Eucalliacinae

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 : 51-55

Subfamily Eucalliacinae Manning & Felder, 1991

Remarks on taxonomy. De Grave et al. (2009) recognized four genera within the subfamily: Calliax de Saint Laurent, 1973; Calliaxina Ngoc-Ho, 2003; Eucalliax Manning & Felder, 1991 ; and Paraglypturus Türkay & Sakai, 1995 . Ngoc-Ho (2003) provided an account of morphological differences between the Eucalliacinae genera. Sakai (2005) recognized Eucalliax and Calliaxina as junior synonyms of Calliax ; this synonymization was criticized by Dworschak (2007: 159). Later, Sakai (2011) recognized all three genera, Calliax , Eucalliax and Calliaxina , as valid, but his concept of Eucalliax and Calliaxina differs markedly from that of Ngoc-Ho (2003). Sakai (2011) restricted Eucalliax to Callianassa quadracuta Biffar, 1970 only (type species of Eucalliax ), and for Calliaxina listed C. aequimana ( Baker, 1907) , C. bulimba ( Poore & Griffin, 1979) , C. jonesi ( Heard, 1989) , C. mcilhennyi ( Felder & Manning, 1994) , C. panglaoensis ( Dworschak, 2006) , C. novaebritanniae ( Borradaile, 1900) , C. punica (de Saint Laurent & Manning, 1982) and C. sakaii (de Saint Laurent & Le Loeuff, 1979). Sakai (2011) based his concept of the genus Calliaxina mostly on the presence of a cardiac sulcus or sulci and the typical forms of Mxp3. The presence of Mxp3 exopod, one of the most important characters used by Ngoc-Ho (2003) to define the genus, together with the morphology of chelipeds (P1) were not considered of great taxonomic importance by Sakai (2011). The original genus concept of Ngoc-Ho (2003) is followed here because of greater stability of diagnostic characters and because it evaluates also cheliped morphology, i.e. body parts commonly preserved in the fossil record. As a result, only the last three mentioned species from the list above are considered herein as members of Calliaxina , with the remainder as members of Eucalliax . It is also worth mentioning that Eucalliax kensleyi Dworschak, 2005 a was omitted from the last monograph of Sakai (2011). The taxonomic history of generic assignment of all extant Eucalliacine taxa is summarized in Table 1.

Sakai (2011) raised the Eucalliacinae to family level. Following the classification of De Grave et al. (2009) the taxon is here still treated as a subfamily.

Chelipeds of the Eucalliacinae . Manning & Felder (1991) noted that the lower meral margin of the major cheliped bears some important characters for distinguishing genera of the family Callianassidae . There are, in addition, taxonomically important characters also present on the propodus (e.g. in Glypturus Stimpson, 1866 , see Hyžný & Müller in press). Ngoc-Ho (2003) distinguished genera within the subfamily Eucalliacinae , i.e. Calliaxina , Calliax , Eucalliax and Paraglypturus , mainly on the basis of 'soft' part morphology (features on dorsal carapace, eye cornea, maxillipeds, pleopods and uropods); however, she also pointed out differences in chelipeds, which are of greatest fossilization potential and therefore useful for palaeontologists. For Eucalliax and Calliaxina , subequal and similar first pereiopods are typical. Moreover, Calliaxina always possesses laterally compressed chelipeds. In Calliax they are also laterally compressed, but unequal and dissimilar, whereas in Paraglypturus they are unequal, dissimilar and massive.

Many Eucalliacinae species possess a distinct ridge extending obliquely along the fixed finger laterally and may extend to the propodus (as in Eucalliax panglaoensis ; for details see Dworschak 2006). The presence of the ridge together with its typically square manus, usually converging distally, and relatively short fixed finger often with a triangular tooth at its base can be used to identify members of the Eucalliacinae , although not all of these characters are present in all Eucalliacinae genera. The oblique ridge on the base of the fixed finger is rather typical for Eucalliacinae genera, notably Eucalliax and Calliaxina ( Fig. 2 ). A similar ridge is also present in extant Callianassa acutirostella Sakai, 1988 ; the shape and ratios of cheliped elements ( Sakai 2005: fig. 14A, B) are, however, completely dissimilar to any member of the Eucalliacinae . In Eucalliax and Calliaxina there is usually also a depression present in such a position, the ridge forming its lower border. There is a ridge and a deep depression in major cheliped of some Lepidophthalmus Holmes, 1904 species too (e.g. L. rafai Felder & Manning, 1998 , L. siriboia Felder & Rodrigues, 1993 ; L. richardi Felder & Manning, 1997 ). In this genus development of mentioned characters seems to be correlated with sex and size/age (e.g. Felder & Lovett 1989). The shape of propodus is markedly different from any of Eucalliax and Calliaxina species.

Such characters as “robustness” of P1 propodus can be checked on a single fragment, but, to observe the most important characters both chelipeds are usually needed. When working with fossils, the preservation of both chelipeds from the same animal is a quite rare event. Nevertheless there are a few examples when members of the Eucalliacinae were identified on the basis of both chelae (Beschin et al. 2002; Karasawa 1992, 1997). The nature of the minor chela can be diagnostic for Calliax sensu Ngoc-Ho (2003), in which the fixed finger is shorter than, and separated from, the dactylus by a wide gap, bearing a large triangular proximal tooth ( Fig. 2 H). In Eucalliax , the minor cheliped seems to be more variable. In E. aequimana it is more-or-less identical to the major one ( Figs. 2 C–D), and in other Eucalliax species it is usually slightly smaller (with relatively shorter manus) than the major one. In Calliaxina the minor cheliped is similarly slightly smaller than the major one and, moreover, a deep depression is present on the minor propodus only ( Fig. 2 B).

Minor chelipeds in general are usually less calcified and therefore there is a strong bias toward preservation of major chelae in the fossil record, although minor chelipeds should be present in statistically robust samples (e.g. Hyžný & Hudáčková 2012). On the other hand, when dealing with taxa with subequal chelipeds (as some species of Eucalliax and Calliaxina are), identification of minor chelae may be obscure. In such a case, thus when the material consists of isolated elements, a mixture of two (or more) different “species” can be recognized. Precise morphometry and a check of taxonomically important characters can usually resolve this problem as exemplified by this study. Intraspecific variation can be considerable, although some characters are usually consistent within a species.

Eucalliacinae in the fossil record. The fossil record of the Eucalliacinae with the emphasis on the genera Calliax and Eucalliax was recently briefly discussed by Hyžný & Hudáčková (2012). They commented fossil occurrences assigned at one time to one of respective genera. Here some additional notes on fossil taxa so far treated as members of Callianassa (sensu lato) are presented. The combination of characters typical for Eucalliacinae , as discussed above, is present e.g. in Callianassa atrox Bittner, 1893 from the Middle Eocene (Lutetian) of Romania; C. beberibae Beurlen, 1962 from the Turonian of Brazil; C. burckhardti Böhm, 1911 from the Maastrichtian and Lower Paleocene (Danian) of Argentina (see also Aguirre Urreta 1989 and Feldmann et al. 1995); C. rovasendae Crema, 1895 from the Middle Miocene of Italy; and C. saetosa Förster & Stinnesbeck, 1987 from the Maastrichtian of Chile. The latter species was already suggested to be placed within the Eucalliacinae by Swen et al. (2001). Contrary to that, Schweitzer et al. (2006) considered the species to be a member of the extinct genus Protocallianassa Beurlen, 1930 and as such it also appeared in the list of fossil decapod species ( Schweitzer et al. 2010). In this case the assignment to Protocallianassa was based virtually on a single character, the angle of the carpus/propodus articulation being more than 90°, and typically 120°. Callianassa saetosa , however, has very little in common with Callianassa archiaci A. Milne-Edwards, 1860 , the type species of Protocallianassa . Moreover, the angle of the carpus/propodus articulation is a rather subjective and variable character. For instance, in extant E. panglaoensis the carpus/propodus articulation is clearly more than 90° (although definitely not 120°; see Dworschak 2006), although the same can not be said for all Eucalliax species.

Protocallianassa klofi Bishop, 1983 from the Albian of Texas ( USA) was described on the basis of mostly isolated propodi; no articulated carpus with propodus has been found ( Bishop 1983: 40). The species exhibits several characters very typical for members of Eucalliacinae (as short triangular fixed finger with ridge on its outer surface, square manus with keeled lower margin) and this species is morphologically very close to Calliaxina chalmasii comb. nov. as recognized herein.

Another interesting case is the co-occurrence of Callianassa burckhardti and Protocallianassa sp. in the Masstrichtian and Danian strata of the Neuquén Basin ( Argentina) reported by Feldmann et al. (1995). Possible affinity of C. burckhardti to Eucalliacinae has already been mentioned above. The material of Protocallianassa sp. consists of several isolated chelae which are morphologically very close to minor chelipeds of several extant species of the genus Eucalliax . The figure published by Feldmann et al. (1995: fig. 4.4) shows a large manus with rather oblique proximal margin and elongated fixed finger with distinctly developed ridge. Such a morphotype corresponds e.g. to the minor chela of E. quadracuta . In fact, both minor and major chela of E. quadracuta figured by Biffar (1970: fig. 2h) show an oblique angle of propodus/carpus articulation. As a result C. burckhardti might represent a member of the genus Eucalliax .

Recent re-examination of the type material of C. archiaci , the type species of Protocallianassa , by Schweitzer & Feldmann (2012) shows that the carpus/propodus articulation is at 90° angle, whereas the carpus/propodus articulation at 100–110° angle is typical for another species, Protocallianassa faujasi ( Desmarest, 1822) , currently classified within the genus Mesostylus Bronn and Roemer, 1852 . Mesostylus was once considered a senior synonym of Protocallianassa and simultaneously a nomen oblitum by Karasawa (2003). After ressurection of Mesostylus the composition of Protocallianassa as listed in Schweitzer et al. (2010) needs to be reevaluated.

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.