Stenodactylina australis

Stenodactylina australis (Secrétan, 1964)

(Fig. 17 C-F)

Erymastacus australis Secrétan, 1964: 72, pl. 1, figs 2-6, pl. 2, figs 1-5. — Förster 1966: 135. — Taylor 1979: 36. — Schweitzer et al. 2010: 23. — Hyžný et al. 2015: 376.

Palaeastacus australis – Förster & Rieber 1982: 377.

Eryma australe – Charbonnier et al. 2012a: 327, fig. 11.

Stenodactylina australis – Devillez et al. 2016: 524, table 1.

TYPE MATERIAL. — Holotype MNHN.F.R03972; three paratypes MNHN.F.A31660, A33207, R03971. TYPE LOCALITY. — Nord of Analavelona Massif, Sikily region, Tulear province, Madagascar. TYPE AGE. — Tithonian.

DESCRIPTION

Carapace

Sub-cylindrical carapace; elongated cardiac region; deep cervical groove, strongly inclined, joined to dorsal margin and to antennal groove; shallow and narrow antennal groove; short, shallow gastro-orbital groove, oblique, originating as a slight median inflexion of cervical groove; postcervical and branchiocardiac grooves subparallel; postcervical groove deep and wide dorsally, narrowing and shallowing ventrally, strongly inclined and inflected forward, joined to dorsal margin and interrupted in hepatic region; shallow and narrow branchio-cardiac groove, not joined to dorsal margin, joined to hepatic groove; shallow and narrow hepatic groove, concavo-convex, joined to cervical groove; flat ω and χ areas; narrow inferior groove, joined to hepatic groove.

Chelate P1; P1 propodus elongated, subrectangular, slightly globose; inner margin more compressed than outer margin; deviation of outer margin at the basis of the index; wide, inflated dactylar bulge; slender, elongated P1 fingers; curved downward; occlusal margin with short conical teeth regularly spaced.

Carapace densely covered by tubercles preceded by depressions, the tubercles are coarser and the depressions are wider and deeper in the dorsal third of the carapace; P1 propodus covered by rounded tubercles; inner margin with an irregular row of strong subspiny tubercles, directed forward; basis of inner margin of the dactylus with two strong spines.

DISCUSSION

Secrétan (1964) assigned this species, described from fragments of P1, to Erymastacus Beurlen, 1928. Later, Devillez et al. (2016) assigned this species to Stenodactylina because of its subrectangular P1 propodus, the inflated dactylar bulge, the deviation of the outer margin at the basis of the index and the slender fingers. A cast of a carapace has been recently found in the MNHN collections. It comes from the same stage than the type material of Stenodactylina australis and from a locality where one paratype was found. This carapace exhibits the typical groove pattern of Stenodactylina: short gastro-orbital groove, sinuous hepatic groove, postcervical and branchiocardiac grooves not joined, postcervical groove interrupted in hepatic region, and branchiocardiac groove joined to posterior extremity of hepatic groove. The correlation of the groove pattern and the shape of P1 chelae, characteristics of Stenodactylina, and the stratigraphic and geographic arguments lead us to consider the cast of the carapace as a specimen of S. australis.

Stenodactylina australis is one of the rare species of the genus, with S. burgundiaca, S. deslongchampsi, S. lagardettei, and S. triglypta, for which both carapace and P1 chelae are known. The carapace of S. australis is distinct from all other species by its shallow postcervical and branchiocardiac grooves. These grooves are also clearly more inclined than those of S. burgundiaca, S. pseudoventrosa, S. triglypta, and S. walkerae. The flat ω area of S. australis is also distinct from S. burgundiaca, S. granulifera, S. guisei, S. lagardettei, S. shotoverigiganti n. sp., S. triglypta, and S. walkerae. Moreover, S. australis is the only species, with S. triglypta, to have a coarser ornamentation on the dorsal part of the the carapace. There is also no antennal row, contrary to S. lagardettei, S. pseudoventrosa, S. shotoverigiganti n. sp., and S. walkerae. The P1 chelae of S. australis are clearly distinct from those of S. armata, S. falsani, S. lagardettei, S. liasina, S. rogerfurzei, S. spinosa, S. strambergensis, and S. triglypta because of their finer ornamentation without rows of coarse tubercles on dorsal and ventral surfaces. The P1 propodus of S. australis has a row of spines on its inner margin, this row is absent in S. australis, S. burgundiaca, S. deslongchampsi, S. falsani, and S. insignis.