Thalassozetes balboa, Pfingstl & Lienhard & Baumann, 2019

Thalassozetes balboa View in CoL sp. nov.

Type material/locality

Holotype: adult female preserved in ethanol, Panama, Bocas del Toro, Isla Colon , Paunch (PA_37), intertidal algae ( Bostrychia ) from rock, 7 February 2017, deposited at the Naturhistorisches Museum Wien . Four paratypes preserved in ethanol: adult females; Panama, Bocas del Toro, Isla Colon, Boca del Drago (PA_43), intertidal algae ( Bostrychia ) from rock, deposited at Museo de Invertebrados Fairchild, Universidad de Panamá. Additional non-type specimens from all locations are stored in the collections of the Institute of Biology, University of Graz.

Etymology

As this species was found in Panama and Florida, the name was chosen to somehow relate to both locations. The specific epithet “balboa ” (given as noun in apposition) refers to the Spanish explorer Vasco Núñez de Balboa; he led the first European expedition that crossed the Isthmus of Panama in 1513 and the Panamanian currency is named after him. It also refers to Rocky Balboa, a well-known movie character, a descendant of immigrants who made his fortune in the USA. The new species similarly may be an immigrant that has now successfully settled in North America. Moreover, T. balboa sp. nov. was predominantly found on “ rocky ” substrate.

Diagnosis

Dark brown sclerotized mites. Length 277 – 312 µm, width 154 – 194 µm. Notogaster oval in dorsal view with characteristic reticulate-foveate pattern. Lamellar ridges present. Sensillus clavate, distal half spinose. Pair of weak anterior notogastral ridges present, mediad of elliptic depressions. Fourteen pairs of setiform, notogastral setae. Median sternal depression on epimeron I, shaped like inverted pear. Three pairs of genital setae, two pairs of adanal and anal setae. Lyrifissure iad oblique, next to anterior corner of anal orifice. Legs monodactylous, claws with two ventral teeth.

Remarks

T. balboa sp. nov. can be distinguished from the other three Thalassozetes species by its specific reticulate-foveate cuticular pattern, with the centre of notogaster covered with regularly distributed conglomerates of irregular circular or elliptic depressions, fading laterally and caudally in smaller foveate pattern; by two pairs of adanal setae instead of three; and by having two ventral teeth on each claw instead of one.

Description

Measurements. Females (N = 26), length: 280 – 312 μm (mean 303 μm), width: 172 – 194 μm (mean 182 μm); males (N = 64), length: 277 – 305 μm (mean 289 μm), width: 154 – 182 μm (mean 170 μm).

Integument. Colour dark brown.

Prodorsum. ( Figures 7 View Figure 7 (a) and 8(a)) Cerotegument finely granular. Rostrum nearly triangular in dorsal view, projecting anteroventrally in lateral view. Rostrum demarcated from remainder of prodorsum by faint transverse ridge. Pair of inward-curving, slender lamellar ridges, reaching from bothridium to lamellar seta. Rostral seta (ro) and lamellar seta (le) short, setiform, smooth (approx. 5 – 6 µm). Interlamellar seta (in) short and setiform (approx. 5 µm), exobothridial seta (ex) minute. Bothridium large and strongly protruding, orifice circular. Sensillus of normal length (approx. 55 µm), clavate, distal half spinose.

Gnathosoma . Typical for genus. Distal part of rutellum developed as thin triangular membrane, slightly curved inward with obvious longitudinal incision ( Figure 9 View Figure 9 (a)). Setae a and m robust and slightly barbed unilaterally (approx. 15 µm). Mentum regular, seta h setiform, robust (approx. 20 µm). Palp setation 0-2-1-3-8 (solenidion not included), trochanter very short, femur longest segment, genu, tibia and tarsus of almost equal length ( Figure 9 View Figure 9 (b)). Cheliceral digits with two teeth. Seta cha dorsally and chb laterally slightly pectinate, both setae of the same length (approx. 25 µm) ( Figure 9 View Figure 9 (c)). Träghård ’ s organ (tg) slender blunt finger-like oncophysis.

Gastronotic region. ( Figures 7 View Figure 7 (a) and 8(a)) Oval in dorsal view, convex in lateral view; dorsosejugal suture incomplete. Nearly triangular clear spot (vestigial lenticulus) with irregular borders on anterior notogastral median area. Cuticle with specific reticulate-foveate pattern, centre of notogaster covered with regularly distributed conglomerates of irregular circular or elliptic depressions, fading laterally and caudally in smaller foveate pattern. Pair of weak and highly variable (in shape) concave notogastral ridges framing light spot. Laterad of ridges, elliptic depressions lined with fine and densely packed granules. Fourteen pairs of setiform notogastral setae (approx. 10 µm), c 1-2, da, dm, dp, la, lm, lp, h 1-3, p 1-3; seta c 3 absent. Five pairs of notogastral lyrifissures present; ia in humeral area adjacent to anterior border of elliptic cavity; im laterad of seta la; ih laterad and anterior to h 3; lyrifissures ip and ips laterally of seta p 3 and p 2 respectively. Orifice of opisthonotal gland (gla) laterad between seta la and lm.

Lateral aspect. ( Figures 7 View Figure 7 (c) and 8(c)) Cerotegument basically finely granular, larger granules on pedotectum I and in areas surrounding acetabula. Lateral sejugal furrow broad and deep, with dense granulation. Next to lateral border of bothridium triangular protrusion orientated caudally, slightly projecting above lateral sejugal furrow. Pedotectum I small rounded, slightly projecting. Pedotectum II absent. Lateral enantiophysis present, anterior projection triangular, well developed, posterior protrusion triangular and small. Discidium present, developed as strongly projecting triangular bulge between acetabulum III and IV.

Podosoma and venter. ( Figures 7 View Figure 7 (b) and 8(b)) Cerotegument with larger granules next to acetabula and fine granules surrounding anal opening. Epimeral setation 1-0-1-1, all setae setiform and smooth, seta 1b longest (approx. 45 µm), others significantly shorter (ca. 7 µm). Internal borders of all epimera well visible. A densely granulated median sternal cavity on epimeron I with slightly concave lateral borders resulting in inverted pear-like shape. Rounded genital plates with three pairs of fine setae (approx. 8 µm) arranged in longitudinal rows. Aggenital setae absent. Lyrifissure iad oblique adjacent to anterior corner of anal orifice. Outer part of preanal organ rectangular with rounded edges, inner part shaped like a transverse bar. Two pairs of short anal setae, an 1-2 and two pairs of short adanal setae, ad 1-3 (all approx. 8 µm).

Legs. ( Figure 10 View Figure 10 ) Monodactylous. Long, strong hook-like claws, dorsally with slight dentation, hardly visible. Two ventral teeth on each claw, proximal one conspicuous and distal one weakly developed. Cerotegument generally finely granular, larger granules on all trochanters and femora. Femora with ventral carina. No porose areas discernible. Femoral setae serrate. Lateral setae of all genua thickened, blunt and slightly serrate. Ventral setae of tarsus serrate. Famulus ε developed as short broad knob. Solenidion ω 2 in lateral position. Chaetome and solenidia see Table 2 View Table 2 .

Morphometrics

Univariate Statistics: Litoribates . The two Litoribates species L. bonairensis and L. floridae differ significantly in only 5 of the 15 measured variables ( Table 3 View Table 3 ). The variability as indicated by cv is moderate (cv ≤ 0.10) in all characters.

Multivariate analyses: Litoribates . The two Litoribates species can be separated only partly by PCA on raw data and totally overlap in the PCA on size-corrected data ( Figure 11 View Figure 11 ). In the PCA on raw data, PC 1 (explaining 38.5% of the total variation) is responsible for the slight separation. The variable with by far the highest loading on PC 1, and thus contributing most to the separation, is the lenticulus length ll ( Table 4). PC 1 also correlates slightly with “ size ” as defined by the geometric mean (r = 0.81), indicating that L. floridae individuals are slightly larger than those of L. bonairensis . The combination of PC 1 and PC 2 (explaining 25.0% of the total variation) reveals a sexual dimorphism. In L. floridae , males and females are clearly separated, while the two sexes overlap in L. bonairensis . The variable contributing the most to separation along PC 2 is the length of the genital opening gl ( Table 4).

Size correction resulted in a decrease of 87.1% of the total variation. After size correction, PCA no longer separates the two Litoribates species ( Figure 11 View Figure 11 ). The sexual dimorphism of L. floridae is not visible in the size-corrected data, but a slight separation of the sexes becomes apparent along PC 2 in L. bonairensis . The variable with the highest loading on PC 2 is dcg ( Table 4).

The LDA on both raw and size-corrected data revealed that the two species are mainly separated by the variable ll, and the Hotelling ’ s T-test showed highly significant differences (p <0.001) between them. In the raw data, 100% of the individuals can be correctly classified by all-samples LDA and 80% after leave-one-out cross-validation. After size correction, all-samples LDA still correctly classifies 97.14% and leave-one-out cross-validation LDA correctly classifies 74.29%.

Univariate Statistics: Thalassozetes . Thalassozetes barbara from Barbados and T. balboa from Panama differ significantly in 11 of the 20 measured variables ( Table 5 View Table 5 ). The variability of almost all characters is moderate with a cv ≤ 0.10 in all populations, only efw 2 shows slightly higher values (cv between 0.11 and 013).

Multivariate analyses: Thalassozetes . In PCA on both raw and size-corrected data, PC 1 (explaining 33.6% of the total variation in raw data and 29.1% in size-corrected data) separated T. barbara from T. balboa with a very small overlapping area ( Figure 12 View Figure 12 ). The variation within T. balboa seems to be larger than that of T. barbara , and the larger variation is not caused by different sample sites as the three populations from Panama always overlap. In PCAs on both raw and size-corrected data, the variables with the highest loadings on PC 1 were ll and efw2 ( Table 6). A pronounced sexual dimorphism is revealed by PC 2 (explaining 25.6% and 17.0% of the total variation, respectively) in both raw and size-corrected data ( Figure 12 View Figure 12 ). The differences between the two sexes are more pronounced in T. barbara than in T. balboa PC 2 is strongly correlated with size (geometric mean) in the raw data (r = 0.96), indicating that females of both species are considerably larger than males. Variables contributing most to PC 2 were gl and gw, length and width of the genital opening. In the size-corrected data, there is only a weak correlation between PC 2 and size (r = 0.68). Here, the differences between the two sexes are again mainly caused by the variables gl and gw, which have the highest loadings for PC 2 ( Table 6). The total variation decreased strongly, by 88.7%, after size correction.

LDA showed again that separation of T. barbara from T. balboa was mainly caused by the variables ll and efw 2 in both raw and size-corrected data. All-samples LDA on raw data correctly classified 100% of all specimens and 96.3% after leave-one-out cross-validation. After size correction, the percentages of correctly classified individuals slightly dropped to 99.1% in all-samples LDA and increased to 97.3% after leave-one-out cross-validation, Hotelling ’ s T-test revealed highly significant differences between the two species.

Molecular genetic analyses

To ensure the genetic distinctness of the investigated Litoribates species, classical barcoding by means of COI data was applied ( Figure 13 View Figure 13 ). The COI topology clearly separates L. floridae and L. bonairensis . The distinctness of these two species is underlined by a clear “ barcoding gap ” with high genetic differences. The highest intraspecific distance (uncorrected p -distance) amounted to 1.4% and the lowest interspecific distance to 9.6%.

The 18S topology clearly demonstrates the monophyly of all investigated genera ( Figure 14 View Figure 14 ). Although the 18S rRNA gene is typically not suitable for species identification, T. balboa and T. barbara could be clearly separated with high statistical support. Thalassozetes species form the sister group of the Schusteria and Thasecazetes clade and together with the recently described Indopacifica species and Rhizophobates (= “ Thalassozetes shimojanai , ” for explanation of diverging taxon name, please refer to discussion) they build a monophyletic clade of Selenoribatidae . Litoribates spp. are placed as sister group of the Pacific Alismobates species; however, members of Fortuyniidae are shown to be paraphyletic with the genus Fortuynia being placed closer to Selenoribatidae .