Spelaeomysis bottazzii, Caroli, 1924

Grams, Markus, Klinger, Michael & Richter, Stefan, 2023, Neither leg nor jaw-nor always the same: a critical revision of the eumalacostracan maxilliped, Zoological Journal of the Linnean Society 197 (4), pp. 965-1004 : 993-995

STYGIOMYSIDA: SPELAEOMYSIS BOTTAZZII

The first pair of thoracopods (Thp1) is modified in comparison to the third to eighth pairs (Thp3–8) of pediform thoracopods, while Thp2 has a somewhat intermediate morphology. The following description is based on a detailed examination of the right first thoracopod of one female of S. bottazzii ( Fig. 15 ).

Cuticle and skeletal structures of Thp 1 in S. bottazzii

The more or less rectangular protopod (almost as wide as long) of S. bottazzii consists of the coxa (one-third) and basis (two-thirds of the total length of the protopod). It appears clearly separated from the thorax, although our examination allowed no specific statement on the articulation or connection of the thorax and coxa.

The coxa (Coin Fig. 15C ) appears as a broad ring with a slightly protruding distomedial margin. Laterally, a lamellar, elongate epipod attaches (Ep in Fig. 15C ). It broadens somewhat in the anterodorsal direction shortly after its narrow stem, continues as a longish blade with a concave posterodorsal surface and narrows distally into an anterodorsal tip. Its proximal and anteroventral margins appear strongly cuticulized.

The basis (Ba in Fig. 15C ), from a posterior perspective, appears about as long as wide. Its anteromedial distal margin, however, extends into a prominent distally directed setose endite almost as long as the ischium and merus together, covering part of the anterior surface of the ischium.

A lamellar leaf- or spade-shaped exopod attaches proximolateral on the basis (Ex in Fig. 15C ). It is almost as long as the basis, with flat anterior and posterior surfaces. It carries two distally directed setae on its tip and a row of finer setae on its dorsal margin.

The crescent-shaped endopod consists of the ischium, merus, carpus, propodus and dactylus. In relationship to the following podomeres, the ischium appears short (Is in Fig. 15C ). Anteromedially, however, its distal margin extends into a prominent distally directed setose endite almost as long as the merus, covering part of the anterior surface of the merus. With the medial side of the ischium being about twice as long as its lateral side, its distal margin is displaced by ~35° in the lateral direction.

The merus (Me in Fig. 15C ) measures about two to three times the length of the ischium. Distomedially, it protrudes into a setose lobe, but is not as prominent as the endites of the basis and ischium. The distal opening of the merus is not oriented distally but displaced ~90° in the lateral direction.

The carpus (Ca in Fig. 15C ) is slightly longer than the merus. Its proximal margin (connected to the merus) faces medially, whereas its distal margin faces in the distal direction.

The propodus (Pr in Fig. 15C ) is about as long as the merus and has a somewhat bulged and setose medial margin. The distal margin of the propodus is oriented in the medial direction.

The dactylus (Da in Fig. 15C ) is slightly shorter than the propodus. It curves somewhat medially and tapers into a distal tip. Four cuspidate setae are present anterodistally.

No articulations could be recognized in the present analysis. Judging from the musculature ( Fig. 15A ), all the endopodal joints seem to be movable in an anterior–posterior axis (i.e. performing adduction/ abduction).

Figures

Figure 15. Cuticle and muscles of thoracopod 1 (Thp1; right) of Spelaeomysis bottazzii (female); confocal laser scanning microscopy volume rendering; colour code of podomeres and podomere outlines as in Figure 1. A, B, orientation as labelled in C; coloured lines emphasize the outlines of the podomeres; white lines outline muscles, with dashed and dotted lines indicating concealed areas; dotted lines also indicate a position further in the anterior background. A, posterior view; concealed anterior attachment sites of muscles CB2, CB6, MC1 and CP1 indicated by dotted lines. B, same perspective, with other muscles outlined. C, posterior view, showing cuticle of podomeres.Abbreviations:Ba, basis; Ca, carpus; Co, coxa; Da, dactylus; dis, distal; Ep, epipod; Ex, exopod; Is, ischium; Me, merus; med, medial; Pr, propodus; Th, thorax. Numbered muscle labels are as in Table 6.