Calliaxina

Hyžný, Matúš, 2012, Calliaxina chalmasii (Brocchi, 1883) comb. nov. (Decapoda: Axiidea: Callianassidae: Eucalliacinae), a ghost shrimp from the Middle Miocene of Europe, with reappraisal of the fossil record of Eucalliacinae, Zootaxa 3492, pp. 49-64 : 55-56

Genus Calliaxina Ngoc-Ho, 2003

Type species. Calliax punica de Saint Laurent & Manning, 1982.

Extant species included. From the reasons stated above, Ngoc-Ho (2003) rather than Sakai (2011) is followed here in recognizing three species of the genus: C. novaebritanniae ; C. punica ; and C. sakaii .

Fossil species included. C. chalmasii ( Brocchi, 1883) comb. nov. More fossil taxa might be accomodated within the genus (see above).

Diagnosis. Chelae on first pereiopods subequal, similar, and laterally compressed. Carpus triangular, rounded at corners. Major propodus with well developed ridge running along the fixed finger, fixed finger with tooth on the occlusal margin. Minor propodus with deep depression on the lateral surface at the articulation of dactylus, depression elongate with lower border straight distally and distinctly rounded proximally. Fixed finger of both chelipeds rather short and roughly triangular in outline. Dactylus of both chelipeds unarmed. For diagnostic characters of soft part morphology see Ngoc-Ho (2003: 493).

Remarks. Concerning the shape of P1 chelipeds, Calliaxina mostly resembles Eucalliax which also possesses subequal and similar first pereiopods. The distinction between these two genera proposed herein concerns the nature of the minor cheliped, specifically the presence of a well-developed elongate depression on the lateral surface near the base of the fixed finger in Calliaxina with an often granulated lower border (parallel to lower margin of propodus), which is straight distally and distinctly rounded proximally. The depression was clearly depicted and mentioned in descriptions by several authors (in C. novaebritanniae by de Man 1928: fig. 20d; in C. punica by de Saint Laurent & Manning 1982: 219, fig. 4d, and Ngoc-Ho 2003: 496, fig. 19C; and in C. sakaii by Sakai 1966: 166, fig. 3b). Concerning the handedness, Sakai (1966) identified a cheliped with a depression as a minor one in C. sakaii , but, de Saint Laurent & Manning (1982) identified it as a major one in C. punica . Ngoc- Ho (2003) did not state whether the larger depression is present on only one cheliped and if so, on which one. Calliaxina possesses almost equal chelipeds with slight size differences between them. Cheliped measurements of two extant specimens of Calliaxina novaebritanniae (NHMW 25399, 25400) clearly show that the cheliped with the larger propodal depression is a minor one (pers. observation). The depression is much less if developed at all on the major cheliped, which usually possesses a ridge (sometimes termed „keel“) at the base of the fixed finger ( Fig. 2 A). Moreover, the lower margin of the minor propodus in Calliaxina is virtually always straight along its entire length including the fixed finger ( Fig. 2 B).

Other genera of Eucalliacinae may have a similar propodal depression at the base of the fixed finger of the minor chela. However, these are never developed so strongly and the transition between the depression and the rest of the lateral propodal surface is not as abrupt as in Calliaxina . The most similar genus, Eucalliax , usually has the manus of the minor cheliped shorter than that of the major cheliped (e.g. Biffar 1970: figs. 2h–i; Heard 1989: figs 1, 4A–B; Felder & Manning 1994: figs 2b–d). Thus, the shape of the depression as stated above is considered of taxonomic significance at the genus level.

The Middle Miocene species, Callianassa chalmasii , is reassigned to Calliaxina on the basis of 1) the general shape of P1 propodus, which is slightly tappering distally, with keeled upper and lower margins, a rather short fixed finger, and being laterally compressed; 2) the presence of a deep depression on the outer lateral surface of the minor propodus at the base of fixed finger; 3) the shape of the depression being straight (parallel to the lower margin of the propodus) at its lower margin and rounded proximally; 4) the presence of a well developed ridge extending along the base of the fixed finger of the major propodus; and 5) the shape of P1 carpus, which is triangular, rounded at the corners, and keeled on the upper and lower margins. The combination of these characters is considered to be of taxonomic significance for assignment of callianassid material to the genus Calliaxina .

Figures

FIGURE 2. Generalized chelae (two distal elements) of Eucalliacine ghost shrimps. Left column: major chela; right column: minor chela, lateral view. A – B, Calliaxina novaebritanniae (Borradaile, 1900); C – D, Eucalliax aequimana (Baker, 1907); E – F, Eucalliax quadracuta (Biffar, 1970); G – H, Calliax doerjesti Sakai, 1999. Sketches after Biffar (1970) (F), Sakai (1999) (G – H), and personal observation. Note that the figures do not consider the presence of setae and intraspecific variations.