A taxonomic review of the crab spider genus

Four Neotropical species of Sidymella Strand, 1942, S. furcillata Keyserling, 1880, S. longispina (Mello-Leitão, 1943), S. lucida (Keyserling, 1880), and S. kolpogaster (Lise, 1973) are redescribed from both sexes. The holotype of S. nigripes (Mello-Leitão, 1947) is lost and this taxon is considered a species inquierenda. Sidymella obscura (Mello-Leitão, 1929), S. parallela (Mello-Leitão, 1929), and S. spinifera (Mello-Leitão, 1929) are all nomina dubia. Two new species are described: Sidymella excavata sp. nov. (males and females) and S. marmorata sp. nov. (female).


Introduction
Crab spiders (Araneae, Thomisidae) are distributed worldwide but the highest diversity is found in tropical regions (WSC 2019). The group has been studied in many recent phylogenetic works, but its relationships are still being discussed (Benjamin et al. 2008;Benjamin 2011;Ramírez 2014;Wheeler et al. 2017) and broader relationships among basal thomisids such as the subfamily Stephanopinae remain weakly supported and unstable (Ramírez 2014). The presence of cheliceral teeth, which was previously considered as a synapomorphy for this group (Ono 1988), was recovered as a plesiomorphy by Benjamin (2011), and this subfamily remains as the most controversial and the least studied group in Thomisidae; it has many genera in need of revision and a considerable number of species yet to be described (Benjamin 2011). Based on the work of Mello-Leitão (1929), subsequent efforts were made to update the taxonomy of some Neotropical stephanopines (Lise , 1981Bonaldo and Lise 2001;Machado et al. 2015Machado et al. , 2017Silva-Moreira and Machado 2016;Prado et al. 2018). However, many genera are still known only from the original descriptions and poor diagnoses, and the accurate identification of many species is practically impossible.
The genus Sidymella Strand, 1942 is a prime example of such difficulties. The genus has a disjunct Gondwanan distribution, with 11 described species occuring in Australia and New Zealand whilst 10 are found in the Neotropics (WSC 2019). Sidymella is currently defined by a convex prosoma, both anterior and posterior eye rows recurved, anterior tibiae and metatarsi (I and II) with stout and spiniform macrosetae, and opisthosoma posteriorly bifurcated (Strand 1942;Mello-Leitão 1929;. Although the Neotropical Sidymella have been revised by , this author focused on somatic characters to describe and diagnose the species, neglecting both external and internal structures of female genitalia and the position, shape, and size of palpal apophyses of males. Therefore, the present paper provides a taxonomic review of the Neo-Diagnosis. Sidymella is similar to Coenypha Simon, 1895 and some species of Stephanopis (e.g. S. antennata, S. ditissima, and S. nodosa) and these species share a male palp with a long, thin and curled embolus, well-developed pars pendula, and a retrolateral tibial apophysis with a short basal branch (Figs 1A,B,13D); the epigynes have a septum formed by the posterior folds of the epigynal plate and long and coiled copulatory ducts (Figs 1C, D, 10C-F). However, Sidymella species can be recognized and distinguished from these genera by having a bifid opisthosoma (Fig. 1E, F), presence of spiniform macrosetae on the mesial surface of femora I and above the ALE (Fig. 10A, B), the epigyne have a single pair of walnut-shaped spermathecae compartmentalized in several smaller chambers, with accessory glandular heads (Figs 4D, F, 6D, F, 8D, F, 10D, F, 12D, F, 13D, F) while the male palp has a tibial trichobothrium and the RTA have a nodose surface (Fig. 1A, B) unlike other Stephanopinae which present a grooved RTA (with parallel creases on its surface).
Description. Small spiders (total length 3.00-3.96 in males, 4.68-7.93 in females) with slight sexual size dimorphism, presenting evidence of predominant green colouration in vivo (Fig. 1E, F). Prosoma longer than wide, covered with short and conical setae. Both anterior and posterior eyes disposed in two recurved rows; ALE almost two times larger than the other eyes; ocular macrosetae may be present only above the ALE or on the MOQ area; sternum heart-shaped with concave anterior border, and clypeus with a pair of macrosetae; labium trapezoidal and endites with rounded edges, longer than wide. Opisthosoma with two projections of different sizes, shapes and angles in relation to the opisthosomal axis, varying from rounded and short ones, disposed horizontally/posteriorly, or long, acute and vertically oriented (Figs 2A-F, 3A-F). Leg formula: 1-2-4-3; anterior tibiae and metatarsi (I and II) ventrally armed with stout macrosetae. Epigynum with membranous and hyaline copulatory ducts, long spermathecae with many chambers or with a single median constriction (Fig. 10D); male palp with RTA rounded or truncated, discoid tegulum and ribbon-like embolus and ( Fig. 10C-F).
Distribution. Ecuador, Colombia, Peru, Brazil, Argentina, and Uruguay (Fig. 15).     Etymology. The specific name refers to the shape of the anterior border of the opisthosoma with a remarkable median re-entrance/excavation.

Diagnosis.
Females of S. excavata sp. nov. resemble those of S. marmorata sp. nov. by the large body size, short opisthosomal projections and long copulatory ducts; however, they can be distinguished by the presence of long needle-shaped macrosetae on the ocular area ( Fig.  4B), and by having five mesial macrosetae on femora I and II (Fig. 4A). Males are similar to those of S. lucida, but can be recognized by cephalic setae and a basal branch of the RTA which is truncated instead of conical ( Fig. 5C-F).
Description. Female: Prosoma, sternum and legs totally orange; legs I and II covered by numerous spiniform setae; opisthosoma predominantly light-yellow with a dark median stain on the dorsum that splits posteriorly towards to the tips of the projections (Fig. 4A). Epigynum with a wide septum formed by the median junction of the posterior folds of the epigynal plate ( Fig. 4C, E); copulatory ducts hyaline, long and coiled, leading to a pair of walnut-shaped spermathecae (Fig. 4D, F).
Male: Prosoma yellow with a darker median stain; legs I and II yellow with brownish spots on the femo-ral setiferous tubercles and at the distal portion of each leg segment; legs III and IV light-yellow. Opisthosoma as in female (Fig. 5A). Palpi with a well-developed pars pendula and embolus emerging at three o'clock, curling at the tip ( Fig. 5C-F); basal branch of RTA stout and directed retro laterally while the RTA is short, rounded and oriented vertically (Fig. 5D, F).
Measurements: eyes diameters and eyes interdistances: AME 0.05, ALE 0.07, PME 0.05, PLE 0.05, AME-AME 0.13, AME-ALE 0.05, PME-PME 0.11, PME-PLE 0.13, MOQ length 0.17, MOQ width 0.11; leg formula: Diagnosis. Females of S. furcillata are similar to those of S. longispina by having macrosetae above the ALE and long opisthosomal projections that are directed vertically (Fig. 2B); however, in S. furcillata the projections are rounded at the apex with a smaller terminal tubercle (Fig.  2B). They can be also distinguished by having a group of clavate setae on the median region of the prosoma (Fig.  6B), a triad of mesial macrosetae on femora I, presence of seven pairs of ventral macrosetae on tibiae I, a dark transversal line on the dorsum of opisthosoma (Fig. 6A), and by the long and coiled copulatory ducts (Fig. 6D, F). Males can be distinguished by having tubercles at the apexes of the opisthosomal projections (Fig. 3B), wide pars pendula (Fig. 7C, E), retrolateral tegular process, and the bifid basal branch of the RTA (Fig. 7D, F).
Male: Prosoma dark-yellow, legs I and II predominantly light-brown with dark spots; tibiae I yellowish on the median region; legs III and IV yellowish (Fig. 7A). Opisthosoma yellowish with a pair of dorsolateral and a median posterior black spot (Fig. 7A). Embolus long, emerging from tegulum at four o'clock, with wide pars pendula and curled at the tip; RTA rounded and with central excavation (Fig. 7C-F).
Measurements: eyes diameters and eyes interdistances: AME 0.03, ALE 0.07, PME 0.05, PLE 0.05, AME-AME 0.11, AME-ALE 0.09, PME-PME 0.17, PME-PLE 0.13, MOQ length 0.31, MOQ width 0.11; leg formula: 1-2-4-3: leg I -femur 3.08/ patella 1.  (Fig. 16). Diagnosis. Females of S. kolpogaster are similar to those of S. lucida by the general shape of the spermathecae, short copulatory ducts, and femora I with two mesial macrosetae. However, females of S. kolpogaster can be easily distinguished from congeners by curved tibiae I and II, flattened prosoma, dark body colouration, varying from dark-brown to black and contrasting with their vivid yellow legs III and IV (Fig. 8A). The males can also be recognized by their body colour pattern, which is the same as in females, and by their truncated RTA fused with basal branch (Fig. 9D, F).

Description.
Female: Prosoma dark-brown, lighter on the ocular area and clypeus, covered by hyaline setae and dorsoventrally compressed (Fig. 8B). legs I and II entirely darkbrown, except for the reduced and yellowish tarsi; metatarsi I and II curved; legs III and IV entirely light-yellow (Fig.  8A). Opisthosoma dark-brown with posterior projections stout and conical. Epigynal plate wide and with short septum; copulatory ducts short and hyaline (Fig. 8C-F).

Diagnosis.
Females of S. longispina are similar to those of S. furcillata by their long and vertically oriented opisthosomal projections (Figs 2A, 10A), and the presence of stout macrosetae above the ALE (Fig. 10B); however, their opisthosomal projections have pointy conical apexes instead of being rounded with a small apical protuberance as in S. furcillata. The females of S. longispina also have shorter copulatory ducts (Fig. 10D, F). Males of S. longispina resemble those of S. furcillata but their palpi bear a truncated RTA with a conical and well-developed basal branch (larger than the RTA itself) (Fig. 11D, F); the male palp has a long, acute tegular process and a dorso-basal projection (Fig. 11D, F). Both males and females have just one mesial macroseta on femora I (Fig 11A).
Description. Female: Prosoma yellowish-orange, darker on the cephalic area and presenting a pair of needle-shaped macrosetae on conical projections above the ALE ( Fig  10B). Legs yellowish-orange; femora I with a single prolateral macrosetae; both the anterior tibiae and metatarsi (I and II) ventrally armed with five pairs of ventral macrosetae. Opisthosoma light-yellow with posterior projections long, pointed and vertically oriented (Figs 2A, 10A).
Measurements: eyes diameters and eyes interdistances: AME 0.05, ALE 0.09, PME 0.05, PLE 0.05, AME-AME 0.15, AME-ALE 0.11, PME-PME 0.15, PME-PLE 0.   Diagnosis. Females of S. lucida resemble those of S. excavata sp. nov. and S. marmorata sp. nov. by their short and rounded opisthosomal projections (Figs 2F, 12A). They can be distinguished by shorter copulatory ducts and spermathecae with just a median twisted constriction instead of many chambers (Fig. 12D, F). Males are similar to those of S. excavata sp. nov. by the colour pattern of the opisthosoma and the shape of its posterior projections. However, males of S. lucida have a roundish RTA with a discrete basal branch (Fig. 13D, F), narrower pars pendula, and a shorter embolus emerging from tegulum at five o'clock ( Fig. 13C, E).
Description. Female: Prosoma yellowish, with cephalic ridges delimited by lines of small papules; needle-shaped setae concentrated on the median area of prosoma, being the largest ones disposed right back of the PLE (Fig.  12B). Legs yellowish, with femora I bearing three equalsized needle-shaped macrosetae on their mesial surface (Fig. 12A); both the anterior tibiae and metatarsi (I and II) ventrally armed with five pairs of ventral macrosetae; tibiae I also bear a pair of smaller macrosetae along their mesial surface (Fig. 12A). Opisthosoma light-yellow with a median black stain on its anterior portion; posterior projections stout, obtuse and vertically oriented (Fig.  12A). Epigynal plate wide, depressed on the median field; posterior folds thick and converging in the middle to form a septum (Fig. 12C, E).  Etymology. The epithet means marbled or overlaid with marble and refers to the reticulated colour pattern of the opisthosoma.
Diagnosis. Females of S. marmorata sp. nov. resemble those of S. excavata sp. nov. by the large body size and the general shape of opisthosoma with an anterior concavity and short posterior projections (Figs 2E, 14A). However, females of S. marmorata sp. nov. bear numerous spiniform macrosetae on the mesial surface of femora I and II and five, instead of four, pairs of ventral macrosetae on tibiae I and II (Fig. 14A).
Description. Female: Prosoma and legs I and II entirely orange while the posterior legs (III and IV) are yellowish. Opisthosoma predominantly yellow but with brownish irregular stains distributed randomly, giving a "marbled" aspect to the spider's dorsum (Fig. 14A); opisthosoma projections short and stout and anal region projected backwards (Figs 2E, 14A). Epigynal plate elevated, with a wide septum and lateral folds concentrically developed towards to the copulatory openings (Fig. 14C, E) copulatory ducts long, hyaline and coiled, leading to a pair of walnut-shaped spermathecae subdivided in chambers and with a tubular glandular-head (Fig. 14D, F).