C). A globose tibia is a synapomorphy of Mysmenopsis (Figs 55A, C, 58A, 60A).
Most mysmenid palpal tibiae are small, shorter than cymbium, as in other symphytognathoids (Figs 10A, 27B, 30D, 47A, B, 63B, C, 71D, 106C, 110E). A large tibia is synapomorphic for Mysmenopsinae (Figs 1A, 4A, 55A, C). In addition, no distinct tibial processes occur in Mysmenidae, except for a prolateral extension in Mysmeniola (Fig. 134D; see also Thaler, 1995: figs 5, 7) and an apical ventral (sometimes ventroretrolateral) excavation usually bearing spurs in Mysmenopsis (Figs 53A, 58A, 60A). Mysmenopsines have modified setae distally on the tibiae, such as spurs in Mysmenopsis (as mentioned above, Figs 53E, 55H, 58E, 60B), or spine-like, strong setae in Isela (Figs 1A, B, 4A, E). Mysmenid tibial rim setae are longer than remaining tibial setae, and are arranged distally in one or two rows (Figs 4E, 10D, 18A, 32E, 36D, 42B, 45C, 53B, 55C), except in Trogloneta and a few other mysmenids where the setae are equally short and dispersed in an irregular conformation (Figs 63C, 66A).
Cymbium: general morphology
(see Fig. 126 for reference)
The size of the cymbium and bulb (relative to the size of the carapace, in lateral view) varies across mysmenid taxa. Although small male palps are common in adult spiders, medium-sized palps are widespread within symphytognathoids, including mysmenids (i.e. the cymbium-bulb complex is about half the size of the carapace; Figs 27F, 66A, 141K). The cymbium bulb becomes secondarily small (about one-fifth the size of the carapace) in Maymena mayana and mysmenopsines, however (Figs 2B, 140E, 141D). A very large cymbium-bulb complex (i.e. as large as the prosoma) has evolved independently in some distal clades within Microdipoena and Mysmena, including Mysmena leucoplagiata (Figs 19B, 142A), in Theridiosomatidae, and the synaphrid genus Cepheia. Superficially, there appears to be a tendency towards an increase in palpal size, which suggests a correlation with the reduction of body size in symphytognathoids; however, most symphytognathoids are equally minute in body size, regardless of their familial placement or size of the palp. For example, most Microdipoena species (and also theridiosomatids) with huge palps are as small as any other mysmenine or even larger than members of Symphytognathidae, which possess medium-sized palps. Taphiassa, a small micropholcommatine anapid, also has small palps.
The cymbium in most mysmenids is uniquely oriented ventrally or prolatero-ventrally in the palp (Figs 38A,B, 42B, 66A). The cymbium evolved independently to a prolateral position in Mysmenopsis, Mysmeniola, and the mysmenine MYSM-023-MAD (Fig. 50B), or to a retrolateral–dorsal position in some Maymena species (Fig. 15B).
In some symphytognathoids the cymbium is sometimes modified relative to the typical cymbium of most araneoids, which is scoop-shaped and round to oval in dorsal view (e.g. Griswold et al., 1998: figs 16A, 18F). This is especially so in mysmenids. Without taking into account any other cymbial structures (such as cymbial conductors, apophyses, paracymbia, expansions, etc.; see comments below), an oval cymbium is plesiomorphic in Mysmenidae (Figs 10A, 14A), and it has independently evolved in MYSM-005-ARG (Mysmena; Fig. 28B). A cymbium as long as wide occurs in mysmenopsines and independently in a clade comprising most mysmenines (Figs 1A, 4C, 22F, 30D, 41B, 55B), whereas a distinctly flat and tapering cymbium is unique to Trogloneta (Fig. 63C; convergent in some symphytognathids).
The cymbium of mysmenids is greatly modified when compared with other symphytognathoids. There seems to be a pattern of shared modifications, such as grooves, processes, and modified setae, which can be recognized in the cymbium (Fig. 126). Not all mysmenids have all the cymbial structures that we describe. Furthermore, different combinations of these features usually vary among (and are distinctive of) each genus. A summary of these cymbial features is presented below (refer to Fig. 126).
Primary and secondary cymbial conductors (CyC1 and CyC2): Up to two apical grooves, which seemingly interact with the distal portion of the embolus, can occur in mysmenid cymbia. Both structures are here considered cymbial conductors.
The ‘primary cymbial conductor’ (CyC1) is located internally (i.e. closer to the bulb; Figs 4G, 10C, G, 14A, B, D, 22C, 27A, 30F, 43C, 47C, 63B, C), and it can bear the cymbial fold (CyF, see below). This internal conductor is a synapomorphy of Mysmenidae, although it is secondarily absent in Mysmenopsis (Figs 53D, 60D). Usually, the CyC1 is pointed apically, which is the plesiomorphic condition in Mysmenidae (Figs 4G, 30F, 40B, 43C, 47C); however, the CyC1 evolved independently into different shapes. A ‘half-circle’ shaped conductor is characteristic of Trogloneta (Fig. 63B, C, F). A CyC1 consisting of prolateral, retrolateral, and apical projections occurs in the clade comprising Microdipoena and Mysmeniola, independently occurring in Mysmena (= Calomyspoena) santacruzi (Fig. 27A). A spiral cymbial conductor occurs in Microdipoena s.s. (Fig. 22C). In Maymena, the characteristic CyC1 comprises a particular apical cymbium that is bent over the ventral side (Fig. 10D, G).
The ‘secondary cymbial conductor’ (CyC2) is external, located on the edge or dorsally on the cymbium (e.g. Figs 30F, 31C, 43C). This external conductor is plesiomorphically absent in Trogloneta, Maymena mayana, and in most Mysmenopsis species (Fig. 63C). Within Mysmenidae, the CyC2 has evolved convergently in Maymena (excluding M. mayana), Isela, Mysmenopsis penai, and Mysmeninae (Figs 4G, 10G, 31C, 40A, 41D, 43C, 60D). The CyC2 has been secondarily lost in the clade comprising Microdipoena and MYSM-019-MAD (Fig. 22F).
Cymbial fold (CyF): The external cuticle of the cymbium is usually hirsute, the internal one is glabrous. Although the external cuticle can also cover the internal side of the cymbium, both cuticles are delimited by a well-defined border (e.g. Figs 86G, 102D). In some mysmenids the delimitation or border between external and internal cuticles (or cymbial areas) is rather clear, often corresponding to the outline of the cymbium; however, the internal cuticle on the tip of the cymbium bears setae (and can also bear the tarsal organ), and it frequently appears flattened against the outer cuticle. The internal cuticle can also be modified into a primary cymbial conductor. This suggests that the inner cymbium, at least apically, might be composed of part of the external cuticle. This condition is here referred to as a ‘fold’, and it is different from a twisted tip of the cymbium, where the same external cuticle is bent inwards, i.e. ventrally (compare with Figs 10G, 14B). The ‘cymbial fold’ is a synapomorphy of Mysmenidae (Figs 4G, 18E), secondarily and independently lost in Maymena mayana, Mysmenopsis, and Microdipoena (= Mysmenella) illectrix (Fig. 60D).
On the cymbial fold cuticle, a distinct row of setae can be present, usually associated with the primary cymbial conductor (CyFs). Fold setae arise independently in Isela, the clade comprising Brasilionata and Microdipoena, and in a large clade within Mysmena (Figs 4G, 43E). The row setae can be similar to the surrounding setae at the tip of the cymbium (Figs 40D, 43E), or can be distinctly minute (Figs 4G, 17A, 18E, 22C, 132A, D, 134A).
Cymbial tarsal organ (to): In most spiders, and basally in Mysmenidae, the tarsal organ is located externally on the cymbium (e.g. Figs 10I, J, 44D, 58C). An internal tarsal organ, located within the cymbial fold, optimizes as independently synapomorphic in Trogloneta, Isela, Mysmena- MYSM-015-MAD (Mysmena), and the mysmenine MYSM-020-MAD (Figs 4I, 40B, C, 63B, F).
Cymbial groove (CyG): A diagonal groove of varying depth can occur dorsally on the cymbium of some mysmenids (Fig. 126). The cymbial groove can be either a shallow and wide irregular depression (Figs 36E, 51A, B) or a narrow and deep furrow (Figs 18E, 22F, 28B, 30B, C, 45A, 134D). Besides the depth and width of this groove, its position and length appear to be correlated: apical grooves are always shorter than medial or basal grooves (Figs 36E, 45A). The latter are longer, extending sometimes into the prolateral basal expansion of the cymbium (Figs 18E, 22F, 28B, 30A, C; see below).
Cymbial process (CyP) (Kraus, 1967: ‘Kegeldorn des paracymbium’; Baert & Maelfait, 1983: ‘cymbial thorn’): In most mysmenids there is a process, often pointed, on the dorsal surface of the cymbium. The process is located often apically, retrolateral to the cymbial tip (Figs 1A, E, 4C, 40F, 51A, 63C, 133G, 134G, H), or basally and prolaterally, at the end of the cymbial groove (Figs 45A, 132D, E), or it can be located apically, but prolateral to the cymbial tip (Fig. 43C, D).
Paracymbium (PC): As in most araneoids (except Theridiidae), a retrolateral paracymbium is present in all symphytognathoid families, except for Anapidae (Figs 71F, 92A). Although the loss of the paracymbium is synapomorphic for Anapidae, it has secondarily evolved in Comaroma (Fig. 81B). Almost all mysmenids have a paracymbium; within this data set, it is secondarily absent in Maymena rica and Isela (Fig. 4D, E). Although in recent studies the paracymbium was considered to be absent in mysmenids (Coddington, 1990; Griswold et al., 1998; Miller et al., 2009), it had been previously reported as present by some authors (e.g. Kraus, 1967).
Our phylogenetic hypothesis suggests that the mysmenid paracymbium evolved from a basal hookshaped paracymbium into a characteristic shape and position (e.g. as in Mysmena tasmaniae, Fig. 51B). In mysmenids the paracymbium is flat and rounded, with a uniform transition to the cymbium, and it is located medially, not basally (i.e. as a medial flat extension of cymbial edge; Figs 18B, 22G, 27B, 30E, 32A, 36A, 45B, 63A). A flat, rounded paracymbium evolved independently as synapomorphic for Mysmenidae, but also in Iardinis mussardi and in Synaphris. The paracymbium becomes secondarily basal in Trogloneta (Fig. 63A), and secondarily hook-shaped in Mysmenopsis, where it is a thick (i.e. not flat), short distinct process, usually as long as wide (Figs 53D, 60D). Furthermore, in Mysmenopsis, the paracymbium is bent inwards and is seemingly interacting with a tegular groove located dorsally on the bulb (Figs 53F, 55F, 58D, 60D). The interaction is here considered tentative. The dorsal tegular groove does not appear to have a ‘conductor’ function related to the embolus, and the paracymbium– bulb interaction as a locking mechanism is not evident, as in the case of theridiids (Levi, 1961; Saaristo, 1978; Agnarsson, 2004; and references therein).
Prolateral basal expansion: This prolonged cuticle on the prolateral basal edge of the cymbium was originally observed in Theridiosomatidae, and has been termed the ‘prolateral basal paracymbium’ by Schütt (2003). The term ‘paracymbium’, however, has been proposed and long used for the classical araneoid retrolateral process on the cymbium (e.g. Comstock, 1910; Coddington, 1986b, 1990; Griswold et al., 1998; and references therein). Here, this prolateral structure is simply referred to as ‘prolateral basal expansion’. Furthermore, both the paracymbium and the prolateral basal expansion can co-occur in the palp of some species. Such conjunction refutes the homology statement among the two structures. The prolonged cuticle of the basal expansion surrounds the bulb ventrally in varying degrees and occurs in theridiosomatids and most mysmenids (Figs 4B, 27A, 30B, C, 36C, 47B, 66D), but is absent in Maymena and most mysmenopsines (Figs 10B, C, 55A).
Mysmenid bulb: general morphology
The median apophysis is absent in all mysmenids. In Trogloneta and independently in the clade comprising Brasilionata, Mysmeniola, and Microdipoena, a tegular groove housing the embolus can occur (Figs 27A, 63E, 66C; see below).
Embolus: The general shape of the embolus varies greatly within Mysmenidae, and no general pattern can be proposed. The embolus of mysmenids can be thin (or filiform) and coiled (Figs 47B, 134G), or thick (and flattened) and either coiled (Figs 4H, 27A, 36B, 131H, 132B, D, E), or straight (Figs 10E, 28D, 60F, 63B, E, 131A). Thick and straight emboli occur in Trogloneta, Maymena, and Mysmenopsis, whereas thick and coiled emboli occur in Microdipoena, Isela, and some Mysmena species. An apical switch in the coiling direction of the embolus is characteristic of the clade comprising Brasilionata and Microdipoena [secondarily absent in Microdipoena (= Anjouanella) comorensis] (Figs 18C, F, 27C, 132A–F). In addition, the embolus surface can be smooth (Figs 10H, 18F, 27C, 60F) or ridged (Figs 28C, 32G).
As in most symphytognathoids, the embolus of mysmenids is often long (i.e. much longer than the bulb, Figs 4A, 10E, 27A, 63E, 132E), usually tapering apically without further modifications (Figs 1D, 36B, 60F, 63B). Short emboli occur in Mysmenopsis (Figs 60F, 131A–C) and in Trogloneta granulum. In some Maymena, Trogloneta, and a few other mysmenids, distal modifications of the embolus can occur, such as a distal apophysis (Figs 10H, 18F) or a distal irregular membrane (Fig. 27A, C).
The embolic base can be simple, or it can be lobed and bearing an apophysis, as in Mysmenopsis and Trogloneta (Figs 55G, 60F, 63E, 66E, 131A). In Mysmeninae, the basal or medial embolic trajectory has a pars pendula (Comstock, 1910), a membrane that houses the spermatic duct before entering to the embolus (Figs 32H, 36B, 132C, E, F, 133C). Therefore, the spermatic duct enters the embolus not at its origin but further distally, meaning also that the embolus is actually longer than the embolic portion of the ejaculatory duct. Although found in other spider families (e.g. in some theridiids, linyphiids, cyatholipids, and agelenids), the pars pendula is an ambiguously optimized synapomorphy for Mysmeninae (ambiguously optimizes at its node because of missing information on the basal clade of this group), and it is secondarily absent in MYSM-005-ARG (Mysmena).
Tegular conductor: As in most symphytognathoids, most mysmenids have a conductor. Mysmenid conductor is distinctly voluminous and membranous, and originates subterminally from the tegulum, close to the embolic base (Figs 17A, 18D, 27A, B, 30E, 36C, 41D, 63B, D). This structure has been named ‘bulbal shield’ (e.g. Baert, 1984a; Schütt, 2003), and other than the embolus, it appears to be the only tegular sclerite. In mysmenids, the conductor often embraces and even covers the embolic base (Figs 41C, 43A, B). In some species there is a groove on the conductor surface housing the basal portion of the exposed embolus (Figs 36B, C, 47E); however, a groove housing the distal portion of embolus is absent in the tegular conductor of mysmenids, and the tip of the embolus is instead housed by one of the two conductors on the cymbium (see above). Within symphytognathoids, the occurrence of a tegular conductor is symplesiomorphic and widespread, with few independent losses of this sclerite occurring in anapids, symphytognathids, and mysmenids. Within Mysmenidae, the conductor is lost two times: in the clade that includes Maymena and Mysmenopsinae, and in Mysmena MYSM-005-ARG (Figs 4A, 10E, 28D).
Spermatic duct trajectory (SDT; refer to Fig. 127 and characters 220–228): As with most of the aforementioned palpal features, there does not seem to be a consistent pattern in the trajectory of the spermatic duct across the family, although there is some regularity within clades. The spermatic duct usually travels clockwise from the fundus (in left palp). If a switchback (SB) occurs, it alters this direction to travel counterclockwise. Usually, a counter-switch also occurs to return the duct trajectory to its original clockwise direction. Therefore, when SBs are present, they usually occur in pairs of switchbacks. The trajectory of the spermatic duct in Trogloneta differs from all other mysmenids in that the pair of switchbacks that occur before the spermatic duct completes one loop from the fundus (i.e. SB I and II, see Fig. 127) are absent, therefore the trajectory is completely spiralling or has one complete loop before the ‘second’ pair of switchbacks (SB III and IV) occurs (Fig. 131E, F). Although the general arrangement of the spermatic duct in all other mysmenid species examined in this study (except Trogloneta) is not necessarily similar among clades, all have the first pair of switchbacks on their trajectories (SB I and II; Figs 131I, 132B, D).
The position of switchback I (SB I) varies within Mysmenidae also. A distal SB I (apart from basal fundus, on the opposite area of the bulb) occurs in most mysmenines, most Maymena, and in Isela okuncana (Figs 131H, I, 132B, E, 133A, B, 134B, C). A basal SB I that does not reach the distal part of the bulb can occur in other mysmenines, however (Figs 133H, I, 134F– H); whereas in most mysmenopsines and Maymena mayana the SB I occurs close to the fundus, after the spermatic duct has reached the distal wall of the bulb (i.e. ‘beyond distal’; Fig. 131C, G, J).
In most mysmenids, the portions of spermatic duct forming the SB I are divergent, and SB II occurs relatively close to SB I (Figs 131B, H, J, 133A, B, 134D–G). In Microdipoena and most Mysmena species, the portions of spermatic duct comprising SB I run close to each other, and the SB II occurs close to the midpoint between SB I and the fundus, or even closer to the fundus (Figs 131I, 132B–D, 133D, E, 134A–C).
The plesiomorphic condition in Mysmenidae is to have two or more ascending loops in the last portion of the coiling reservoir before entering the embolus. This occurs basally within Mysmeninae (Figs 133D, E, 134E, H). Within the family, the number of loops decreases independently in distal clades (no loops or less than one entire loop, Figs 131B, E, H, I, 132F, 133A, B, 138C, G, 139E; or about one and one and a half loops, Figs 131D, 139C).
A pair of switchbacks (SB III and IV) can occur either after SB II, or if SB I and II are absent, after a complete loop of the spermatic duct (e.g. as in Symphytognatha picta; Fig. 139C). In this data set, an absence of pairs of extra switches (i.e. SB III and IV) is plesiomorphic for both symphytognathoids and Mysmenidae (Figs 131D, E, J, 133A, B, D, E, H, I, 134E). Switchbacks III and IV evolve independently in Microdipoena, Mysmena MYSM-007- MEX, Isela okuncana, and Trogloneta cantareira (Figs 131F, H, 132B–E). Furthermore, a distinct trajectory of the spermatic duct where several pairs of switchbacks occur evolved convergently in the mysmenines MYSM-020- MAD and MYSM-023-MAD (Figs 134F–H).
Epigynum (refer to characters 59–87)
Mysmenids are entelegyne spiders. That is, they have fertilization ducts leading from the spermathecae to the uterus externus and copulatory ducts connecting external openings to the spermathecae (e.g. Wiehle, 1967; Uhl, 2002). No comparative study of mysmenid female genitalia has ever been performed. In most female mysmenids, particularly mysmenines, the ducts and sometimes even the spermathecae are extremely membranous, almost invisible under light microscopy. A few authors describing mysmenid species have published detailed illustrations and have attempted to identify the different components of female genitalia in as much detail as possible (e.g. Kraus, 1967; Loksa, 1973; Thaler, 1975; Baert, 1984a, b, 1986, 1988; Snazell, 1986; Baert & Murphy, 1987). Given the membranous and almost undetectable nature of mysmenid female genitalia, the interpretation of these structures is often difficult. Furthermore, the great diversity of mysmenid female genitalic morphology (see below) makes diagnosis of the family a challenging task if only based on this system of characters. Our interpretations and homology statements of female genitalic structures are based on light and SEM microscopy data.
External genitalia
The epigynum, as a sclerotized modification of the cuticle, is absent in most of the members of the subfamily Mysmeninae. In addition, the copulatory openings are located within the epigastric furrow (i.e. the epigynal area containing the copulatory openings is hidden within it; Fig. 24A). This latter trait has convergently evolved in most anapids. All representatives of Mysmeninae here examined have a membranous atrium (Figs 59H, 129A, E, G, 130B). The atrium has been defined as a ‘widened cavity into the copulatory ducts’ (Sierwald, 1989: 2), and can occur independently of the location (external or internal) of the copulatory openings. In most mysmenids, however, the seemingly epigynal area located centrally between the copulatory openings (here regarded as the ‘dorsal plate’ sensu Millidge, 1984; ‘middle field’ on Sierwald, 1989) is projecting, i.e. it is exposed or protruding from the epigastric furrow (Figs 11B, C, 12D, E, 37C, 42C, 44A, 49D, 67A, B). The dorsal plate is secondarily internal (i.e. neither exposed nor projecting) in Mysmenopsinae, Maymena rica, Microdipoena, and few other mysmenines (e.g. Fig. 24B).
Trogloneta, Maymena, Mysmenopsinae, and the mysmenine MYSM-023-MAD have a modified copulatory area or epigynum in the form of a sclerotized plate or a protruding modification of the cuticle, usually bearing setae and the copulatory openings (Figs 5A, B, 11B, C, 12D, E, 49D, E, 59H, 61A, 67A, B, 140D, I, 141G, H, 142C). The copulatory openings are exposed caudally (i.e. posteriorly) in the epigynal area (Figs 49D, 59H, 61B). A sclerotized external atrium is present in a few Mysmenopsis species (e.g. Fig. 59H). On the other hand, in most Mysmeninae the epigynal area is weakly modified or even absent (i.e. the cuticle in this area is similar to surrounding abdominal cuticle), and it is usually translucent (spermathecae can be observed beneath it; Figs 14C, 37A, 52F, 141I). Although seemingly widespread among araneoids (Levi & Levi, 1962; Millidge, 1984; Scharff & Coddington, 1997; Griswold, 2001), the ventral scape of most mysmenines is unique within symphytognathoids (Figs 24B, 29C, 31G, 37C, 42C, 129E).
Internal genitalia
Copulatory ducts: Within Mysmenidae, the copulatory ducts show varying degrees of sclerotization and width. In Maymena and most Mysmenopsinae the copulatory ducts are short, relatively sclerotized, narrow, and of invariable diameter (Figs 11D, 37D, 128A, D, G, 129G). In Trogloneta the walls of the distal portion of the long copulatory ducts are rather smooth, relatively sclerotized, and uniform in diameter; however, the proximal portion of the ducts of Trogloneta is highly membranous and has a larger diameter than the distal part (Figs 64A, 128F). In the aforementioned taxa (i.e. Trogloneta, Maymena, and Mysmenopsinae), the trajectory of the copulatory ducts is in most cases recognizable. Conversely, the copulatory ducts of Mysmeninae differ from all other mysmenids (with the exception of a few taxa). The walls of the ducts are extremely membranous, imperceptible under light microscopy, and are of uneven diameter. These irregular membranous ducts follow a convoluted and long trajectory of unclear course. The ducts seem to extend ventrally and anteriorly to the spermathecae, although without a definite pattern (Figs 18G, 27D, 129A, C, E, H, 130B). In some species the ducts can be subtly more sclerotized and definite, and a coiled trajectory can be observed (Figs 37D, 129G). The increase in the diameter of the proximal portion of the copulatory ducts (i.e. the first half of the ducts from the copulatory openings) has been termed ‘bursae’ by Schütt (2003: character 77), although it is not clear from that study whether the increase in diameter refers to the copulatory ducts or to the membranous atrium (see above).
Within Mysmeninae, there is a particular turn occurring proximally in the convoluted and membranous copulatory ducts, seemingly originating close to the internal atrium, but immediately before becoming widened and convoluted. This duct turn is characterized by a subtle but consistent sclerotization. This feature occurs in Microdipoena, and also evolved independently in two clades within Mysmena and in MYSM-029-MAD (Figs 129A, B, 130A).
A convoluted trajectory of the copulatory ducts characterizes Mysmenidae, although the ducts can vary greatly in terms of sclerotization and diameter. Straight ducts evolved independently twice: once in the clade comprising Maymena and Mysmenopsinae and once in Mysmena MYSM-034-MAD. Although rare in the current mysmenid taxon sample, coiled and more distinct copulatory ducts of mysmenines (as in Figs 37D, 129G) appear to be more common than represented here (e.g. Lopardo, Dupérré & Paquin, 2008; Miller et al., 2009; L. Lopardo, A. Janzen, C. Griswold & P. Michalik, unpubl. data). These distinct ducts might represent a plesiomorphic but intermediate condition (i.e. between sclerotized and fully membranous ducts) in the evolution of convoluted and highly membranous copulatory ducts, and might help in elucidating our current interpretation of their trajectory, as well as their identification.
Spermathecae and accessory glands: Most mysmenids have one sperm-storage compartment in each spermatheca (e.g. Fig. 33A). Trogloneta and some anapids have two pairs of compartments in each spermatheca (Fig. 128F). The spermathecae are usually defined by a thick sclerotized wall (Figs 129A, 130B), although exceptions occur (e.g. in mysmenine MYSM-023-MAD and a few anapids; Figs 49A, 130D).
Ovoid spermathecae are plesiomorphic for both symphytognathoids and Mysmenidae. Nevertheless, the diversity of spermathecal shapes within Mysmenidae is immense, seemingly following no particular phylogenetic pattern, not even at the genus level. Spermathecae can be ovoid (Figs 11D, 18G, 37D, 128D, 129A, G), C- or cup-shaped (Figs 27D,E, 42D, 128E, 130C), coiled within the same spermathecal structure (Figs 33A, B, 51D, 129C, 130B, G), tubuliform (as one large tube, sometimes like tracheoles; Figs 5D, 49A, 128A, C, 130D), clavate (Figs 12C, 128B), or even irregular (although consistent within each species), where no particular shape can be defined (Fig. 129D).
An additional paired structure occurs in the internal genitalia of Trogloneta, the mysmenine MYSM-029-MAD, Mysmena MYSM-005-ARG, Microdipoena, and the anapid Tasmanapis. This structure resembles either an apodeme or a glandular structure, and appears related to the copulatory ducts or the spermathecae (Figs 22B, 27D, 29A, 64A, 129B, E, H, 130A, F). It is better observed by SEM, although it can be distinguished in transparent preparations of the vulva by a higher degree of sclerotization, comparable with that of the spermathecae (Figs 129B, E, H, 130A, F; see also Brescovit & Lopardo, 2008: fig. 6C– E). Whether these structures are functional glands, muscle attachment points, or perform other functions remains unknown. They are regarded here as accessory glands.
Fertilization ducts: The morphology of fertilization ducts is also variable within the family. Fertilization ducts were identified in Mysmenidae by discerning the ducts connected to and from the spermathecae, and, with the help of SEM, an attempt was made to follow the trajectory of these ducts. Usually fertilization ducts are located either dorsal to or on the central internal lateral side of the spermathecae. As a convention, when the genital system was mainly composed by membranes, highly developed and convoluted copulatory ducts were first identified, and then fertilization ducts were distinguished by elimination. The degree of sclerotization of the fertilization ducts appears highly homoplastic. Weakly sclerotized fertilization ducts with a distinguishable wall are plesiomorphic for Mysmenidae (although ambiguously optimized), and occur in Isela, mysmenine MYSM-023-MAD, and most Mysmena (Figs 42D, 49A, 128A, 129G); however, membranous, translucent, and almost imperceptible fertilization ducts also occur within the family, in Trogloneta, most Mysmenopsis, and all members of Microdipoena (Figs 18G, 27D, 51D, 60H, 64A, 128F, 136D).
Small, short fertilization ducts providing a direct connection between the spermathecae and the uterus externus (usually in straight fashion and unmodified) are plesiomorphic and widespread within Mysmenidae (Figs 42D, 49A, 64A, 128A, F). Large, long fertilization ducts, most often longer than the size of the spermathecae, might be provided with modifications or expansions (Figs 11D, 18G, 27D, 51D, 60H, 92F, 129G, 136D). They occur independently in most Maymena, most Mysmenopsis, most species of Microdipoena, and few Mysmena.
Spinneret silk gland spigot morphology (refer to characters 304–340)
The spinning organs of Mysmenidae have been described for a few species, including the kleptoparasitic Isela okuncana (Griswold, 1985), an undescribed Isela from Cameroon, Mysmenopsis penai, the Australian Mysmena tasmaniae and M. leichhardti (Lopardo & Michalik, 2013) and Maymena mayana (Griswold et al., 1998). Recently, the gland spigot patterns of Trogloneta cantareira (Brescovit & Lopardo, 2008) and several Chinese mysmenids (Mysmena, Gaoligonga, Chanea, and Maymena, Miller et al., 2009) were also described. The data in the aforementioned works suggest that mysmenids have the typical symphytognathoid and higher araneoid silk gland spigot conformation on the anterior lateral and the posterior median spinnerets (ALS and PMS, respectively): few ALS piriform gland spigots, few aciniform gland spigots on posterior (median and lateral) spinnerets, a furrow between major ampullate and piriform fields, and reduced piriform bases. In this study we examined in detail the spinneret gland spigot conformation of 30 mysmenid species. In the following section, the general arrangement of mysmenid spinneret gland spigots is described. Exceptions, singular features, and synapomorphies for the main mysmenid clades are noted below. See Appendix 2 for an explanation of cuticular textures.
In general, the colulus is fleshy and usually relatively large, bearing three or less setae (Figs 24E, 33C, 56D, 59I). On the anterior lateral spinnerets, a glabrous tuberculate intersegmental cuticle occurs (Figs 6A, 16B, 23A, C, 33F, 52B, 61C). The major ampullate gland spigot is accompanied by a nubbin and a tartipore (Figs 6B, 23A, C, 61C). The base of the piriform gland spigots is reduced (Figs 6B, 52B, 61C), and the cuticle surrounding those piriform gland spigots can be either fingerprint (in Mysmeninae and most Mysmenopsinae) or rugose (in Maymena, Trogloneta, and the Isela representative Kilifina- MYSM-002- KENYA; Fig. 6B). Two aciniform, one posterior minor ampullate, and (in females) one cylindrical gland spigot occur on the posterior median spinnerets (Figs 11F, 33D, 58F). The minor ampullate can be accompanied by a tartipore, a tartipore plus a nubbin, or by none of these. The posterior lateral spinnerets bear two cylindrical gland spigots, where both (Figs 11G, H, 13F, 67D) or only the posterior spigot is peripheral to the spinning field (the anterior spigot on the edge of the field; Figs 23B, 37B, 58H), and some aciniform gland spigots. The triad (the assemblage of one flagelliform and two aggregate gland spigots producing sticky silk in araneoids) is present in most female mysmenids (Figs 11G, 23B, 37B, 52C, 67D), as is usually the case in Araneoidea. Some exceptions occur, however (see below). Both aggregate and flagelliform gland spigots are similar in size (Figs 13F, G, 37B, 52C). In most species, the triad on males is vestigial, were remnants of previously functional gland spigots can be observed (Figs 23E, 33H). In some species, the triad is retained in adult males (Fig. 13G; this change is ambiguously optimized at the base of Mysmenidae).
The spinnerets of mysmenids differ from that of all other families represented in this data set by the presence of a lobe on the intersegmental groove of the ALS (Figs 23A, C, G, H, 52B). This lobe is also present within Anapidae, although with high homoplasy. Mysmenids also differ from other families in the separation of the major ampullate and piriform fields by a subtle (shallow) groove (Figs 13C, 23C, 33F, 52B, 61C, 64C), where the connection between both fields is distinctly evident proximally within the ALS segment (ambiguously occurring in Theridiosomatidae). Finally by the characteristic shape of a seta on the major ampullate field, with either one or two rows of long ‘branches’ (Figs 6A, 23F, 33F, 52B, 61C).
Trogloneta is the only symphytognathoid so far examined with minute but distinguishable colulus (Figs 64D, 67F, 68C; as opposed to the remnant colulus of Patu, see character 317). An additional anterior discrete cluster of cuticular protuberances of unknown function also occurs in the ALS of Trogloneta (Figs 64C, 66F). Other attributes occurring in Trogloneta, although not exclusive to this genus, include: a rugose cuticle on the piriform field on ALS (Fig. 64C); minor ampullate gland spigot accompanied solely by a tartipore on PMS; both PLS cylindrical gland spigots equally large and larger than the flagelliform gland spigot (Fig. 67D); and triad spigots retained in adult males (at least in T. granulum).
In Maymena, the shape of the seta on the major ampullate field has a distinct single row of long ‘branches’ (Figs 11E, 13C, 16B); in other mysmenids, two rows occur. The PMS minor ampullate gland spigot is accompanied by a nubbin and a tartipore (Fig. 11F). The following features occur independently in both Maymena and Mysmeninae, and were not observed in any other taxa examined in this data set: an anterior distinctly flat spatulate modified seta on PLS (Figs 11G,H, 13E) and aciniform gland spigots of different shape in both the posterior spinnerets (median and lateral, Figs 11F, G, 13F, G; see character 304). Other attributes occurring in Maymena, although not exclusive of the genus, include: rugose cuticle on piriform field on ALS (Figs 11E, 16B), and both PLS cylindrical gland spigots equally large and larger than the flagelliform gland spigot (Figs 11G, H, 13F). Triad spigots are retained in adult males of M. mayana (Fig. 13G), but this retention appears autapomorphic for this species rather than a generic condition, given that the triad is vestigial in at least M. rica.
In Mysmenopsinae the adult male aggregate gland spigots are absent, and those of the females are distinctly absent as well (see below). Other spinneret features of this subfamily include: a fingerprint cuticle on ALS piriform field; PMS minor ampullate gland spigot accompanied by neither nubbin nor tartipore (Figs 6C, F, 58F, 61D); and both PLS cylindrical gland spigots slim as other gland spigots (not larger) and subequal to flagelliform gland spigot (Fig. 58H). In Mysmenopsis, the colulus bears four or more setae (Figs 56D, 59I). Although both aggregate gland spigots are absent in males and females, the flagelliform gland spigot in the representatives of Mysmenopsis studied has been retained, and seems to be functional in both sexes (Fig. 58G, H). In Isela both flagelliform and aggregate gland spigots are distinctly absent in both sexes (Fig. 6D, G).
Finally, the subfamily Mysmeninae shares with Maymena the anterior distinctly flat spatulate modified seta on PLS (Figs 23B, E, 33G, H, 37B, 52C) and aciniform gland spigots of different shape in both posterior spinnerets (median and lateral, Figs 23D, 33D, 37B; see character 304). These two features evolved independently in the two clades. Other features occurring in mysmenines include a fingerprint cuticle on ALS piriform field (Figs 23C, 52B); PMS minor ampullate gland spigot accompanied solely by a tartipore (Figs 19F, 23D, 33D); both PLS cylindrical gland spigots slim as other gland spigots (not larger) and subequal to flagelliform gland spigot (Figs 23B, 37B, E, 52C); and vestigial triad in males (Fig. 23E), independently functional in Mysmena MYSM-005-ARG and Mysmena tasmaniae.
Other morphological features of Mysmenidae
Clasping spines
The males of all mysmenids except Maymena mayana have a prolateral metatarsal clasping spine (macroseta) on leg I (e.g. Fig. 34C). The phylogenetic hypothesis from the total-evidence analysis agrees with the morphological hypothesis from this study and with previous studies that have suggested this macroseta as a synapomorphy (or diagnostic) for the family (Thaler, 1975; Platnick & Shadab, 1978; Brignoli, 1980; Griswold, 1985; Wunderlich, 1995; Griswold et al., 1998; Schütt, 2003). Although some members of Anapidae have a clasping structure on the first legs, these structures are not spines (macrosetae) but spurs (short and stout seta), and can occur in both sexes. The clasping spines of mysmenids are sexually dimorphic, occurring in males, are unique for the family, and might be involved in mating behaviour (Schütt, 2003). The widespread condition is a medial and straight metatarsal clasping spine (Figs 34C, 42H, 45H, 65C), but the spine can be basal (e.g. Maymena; Figs 16G, 141K), apical (few Mysmenopsis and mysmenines species; Figs 50H, 59B, 143C, 144A), twisted (Isela and Microdipoena; Figs 3B, 8B, C, 26C, 140E, F, 141K, L, 142N), or strongly curved proximally and accompanied by adjacent strong setae (most Mysmenopsis; Figs 54D, 57I, 59B). Additional apical tibial clasping spines can also be found in some mysmenids, as is the case of one tibial clasping spine occurring in all Maymena species (except M. mayana) and in Mysmenopsinae (Figs 3A, 8D, 16G, 54C, 59B, 62E, F, 140E, J, K); or two clasping spines in Mysmenopsis dipluramigo (Fig. 140H) and Microdipoena (Figs 26C, 27I, 57F, G, 141L, O).
Femoral spot or other femoral structures
The femoral spot has been previously suggested as diagnostic or synapomorphic for the family (Thaler, 1975; Platnick & Shadab, 1978; Brignoli, 1980; Griswold, 1985; Wunderlich, 1995; Griswold et al., 1998; Schütt, 2003), as this cuticular structure is unique to mysmenids. The results of our study corroborate this hypothesis. The adult females of all mysmenid species have either a sclerotized spot (Figs 34A, 39D, 140G, 141C, 143N) or a cuticular projection (Fig. 57A, E) on the apical ventral surface of at least femur I, although a few exceptions occur (e.g. Mysmena MYSM-005-ARG and a few Mysmenopsis species). The femoral structure of most female mysmenids occurs in both femora I and II (symplesiomorphic in this data set, Figs 141C, 142B). The occurrence of this feature only on femur I is convergent in Trogloneta, Mysmenopsis (when present), and a number of times within Mysmena (Fig. 140G). The femoral sclerotization (i.e. spot) was first described by Marples (1955) for Tamasesia (= Mysmena). Its function remains unknown. The absence of pores in its surface indicates that we should rule out a glandular function. It has been suggested that the spot could be a ‘... functionless remnant of an unknown structure, because it shows a great variability in size and shape among specimens and can be differently pronounced on the two first femora of a single specimen. It is too large to be the socket of a former spine and apart from this there is no space for a large spine so close to the patella...’ (Schütt, 2003: 143). Based on the results of the combined analysis, the spot originates at the node of Mysmenidae, becomes a femoral projection in Mysmenopsis, and is lost distally in some species. Whether the femoral spot actually has a function (e.g. a behavioural function), or is just a remnant of a functional structure, remains an unsolved puzzle.
All femoral structures are absent in juvenile mysmenids (which argues against the remnant hypothesis), although they can sometimes be perceived in subadult stages. The femoral projection occurs only in females of some species of Mysmenopsis. The femoral spot, however, can also occur on males (Fig. 21A). Male femoral spots evolved ambiguously in Trogloneta and Maymena, independently in Microdipoena [excluding its basal species M. (= Mysmenella) samoensis], and in two instances within Mysmena. In contrast with females, most mysmenid males have the femoral spot (when present) only on femur I (Fig. 141O), although in two cases the spot occurs in both femora I and II (Maymena ambita and Mysmena tasmaniae; Fig. 140M).
Prolateral row of modified setae in the male first leg tarsi
First observed and described as a ventral row of modified setae by Thaler (1975, 1995) for males of Trogloneta granulum and Mysmeniola spinifera (respectively), this prolateral row of modified setae (see below) is an ambiguously optimized synapomorphy for Mysmenidae. As is the case of most morphological features within Mysmenidae, and even though this row of modified setae occurs in all examined species, the particular details of this feature differ among clades. The modified setae are usually shorter than the surrounding tarsal setae, and can be slimmer and curved or stouter and straight. These modified setae can also be distributed along the entire length of the tarsus or just on the distal half. In Mysmeninae, the setae are slimmer and the row occupies the distal half of the tarsus (except in Mysmeniola, see below; Figs 26A, 34D, 45I, 50F). In Maymena rica and in Mysmeniola spinifera the setae are also slimmer but the row is distributed all along the segment (Fig. 16H). Trogloneta and Isela both have stout setae distributed along the tarsus (Figs 8F, 65D, 68A). And lastly, Mysmenopsis also have stout setae but, as in Mysmeninae, the row occupies the distal half of the tarsus (Figs 54G, 59D). Although the function of this row of modified setae remains unknown, the fact that these setae are found only in the males suggests that it may be involved in mating behaviour.
Other morphological features of Mysmenids
Size of the tarsal organ opening on leg I: A large opening of the tarsal organ (i.e. subequal or larger than setal sockets) evolved independently in Mysmenidae and Anapidae (see Figs 26E, 39C, 48F, 50D, 73B, 83E, 95I, 101E, respectively). An opening distinctly smaller than setal sockets is the plesiomorphic condition in symphytognathoids. Within Mysmenidae, the tarsal organ opening becomes secondarily small in Mysmenopsinae, with a reversal in Mysmenopsis palpalis (Figs 3F, 54F, 62H).
Distinctly thick distal promarginal curved seta on chelicerae: Most taxa in this data set have a particularly distinct curved seta located distally at the promarginal edge of chelicerae, near the fang base. This seta differs from surrounding promarginal setae by its thickness and/or serration. Although a distinctly curved seta can also occur on the cheliceral retromargin of some araneomorph spiders (see Griswold et al., 2005, character 34), retromarginal setae of the taxon sample examined in this study do not differ from surrounding setae (e.g. Fig. 7J). Within symphytognathoids, the distinctly curved promarginal seta is lost in Synaphridae and most Symphytognathidae (Figs 108E, 118E, 122A; the optimization of this character under parsimony is ambiguous). All examined mysmenid representatives have a uniquely thicker distal promarginal curved seta (Figs 19E, 25E, 38H, 48B), except Maymena. In some mysmenids this seta is equally serrated as surrounding seta, which is the plesiomorphic condition for the family; however, the thicker seta is strongly serrated on one side independently in Mysmeninae and most Mysmenopsinae (Figs 19E, 38H, 42E, 48B).
Intermediate sternum posterior margin: Pointed and truncate sternal margins are quite distinct in the taxa represented here, although the systematic value of this character has been questioned because of imprecision in shape definition, reliability of observation, homoplasy, and possible influence of overall body proportions on sternum shape (Coddington, 1986a; Griswold et al., 1998; Schütt, 2003). A truncate sternum is a synapomorphy of symphytognathoids, occurring in all families except Mysmenidae. In Mysmenidae, an intermediate condition between pointed and truncate posterior sternal margin is consistently found (Figs 2C, 7C, 25B, 35C, 46A, 59G, 140B, 143B, I); however, an ambiguously optimized reversal to pointed posterior sternum occurs in Maymena (Fig. 141F), and two independent instances of truncate sternum occur within mysmenines (Fig. 143O).
Sparse imbricate cuticular pattern on carapace border: Almost all mysmenids here examined have a typical cuticle pattern on the carapace lateral edges that was not observed in other taxa. It consists of slender (i.e. not prominent) ridges running mostly parallel with each other and with the edge of the carapace, delimiting elongated scales (Fig. 50A). A smooth cuticle is widespread in both outgroup taxa and symphytognathoids (Figs 118A, B, 121B, E). Within Mysmenidae, a smooth cuticle is secondarily and independently present in Maymena mayana and the mysmenine MYSM-019-MAD.
Cheliceral fang furrow denticles: Minute denticles in the cheliceral fang furrow (Figs 7G, 15H, 48B) occur in almost all mysmenids studied (e.g. Forster, 1959; Brignoli, 1974; Thaler, 1975; absent in Microdipoena jobi; Platnick & Shadab, 1978; Griswold et al., 1998; Schütt, 2003), and have been proposed as synapomorphic for the family (Platnick & Shadab, 1978). Although not unique for symphytognathoids (cheliceral denticles have been reported at least in nesticids, Wiehle, 1963; uloborids, Peters, 1982; and araneids and nephilids, Hormiga, Eberhard & Coddington, 1995), similar denticles also occur in Theridiosomatidae and some anapids (Coddington, 1986a; see also Schütt, 2003). Within symphytognathoids, denticles are an ambiguously optimized synapomorphy for both Theridiosomatidae and Mysmenidae.
Anterior median eyes on protruded area: Another particular feature shared between mysmenids and theridiosomatids is the arrangement of the anterior median eyes. Character optimization under parsimony for this feature is ambiguous. Both sexes of mysmenids (except Trogloneta, see below) and theridiosomatids have a depression around the anterior median eyes defining a protruded area (Figs 15B, D, 25C, 46D, E, 59C). This area is clearly protruded, not just smoothly raised from the rest of the carapace, and can be best observed with SEM and in frontal view. In Trogloneta, males have all eyes in a tubercle or a narrow elevation of the ocular area (Figs 63G, H, 66A).
description: Published as part of Lopardo, Lara & Hormiga, Gustavo, 2015, Out of the twilight zone: phylogeny and evolutionary morphology of the orb-weaving spider family Mysmenidae, with a focus on spinneret spigot morphology in symphytognathoids (Araneae, Araneoidea), pp. 527-786 in Zoological Journal of the Linnean Society 173 (3) on pages 658-713, DOI: 10.1111/zoj.12199, http://zenodo.org/record/5331625