Metasinella (Sulcuncus) radkei, 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-

Metasinella (Sulcuncus) radkei sp. nov. Soto-Adames & Anderson ( Figs. 16–30 )

DESCRIPTION

Size. Largest specimen 1.2 mm; holotype 1.1 mm.

Color. Light blue, evenly distributed through head and body; most intense on eye patch.

Scales distribution. Head, body, and ventral face of furcula.

Head. Antennae 0.34 times as long as head and body. Ant. 4 without apical bulb; subapical sense organ with capitate sensillum and apically truncate guard seta. Eyes 2+2. Head dorsal chaetotaxy as in Fig. 16 : row An with 8 macrosetae; inner margin of eye patch with 1 macroseta; 1 unpaired (A0) and 2 paired (A2, A3) anterior macrosetae; 1 paired posterior macroseta (Pa5) present; row S with 1 unpaired (S0) and 4 paired microsetae (S2, S3, S4, S5); microsetae Ps2, Ps3, and Ps5 present. Prelabral setae ciliated; proximal row of labral setae sparsely ciliated, setae on medial and distal rows smooth; distal margin of labrum smooth. Pleural setae ciliated, proximal seta longer than distal. Maxillary palp with basal seta coarsely ciliated, apical appendage smooth and as long as basal seta; sublobal plate with 3 smooth seta-like appendages. Labial papilla E with 3 guard appendages; lateral appendage anteriorly curved, blunt and surpass- ing tip of papilla. Proximal labial setae 5, all serrated ( Fig. 17 ). Labial triangle ( Fig. 18 ) as M1M2rEL1L2A1-5: r a conic microseta, all other setae coarsely ciliated; L1 shorter than L2. All postlabial setae ciliated, with 3+3 setae along cephalic groove ( Fig. 18 ); field of columns C-O with 6–10 setae.

Body. Body macrosetae formula 10/0232+0+4; regular sensilla (labeled “s” in figures) formula for Th. 2 to Abd. 3 11/011; micro sensilla (labeled “ms” in figures) formula 10/101. Mesothorax ( Fig. 19 ) with macroseta p3; anterolateral regular and micro sensilla present; all setae smooth. Metathorax as in Fig. 20 , inner posterior setae longer than those on anterior and medial rows: p1 longest, a2 shortest; seta m4 absent, latero-anterior regular sensillum present. First abdominal segment ( Fig. 21 ) with 8 setae and 1 latero-anterior micro sensillum; setae a3, a5, and a6 absent. Chaetotaxy of Abd. 2–3 as in Figs. 22–23 ; relative insertion of micro sensillum d2 on Abd. 3 variable. Fourth abdominal segment with 2 inner and 5 lateral macrosetae ( Fig. 24 ); posterior setae absent. Fifh abdominal segment with 13 macrosetae, and 3 regular sensilla distributed as in Fig. 25 .

Legs. Trochanteral organ V-shaped, with up to 13 setae ( Fig. 26 ). Femoral organ with 9–12 short blunt ciliate setae ( Fig. 26 ). Tenet hair smooth, weakly spatulate ( Fig. 27 ). Unguis with 3 inner teeth ( Fig. 27–28 ): basal teeth asymmetric, one longer; unpaired tooth as long as or longer than smaller of basal teeth. Dorsal ungual tooth minute, inserted at base of ungues; lateral teeth inconspicuous, ending on basal quarter. Unguiculus lanceolate, with large posterior tooth ( Fig. 27 ).

Collophore. Posterior face with 3 rows of finely ciliate or denticu- late setae, distal row with 3+3 setae ( Fig. 29 ).

Furcula. Mucro bidentate, with basal membrane, without basal spine ( Fig. 30 ); teeth subequal.

TYPE MATERIAL

Holotype, male: 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, 1 male and 2 females, same as holotype, on slides, 5 in alcohol; 1.2 km WSW Brick Kiln , 17.16519°N, 62.57144°W; 277.7 m elevation, leaf litter; 19.XII.2014; 3 in alcohol .

DISTRIBUTION AND HABITAT

Endemic to Nevis. Leaf litter in moist tropical forest.

REMARKS

Following Mari Mutt & Gruia (1983), the presence of a femoral organ places the new species in the subgenus Sulcuncus . Metasinella (Sulcuncus) radkei sp. nov. is the only member of the genus with bidentate mucro, 2 eyes, and 3 paired (A2, A3, Pa5) dorsal head macrosetae; all other described Metasinella have 5 (A2, A3, M2, S3, Pa5) or 6 (A2, A3, A5, M2, S3, Pa5) paired macrosetae. The new species keys out to M. (S.) millsi Mari Mutt & Gruia in Mari Mutt & Gruia (1983), but M. millsi carries 5 paired dorsal head macrosetae whereas M. radkei sp. nov. has 3 macrosetae; in addition, M. millsi has 4 inner ungual teeth and the dorsal tooth is inserted at the level of the basal inner teeth, whereas the new species carries 3 inner teeth and the dorsal tooth is inserted near the base of the unguis.

The genus Metasinella comprises 2 well characterized subgenera ( Mari Mutt & Gruia 1983): Metasinella s. str. with long antennae, 2 mesothoracic macrosetae, trochanteral organ with long flexible setae, dental spines, and lacking femoral organ; and Sulcuncus with short antennae, 1 mesothoracic macroseta, trochanteral organ with short, stiff, spine-like setae,femoral organ present, and without dental spines. The separation of the genus Metasinella into 2 subgenera is taxonomically sound, as each taxon is diagnosable by non-overlapping discreet characters, but they clearly are part of the same lineage. Most species in the subgenus Sulcuncus are known only from surface collections and show few adaptations to subterranean life. Some of the distinguish- ing characters of M. (M.) acrobates Denis , on the other hand, likely represent adaptations to living in caves. For example, evolution of large body size and long antennae is common in troglomorphic species ( Christiansen 1961), and the dental spines may provide traction while jumping in wet, slippery surfaces. Similar adaptations are present in Pseudosinella spinosa (Delamare-Debouteville) , the largest Pseudosinella in North American, and one of the most morphologically adapted cave forms ( Delamare-Debouteville 1949). Thus, it seems appropriate to retain Sulcuncus as a subgenus of Metasinella .

As pointed out by Soto-Adames (2002), the dorsal chaetotaxy of the metathorax and 1st abdominal segments in Metasinella is reduced with respect to most Lepidocyrtus and Pseudosinella (cf. Figs. 20–21 and 31–32 ). The original interpretation of the metathoracic chaetotaxy by Soto-Adames (2002) indicated the absence of seta m2, a seta considered by Szeptycki (1979) to be diagnostic of Lepidocyrtini . The interpretation of Soto-Adames (2002) is here amended ( Fig. 20 ) based on the clear observation of the complete chaetotaxy of the segment; the small size of the inner element closest to the pseudopore suggests it is m2, whereas the long element external to m2 is interpreted as p2. Provided this new interpretation, the only element missing in the metathorax of Metasinella is m4. The nomenclature of Abd. 1 ( Fig. 21 ) is also amended with respect to that proposed by Soto-Adames (2002). Based on their relative size and insertion, the elements external to a2 are most likely homologous to m3 and m4. The new species also carries element m5, which is absent in the species from the Virgin Islands.

Minor reductions in idiochaetotaxy are relatively common in Lepidocyrtini . Some species of Lepidocyrtus lack Abd. 1 seta a6 (e.g., L. lanuginosus [Gmelin]), whereas in P. hirsuta (Delamare-Debouteville) and L. nigrosetosus species groups Abd. 2 lacks seta m3e ( Christiansen & Bellinger 1998; Bernard et al. 2015). A more extensive reduction in the chaetotaxy of Th. 3 and Abd. 1 is seen in P. violeta Mari Mutt ( Figs. 33–34 ). Pseudosinella violeta is also an Antillean species and it might represent part of the lineage from which Metasinella was derived.

ETYMOLOGY

The epithet honors Garett Radke, who provided accommodations in Nevis that made the collecting trip possible.

Figures

Figs.16–20. Metasinella radkei sp. nov. (16) Dorsal chaetotaxy of head. (17) Proximal setae of labial palp.(18) Labial and postlabial setae,all elements are coarsely ciliate. (19) Mesothorax. (20) Metathorax.

Figs. 21–25. Metasinella radkei sp. nov. Abdominal chaetotaxy on (21) 1st segment; (22) 2nd segment; (23) 3rd segment,hatched line shows alternative insertion of d2; (24) 4th segment; (25) 5th segment.

Figs. 26–34. (26–30) Metasinella radkei sp. nov. (26) Inner face of hind leg trochanter and femur showing trochanteral and femoral (enclosed by hatched line) organs,arrow points basally.(27) Hind claw complex.(28) Hind unguis in holotype.(29) Posterior face of collophore.(30) Mucro.(31–32) Lepidocyrtus nigrosetosus. (31) Metathorax. (32) First abdominal segment. (33–34) Pseudosinella violeta. (33) Metathorax. (34) First abdominal segment.