Eucalliax capsulasetaea, Kiel & Hybertsen & Hyžný & Klompmaker, 2020

Kiel, Steffen, Hybertsen, Frida, Hyžný, Matúš & Klompmaker, Adiël A., 2020, Mollusks and a crustacean from early Oligocene methane-seep deposits in the Talara Basin, northern Peru, Acta Palaeontologica Polonica 65 (1), pp. 109-138 : 130-133

Eucalliax capsulasetaea sp. nov.

Fig. 18 .

Zoobank LCID: urn:lsid:zoobank.org:act:3742EC6D-CCAA-443D-A113-16EA7C8C30CD

Etymology: In reference to capsulated setae, one of diagnostic features of the species.

Type material: Holotype: right propodus ( NRM Ar69394) from block 2 . Paratypes: right propodus ( NRM Ar69376) from block 6, left carpus ( NRM Ar69377) from block 7, right propodus ( NRM Ar69383) from block 4, and four specimens from block 2: left propodus ( NRM Ar69393), right propodus ( NRM Ar69397), right propodus ( NRM Ar69398), left propodus ( NRM Ar69401) .

Type locality: Cerro La Salina seep deposits, Talara Basin, Peru .

Type horizon: Presumably the early Oligocene part of the Heath shale.

Material. —The type material and further fragmentary specimens from Cerro La Salina blocks 1, 2–4, 6–8. Complete left carpus (NRM Ar69377), block 7. Seven near-complete left propodi: NRM Ar 69378, block 7 ; NRM Ar 69380 (counterpart NRM Ar 69379), block 7 ; NRM Ar 69381, block 7 ; NRM Ar 69389 (counterpart NRM Ar 69390), block 8 ; NRM Ar 69393, block 2 ; NRM Ar 69401 (counterparts NRM Ar 69395, NRM Ar 69400) block 1 ; NRM Ar 69402, block 2. Five near-complete right propodi : NRM Ar 69376, block 6 ; NRM Ar 69383 (counterparts Ar 0069384, NRM Ar 69385), block 4 ; NRM Ar 69394, block 2 ; NRM Ar 69397, block 2 ; NRM Ar 69398, block 2. Three fragmentary propodi : NRM Ar 69382, block 7 ; NRM Ar 69387, block 1 ; NRM Ar 69396, block 2. One broken right fixed finger : NRM Ar 69399, block 2. One complete right dactylus : NRM Ar 69388, block 1. One fragmentary dactylus : NRM Ar 69386, block 1. All upper Oligocene, Talara Basin, Peru .

Dimensions (in mm).—Measurements are given only for sufficiently preserved propodi (maximum height and length of the manus). NRM Ar69376, H = 12.6, L = 11.5; NRM Ar69378, H = 11.9, L = 12.8; NRM Ar69383, H = 16.0, L = 16.2; NRM Ar69389, H = ~10.0, L = 11.4; NRM Ar69393, H = 18.3, L = 18.1; NRM Ar69394, H = 11.6, L = 10.5; NRM Ar69397, H = 8.6, L = 8.5; NRM Ar69398, H = 12.2, L = 11.4; NRM Ar69401, H = 15.2, L = 19.1.

Diagnosis. —Major manus subrectangular; outer and inner lateral surfaces of manus densely covered with round tubercles, often with individual or serial setal pits; fixed finger with longitudinal keel.

Description. —Chelipeds (pereiopod 1) robust. Major carpus taller than long, not armed; upper margin keeled; lower and proximal margins forming continuous rounded margin with an indent at articulation with merus; distal margin with flange. Major propodus rectangular, robust; upper and lower margins keeled, parallel to each other or slightly converging distally; distal margin with or without blunt tooth below articulation with dactylus; area around articulation with dactylus forming bulge; inner and outer lateral surfaces strongly convex, densely covered with tubercles, tubercles closer to margins larger than those closer to longitudinal axis; larger tubercles occur closer to margins; tubercles usually with individual or serial setal pits. Outer lateral surface of fixed finger with longitudinal keel; occlusal margin of fixed finger with serrated keel forming blunt tooth distally. Dactylus robust, unarmed, tip slightly hooked; outer lateral surface with row of round setae positioned close to occlusal margin.

Remarks. —The species is placed within Eucalliax based on the subrectangular manus, the relatively short fixed finger with a triangular outline, and the presence of a longitudinal keel on the outer lateral surface of the fixed finger. This combination of features is characteristic for the genus as discussed in detail previously (Hyžný 2012; Hyžný and Hudáčková 2012).

Eucalliax capsulasetaea sp. nov. was presumably heterochelous, as are most representatives of Callianassidae (Dworschak et al. 2012; Hyžný and Klompmaker 2015). Consequently, all the studied, rather large and massively built cheliped elements are interpreted to represent remains of major claws of pereiopod 1. The remains are nearly equally distributed between right and left chelae (five versus six propodi, respectively). Callianassid ghost shrimps in general show random asymmetry (sensu Palmer 2009) in Recent (e.g., Sakai 1969; Labadie and Palmer 1996) and fossil examples (e.g., Hyžný 2012; Hyžný and Hudáčková 2012), and Eucalliax capsulasetaea sp. nov. supports this observation.

In Eucalliax capsulasetaea sp. nov., the manus is approximately as long as tall (H/L ratio = 0.93–1.10), but one relatively large specimen is distinctly longer (H/L ratio = 0.80; see Dimensions above). NRM Ar69401 is also less tuberculate than other specimens. Nevertheless, all specimens are considered conspecific for several reasons. In extant representatives of Eucalliacinae (i.e., the species of Calliax Saint Laurent, 1973 , and Eucalliax Manning and Felder, 1991 ), considerable variation in the manus H/L ratio is observed and distinctly elongated forms are not uncommon, especially in larger individuals ( Dworschak 2006; Hyžný and Gašparič 2014). Also, the presence of setal pores on top of the tubercles covering the lateral surfaces of the elongated manus supports the conspecificity of all callianassid specimens from Cerro La Salina.

The setal pits positioned at the top of tubercles represent capsulated setae. They are not uncommon in hermit crabs (Paguroidea) and have been documented both in Recent ( Komai 2003; Osawa 2012; Komai and Rahayu 2014) and fossil forms ( Fraaije et al. 2011, 2015; Hyžný et al. 2016). Capsulated setae are rare in ghost shrimps. They have not been mentioned in taxonomic descriptions, but a quick survey of the published figures indicates their presence at least in fossil and extant species of Callianopsis Saint Laurent, 1973 ( Karasawa 1997; Schweitzer Hopkins and Feldmann 1997; Lin et al. 2007), although they are limited to a more distal region (i.e., close to the articulation with the dactylus) and their number usually is not exceeding ten. In extant Neocallichirus karumba ( Poore and Griffin, 1979) and its supposed fossil relatives, there are several (1–3) such tubercles present at the area of articulation with the dactylus ( Dworschak 2008; Hyžný et al. 2016). Thus, Eucalliax capsulasetaea sp. nov. bearing numerous tubercles with capsulated setae is unique among both extant and fossil ghost shrimp species described to date, to our knowledge. The new species is morphologically closest to Eucalliax burckhardti ( Böhm, 1911) from the Maastrichtian and Danian of Argentina and Mexico ( Hyžný et al. 2013). Both species share densely tuberculated propodi; E. burckhardti , however, does not possess capsulated setae. Besides the presence of capsulated setae, the new species further differs from the type species E. quadracuta in the absence of diagnostic acute projections on the distodorsal and distoventral corners of the carpus and on the distodorsal corner of the propodus ( Biffar 1970). Cenozoic representatives, such as E. vicetina Beschin, Busulini, De Angeli, and Tessier, 2002 , from the middle Eocene of Italy; E. pseudorakosensis (Lőrenthey in Lőrenthey and Beurlen 1929) from the middle Miocene of Europe; E. yatsuoensis ( Karasawa 1993) from the middle Miocene of Japan; and E. miyazakiensis Karasawa, 1993 , possess smooth lateral surfaces of the major cheliped propodi. In contrast to the new species, E. yoshihiroi Karasawa, 1992 , from the middle Eocene of Japan has sparse tubercles on the lateral surfaces of the major cheliped propodus, but it is not clear from the published figures alone whether setae are present at the top of the tubercles; no further details on this feature are mentioned in the description ( Karasawa 1992). Newly presented material of Eucalliax reported from the late Eocene of Italy ( Beschin et al. 2019) is too fragmentary and, based on the published figures, these specimens may not be congeneric with Eucalliax .

McLaughlin and Lane (1975) hypothesized that capsulated setae might act both to detect and repel predators, but more studies are needed to assess their function. The function of a limited number of capsulated setae in the ghost shrimps Neocallichirus and Callianopsis may be different than in hermit crabs and the here described new species of Eucalliax with numerous such setae. It is also worth noting that, whereas all Callianopsis species seem to possess capsulated setae, in Neocallichirus they are present only in the group of species morphologically close to N. karumba , a species differing profoundly from N. horneri Sakai, 1988 , the type species of Neocallichirus . Consequently, the presence or absence of capsulated setae on ghost shrimps are not always a feature of generic importance, as currently understood.

Muscle scars are preserved in a number of specimens of Eucalliax capsulasetaea sp. nov. These are observed in specimens in which the cuticle is not fully preserved on the inner and outer sides of the manus ( Fig. 18F ), or, sometimes, on the cuticle. These scars represent closer (adductor) muscles (see Klompmaker et al. 2019), whereas the much smaller (abductor) opener is not seen here.

Eucalliax spp. have been found in the Late Cretaceous, Paleocene, Eocene, Miocene, Pliocene, and Recent ( Hyžný and Klompmaker 2015: supplementary file 1). Thus, the new species is the first record from the Oligocene.

Stratigraphic and geographic range.— Type locality and horizon only.

Figures

Fig. 18. The callianassid ghost shrimp Eucalliax capsulasetaea sp. nov. from early Oligocene seep deposits at Cerro La Salina, blocks 2, 4, 6, 7, in the Talara Basin, northern Peru. A. Holotype (NRM Ar69394), right propodus in outer lateral view. B. Paratype (NRM Ar69376), right propodus in inner lateral view. C. Paratype (NRM Ar69383), right propodus in dorsal (C1), dorso-lateral (C2), outer lateral (C3), and inner lateral (C4) views. D. Paratype (NRM Ar69398), right propodus in outer lateral view. E. Paratype (NRM Ar69393), left propodus in outer lateral view. F. Paratype (NRM Ar69401), left propodus in inner lateral (F1), outer lateral (F2) and dorso-lateral (F3, F4) views. G. Paratype (NRM Ar69397), right propodus in outer lateral view. H. Paratype (NRM Ar69377), left carpus in outer lateral view. I. NRM Ar69399, right fixed finger in occlusal view. J. NRM Ar69388, right dactylus in outer lateral view. K–N. Details of capsulated setae on outer lateral surfaces of major cheliped propodi. K. NRM Ar69398. L. NRM Ar69393. M. NRM Ar69394. N. NRM Ar69383. Scale bars 5 mm.