Introduction
Zametopina Simon, 1909, is a genus of crab spiders belonging to the family Thomisidae. Referred to as crab spiders, due to their elongated first two leg pairs and their habit of moving sideways, Thomisidae are among the most species-rich spider families with more than 2,100 species across 171 genera (World Spider Catalog 2025). Despite its inclusion in this diverse group, Zametopina remains relatively obscure and taxonomically unrevised. Initially, the genus comprised only a single species, Zametopina calceata Simon, 1909, which had been inadequately understood for decades due to a lack of illustrations in the original description. A significant update came with the work of Tang et al. (2010), who revisited and redescribed the type species. Through meticulous examination of the type specimen, they provided detailed illustrations and descriptions, thereby clarifying the diagnostic features of the genus and aiding in its taxonomic circumscription. This effort significantly enhanced the understanding of Zametopina and set the stage for future taxonomic studies. Recently, a second species, Zametopina wanliae Lin & Li, 2023, was described in Lin et al. (2023), further enriching the diversity of the genus.
By contrast, the genus Nyctimus Thorell, 1877, has received limited taxonomic scrutiny since its initial description. Historically, Nyctimus included two species: the type species Nyctimus bistriatus Thorell, 1877, from Indonesia (Sumatra and Sulawesi), and Nyctimus trimeni (Simon, 1895) from South Africa. Originally described as Zametopias trimeni, the latter is likely misplaced, indicating a need for taxonomic revision. Additionally, Zametopias speculator Thorell, 1892, was transferred to Nyctimus and synonymised with N. bistriatus by Lehtinen (2016). However, this transfer was made without accompanying illustrations or a comprehensive re-examination of the type material, leaving the taxonomy of both species inadequately resolved.
This paper aims to address some of these gaps by reviewing the poorly known species of both Zametopina and Nyctimus, primarily drawing on specimens collected from tropical Asia by the late Christa L. Deeleman-Reinhold, as well as from the EFForTS project in the lowlands of Jambi Province, Sumatra, Indonesia (Drescher et al. 2016). This review aims to clarify the taxonomy and provide updated descriptions, contributing to a more robust understanding of these genera and their roles in the biodiversity of the regions they inhabit. The study highlights the importance of revisiting historical collections and underscores the need for continued exploration and documentation of lesser-known spider taxa.
Materials and methods
Sample collection
Specimens from the late Christa L. Deeleman-Reinhold’s personal collection, housed at her residence, were selected by Suresh P. Benjamin (SPB) and transferred to the Zoological Research Museum Alexander König (Bonn, Germany, ZFMK) for this study. These specimens, along with the rest of her collection, will ultimately be deposited at Naturalis Biodiversity Center, Leiden, Netherlands (RMNH). Spiders from Jambi Province were part of a collection of more than half a million canopy arthropods (Pollierer et al. 2023) sampled by canopy fogging across rainforest, jungle rubber, and monocultures of rubber and oil palm in the lowlands of Jambi, Sumatra, Indonesia as part of the German-Indonesian EFForTS research project (Drescher et al. 2016). Overall, more than 10,000 spider individuals from at least 30 families and 400 species were captured (Ramos et al. 2022; Dhiya’ulhaq et al. 2024). The fogging method is detailed in Pollierer et al. (2023) and the EFForTS plot design and general study aims in Drescher et al. (2016).
Identification and photography
The general methodology follows Benjamin (2011) and Ileperuma Arachchi and Benjamin (2019). Specimens used for habitus illustrations were placed in 70% EtOH and photographed with a Zeiss AxioCam HRc camera mounted on a dissecting microscope (Zeiss Discovery V20) with top illumination and a magnification of up to 150×. Images were edited using the Zeiss ZEN Pro software package. Unless otherwise stated, depicted structures are of the left male palp. Alternatively, some specimens were examined under a ZEISS Stemi 2000 microscope. Female genitalia were excised from the specimen’s body and then cleared with 10% KOH for at least one hour to examine the internal copulatory organs. Imaging the specimens was done using a Keyence VHX-7000 digital microscope system or a Zeiss AxioCam HRc camera mounted on a dissecting microscope (Zeiss Discovery V20). The description of colouration is based on specimens in ethanol. Measurements of legs are given as total length (femur, patella, tibia, metatarsus, tarsus). Missing legs or leg segments are marked with “-”, and legs with missing segments do not have their total length recorded. Unmentioned legs did not have their length measured. All measurements are in millimeter.
Abbreviations
ALE anterior lateral eye
AME anterior median eye
CO copulatory opening
FD fertilization duct
PLE posterior lateral eye
PME posterior median eye
RTA retrolateral tibial apophysis of male palp
VTA ventral tibial apophysis of male palp
Repositories
GOETAnimal Ecology Group, J.-F. Blumenbach Institute of Zoology and Anthropology, University of Göttingen, Göttingen, Germany (Jochen Drescher, Stefan Scheu)
MCSNMuseo Civico di Storia Naturale Giacomo Doria, Genoa, Italy (Maria Tavano)
MCZMuseum of Comparative Zoology, Massachusetts (Gonzalo Giribet)
MNHNMuséum National d’Histoire Naturelle, Paris (Christine Rollard)
MZBMuseum Zoologicum Bogoriense, Bogor, Indonesia (Cahyo Rahmadi)
RMNHNaturalis Biodiversity Center, Leiden (Karen van Dorp)
SMFNaturmuseum Senckenberg, Frankfurt a. M., Germany (Jana Grüger, Peter Jäger)
ZMHZoologisches Museum Hamburg, Hamburg, Germany (Nadine Dupérré, Danilo Harms)
Discussion
A key question concerns whether the females assigned to Nyctimus kinabaluensis, sp. nov., are conspecific with the male holotype. These are the only female specimens of Nyctimus included in this study and possess an oval spermatheca and a unique configuration of the copulatory ducts. Interestingly, similar features are observed in the female of Zametopina calceata, as illustrated by Tang et al. (2010), raising the possibility of a male–female mismatch. Nevertheless, we consider such a mix-up unlikely given the strong resemblance in habitus between the males and females. The overall somatic morphology is consistent, and although the genitalia bear superficial similarities to Z. calceata, we regard the differences as sufficient to support the recognition of a distinct species.
This observation leads to a broader taxonomic consideration: whether all species currently attributed to Nyctimus should indeed belong to the same genus. Most species share a remarkably uniform somatic appearance, dark colouration with white markings, a cuboid, granulated prosoma furnished with long setae, and, in males, a prominent scutum. However, genital morphology across the group is highly variable. The type species, N. bistriatus, is morphologically divergent in several key respects: it has widely spaced median eyes, an exceptionally long embolus, a raspy retrolateral tibial apophysis (RTA), and a broad, elongate copulatory duct with a single copulatory opening. These traits set it apart from the other species and raise doubts about the coherence of the genus as currently defined.
All Nyctimus species described here exhibit a weakly granulated, dark-brown prosoma that peaks in height at mid-length and possesses lateral margins lined with long macrosetae, an unusual feature among Oriental Thomisidae. Comparable setae are known only from Tagulis mystacinus Simon, 1895, a species endemic to Sri Lanka, whose closest relatives are found in Africa (Benjamin and Ranasinghe 2019).
All species discussed here possess a highly modified ventral tibial apophysis (VTA) that varies in shape and size. Most known thomisids, informally referred to as “higher thomisids” or the Thomisus clade (Benjamin 2011; Ramírez 2014), represent the bulk of the family’s species diversity. These higher thomisids exhibit a distinct male palpal morphology, characterised by a disk-shaped tegulum (character 11 in Benjamin 2011) and a hook-shaped VTA, which appears to function as a guiding mechanism during hematodochal expansion and rotation (Huber 1994; character 320 in Ramírez 2014).
However, this specific form of VTA is only observed in Nyctimus bistriatus, N. quadripunctatus sp. nov., and Zametopina wanliae. In most of the species discussed here, the VTA is modified in its size, shape, and position on the apical surface of the tibia. In the absence of evidence to the contrary, the most parsimonious assumption is that all these apical ventral apophyses are homologous. If this character system were to be coded for a future phylogenetic matrix, we would propose the following coding scheme: Character #n: VTA, 0, present; 1, absent. Character #n+1: Position, distance from the tibial apex. Character #n+2: Relative size of the VTA.
Among the species discussed, N. mutilloides, sp. nov., is particularly distinctive. The male, for which no female is yet known, displays white dots and bands across the opisthosoma that strongly resemble the aposematic markings of mutillid wasps, whereas other congeners only bear spotted abdominal patterns. Additionally, the male palp is unique: the embolus is beak-shaped and projects prominently from the distal margin of the bulb. To our knowledge, no other thomisids in the Oriental region exhibit such a palp structure. Although this may indicate a distinct lineage within the genus, further material, particularly molecular data and female specimens, is required to test whether this species merits recognition at the genus level.
Clarifying these taxonomic relationships will require molecular phylogenetic data. At present, the evolutionary affinities and higher-level placement of these species remain uncertain. A robust phylogenetic framework would provide essential insights into lineage divergence, character evolution, and genus-level boundaries. In the absence of such data, hypotheses regarding species interrelationships remain speculative and lack firm genetic or evolutionary support. Future studies incorporating both morphological and molecular evidence will be crucial for resolving these questions and establishing a stable classification for this group of crab spiders.