Libitioides, Roewer, 1912

Kury, Adriano B. & Medrano, Miguel, 2023, Once upon a time in America: recognition of the species of Libitioides from USA, with comments on other American Cosmetidae (Opiliones, Laniatores), European Journal of Taxonomy 875 (1), pp. 101-141 : 113-115

[11] Diagnostic characters within Libitioides

Because the easy distinction of L. ornata from the other Libitioides , we have tackled here only the issue of distinction of the western species (morphs B and C: L. sayi ) from the eastern species (morphs D and E: L. albolineata ) by listing the main features which can be used for that purpose.

1) Color background of dorsal scutum and legs ( Fig. 7 ). This character sharply distinguishes two almost allopatric species: (a) western (morph B, C, but also E): yellow to rusty-orange background, with two fuzzy dark spots on scutal area III; trochanters I–IV yellow, gradually getting darker (olive) distally and (b) eastern (morph D): body and legs uniform dark chestnut brown, with only a faint hint of darker spots at area III.

2) Chevron ( Fig. 8 ). We may distinguish three states of this character: [0] chevron entirely absent, [1] chevron reduced to a small median arch, [2] chevron complete, reaching laterals of carapace. The western species (morphs B, C) mainly lacks chevron or has it reduced (0>> 1), while the eastern species (morphs D, E) mainly has well-developed chevron, sometimes reduced (2>> 1).

3) Backbone ( Fig. 9 ). We may distinguish four states of this character: [0] backbone entirely absent, [1] backbone formed by scattered dots, [2] backbone formed by one dash, [3] backbone complete, formed by chained dashes connecting chevron and omega stripe. The western species ( L. sayi ) always lacks any sort of backbone (only state 0), while the eastern species ( L. albolineata ) possesses an entire backbone which undergoes all stages of dissociation (1, 2, 3, and rarely 0).

4) Omega stripe ( Fig. 10 ). We may distinguish seven states of this character: [0] omega stripe entirely absent (the classical sayi facies), [1] omega stripe almost entirely deteriorated, reduced to a single marginal dot, [2] a pair of minute lateral dots, [3] only a pair of tear-shapes dots on posterior margin of area III, sometimes broken in two, [4] a pair or arches almost formed, but each one severed in more than one place, [5] a pair of entire arches, but clearly separated in the middle, [6] omega stripe complete, left and right halves joined in the middle. The western species mostly has no omega stripe and even when present it is rarely complete (states 1 to 4, the more dissociated shapes, correspond to the L. depressa morph C) while the eastern species has only the two more complete stages (states 5 and 6).

5) Ribs ( Fig. 11 ). We may distinguish three states of this character: [1] ribs absent, [2] ribs poorly defined, formed by a few dots on groove I, [3] ribs more well-formed by dashed lines on grooves I and II. The western species (morphs B, C) entirely lacks ribs while the eastern species (morphs D, E) has all degrees of dissociation from entire ribs to none.

6) Markings on lateral areas. This character is exclusively present in the eastern species (morphs D, E) and it is very variable, from absent in both sides to present in a single side (asymmetric).

Figures

Fig. 7. Southeastern USA, showing the contrasting occurrences of prevailing body color backgrounds in the four morphs B/C/D/E of Libitioides Roewer, 1912.

Fig. 8. Southeastern USA, showing the contrasting conformations of the chevron in the four morphs B/C/D/E of Libitioides Roewer, 1912.

Fig. 9. Southeastern USA, showing the contrasting conformations of the backbone in the four morphs B/C/D/E of Libitioides Roewer, 1912.

Fig. 10. Southeastern USA, showing the contrasting conformations of the omega stripe in the four morphs B/C/D/E of Libitioides Roewer, 1912.

Fig. 11. Southeastern USA, showing the contrasting conformations of the ribs in the four morphs B/C/ D/E of Libitioides Roewer, 1912.