Mecistocephalidae Bollmann 1893

FamilyMecistocephalidae Bollmann, 1893 Agnostrup Foddai, Bonato, Pereira & Minelli, 2003. Agnostrup Foddai, Bonato, Pereira & Minelli, 2003: 1254. Agnostrup: Uliana, Bonato and Minelli 2007: 24. Nannarrup Foddai, Bonato, Pereira & Minelli, 2003, syn. nov. Type species. Krateraspis striganovae Titova, 1975 – by original designation. Species included. Agnostrup hoffmani (Foddai, Bonato, Pereira & Minelli, 2003), comb. nov., Agnostrup innuptus (Tsukamoto, 2022), comb. nov., Agnostrup oyamensis (Tsukamoto, 2022), comb. nov., Agnostrup paucipes (Miyosi, 1955), Agnostrup striatus (Takakuwa, 1949), and Agnostrup striganovae (Titova, 1975). Diagnosis. Mecistocephalids with 41 leg-bearing segments; two clypeal plagulae separated by a mid-longitudinal stripe. Clypeal setae are arranged in a transversal band on the anterior part of the plagulae and on a medial part of the areolate clypeus; spiculum absent. Side-pieces of labrum are divided into anterior and posterior alae; the internal margin of each anterior ala is reduced to a point. Posterior alae with or without longitudinal stripes; posterior margin of labrum is not hairy. Mandible is provided with 4–6 pectinate lamellae. Coxosternum of the first maxillae is divided in the middle; coxosternum of the second maxillae is undivided. Telopodites terminals of the second maxillae with or without a claw. Forcipular trochanteropraefemur with one distal tooth pointing forward; forcipular articles II and III with or without teeth. Basal tooth of tarsungulum well developed. Forcipular tergum without median sulcus; sternal sulcus of trunk segments not furcate. 7–15 pores on the ventral surface of each coxopleuron; anal pores are present. Remarks. Agnostrup differs from other genera of the Mecistocephalidae previously recorded in China due to its unusual forcipular teeth: the trochanteropraefemur with one well-developed distal tooth pointing forward and a well-developed basal tooth of the tarsungulum. Agnostrup differs from Mecistocephalus by the presence vs. absence of a pair of spicules projecting from the cephalic pleurites. It differs from Proterotaiwanella in the pattern of clypeal setae and sensilla and the finger-like processes of the labrum (Bonato et al. 2002). It differs from Dicellophilus by the latter having a labrum with longitudinal folds and fringed by marginal bristles (Bonato et al. 2010). From Tygarrup, it differs in having an entire plagula lacking a mid-longitudinal areolate strip (Chao et al. 2020). Finally, it differs from Arrup in the unusual teeth of the forcipules and the later having entire coxosternite of the first maxillae, without a mid-longitudinal suture (Foddai et al. 2003). Agnostrup clearly resembles Nannarrup morphologically and in geographical distribution. Nannarrup was established for a single species discovered in New York, USA, and is considered to have been introduced from western America or East Asia (Foddai et al. 2003). Nearly twenty years later, Tsukamoto et al. (2022) discovered two new Nannarrup species, N. innuptus Tsukamoto, 2022, and N. oyamensis Tsukamoto, 2022, from Japan based on morphological characteristics and DNA analysis, confirming the East Asian origin of this genus. These two genera both share unique characters of forcipular article I with one well-developed distal tooth and a tarsungulum with one large basal tooth (Foddai et al. 2003; Tsukamoto et al. 2022). Comparisons of the original descriptions of Agnostrup and Nannarrup reveal several differences between these two genera, such as the presence vs. absence of a frontal line, side-pieces of the labrum fully divided into two alae vs. only incompletely subdivided into an anterior and a posterior ala, the number of setae on the clypeal plagulae, the shape of the pretarsus of the second maxillae, the tooth vs. denticle of the forcipular tarsungulum, the absence vs. presence of claws on the second maxillae, along with different numbers of mandible pectinate lamellae. However, the side-pieces of the labrum are fully divided into two alae in N. innuptus and N. oyamensis (Tsukamoto et al. 2022), and claws of the second maxillae were confirmed to be present in A. striatus after examining the new specimens collected from Shanxi province in China. The size of the teeth on the forcipular tarsungulum is also variable among species within the genus Nannarrup; the type species N. hoffmani is described as “ tarsungulum with a well-developed and slightly pigmented basal tooth, ” which is quite similar to the A. striatus specimen. However, in N. innuptus and N. oyamensis, this characteristic is described as “ tarsungulum with a well-pigmented basal denticle. ” Additionally, we compared the size of the trochanteroprefemur tooth among the three species within Nannarrup and found that N. innuptus and N. oyamensis have a distal tooth on the trochanteroprefemur that is very similar in size to that of A. striatus but significantly larger than that of N. hoffmani. Therefore, the only definite difference between these two genera is the cephalic plate of Agnostrup, which has a frontal line, while Nannarrup lacks one. However, all three Nannarrup species have a smaller body length (ca. 10 mm) compared with the four Agnostrup species (ca. 15–30 mm). The frontal line may be absent in small mecistocephalid species. Uliana et al. (2007) also described a small Arrup species, A. lilliputianus Uliana, Bonato & Minelli, 2007, with a body length of approximately 10 mm that lacks a frontal line. Considering the low genetic distances between Nannarrup and Agnostrup and the morphologically insignificant characters for delineating them as two distinct genera, we consider Nannarrup and Agnostrup to be the same genus. Accompanied by these changes, three species previously belonging to the Nannarrup genus are transferred to Agnostrup as A. hoffmani (Foddai, Bonato, Pereira & Minelli, 2003), comb. nov., A. innuptus (Tsukamoto, 2022), comb. nov., and A. oyamensis (Tsukamoto, 2022), comb. nov.