Willowsia jacobsoni
Creators: name: Cipola, Nikolas Gioia
name: Katz, Aron D.
name: Bu, Yun
name: Godeiro, Nerivania Nunes
Publisher: name: Zenodo
Year: 2025
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Collembola
Entomobryomorpha
Entomobryidae
Willowsia
Willowsia jacobsoni

description: Willowsia jacobsoni (Börner, 1913)
Figs 1–13 and Tables 2–3
Sira jacobsoni Börner, 1913: 49, fig. 4, Java, Indonesia (orig. descr.)
Seira jacobsoni; Salmon, 1964: 503 (comb.)
Willowsia jacobsoni; Stach, 1965: 362
Synonyms:
Sira jacobsoni var. lipostropha Börner, 1913: 51 synonymized Zhang et al. 2011: 8.
Sira tricincta Schött, 1917: 31 synonymized by Womersley 1937a: 156.
Sira jacobsoni var. indica Handschin, 1929: 240 synonymized by Mari Mutt 1981: 370 (?).
Sira parajacobsoni Denis 1929: 105 synonymized by Denis 1941: 44.
Sira jacobsoni var. handschini Uchida, 1944: 4–5 synonymized by Mutt 1981: 370 (?).
Sira jacobsoni var. africana Delamare-Deboutteville 1950: 82 synonymized by Mari Mutt 1981: 370 (?). Willowsia mesothoraxa Nguyen, 2001: 25 synonymized by Zhang et al. 2011: 8.
Diagnosis. Adult specimens with violet pigment generally over most of the antennae, anterior dorsal margin of the head; females with Th II all pigmented; a dark blue transverse band formed by the posterior margin of Abd II and all Abd III and another dark blue band in Abd IV distally; coxae I–II with weakly pigments; femur III with a distal spot and tibiotarsus I–III with a median strip (Figs 2–3). Scales lance-shaped, with interrupted ribs covering the proximal 1/3 or more (but not completely), present on head and trunk, absent on the appendages (Fig. 6). Ant IV with a unilobed apical bulb (Fig. 4A). Dorsal chaetotaxy with 6 ‘An’, 4 ‘A’, 3 ‘M’, 4 ‘S’, 3 ‘Pa’, 4 ‘Pm’, 7 ‘Pp’ and 4 ‘Pe’ mac (Fig. 9E). Prelabral chaetae ciliate; labral p0–1 chaetae longer than the others (Fig. 5A); labral inner papillae with 4–5 projections and outer papillae with 3–4 projections (Fig. 5B); maxillary palp with 3 inner sublobal appendages; papilla E lateral process finger-shaped and almost reaching the base of the apical appendix; basolateral and basomedian labial fields with M, R, E, L1–2 ciliate, R smaller than the others (Fig. 5A). Th II a, m and p series with 2(a5–5i), 0 and 4(p1–3, p5) mac; Th III a, m and p series with 1(a6), 3(m5–7) and 4(p1–3, p6) mac (Fig. 10E); Abd I–IV macrochaetotaxy formula with 4, 2+1, 2+3, 3–4(5)+12–15 mac (Figs 11E and 12E); tenent hair ciliated and apically capitate; unguis basal teeth on the basal half, median tooth on distal 1/4 and smaller than the basal teeth, apical tooth on distal 1/8 and smaller than others; all unguiculus lamellae (ae, ai, pe, pi) smooth and acuminate, except for unguiculus III pe serrated (Fig. 7A–B); male genital plate papillate, with about 9+9 circumgenital chaetae; mucronal teeth subequal, spine surpassing the apex of the proximal tooth (Fig. 7C).
Remarks. Willowsia jacobsoni has been redescribed a few times throughout history, and in general its morphology was depicted similarly by different authors (e.g. Börner 1913; Schött 1917; Handschin 1925; Denis 1929; Mari Mutt 1981; Christiansen & Bellinger 1992; Nguyen 2001; Katz 2017). Even so, there are some differences listed by the previous authors that may be related to variations and/or interpretations, or even observational mistakes.
The specimens analyzed here, including the juveniles (Figs 2–3), have the same color patterns and sexual dimorphism reported by Mari Mutt (1981) to specimens from Puerto Rico, except the depigmented Th III and the body completely pigmented. On labial posterior row, Mari Mutt reported the occasional presence of two extra chaetae (in basomedian field), and also illustrated (but did not report in his description) two smooth chaetae (L1–2) on basolateral field (Mari Mutt 1981). However, in our analyzed specimens (including a few from Puerto Rico), no extra chaetae were observed, and L1 and L2 were always ciliated, so we do not know whether it could be a very atypical variation or an observational mistake.
The different interpretations (mac, mes or intermediate chaetae) can be considered in the Th. II dorsal chaetotaxy on to posterior row, with five mac reported by Mari Mutt (1981), four mac observed in our study (Fig. 10E), three mac depicted by Nguyen (2001), or two mac posteriorly seen by Katz (2017). The same happens in Th III, with three (p1–3) (Fig. 10) or one (p3) inner mac, the latter being likely mistakenly described by Nguyen (2001). Katz (2017) considered one inner mac (m4) on Abd I, while other authors (Mari Mutt 1981; Nguyen 2001), including the present work, considered three mac (m2–4) (Fig. 11E). On Abd IV, there may rarely be five inner mac (Mari Mutt 1981), due to the intermediate size (mac or mes) of A3 chaeta (Fig. 12E), but the most common morphology varies between four or three (Sm absent) mac, the latter being a more frequent morphotype (e.g. Nguyen 2001). Still in Abd IV, other variations are revealed here for the first time, as three lateral mac (Fe2a2, Fe2, Fe2p), which were described as always present in Mari Mutt (1981). Concerning variable chaetae, on the head, three mac (p1e2, p2e2–e3) can also be present or absent. In addition, the S6 chaeta was not observed in Katz (2017), but is reported as mic or mac in Mari Mutt (1981). In the present work, S6 chaeta was observed as mac/mes only in the immature’s stages, except in 1 st instar (Fig. 9).
The differences between the redescriptions herein reported for W. jacobsoni can influence comparisons (e.g., Katz 2017) and/or identifications, and consequently support descriptions of synonyms (e.g. W. parajacobsoni, W. mesothoraxa). This subject has already been discussed before to other Entomobryidae (e.g. Viana et al. 2022, 2024). Once again, we reinforce caution in the interpretation, and consequently, in the diagnosis of Willowsia species.
Examined material. 1 female on slide (INPA): Brazil, Amazonas, Manaus municipality, on laboratory benchtop in entomology department at the INPA, 03°05’42”S, 59°59’24”W, urban area, 82 m, 16.ii.2020, manual collect, NG Cipola coll. 2 males and 11 females on slides and 14 specimens in alcohol (INPA): idem, except 12-15.iv.2021, JMC Nascimento coll. 9 specimens in alcohol (INPA): Tarumã neighborhood, floating in the pool of the "Residencial Nascentes do Tarumã", 02°59’32”S, 60°02’09”W, urban area, 44 m, 05.i.2022, T Mahlmann coll. 1 female on slide (INPA): Pará, Ananindeua municipality, urban area of “Águas Lindas” neighborhood, 01°23’24.4”S, 48°22’25.0”W, 31 m, 10-13.viii.2023, pitfall-trap, SS Viana coll. 8 specimens (1 male, 4 females and 3 undetermined) on slides (INHS 148–810): USA, Puerto Rico, Aguada, Coloso Sugar Cane Mill, 18°22'52"N, 67°09'40", on sugar cane litter, 16-17.vi.1999, F. Soto-Adames coll. 1 male and 1 female on slides and 2 specimens in alcohol (20HN-SY7/ NJAU): China, Hainan Province, Sanya Bay, Sanya, 18°16’41.5”N, 109°29’02.2”E, 2 m., 17.i.2020, D Yu coll. 2 males and 2 females on slides (NUS): Singapore, National University of Singapore (NUS), Kent Ridge campus, Lower Kent Ridge Rd, forest edge near University Hall building, 01°17’49.6”N, 103°46’35.7”E, Secondary tropical forest, Adinandra Belukar, 03.vi.2015, Malaise-trap, Maosheng Foo coll. 1 juvenile in 1 st instar, 4 juveniles in 2 nd instar, 2 juveniles in 3 rd instar, 3 juveniles in 4 th instar, 2 males and 11 females on slides and 82 specimens in alcohol (NUS), plus 3 females on slides (INPA): idem, except in Botany Department of the National University of Singapore, 01.xi.1990, HK Lua coll.
Geographical records (Fig. 8). INDONESIA: Java, Samarang (= Semarang) (type locality) (Börner 1913: 49); West Java, Tjibodas (actually Cibodas) (Handschin 1925: 237); New Guinea (actually Papua, Indonesia), Cyclops Mountains (Womersley 1937b: 205); Sumatra, Jambi Province (Mawan et al. 2022: 5); Sumatra, Ranau and Wadi Kuala (Handschin 1931: 481). PHILIPPINES: Luzon (Gapud 1971: 14); Laguna, Mount Makiling (Alviola et al. 2021: appendix). AUSTRALIA: North Queensland, Cedar Creek (Schött 1917: 31); Victoria, Cumberland (Womersley 1942: 28). PACIFIC OCEAN ISLANDS: Micronesia, Mariana and Caroline (Uchida 1944: 4–5). JAPAN: Ogasawara, Marcus Island (Uchida 1955: 203). CAMBODIA: Bokkor (= Bokor) (Denis 1948: 240). VIETNAM: Nhatrang (= Nha trang) and DEo-Ca (= Cả Pass) (DEnis 1948: 240); THái BìnH (NGUYEn 2001: 25). NEPAL: Jumbesi and Maedane Karka (Yosii 1966: 509). INDIA: West Bengal (Mandal et al. 2024: 221). SRI LANKA (Handschin 1929: 240). MADAGASCAR: Tamatave (= Toamasina) (Denis 1929: 105). IVORY COAST (Delamare-Deboutteville 1948: 316, 1950: 82, 1952: 73). USA: Maui and Oahu Islands (Folsom 1932: 66; Christiansen & Bellinger 1992: 258). PUERTO RICO: Mayagüez (Mari Mutt 1981: 367); Aguada (Katz 2017: 552). TAIWAN: Taichung (Lee & Park 1989: 275). CHINA: Hainan, Sanya Bay (new record). SINGAPORE: National University of Singapore (new record). BRAZIL: Amazonas, Pará states (new record).
Postembryonic development of the dorsal chaetotaxy in W. jacobsoni
Head dorsal chaetotaxy (Fig. 9). The 1 st instar has 41 primary chaetae in series: 3 ‘An’, 5 ‘A’ (A4 absent), 1 ‘Am’, 5 ‘M’, 3 ‘IO’, 5 ‘S’ (S1, S4, S6 absent), 3 ‘Ps’, 7 ‘Pa’ (Pa4 absent), 2 ‘Pm’ (Pm2 absent), 6 ‘Pp’ and 1 ‘Pe’. In the 2 nd instar, nine secondary chaetae appear, six of which as mac (An1a, An3a, M4i, S6, Pp1e, P2e), besides the modification of mac to mes of many primary chaetae, except the original ‘An’, ‘A’ and ‘IO’ series and other nine mac (M4, S5, S7, Pa1, Pa5, Pm1, Pp1–2, Pe3). Contrarily, Pp5 changes from mes to mac. In the 3 rd instar, only one chaeta appears (Pe5), Pa3 changes to mac, and seven chaetae change as mes (v, t, M4–4i, S6, Pa7, Pp6). In the 4–5 th instars, five more chaetae emerge (Pa7e, Pe6 and two unnamed) and 1 ‘IO’ scale (r), but 5–7 chaetae turn into mac (M1–2, M4, S2–3, Pm3 and Pe4, M1 and S2 as mac or mic) and three others to mic (Ps2, Pa2–2i). Regarding the adults, 16 other chaetae appear (An3a2, An3p, q, s, Ps2i, Pm1e–1e2, Pp1e2, Pp2e–2e3, Pe3i, plus four without clear homologies), 8 of which as mac (Pm1e2, Pp2e2 and Pp2e3 present or absent). Furthermore, three chaetae change to mac (M1, S2 and Pp3), while another eight change to mic (M3, M4i, S6, Ps3, Pa7, Pp4i–5). Both of the extra chaetae (?), as well as Pe6 seen in 4–5th instars, disappear in adults.
Th II dorsal chaetotaxy (Fig. 10). The 1 st instar a, m and p series have 7 (a1–7), 6 (m1–2, m4–7) and 6 (p1–6) primary chaetae, respectively, plus an atypical extra chaeta anteriorly (aa). In the 2 nd instar, nine secondary chaetae appear (a3i, a4e, m5a, m5e, m6p, m7p–p2, p6e, p6p), all as mac, except a3i as mes. Furthermore, of the primary chaetae, 11 of them remained mac (aa, a2–6, m6, p1–3, p5), while the other primary chaetae changed from mac to mes or remained as mes. In the 3 rd instar, 2 internal scales plus 1 unpaired appear anteriorly, 3 mes from the post-posterior row, plus 8 additional chaetae (a1e, a4p, a4e2, a5i, a6p, a7e, a7p3 and unnamed one), four of which as mac (a1e, a4p, a4e2, a6p), and the rest as mic. Furthermore, two chaetae change from mes to mac (a1, a3i). In the 4–5 th instars, at least 16 chaetae emerge (a3e–3e2, a4a, a4e2a, a4e2p, aap, a5a, a6i–ip, a6p2–p3, m6p2, m7e, p1a, p2e, p 6ei) and 2 scales and 5 mes on the post-posterior row. Additionally, six chaetae of m series (m1–2, m4, m5a–5e) modify from mes to mic. Finally, in adults, several chaetae appear in the anterior collar plus about 15 scales on the post-posterior row, while two mes of p series (p4, p6) change to mic.
Th III dorsal chaetotaxy (Fig. 10). The 1 st instar a, m and p series have 7 (a1–7), 5 (m1, m4–7) and 6 (p1–6) primary chaetae, respectively. In the 2 nd instar, four secondary chaetae appear (m5i, m5p, m6p, m6e), and most chaetae remain as mes, except six mac (a6, m5–6, p1–3). In the 3 rd instar, a7e chaeta appears, p6 turns into mac and a5p into mes. In the 4–5 th instars, three chaetae emerge (a7a, a7e2, m7e), six more are added to the post-posterior row, and ten change from mes to mic (a1–5, m1, m4, m5p, p4–5). In adults, three chaetae appear on the inner region (a4i–4i2, p2e), at least 18 unnamed chaetae laterally and 17 scales on the post-posterior row.
Abd I dorsal chaetotaxy (Fig. 11). The 1 st instar a, m and p series have 5 (a1–3, a5–6), 5 (m2–6) and 2 (p5–6) primary chaetae, respectively. In the 2 nd instar, no new chaeta appears, but most chaetae change to mes, except four of m series which remain as mac (m2–4, m6). In the 3 rd instar, one lateral (el) and one chaeta on the post-posterior row appear, and p6 changes to mac. In the 4–5 th instars, one unnamed lateral and five chaetae on the post-posterior row emerge, plus one inner scale. Furthermore, all chaetae of a series transform into mic, except a1. In adults, six chaetae appear (a4i and five unnamed), plus at least 16 scales and two chaetae on the post-posterior row. On m series the m6 chaeta changes from mac to mes.
Abd II dorsal chaetotaxy (Fig. 11). The 1 st instar a, m and p series have 6 (a1–3, a5–7), 6 (m2–7) and 4 (p4–7) primary chaetae, respectively, plus el chaeta. In the 2 nd instar, three inner chaetae (a1e, m3e–3ea) and three chaetae on the post-posterior row appear. Furthermore, some chaetae change into mic (e.g. a2–3, a6, m4), while others change into mes, except five chaetae (m3, m5–6, p6, el) that remain as mac. In the 3 rd instar, no new chaetae appear and only the p7 mes changes to mac and three chaetae (a1, a7 and p5) change to mic. In the 4–5 th instars, one inner (m3ep) and four unnamed outer chaetae emerge, as well as five chaetae on the post-posterior row. Furthermore, m3e changes to mac and two mac change to mes (p7, el). In adults, one inner and several unnamed outer chaetae appear, including eight and six accessory chaetae on a2 and m2 bothriotricha, respectively, as well as five chaetae and at least 20 scales on the post-posterior row. Among the modifications, a1 become a scale, a7, m6 and p6 become mes, and p4 become a mic.
Abd III dorsal chaetotaxy (Fig. 11). The 1 st instar a, m and p series have 7 (a1–3, a5–8), 7 (m2–5, am6, pm6, m7) and 4 (p3, p5–7) primary chaetae, respectively, plus el chaeta. In the 2 nd instar, two chaetae (a1a, p6pe) and six unnamed additional chaetae appear on the post-posterior row. Only six primary chaetae remain as mac (a7, m3, am6, pm6, p6–7), while the others change to mes or mic. In the 3 rd instar, two inner (a1e, m3e) and two outer chaetae (unnamed) appear, plus three chaetae on the post-posterior row. Furthermore, two chaetae change to mes (a6, m7), two mes to mic (p3, p5), a1a becomes a scale, and el chaeta apparently disappears (or was not seen). In the 4–5 th instars, three inner (a1p, a2i, a5i) and at least 21 unnamed (plus m7i) outer chaetae emerge, as well as four chaetae on the post-posterior row. Clear modifications include three chaetae (a1, a6, m4) that changed from mes to mic and a1a scale apparently disappears. Additional chaetae appear in adults, including several unnamed outer chaetae, seven accessory chaetae on m2 bothriotrichum, about 12 accessory chaetae around m2 and m5 bothriotricha, and at least 25 scales on the post-posterior row. Among the chaetal changes, one mic become mac (a2) and two mac become mes (a7, p6pe).
Abd IV dorsal chaetotaxy (Fig. 12). The 1 st instar A–C, T, D–F series have 5 (A1–3, A5–6), 5 (B1–3, B5–6), 4 (C1–4), 7 (T 1–7), 3 (D1–3), 3 (E1–3) and 3 (F1–3) primary chaetae, respectively, plus nine type II sens on inner region. In the 2 nd instar, 12 secondary chaetae (Ae1, Sm, D1p, De3, E1a, D2–2p, E4p, F1a, F2p, Fe2 and one unpaired unnamed chaeta) appear, as well as a posterior sens and four chaetae on the posterior membrane. Additionally, six more mes change to mic (A2–3, B3, C1, D1, E1) and three mes to mac (D3, F1–2). In the 3 rd instar, 14 additional chaetae (Ai1, A5a, Ae5–6, Be1, D3p, De1, Fe2a, Fe2p and five unnamed, one unpaired) and four anterior scales (one unpaired) appear, two mes change to mac (E4p, F2p), and A5 turns into mes. In the 4–5 th instars, 27 chaetae (Ai2, Si, Be3, D2p, F1p, F3p, Fe2a2 and about 20 unnamed emerge, some of which likely as accessory chaetae not yet formed), as well as a median sens and three chaetae on the posterior membrane. In adults, about 10 chaetae (Ai1a and about nine unnamed) appear, as well as two chaetae on the posterior membrane and seven and three accessory chaetae on T 2 and T 4 bothriotricha, respectively. The transformation for mac occurs in five chaetae (F1a, F2p–3, Fe2–2p), but some of them, along with others (A3, Sm, Fe2a2, Fe2p), may show polymorphisms as mac or mes, and at least two chaetae may be present or absent (De1, Fe2).
Abd V dorsal chaetotaxy (Fig. 12). The 1 st instar a, m and p series have 4 (a1, a3, a5–6), 3 (m2–3, m5) and 5 (p1, p3–6) primary chaetae, respectively (p6 is named as “ ap6 ” by Szeptycki 1979 and Zhang et al. 2019). In the 2 nd instar, seven chaetae (a6a, m3a, m5a, p6ai, p1p, p3pi–3pe) appear and all mes change to mac, except a1 and a3 chaetae. In the 3 rd instar, three more chaetae (a5a, p0, p4a) appear and all secondary chaetae remain as mes or change to mes. In the 4–5 th instars, three chaetae emerge (a5ai, p3a, p6e) and the post-posterior series chaetae change to mic. In adults, 12 chaetae appear (a3a, p5a, p6ae, p5pi–6pi and six unnamed) plus at least six chaetae posteriorly. Furthermore, two chaetae change to mac (a6, p6e) and the posterior-posterior series chaetae revert to mes.
Mitochondrial genome
The 10 Gb of sequencing data were sufficient to assemble the mitochondrial genome with adequate read coverage (Fig. 13). The 15,121 bp mitogenome of W. jacobsoni contains all 37 genes usually seen in arthropods and is similar in length and constitution to other Collembola genomes. The Pancrustacean ancestral gene order was partially observed, except for an inversion in the location of trnN (Aspartate) and trnR (Arginine). Normally the order is trnR → trnN, bUt in W. jacobsoni it is trnN → trnR, witH an intErGEnic spacE oF 167 bp in bEtwEEn. THis invErsion was never reported in previous annotations to any other Collembola mitogenome. Typical ATG/ATA (methionine) start and TAA stop codons were present in most of the protein coding genes (Table 2). Nucleotide content was as follows: A(38 %; 5776 bp); T (36 %; 5228 bp); G(10 %; 1568 bp); C(16 %; 2549 bp). The AT rich control region is 479 bp long and is located between s–rRNA and trnI (Fig. 13).
description: Published as part of Cipola, Nikolas Gioia, Katz, Aron D., Bu, Yun & Godeiro, Nerivania Nunes, 2025, Systematics of Willowsia jacobsoni (Börner, 1913) (Collembola, Entomobryidae): morphology, postembryonic development, distribution, mitogenome and phylogeny, pp. 201-233 in Zootaxa 5604 (3) on pages 206-220, DOI: 10.11646/zootaxa.5604.3.1, http://zenodo.org/record/15035740