Symethinae Goeke 1981

Symethinae Goeke, 1981: 972.

Type genus. Symethis Weber, 1795 (= Zanclifer Henderson, 1888).

Genera included. Eosymethis n. gen., Symethis Weber, 1795 (Fig. 31A–F) and Symethoides n. gen.

Diagnosis. Carapace tumid, elongated, suboval, narrowing anteriorly, extending as elongated rostrum. Dorsal surface may appear eroded; cuticle microstructure with fungiform nodes, upright nodes, or pits. Branchiocardiac groove distinct. Anterolateral margin uneven, with 1, 2 small, blunt teeth. Orbitofrontal margin narrow; with postfrontal depressed region, frontal axial ridge may be present. Rostrum considerably produced beyond general outline of carapace into blunt, trilobate process. Orbits small, formed by lateral projection of carapace, ventral suborbital projection, closed internally by the border of the antenna; supraorbital margin with 2 closed fissures. Eyestalk short, folded obliquely or longitudinally forwards; basal article concealed under the rostrum, following article exposed, calcified as carapace; cornea small, hardly visible when stalk retracted into orbit. Antennary fossae situated behind antennulary fossae. Antennule small, deeply located, completely hidden by antenna; basal article developed, following articles small, flattened. Proepistome hidden. Antennae massive, meeting medially; article 1 admedial, fused to carapace, urinal opening at its inner angle; articles 2, 3 fused, expanded, with extremely prominent external prolongation; other articles, flagellum small or lost. Epistome triangular, strongly raised, keeled medially. Subantennary lobe of pterygostome not delimited. One pterygostomial groove, becoming obsolete posteriorly. Mxp3 covering other buccal elements, long, moderately broad; merus much shorter than ischium. Exopod short, wide. Exposed pleurites 5‒7 convex but not forming an excavated plate; branchiostegite developed, excavated, overhanging area of exposed pleurites, limited by P5 strictly apposed along branchiostegal margins. Sternum/pterygostome junction conspicuously narrow. Sternum/exposed pleurite connections between P1 and P2, P2 and P3 highly developed.

Thoracic sternum narrow, strongly deflected at level of sternite 7; sternite 3 short, relatively wide, crown shaped; sternite 4 rather narrow, with elongated, slender anterolateral extensions; suture 4/5 long, distinct, deep, with vertical portion, then prolonged laterally; sternite 5 inflated posteriorly; sternites 6, 7 narrow; sternite 8 perpendicular to sternite 7; medial line along sternites 5‒8. Spermathecal apertures not situated in medial pit, nor recessed: apertures large, widely separated, horizontally located, overhung by 2 calcified hoods.

Chelipeds homochelous, homodontous. Basis-ischium conspicuously short, immoveably fused with massive merus. Propodus swollen, even bulbous, upper, lower margins smooth; fingers conspicuously long, crossing at recurved acute tips; dactylus only slightly deflected, fixed finger more deflected, prehensile border with low, blunt, interlocking teeth. P2‒P4 stout, with spatulate, carinate processes. P5 dorsal, reduced but rather thick, situated along posterolateral carapace margin, strictly adapted to branchiostegal edge. P2‒P5 dactyli sickle shaped.

Abdomen rather short, wide in male, freely articulated, 6 somites plus telson, incompletely folded, first 5 articles dorsal, first somite of about same width as posterior carapace margin. Abdomen only slightly enlarged in female, thus sexual dimorphism indistinct; uropods or sockets absent.

Large posterior branchial orifices present. Only 7 pairs of gills, anteriormost 2 pairs greatly reduced.

Remarks. The exposed pleurites 5–7 (7 smaller) do not form an excavated plate, but the branchiostegite overhangs the area, limited by the P5 strictly apposed along branchiostegal margins, thus a clear passage for the water current. The symethine spermathecal apertures are not situated in a medial trough and are not recessed as in other raninoids, their apertures being large, widely separated, horizontally located and overhung by two calcified, arched hoods; the decalcified portion is located below the hood (Goeke 1981: 976, fig. 2B; Davie 1989: fig. 1c).