Lepidophthalmus Holmes, 1904

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 : 950-952

Genus Lepidophthalmus Holmes, 1904

Type species: Lepidophthalmus eiseni Holmes, 1904 , by monotypy; San Jose del Cabo, Lower California, Pacific .

Species included: Lepidophthalmus crateriferus (Lőrenthey in Lőrenthey and Beurlen, 1929) comb. nov. from the Oligocene of Hungary and several Recent species (see Poore 2012).

Emended diagnosis. ―Carapace with rostral spine; cornea dorsal, subterminal, disk-shaped; antennular peduncle longer and stouter than antennal peduncle; third maxilliped with minute exopod, ischium-merus subpediform, merus not projecting beyond articulation with carpus; chelipeds unequal, merus of major cheliped with meral hook positioned proximally and blade positioned distally; first pleopod slender and uniramous, second pleopod slender and biramous, third to fifth pleopods foliaceous and biramous in both sexes, appendices internae digitiform and distal on second pleopod, stubby, embedded in margin of endopod on third to fifth pleopods in both sexes (emended from Manning and Felder 1991: 778).

Discussion.― Lepidophthalmus was considered indistinguishable from Callianassa by de Man (1928) and Schmitt (1935). The genus was resurrected by Manning and Felder (1991) and it was treated as valid by subsequent authors (e.g., Poore 1994; Felder and Manning 1997; Sakai 1999b, 2005). Manning and Felder (1991) considered the type species ( L. eiseni ) a junior synonym of L. bocourti (A. Milne Edwards, 1870) . Felder (2003) showed that both taxa are distinct. Sakai (2005) still treated L. eiseni as synonymous with L. bocourti . In his latest monograph, Sakai (2011) redefined the genus substantially; he considered both the above mentioned species as distinct and L. bocourti (assuming that it represents the type species) to be the only member of the genus. He erected a new genus Lepidophthalmoides with L. eiseni (!) as its type species for all other previously recognized Lepidophthalmus species. Therefore, Lepidophthalmoides is an objective junior synonym of Lepidophthalmus as both genera are based on the same type species. Thus, in treating Lepidophthalmus as valid we follow here Manning and Felder (1991), Felder (2003), and Poore (2012).

Species of Lepidophthalmus are strongly heterochelous. They usually possess a rather stout major cheliped which can be heavily armed, especially in large males.

The merus of the major cheliped always possesses a proximal hook, which is sometimes bifid (or trifid), and a distally positioned pronounced blade (or lobe). The blade usually possesses serrations or small teeth (e.g., Rodrigues 1971: figs. 29, 30; Felder and Rodrigues 1993: figs. 1d, 1e, 3b, 3c; Felder and Manning 1997: figs. 1b, 2h, 2i, 3a–c; Felder 2003: figs. 13, 22). It seems that the meral blade is already present in small specimens (Peter C. Dworschak, personal communication 2011) and therefore can be considered of taxonomic value for palaeontologists. In extant Lepidophthalmus species, the only exception is L. socotrensis Sakai and Apel, 2002 , in which the merus has a broad lobate projection in larger males instead of a tiny medal hook ( Sakai and Apel 2002: figs. 5c, 6a), and the lower margin, although serrated, does not possess any distal blade. In virtually all Lepidophthalmus species the upper margin of the merus is clearly convex and slightly or strongly concave proximally, sometimes forming a U-shaped notch near the articulation with the ischium ( Sakai 1970: fig. 2a; Felder and Rodrigues 1993: fig. 4c; Felder and Manning 1997: figs. 1b, 2i, 3a; Dworschak 2007: figs. 11, 13). This notch is usually present on large males; thus, its development seems to be correlated with age, size and sex.

The carpus is semirectangular with the lower margin distinctly rounded proximally; the upper margin is slighthly converging proximally. The carpus is approximately as long as the palm, but differs in length between individuals. Holmes (1904) noted that in L. eiseni the carpus is somewhat shorter in males compared to that of females. A distinctly shorter carpus than palm was figured in both sexes for L. rosae (Nobili, 1904) , L. tridentatus (von Martens, 1868) , and L. turneranus ( White, 1861) ( Sakai 2005: figs. 31A–C; Dworschak 2007: figs. 2, 4–7, 11–14, 23–25, 32–35; de Saint Laurent and Le Loeuff 1979: figs. 20a, b; respectively).

The propodus is seemingly sexually dimorphic.Although no extensive study on sexual dimorphism within the chelipeds of Lepidophthalmus has been conducted so far (except for chela measurements, see Felder and Lovett 1989), thorough comparison of published figures and descriptions of all described species clearly shows that males usually have a propodal notch (sometimes termed as gape) with a distal tooth, both positioned just above the fixed finger at the articulation with the dactylus. There may also be a depression on the lateral and mesial surfaces of the palm positioned just between the fingers. This depression is usually well visible in low-angled light, and is usually covered with large tubercles. The depression can be large (up to half of the palm length) and is distinctly triangular in its shape. The depression in females normally is not present or is significantly reduced. Moreover, they have no notch between fingers; rather their fixed finger is broader than in males. Upper and lower margins of the propodus in females are distinctly converging distally; the lower margin can be broadly sinuous. These sexual differences in major cheliped morphology seem to be consistent within the genus, although a few exceptions can be found. In L. turneranus the above described male morphotype is present in females too, at least according to published figures (de Saint Laurent and Le Loeuff 1979: fig. 20b).

Virtually all Lepidophthalmus species have a keeled fixed finger, although this character is not always apparent during examination and may be obscured by compaction when preserved in the fossil state. In many extant species the fixed finger of males possesses a large triangular tooth on its occlusal margin, which can be directed distally (e.g., in L. manningi , see Felder and Staton 2000: fig. 1c; in L. richardi , see Felder and Manning 1997: figs. 4d–f; in L. siriboia , see Felder and Rodrigues 1993: fig. 4c; in L. sinuensis , see Lemaitre and Rodrigues 1991: figs. 3a, 3b). In males the dactylus is heavily armed with several teeth of different shapes depending on species. Females usually have unarmed dactyli, or at least the teeth are less developed than in males.

The minor cheliped is distinctly smaller than the major one and is usually unarmed. The merus is ovoid and may possess or lack a meral hook. The propodus is usually tapering distally and its lower margin is slightly concave at the articulation with the fixed finger. Both fingers are longer than the palm, and the dactylus is keeled.

As mentioned above, Lepidophthalmus socotrensis seems to be different from all other congeners. It has no tuberculation on the lateral surface of the propodus in the major cheliped, no notch or distal tooth on the distal margin at the base of the fixed finger and possesses a strongly armed minor cheliped dactylus. Also the sexual dimorphism in the nature of the major propodus as discussed above is not consistent within this species. As a result, we do not consider it a typical Lepidophthalmus . Indeed recently, Sakai et al. (2014) synonymized L. socotrensis with Podocallichirus madagassus ( Lenz and Richters, 1881) .

Manning and Felder (1991) pointed out the taxonomic importance of the merus on the major cheliped, usually in combination with other characters, as a distinctive feature for the generic assignment of ghost shrimps. The meral hook is present in many callianassoid taxa (mostly in the subfamily Callianassinae ); its development, however, is strongly variable among different genera and in many cases it can help in taxonomic determination. A tiny meral hook in its distal position is present in several genera, although, only Lepidophthalmus and Callianopsis de Saint Laurent, 1973 can be compared to each other as both share rather similar morphology of cheliped elements. In both taxa the general outline of the merus is similar, but contrary to Lepidophthalmus , Callianopsis does not possess a distal meral blade, the proximal meral hook is never bifid and the upper margin has no distinct proximal concavity ( Schweitzer Hopkins and Feldmann 1997: fig. 4A, B; Lin et al. 2007: fig. 1C). Both genera otherwise share similarly shaped major propodus in males and females and possession of tubercles on its lateral surface. Males of Lepidophthalmus species may have a large triangular tooth on the occlusal margin of the fixed finger which is present also in Callianopsis goniophthalma ( Rathbun, 1902) ( Schweitzer Hopkins and Feldmann 1997: fig. 4A). Major distinctions between both genera lie in the presence of a propodal depression in Lepidophthalmus , which is missing in Callianopsis . There may be a distinction in the nature of the carpus which seems to be always shorter than the propodus in Callianopsis but in Lepidophthalmus its length greatly varies and is at least partially dependent on sex. Males usually have a shorter carpus; in females it is at least as long as the palm. The shape of the minor cheliped of both genera is also strikingly different; Callianopsis has a sharp distally oriented tooth situated on the occlusal margin of the fixed finger ( Schweitzer Hopkins and Feldmann 1997: fig. 4C; Lin et al. 2007: fig. 1D; Hyžný and Schlögl 2011: text-figs. 2A, B, E, F), which Lepidophthalmus lacks.

Neontologists rely on the soft part morphology to identify callianassid taxa, which is usually not present in the fossil record. Therefore, the distinctive shape of the merus as discussed above (tiny meral hook and presence of meral blade) can be convincingly used as a proxy character for the generic assignment of fossil material to Lepidophthalmus . The meral hook in Lepidophthalmus is often bifid or even trifid, but due to compaction and general imperfection of preservation in the sedimentological record this morphological feature may be obscured. We propose that the distal meral blade can be considered of taxonomic importance in distinguishing the genera discussed here. The merus in Lepidophthalmus is also somewhat deeper in comparison with Callianopsis , although this feature may be a matter of preservation. In this respect the generic assignment of Callianopsis australis Casadío, De Angeli, Feldmann, Garassino, Hetler, Parras, and Schweitzer, 2004 from the middle Oligocene of Argentina ( Casadío et al. 2004) and C. inornatus Schweitzer and Feldmann, 2001 from the Eocene of Washington, USA ( Schweitzer and Feldmann 2001) may be revisited as the merus in these taxa is distinctly ovoid, a shape not commonly seen in this genus compare Schweitzer Hopkins and Feldmann 1997). On the other hand, the overall morphology of C. inornatus chelipeds Schweitzer and Feldmann 2001: fig. 9.3) clearly excludes the possibility of identifying this taxon as a member of Lepidophthalmus .

The material of Callianassa brevimanus Beurlen, 1939 clearly has a proximal meral hook and a distal unarmed meral blade ( Fig. 2C 2 , C 3 ), which are characteristic of Lepidophthalmus . All other morphological aspects are consistent with with this assignment, notably, the tuberculated area at the base of the fixed finger, a propodal distal tooth and morphology of the minor chela. Some of these characters are shared with Callianopsis , namely tubercles at the base of the fixed finger and a propodal notch with a distal tooth. The morphology of the minor cheliped is, however, distinctly different in both taxa. One specimen of C. brevimanus ( HNHM M.59.4720; Fig. 2D ) that also possesses a minor chela clearly points to the assignment of the species to Lepidophthalmus . Similarly, the material of C. craterifera consisting of isolated propodi shows above mentioned characters known in both Callianopsis and Lepidophthalmus ; several specimens, however, exhibit features which are consistent with their identification as minor chelae of Lepidophthalmus ( Fig. 3I, K ).

Stratigraphic and geographic range. ―Oligocene–Holocene. Until now the only supposed fossil occurrence of the genus has been L. jamaicense ? from the Upper Pleistocene of Jamaica reported by Collins et al. (2009). This occurrence, howev- er, should be questioned, as only a single left propodus was found. On its basis, therefore, the determination is obscure. Collins et al. (2009) argued for its similarity to L. jamaicense figured by Felder and Manning (1997: fig. 3). In fact, at least two more taxa, Sergio mericeae Manning and Felder, 1995 and S. sulfureus Lemaitre and Felder, 1996 , are also very similar ( Manning and Felder 1995: fig. 1b; Lemaitre and Felder 1996: fig. 3a; respectively). Moreover, the material identified as? Neocallichirus sp. and Neocallichirus peraensis from the same locality seems to fall within the morphological variation of the above mentioned Sergio species. As a consequence, all the callianassid material reported by Collins et al. (2009) seems to represent a single taxon seemingly conspecific with one of the Sergio species.

Lepidophthalmus crateriferus comb. nov. is considered to be the first reported and oldest fossil occurrence of its genus. The genus today is widespread in the West Atlantic and In- do-West Pacific; one species, L. turneranus ( White, 1861) is known also from the East Atlantic ( Sakai 2005). The material described here may suggest the Tethyan origin of the genus; however, without any other evidence we are hesitant to draw a firm conclusion.

Figures

Fig. 2. Fossorial shrimp Lepidophthalmus crateriferus (Lőrenthey in Lőrenthey and Beurlen, 1929) comb. nov., Óbuda in Budapest, Late Kiscellian. A. Left major cheliped of presumed male (HNHM M.59.4684b). B. Isolated left major propodus (HNHM M.59.4690). C. Left major cheliped of presumed male (C 1); neotype herein designated (lectotype of Callianassa brevimanus Beurlen, 1939) (HNHM M.59.4684a). Detail of C 1 under different light angle showing carpus and merus (C 2). Line drawing of merus depicted in C 2 (C 3). Note presence of distal meral hook and blade (see also white arrows in A and C 1). D. Presumed female specimen with both chelae (HNHM M.59.4720). E. Imprint of mesial surface of right major propodus (HNHM M.59.4683). Note setal pits close to upper margin of the chela.All specimens except HNHM M.59.4684a are paralectotypes of C. brevimanus selected herein.All specimens are figured to the same scale and were covered with ammonium chloride (except C ) prior to photography. Photographs by MH.

Fig. 3. Fossorial shrimp Lepidophthalmus crateriferus (Lőrenthey in Lőrenthey and Beurlen, 1929) comb. nov., Óbuda in Budapest, Late Kiscellian; presumed male morphotypes unless stated otherwise. A. Right major propodus (KGP-MH OT-007). B. Left major propodus articulated with dactylus of presumed female (KGP-MH OT-003). C. Left major propodus (KGP-MH OT-009). D. Left major propodus (KGP-MH OT-006). E. Fragmentary left major propodus (KGP-MH OT-008). F. Right major propodus (KGP-MH OT-010). G. Right major propodus (KGP-MH OT-001). H. Right major propodus of presumed female (KGP-MH OT-002). I. Right minor propodus of indeterminate sex (KGP-MH OT-011). J. Left major propodus of presumed female KGP-MH OT-005). K. Right minor propodus of indeterminate sex (KGP-MH OT-004). L. Left major dactylus (KGP-MH OT-017). M. Right major dactylus (KGP-MH OT-013). N. Right minor(?) dactylus (KGP-MH OT-012). O. Left major dactylus (KGP-MH OT-016). All elements are depicted in lateral aspect except D–F and J which are depicted in mesial view. All specimens are figured to the same scale and were covered with ammonium chloride prior to photography. Photographs by MH.