Entomobrya decemfasciata (Packard), 1873

Katz, Aron D., Giordano, Rosanna & Soto-Adames, Felipe, 2015, Taxonomic review and phylogenetic analysis of fifteen North American Entomobrya (Collembola, Entomobryidae), including four new species, ZooKeys 525, pp. 1-75 : 27-32

Taxon classification Animalia Collembola Entomobryidae

Entomobrya decemfasciata (Packard), 1873 Figs 2, 3D, 13B, 19, 20, 39

Description.

Body shape and color pattern. Body very elongate and cylindrical with mesothorax forming a slight hump behind head. Color pattern remarkably variable with continuous variation and many intermediate forms (Fig. 19). Typical pattern without thoracic bands but with 2-4 irregular, angled bands on lateral margins of abdomen. Color also variable ranging from white, yellow, orange, or sometimes light blue or purple background with black, dark blue, or brown pigment forming bands. Dark bands outlining posterior and lateral margins of Th. 2 and Th. 3 sometimes present. Apex of femora usually with a dark patch. Head either entirely blue or purple, or lacking all pigment except for the eye patches. Dark patches of pigment usually occur on distal end of antennal segments 2-4. Juveniles usually with light blue pigment background and faint brown abdominal banding.

Head. Apical bulb of 4th antennal segment usually bilobed or simple, but with up to 6 distinct lobes. Long differentiated smooth setae on ventral side of 1st antennal segment ≈3 × short setae. Ornamentation of the distal margin of the labral papillae with single seta or spine-like projection (Fig. 2). Lateral appendage of labial papilla E slightly curved, almost twice as long as papilla. Labial triangle chaetotaxy slightly irregular and atypical for this genus: M1, r, E, L1, L2 ciliate; r significantly smaller than other setae; A1-A5 smooth; sometimes 2 additional ciliate setae inserted internal to M1 and A1, respectively, often relatively difficult to observe. Post labial setae abundant, all type 5. Dorsal head macrosetae (Fig. 20A) An’ 0, An3a3, S’ 0, S6, Ps3, and Pm1i absent; A6 sometimes present. Eyes G and H small and subequal. Eye patch with 5 setae.

Thorax. Thoracic chaetotaxy developed, highly variable, with many supplemental macrosetae. Th. 2 macrosetae p6, p6e and p6ep absent. Macrosetae in Zone A so abundant that usually merge with medial macrosetae, forming a single, large patch of setae (Figs 3D; 20B). Th. 3 macrosetae a5e3, m4, m5p, a6i, a7, and m7 absent (Fig. 20C). Macrosetae in Zone Pm also very abundant on both thoracic segments, with many supplemental macrosetae present forming wing-like patches of posterior setae extending near the anterior row (Fig. 3D). Insertion of pseudopore on Th. 3 different from most Entomobrya , displaced anteriorly, very close to macrosetae a1, a2, and a3. Additional duplicate or supplementary setae often form columns internal to a1.

Legs. Trochanteral organ with rectangular setal pattern and up to 86 setae. Unguis with 4 internal teeth; basal teeth located approximately middle of inner claw length.

Abdomen. Abdominal chaetotaxy extensively developed. Row of microsetae along entire posterior margin present in all segments (not displayed in figure). Abd. 1 with 16 -30 macrosetae (Fig. 20D). Abd. 2 macroseta M3ei always present, with up to 4 additional supplementary macrosetae (possibly including M3eai) internal to m3e; macrosetae a2, a3, m3, m3e, m3ep, m3ep2, m3ea, m5, p5, and p6 present (Fig. 20E). Abd. 3 with macrosetae a2, a3, m3, am6, pm6, and p6; a1 absent (Fig. 20F). Abd. 4 very elongated, with at least 25 inner macrosetae (Fig. 20G), but number of macrosetae extremely variable between individuals and even within a single individual (Fig. 13B). Insertion of pseudopores on Abd. 4 varying with respect to macroseta and bothriotricha even in same individual (Fig. 13B). Basal mucronal tooth enlarged.

Remarks.

Entomobrya decemfasciata can be distinguished by the absence of parallel, longitudinal bands on the thorax, the presence of 2-4 irregular, angled bands on lateral margins of abdomen, and the presence of head macroseta Ps5 (see Table 2 for additional diagnostic characters). This species belongs to the Entomobrya bicolor group (see remarks for Entomobrya bicolor ), and exhibits high levels of variation in both color pattern and chaetotaxy. Entomobrya decemfasciata is perhaps the most setaceous species of Entomobrya reported for North America, clothed in hundreds of macrosetae. This abundant and hyper-variable chaetotaxy provides few characters to differentiate Entomobrya decemfasciata from Entomobrya bicolor and Entomobrya quadrilineata . However, clear differences in color pattern can be observed between these species; Entomobrya bicolor lacks band or stripes, Entomobrya quadrilineata always has two parallel longitudinal stripes extending from the thorax through Abd. 2 and Entomobrya decemfasciata never has bands or stripes on the thorax. Table 5 details important diagnostic characters to separate species within this species complex.

The considerable variation in chaetotaxy and color pattern and relatively high molecular divergences between Entomobrya decemfasciata color forms suggest the presence of a cryptic species complex ( Katz et al. 2015). However, the lack of diagnostic morphological characters between color forms does not allow the circumscription of new species at this time. More specimens and additional molecular and morphological analyses are needed for further action.

This species has a long history of taxonomic issues ( Christiansen 1958b) and its separation from Entomobrya quadrilineata only became evident after a thorough molecular analysis ( Katz et al. 2015). Christiansen (1958b) separated Entomobrya decemfasciata from Entomobrya quadrilineata using color pattern, male genital plate, antennal ratios, and later added chaetotaxy in The Collembola of North America ( Christiansen and Bellinger 1998). High variability in color pattern and chaetotaxy, deformation of antennae after slide mounting, and the difficulty of discerning the morphology of setae on the genital plate, lessens the utility of these characters for diagnosis. Christiansen and Bellinger (1998) even suggested Entomobrya quadrilineata may be a variant form of Entomobrya decemfasciata and seemed uncertain regarding differences in chaetotaxy. Furthermore, Christiansen (1958b) reported three distinct color forms for Entomobrya decemfasciata (all of which had a V-shape or two angled lateral bands on Abd. 2 and lacking thoracic stripes) and three distinct color forms for Entomobrya quadrilineata , one of which also lacks thoracic stripes. During the course of this study, many color forms were collected, including forms both with and without thoracic stripes occurring together in the same sample. These sympatric forms lacked a V-shape or two lateral angled bands on the 2rd abdominal segment, and, following Christiansen and Bellinger’s (1998) concept, were diagnosed as Entomobrya quadrilineata . However, large molecular distances made it apparent that forms with and without thoracic stripes were separate species ( Katz et al. 2015), warranting further diagnostic inquiry. Type specimens from the Illinois Natural His tory Survey were attained for both Entomobrya quadrilineata and Entomobrya decemfasciata . Though both types, preserved in alcohol, were in relatively poor condition, two longitudinal thoracic stripes were clearly observed on the Entomobrya quadrilineata specimen (Suppl. material 3: A, B). Thoracic banding was not observed on the type specimen of Entomobrya decemfasciata (Suppl. material 3: C). Based on molecular evidence ( Katz et al. 2015) and the observations of types, specimens with the morphology corresponding to both Entomobrya quadrilineata and Entomobrya decemfasciata can be diagnosed by the presence or absence of parallel thoracic longitudinal stripes. Christiansen’s (1958b) report of an Entomobrya quadrilineata color form lacking thoracic stripes may have been a case of misidentification of Entomobrya decemfasciata . If individuals with and without longitudinal bands were collected together, similar morphology and abdominal pigmentation may have led him to conclude that they were both Entomobrya quadrilineata . However, we now know that both species can occur in sympatry.

Distribution.

Endemic to North America (Suppl. material 2: F).

Material examined.

USA: "Type material", 1 on slide, Knoxville, Tennessee (Dr. Curtis), INHS Cat. No. 528,321; Cotype, 1 on slide, no locality information; 1 on slide, 17 in vial, Alabama, Clay Co., Talladega National Forest, CR-7 & Hwy148 (33.19723,-86.06325), leaf litter, 2.i.2012, AK12-2; 3 on slides, 20 in vial, Illinois, Union Co., Anna, Shawnee National Forest, Rich’s Cave, vestibule of back high entrance, moist leaf litter along the wall and some dry litter from the center of the vestibule, 21.vi.2012 (F. Soto-Adames, S. Taylor & A. Katz); 16 in vial, Illinois, Union Co., Anna, Shawnee National Forest, Rich’s Cave, humid and cool litter in side niche near main entrance, 21.vi.2012 (F. Soto-Adames, S. Taylor & A. Katz); 4 on slides, 2 in vial, Tennessee, Sequatchie Co., Moonshadow (35.64167,-83.76359), forest leaf litter, 14.i.1997 (M. M. Gibbs); 2 on slides, Tennessee, Sevier Co., Great Smoky Mountains National Park, ATBI plot, Goshen Prong (35.67961,-83.50021), malaise 22 83 32 34 35 36 38, 12.xi.2001-5.xii.2001 (Parker, Stocks & Peterson); 2 on slides, 3 in vial, Tennessee, Stewart Co., Land Between the Lakes National Recreation Area, Fox Ridge Rd (36.66392,-87.98596), leaf litter, 7.viii.2011, AK11-105; 2 on slides, 50+ in vial, Tennessee, Stewart Co., Land Between the Lakes National Recreation Area, Fox Ridge Rd. (36.66392,-87.98596), leaf litter, 7.viii.2011, AK11-107; 2 on slides, 11 in vial, Tennessee, Stewart Co., Land Between the Lakes National Recreation Area (36.53830,-87.91428), leaf litter, 7.viii.2011, AK11-108.