Dicranocentrus icelosmarias, Soto-Adames & Anderson, 2017

Soto-Adames, Felipe N. & Anderson, Evan W., 2017, Two new species and new records of springtails (Collembola: Entomobryidae, Paronellidae) from Nevis, Lesser Antilles, Florida Entomologist 100 (1), pp. 32-32 : 32-

Dicranocentrus icelosmarias sp. nov. Soto-Adames & Anderson

( Figs. 1–12 )

DESCRIPTION

Size. Largest specimen (holotype) 2.6 mm.

Color. Background color greenish white or orange.

Scale Distribution. Antennal segments 1 to 3, head, body, legs to tibiotarsus, collophore scales only on posterior face, and ventral face of furcula.

Head. Antennae missing 2 apical segments. Eyes apparently 6+6, but actual number and relative size of individual eyes not clearly seen; interocular setae 3 or 4, scales absent. Dorsal chaetotaxy as in Fig. 1 : row An with 7 to 10 macrosetae; rows A, M, and S with 3, 3, 6 paired macrosetae, respectively, unpaired macrosetae A0 and S0 present; anterior microsetae A5, M3p, Ps2, Ps3, and Ps5 present; macroseta Pa5 present, all other postero-medial macro- and microsetae absent. Prelabral and labral setae smooth; inner labral papilla conic, outer papilla blunt ( Fig. 2 ). Basal seta of outer maxillary palp variable, either sharply tapered ( Fig. 3 ) or parallel-sided ( Fig. 4 ), macroseta-like; sublobal plate with 4 smooth appendages. Labial papilla E with 5 guard seta-like pro- jections, lateral appendage short, not reaching tip of papilla. Labial palps with 5+5 smooth proximal setae. Labial triangle series M with 6 or 7 setae of diverse sizes, 2 innermost setae ciliate, other setae in series M smooth; R smooth and slightly shorter than E; E, L1, L2, and series A smooth. Postlabial setae smooth, consisting of 3+3 setae along cephalic groove, 2+2 companion setae, and 12 lateral setae ( Fig. 5 ).

Body. Dorsal macrosetae on Th. 2 to Abd. 4 as 10, 9/3, 3, 4, 5 + 0 + 7 and distributed according to Figs. 6–8 , 10–12 . Abd. 4 ( Fig. 12 ) macroseta A5 inserted in field anterior to pseudopore and bothriotrix T4; macroseta B6 anterior to, but displaced towards seta Ae; only 1 macroseta external to column F.

Legs. Trochanteral organ L-shaped, with up to 23 smooth, stiff, acu- minate setae. Posterior face of hind tibiotarsus with 2 rows of smooth setae. Tenet hair smooth and spatulate on all legs ( Fig. 9 ). Unguis with 3 small inner teeth ( Fig. 9 ), basal pair aligned and subequal, slightly longer than unpaired tooth. Unguiculus lanceolate, smooth.

Furcula. Manubrium dorsally with 4+4 erect, stiff, smooth setae; 2+2 similar setae present on base of dens. Dens with 2 inner rows of short spines, one row with ≈ 9 spines, other row with 11 spines. Mucro bidentate, apical tooth longer than basal tooth; basal spine smooth, reaching basal tooth.

TYPE MATERIAL

Holotype: Nevis, 2.4 km WSW Brick Kiln , 17.16374°N, 62.5723°W; 298.4 m elevation, leaf litter; 19.XII.2014; slide mounted . Paratypes: same information as holotype, 1 on slide and 9 in alcohol; 1.2 km WSW Brick Kiln , 17.16519°N, 62.57144°W; 277.7 m elevation, leaf litter; 19.XII.2014, 1 on slide and 1 in alcohol .

DISTRIBUTION AND HABITAT

Nevis and Panama (see Remarks below), leaf litter in moist tropical forest.

REMARKS

Dicranocentrus icelosmarias sp. nov. is the only member of the D. marias group with 3 inner macrosetae on Th. 3 that also carries lateral macroseta a6i on Th. 3 (arrow in Fig. 7 ) and 5 inner macrosetae on Abd. 4. The new species is part of the D. marias species complex (see below) and differs from D. marias Wray from Puerto Rico in having macroseta a6i on Th. 3 (microsetae in D. marias ) and in having 5 macrosetae on Abd. 4 (4 in D. marias , Fig. 13 ). We examined 17 individuals of D. marias collected at various locations throughout Puerto Rico, including populations from Isabela (Guajataca), Mayaguez (Miradero), Villalba (Toro Negro), Orocovis, and Rio Grande (el Yunque), and all of them lack macroseta a6i on Th. 2 and all have 4 inner macrosetae on Abd. 4 The new species also differs from D. marias in that head element A5 is always a microseta, but in small adults of D. marias A5 is also a microseta.

In his revision of the genus Dicranocentrus, Mari Mutt (1979) reported 4 forms of D. marias , each with a unique combination of macrosetae on Abd. 1 and Abd. 4. Populations of D. marias from Mexico have 2 macrosetae on Abd. 1 and 4 or 5 on Abd. 4; individuals from Puerto Rico (species type locality) and Panama carry 3 macrosetae on Abd.1, but whereas the Puerto Rican form has 4 macrosetae on Abd. 4, the individuals from Panama carry 5 macrosetae. Given the geographic isolation of each variant and the apparent stability in the number of macrosetae, it is likely that all these forms represent distinct species. The new species from Nevis is identical in all described details to D. marias from Panama, but the condition of macroseta a6i on Th. 3 remains unreported for the Panamanian form. We are provisionally assigning the populations from Panama to D. icelosmarias sp. nov., but a final decision on their identity awaits analysis of fresh material.

As indicated in the introduction, the idiochaetotaxy (i.e., all dif- ferentiated elements of the chaetotaxy, including microsetae, macrosetae, and sensilla) of Dicranocentrus is represented as diagrammatic macrosetae maps that lack the necessary information to evaluate the homology of individual elements. Figures 1, 6–8 , and 10–15 show a first attempt at describing the dorsal idiochaetotaxy within the framework developed by Soto-Adames (2008) and Szeptycki (1979). Comparison of the idiochaetotaxy of D. icelosmarias sp. nov. with that of Orchesella flavescens (Bourlet) , Heteromurus nitidus (Templeton) , Pseudosinella alba (Packard) , Cyphoderus albinus Nicolet , and Seira dowlingi (Wray) ( Szeptycki 1979; Soto-Adames 2008) indicate that:

A. The anterior chaetotaxy of the head (i.e., rows A, M, S, and Ps) is almost complete, only element M0 is absent. The nomenclature proposed for elements in row S ( Fig. 1 ) is provisional, based on the align- ment of S3 and S5 with Ps3 and Ps5. The posterior section of the head of all mounted specimens is densely covered by scales and with the exception of element Pa5 appears to lack all setae posterior to row Ps. The D. marias species group is characterized by the absence of posterior head macrosetae and it is possible that even the inner microsetae in rows Pa–Pp have been lost.

B. The idiochaetotaxy of the mesothorax ( Fig. 6 ) includes the primary elements retained in most scaled species, except, perhaps, m1. The identity of the elements closest to the pseudopore is unclear; they may represent m1 and m2, or a duplicated m2 (i.e., m2 and m2i). The simplest interpretation is to consider these setae as m1 and m2. However, the relative position of the elements to each other and to the pseudopore suggest they represent m2 and m2i; when present, m1 is inserted well anterior to m2, whereas in D. icelosmarias sp. nov., the 2 macrosetae are very close to each other, forming a row. Following the simple assumptions proposed by Szeptycki (1979) for identifying the homology of individual elements, we propose the inner macroseta is m1 ( Fig. 6 ). Nevertheless, this interpretation will need to be confirmed with evidence from studies of postembryonic development.

C. The metathorax ( Fig. 7 ) retains all the primary elements, al- though the identity of p6 is unclear and it is not identified in Fig. 7 . Most macrosetae can be identified with primary elements and only macroseta a6i is the result of a duplication.

D. The 1st abdominal segment ( Fig. 8 ) retains all primary elements except p5. Seta p5 is also lost in adult H. nitidus and C. albinus .

E. The idiochaetotaxy of the 2nd abdominal segment ( Fig. 10 ) is almost identical to that in H. nitidus , including the absence of element m4. Seta m4 is also absent in Seira and Cyphoderus , but whereas in Heteromurus the seta is absent in the 1st instar, in Seira and Cyphoderus the loss is secondary.

F. The 3rd abdominal segment ( Fig. 11 ) retains all primary elements and is identical in organization to that of H. nitidus .

G. The number of inner elements on the 4th abdominal segment is reduced and their homology is difficult to ascertain. Figures 12 and 13 show putative homologies in D. icelosmarias sp. nov. and D. marias , respectively, following the pattern proposed by Szeptycki (1979). Homologies in those figures are based on the chaetotaxy of O. flavescens because in H. nitidus the number of elements is even more reduced than in Dicranocentrus and homologies are also uncertain. Figures 14–15 show alternative homology propositions for D. marias : Fig. 14 is consistent with the unique condition in H. nitidus in which only 2 columns are retained, whereas Fig. 15 is consistent with all other scaled entomobryoids so far described in retaining 3 columns. The lateral chaetotaxy of this segment ( Figs. 12, 13 ) is well conserved and the homology of the 9 main elements (D1–D3, E1–E3, and F1–F3) present in the 1st instar of almost all entomobryoids is evident.

In summary, the chaetotaxy of Dicranocentrus shows clear affinities with that of Heteromurus . This affinity is most evident on the 2nd and 3rd abdominal segments where Dicranocentrus and Heteromurus share the absence of m4 (Abd. 2) and presence of m3e (Abd. 3). The homology of several elements remains uncertain: the identity of lateral elements in series S on the head; the element near the pseudopore on the mesothorax; whether the loss of element p5 on Abd. 1 is primary or secondary; and more crucially, the identity of inner elements on Abd. 4. Resolution of these uncertainties will require analysis of 1st instar chaetotaxy.

ETYMOLOGY

The epithet means ‘similar to marias’, referring to the similarity with D. marias .

Figures

Figs. 1–9. Dicranocentrus icelosmarias sp. nov. Open circles,dots, and “v” represent macrosetae,microsetae, and scales,respectively. (1) Dorsal head chaetotaxy. (2) Papilla on distal margin of labrum, inn and out refer to inner and outer papilla, respectively. (3) Basal setae of maxillary palp in holotype. (4) Maxillary palp in paratype. (5) Distribution of postlabial setae,arrow points anteriorly.(6) Mesothorax. (7) Metathorax.(8) First abdominal segment.(9) Hind leg claw complex,basal paired teeth are subequal and aligned, and only 1 is visible in this perspective.

Figs. 10–11. Dicranocentrus icelosmarias sp. nov. dorsal chaetotaxy. (10) Sec- ond abdominal segment. (11) Third abdominal segment.

Figs. 12–15. Dorsal chaetotaxy of 4th abdominal segment.(12) Dicranocentrus icelosmarias sp. nov. 13–15. Dicranocentrus marias, (13) Nomenclature following Szpetycki (1979). (14–15) Alternative interpretations of homology of inner elements.