Entomobrya darwini Katz, Soto-Adames & Taylor

Katz, Aron D., Taylor, Steven J., Soto-Adames, Felipe N., Addison, Aaron, Hoese, Geoffrey B., Sutton, Michael R. & Toulkeridis, Theofilos, 2016, New records and new species of springtails (Collembola: Entomobryidae, Paronellidae) from lava tubes of the Galapagos Islands (Ecuador), Subterranean Biology 17, pp. 77-120 : 99-102

Taxon classification Animalia Collembola Entomobryidae

Entomobrya darwini Katz, Soto-Adames & Taylor sp. n. Figs 22, 23, 24

Etymology.

A patronym honoring the naturalist Charles R. Darwin (1809-1882) for his work on the Galápagos Islands, which helped inspire his contributions to evolutionary theory. We believe Charles Darwin would have overcome his views on Collembola had he seen the color patterns of this new species: "They [ Collembola ] are wingless, dull-coloured, minute insects with ugly, almost misshapen head and bodies" ( Darwin 1871).

Type material.

Holotype, ♀ on slide, Ecuador, Galápagos, Santa Cruz Island: Cueva Chato 2, leaf litter at entrance, 15.iii.2014 (S. Taylor, J. Jacoby, S. Hagan and R. Toomey), GLP-086, INHS Acc. 567,422.

Paratypes, Ecuador, Galápagos, Santa Cruz Island: 1 on slide, Cueva Cascajo, leaf litter from skylight entrance, 9.iii.2014 (S. Taylor, J. Jacoby and M. Sutton), GLP-031, CDRS; 2♂ on slide, Cueva Cascajo, leaf litter from skylight entrance, 9.iii.2014 (S. Taylor, J. Jacoby and M. Sutton), GLP-031, INHS Acc. 567,423 & 567,424; 1♀ on slide, Cueva Gallardo, leaf litter near entrance, 8.iii.2014 (S. Taylor and J. Jacoby), GLP-047, INHS Acc. 567,425; 1♀ on slide, Cueva Chato 2, leaf litter at entrance, 15.iii.2014 (S. Taylor, J. Jacoby, S. Hagan and R. Toomey), GLP-086, INHS Acc. 567,426.

Description.

Body shape and color pattern. Body slightly dorso-ventrally flattened.

Length up to 1.57mm (♀) and 1.23mm (♂). Males and females with no obvious difference in color pattern. Color pattern with slight variation (Fig. 22): light orange/tan background with black or dark purple pigment forming two irregular lateral tri angles or sometimes broken angled bands on the posterior margin of Abd. III; an additional pair of lateral angled broken bands on Abd. II; dark pigment present along lateral margins of Th. II through Abd. IV, sometimes broken along lateral margin of Abd. III; dark irregular/broken transverse band along posterior margin of Abd. III - Abd. V. Abd. IV usually with an irregular U- or “11” -shaped pattern connecting basally with band along posterior margin. Antennae usually with uniform purple pigment. Legs white, with purple patches on apical end of femora and tibia.

Head. Apical bulb of Ant. IV simple. Apical sense organ of Ant. III enlarged and recessed in shallow pit (Fig. 23A). Apical sense organ on Ant. II with single modified seta. Eyes G and H small and subequal. Eye patch with 3 setae; s, t, and p. Dorsal head chaetotaxy reduced and fixed, no Mc variation observed (Fig. 23B): A6, M3, S’ 0, S0, S1, S4i, S5i, Ps2, Ps3, and Ps5 always absent; Ps5 present as micro- or mesoseta. Labral setae smooth. Prelabral setae ciliate. Ornamentation of the distal margin of the labral papillae smooth (Fig. 23C). Labial lateral appendage of labial papillae slightly curved, relatively thin, length subequal to apex of labial papilla E. Labial triangle chaetotaxy formula: M1rEL1L2A1-5.

Thorax. Dorsal chaetotaxy of mesothorax reduced and stable, no Mc variation observed (Fig. 23D): a5, m4, and posterior Mc p1, p2, p3, and p5 present; anterolateral sensilla straight and extremely elongated; ms and posterior sensilla present. Dorsal chaetotaxy of metathorax reduced and fixed (Fig. 23E): a2, a5, a6, m5, m7, p3, and p6 present; anterolateral sensilla straight and extremely elongated; additional sensillum observed just internal to P3 in one individual.

Abdomen. Abdominal chaetotaxy reduced and stable; no Mc variation observed. Abd. I with 2 Mc (m3 and m5) present; m2 present as mesoseta (Fig. 23F). Abd. II with 5 Mc (m3, m5, a6, p6, and p7) (Fig. 23G). Abd. III with 3 Mc (m3, pm6, p6) (Fig. 24A). Abd. IV with 2 inner Mc and up to 11 outer Mc (Fig. 24B). Mucronal sub-apical tooth larger than apical tooth (Fig. 24C).

Legs. Trochanteral organ (Fig. 24D) with up to 9 setae in a triangular pattern; setae thick and apically recurved, increasing in size toward distal margin of trochanter. Unguis (Fig. 24E) with 4 inner teeth: 2 paired basal teeth located approximately middle of inner claw length, and 2 unpaired distal teeth; 3 short, basal outer teeth: 1 dorsal, 2 lateral. Unguiculus lanceolate and serrated. Tenent hair spatulate.

Remarks.

Entomobrya darwini sp. n. is the only member in this genus with the combination of color pattern and chaetotaxy presented in the description above. In addition, Entomobrya darwini sp. n. has some unique diagnostic characters that, to our knowledge, have not been previously documented: the conspicuously long lateral sensilla on Th. II and Th. III (Fig. 23D, E) and the spine-like setae on the trochanteral organ are uncharacteristically enlarged, stout, and slightly truncated (Fig. 24D)

This species shares a similar color pattern with Entomobrya litigiosa fasciata Denis, 1931 described from Costa Rica, but Entomobrya darwini sp. n. has two dark broken/irregular triangles or angled bands along the lateral margins of Abd. III that are always absent in Entomobrya litigiosa fasciata, in addition, the unguiculus is lanceolate in Entomobrya darwini sp. n., whereas in Entomobrya litigiosa fasciata, it is truncate. The color forms of the Nearctic species Entomobrya decemfasciata (Packard, 1873), sensu Katz et al. (2015b), also include angled bands on Abd. III that superficially resemble those exhibited by Entomobrya darwini sp. n. However, these species can easily be separated by chaetotaxy: Entomobrya decemfasciata is characterized by having an extreme abundance of dorsal Mc, where as in Entomobrya darwini sp. n., the dorsal Mc are generally reduced (Figs 23B, D–G; 24A, B). Entomobrya nicoleti (Lubbock, 1871) also shares a similar color pattern with Entomobrya darwini sp. n. that includes forms with angled lateral bands on Abd. III, but differences in dorsal chaetotaxy (e.g., Entomobrya nicoleti has a1 on Abd. III that is absent on Entomobrya darwini sp. n.) easily separates these two species.

Entomobrya darwini sp. n. was collected from both surface and entrance habitats (Table 3) at three caves. This is the first record of the genus Entomobrya from the Galápagos Islands.

Distribution.

Santa Cruz Island, Galápagos, Ecuador.