Ctenocheles rupeliensis ( Beurlen, 1939 )

Hyžný, Matúš & Dulai, Alfréd, 2014, Deep-water fossorial shrimps from the Oligocene Kiscell Clay of Hungary: Taxonomy and palaeoecology, Acta Palaeontologica Polonica 59 (4), pp. 947-965 : 956-959

Ctenocheles rupeliensis ( Beurlen, 1939)

Figs. 4A–E, 5A–D , 6A–C.

1939 Thaumastocheles rupeliensis sp. nov.; Beurlen 1939: 137, text-fig. 1, pl. 7: 1, 2.

1939 Callianassa nuda sp. nov.; Beurlen 1939: 144, text-fig. 3, pl. 7: 3, 4.

1941 Thaumastocheles rupeliensis Beurlen, 1939 ; Mertin 1941: 179, 185, fig. 10q.

1957 Thaumastocheles rupeliensis Beurlen, 1939 ; Imaizumi 1957: 303.

1996 Ctenocheles cf. rupeliensis ( Beurlen, 1939) ; Polkowsky 1996: 54. 2000 Ctenocheles rupeliensis ( Beurlen, 1939) ; Tshudy and Sorhannus 2000: 481, 484.

2002 Ctenocheles rupeliensis ( Beurlen, 1939) ; Moths and Montag 2002: 6, pl. 5: 2–7.

2003 Ctenocheles sp. ; Mikuž 2003: 90, pl. 1: 1–5.

2004 Ctenocheles chattiensis sp. nov.; Polkowsky 2004: 27, pl. 4: 17–27.

2010 Callianassa nuda Beurlen, 1939 ; Schweitzer et al. 2010: 36.

2010 Ctenocheles chattiensis Polkowsky, 2004 ; Schweitzer et al. 2010: 40.

2010 Ctenocheles rupeliensis ( Beurlen, 1939) ; Schweitzer et al. 2010: 40.

Type material: Lectotype selected herein: HNHM M.59.4694a, paralectotypes: HNHM M.59.4682, M.59.4686, M.59.4689, M.59.4691– 4693, M.59.4694b, M.59.4696–4697, M.59.4700–4701, M.59.4703– 709, M.59.4712, M.66.961.

Type horizon: Upper Kiscellian (lowermost Chattian), Kiscell Clay Formation .

Type locality: Újlak brickyard at Óbuda , Budapest (non existent anymore) .

Other material. ―Single fragmented major propodus ( FI.1339) and numerous uncatalogued cheliped fragments deposited in the Hungarian Geological and Geophysical Institute, Budapest.

Emended diagnosis. ―Major cheliped merus long and slen- der, unarmed, narrowing in both ends; fixed finger at angle of about 20–40° to the long axis of palm fingers about 1.5–2.5 length of palm; both fingers armed with long, needle-like teeth with three sizes, between two large teeth there are one to five small and medium teeth alternating with each other; tips of fingers strongly curved proximally forming large teeth crossing each other and exceeding at least twice the length of the large teeth on the occlusal surface.

Description. ―Chelipeds distinctly unequal in size and dissimilar in shape. In major cheliped, merus slender, unarmed, narrowing in both ends, approximately as long as carpus and palm together ( Fig. 4B); carpus short, higher than long, and cup-shaped ( Fig. 4B); palm bulbous, rounded or slightly elongate, longer than high, narrowing distally; fingers slen- der and elongate, about 1.5–2.5 times as long as palm, fixed finger at angle of about 20–40° to the long axis of palm, occlusal surface of both fingers armed with long, needle-like teeth with three sizes ( Fig. 4), between two large teeth there are one to five small and medium teeth alternating with each other; tips of fingers strongly curved proximally forming large teeth crossing each other and exceeding at least twice the length of large teeth on occlusal surface.

Minor cheliped slender, less massive than larger cheliped ( Fig. 5 ); carpus higher than long, with rounded proximo-lower margin ( Fig. 5D ); palm rectangular, longer than high, only slightly tapering distally; fixed finger long, narrow and straight, approximately as long as palm, occlusal margin of both fingers armed with a row of denticles, occlusal margin of fixed finger usually with proximal concavity (e.g., Fig. 5A ).

Dorsal carapace, pleon, and other appendages insufficiently preserved.

Intraspecific variation. ―Studied material shows variability in the shape of the palm of both major and minor chelae. The major cheliped palm can be nearly globular ( Fig. 4A, B) or slightly elongated ( Fig. 4E), and usually it is longer than high. The minor cheliped palm is usually distinctly longer than high with near-parallel upper and lower margins; in some specimens, though, the palm is shorter with upper and lower margins that are seemingly convex ( Fig. 5A ), thus resembling the bulbous nature of the major palm.The length of the fingers is also rather variable. Most specimens have fingers that are approximately two times longer than palm; however, some are distinctly longer, up to 2.5 times longer than palm (similar to extant C. balssi Kishinouye, 1926 and C. leviceps Rabalais, 1979 ), and one specimen ( HNHM M.59.4705) has a ratio of only 1.5 (similar to extant C. collini Ward, 1945 ). The occlusal surfaces of both major cheliped fingers are usually are armed with three teeth sizes; the pattern of alternating small and medium teeth between two large ones is variable depending on the distance of teeth from the proximal end; in the middle portion of fingers the teeth are usually more numerous (cf. Glaessner 1960). No constant formula can be given except that there are between 1 and 5 (usually 2–3) smaller teeth between two large ones. Similarly the dentition in the minor cheliped is variable; it may consist of two alternating sizes of teeth, or of teeth of uniform size.

Discussion.― Ctenocheles rupeliensis was described by Beurlen (1939) as a member of Thaumastocheles (Astacidea: Nephropidae ). It should be noted that Ctenocheles balssi , the type species of Ctenocheles , was described on the basis of material ascribed by Balss (1914) to? Pentacheles nov. sp. Beurlen (1939) drew attention to the striking resemblance of his Thaumastocheles rupeliensis to the specimen reported by Balss (1914); thus, he clearly recognized the identity of the material, although he did not mention Kishinouye’s work. Later, the species was formally recognized ( Glaessner 1947) to be a member of Ctenocheles .

Beurlen (1939) described the pectinate fingers and propodus of the major cheliped of this species and paid no attention to other preserved parts of the animal. Tshudy and Sorhannus (2000) mentioned that only a few claws of C. rupeliensis had been described. The original material, however, is far richer. In two studied specimens virtually the entire animal is preserved ( Fig. 6B, C). Unfortunately, details of soft-part morphology are obscured because of insufficient preservation.

Beurlen (1939) described Callianassa nuda on the basis of several mostly isolated cheliped fragments showing the palm as distinctly longer than high and with relatively long fingers. The material can be attributed to the minor chelae of Ctenocheles ( Fig. 5 ); they are, thus, considered conspecific with C. rupeliensis .

Differentiation between fossil species of Ctenocheles was discussed by several authors. Collins and Jakobsen (2003) distinguished Ctenocheles anderseni Collins and Jakobsen, 2003 from other northern European congeners on the basis of differences in the arrangement of the denticles lining the occlusal margin of dactylus. Feldmann et al. (2010: 341) argued that, “the outline of the manus; the height of the fixed finger; the longitudinal profile of the fixed finger, whether straight or curved; the form of the denticles on the occlusal surface; and form of the proximal part of the fixed finger are characters diagnostic of species within the genus”. Unfortunately, the intraspecific variation in finger dentition is poorly known. For instance, Glaessner (1960) reported in Ctenocheles cf. maorianus from the Late Pleistocene of New Zealand three to four small teeth between the large ones in the middle portion of the fingers of the major chela but up to six small teeth in the intervals on larger fingers. No tooth formula has been stated in descriptions of extant taxa and on the basis of isolated fingers the taxa probably are difficult, if not impossible, to differentiate from each other. For instance, tooth arrangements in C. balssi and C. leviceps according to published figures ( Sakai 1999a: fig. 2b, and Rabalais 1979: 15–17, respectively) are indistinguishable.

Matsuzawa and Hayashi (1997) provided a key for extant Ctenocheles species. Among other characters they considered the morphology of the major cheliped ischium and merus, as well as the ratio between the length of the palm and fingers, as characters on which basis nominate taxa can be distinguished. Large numbers of entire chelae preserved in Ctenocheles rupeliensis allows for an estimation of intraspecific variation in this species. Although many propodi of studied material are partially compressed, they clearly have rather variable outlines, from almost rounded to more elongate. Interestingly, specimens exhibit variable ratios between the length of the palm and fingers (see above). Similarly, there is rather great variability in the arrangement of teeth on occlusal margins of fingers.

Feldmann et al. (2010) distinguished C. notialis from the Miocene–Pliocene of Chile also on the basis of the angle of the fixed finger. In their diagnosis of C. notialis they noted the angle of the fixed finger to the long axis of the palm to be 35°. One of the figured specimens ( Feldmann et al. 2010: fig. 3A), however, clearly shows an angle of about 50°. Thus, the material exhibits angle values which overlap with other Ctenocheles species. For instance the material of C. rupeliensis shows a range of an angle values 20–40°.

As a result we conclude that the shape of the propodus, the ratio between the length of the palm and fingers, the dentition of fingers, and the angle of the fixed finger are intraspecifically variable characters which are uninformative on the species level if not treated in combination with other characters. The problem seems to be even broader as the comparison of extant Ctenocheles species clearly shows major differences in the nature of the major cheliped ischium and merus. When summarizing these characters one can distinguish three cheliped morphotypes present in extant Ctenocheles : (i) ischium and merus elongate, slender and completely unarmed ( C. balssi ; C. leviceps ; Ctenocheles sp. A sensu Holthuis, 1967; Ctenocheles sp. B sensu Holthuis, 1967); (ii) ischium serrated; merus ovoid with distinctly convex upper margin, unarmed ( C. collini , C. maorianus ); (iii) ischium with spines on lower margin; merus elongate with single median tooth on lower margin ( C. holthuisi ). Ctenocheles serrifrons is not included in this summary, as the major cheliped is unknown in this species ( Le Loeuff and Intès 1974). If one follows Manning and Felder (1991) in considering the merus as of taxonomic importance, then one would interpret these three morphological groups as separate genera.

Ctenocheles rupeliensis clearly can be assigned to the first morphological group as it possesses an elongate and completely unarmed merus ( Fig. 4B). As this group is defined mostly by C. balssi , the type species of Ctenocheles , we are hesitant to deal with the generic assignment of the rest of morphotypes as listed above without proper examination of their soft part morphology.

Mikuž (2003) reported cheliped fragments ascribed to Ctenocheles sp. from the Oligocene of Slovenia. Considering the relative geographical proximity of the Hungarian Kiscell Clay localities these might represent C. rupeliensis . The material itself is, however, too fragmentary to judge with confidence.

Polkowsky (2004) erected a new species, Ctenocheles chattiensis , from the Late Oligocene of Northern Germany. Although this material is slightly younger than C. rupeliensis , we consider it to be conspecific, although its preservation does not allow for much comparison. In fact it is questionable whether the material can form a basis for a new taxon. Supposed morphological differences as stated by Polkowsky (2004), namely the shape of lower and proximal margins of the palm of both major and minor chelipeds, are variable features. Polkowsky (2004) stressed the presence of two rows of setal pits along the fingers of the major cheliped which are actually present in all callianassoid shrimps and can not be considered as characters of taxonomic importance at the species level. Interestingly, Moths and Montag (2002) reported the presence of C. rupeliensis from the type locality (Kobrow) of C. chattiensis as stated by Polkowsky (2004). The material from a different locality (Malliss) reported by Moths and Montag (2002) exhibits more of the preserved characters than the material of Polkowsky (2004) does. As a result, C. chattiensis is considered herein a junior synonym of C. rupeliensis .

There are several Ctenocheles species described from the Eocene and Oligocene of Italy ( Table 2). Direct comparison with C. rupeliensis is difficult, as all of them are described on the basis of propodi and dactyli only (which are subjects of intraspecific variation), and no merus or ischium has been described so far.

Stratigraphic and geographic range. ―The species is known from the Oligocene of Hungary and Northern Germany.

Figures

Fig. 5. Minor chelae of fossorial shrimp Ctenocheles rupeliensis (Beurlen, 1939), Óbuda in Budapest, Late Kiscellian. A. Left minor propodus (HNHM M.59.4700). B. Right minor propodus (HNHM M.59.4869). C. Minor propodus articulated with dactylus (HNHM M.59.4691). D. Articulated left minor chela (HNHM M.59.4682). All specimens are paralectotypes selected herein. All specimens are figured to the same scale and were covered with ammonium chloride (except D) prior to photography. Photographs by MH.