See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/230016920 A new sea spider (Arthropoda: Pycnogonida) with a flagelliform telson from the Lower Devonian Hunsrück Slate, Germany Article in Palaeontology · August 2006 DOI: 10.1111/j.1475-4983.2006.00583.x CITATIONS READS 15 161 2 authors: Markus Poschmann Jason A Dunlop 74 PUBLICATIONS 459 CITATIONS 198 PUBLICATIONS 2,062 CITATIONS General Direction for Cultural Heritage of Rhi… SEE PROFILE Museum für Naturkunde - Leibniz Institute fo… SEE PROFILE Some of the authors of this publication are also working on these related projects: Rhenish Lower Devonian biota from marine/terrestrial transitional facies. View project Ammonoids from the Hunsrück Slate: importance for biostratigraphy or paleoecology View project All content following this page was uploaded by Jason A Dunlop on 09 September 2014. The user has requested enhancement of the downloaded file. All in-text references underlined in blue are added to the original document and are linked to publications on ResearchGate, letting you access and read them immediately. [Palaeontology, Vol. 49, Part 5, 2006, pp. 983–989] A NEW SEA SPIDER (ARTHROPODA: PYCNOGONIDA) WITH A FLAGELLIFORM TELSON FROM THE LOWER DEVONIAN HUNSRÜCK SLATE, GERMANY by MARKUS POSCHMANN* and JASON A. DUNLOP *Department for the Protection of Cultural Monuments of Rhineland-Palatinate, Section for Geological Sites, Große Langgasse 29, D-55116 Mainz, Germany; e-mail: mposchma@rz-online.de Institut für Systematische Zoologie, Museum für Naturkunde der Humboldt-Universität zu Berlin, Invalidenstraße 43, D-10115 Berlin, Germany; e-mail: jason.dunlop@museum.hu-berlin.de Typescript received 24 March 2005; accepted in revised form 25 July 2005 Abstract: A new Lower Devonian sea spider (Arthropoda: Pycnogonida) from the Hunsrück Slate, Germany, is described as Flagellopantopus blocki gen. et sp. nov. This is only the sixth fossil pycnogonid species to be described. Its most remarkable and unique aspect is the long, flagelliform telson. Although our fossil apparently lacks chelifores (an apomorphy), the retained telson and the segmented trunk end behind the last pair of legs resolve F. blocki to a fairly basal position in the pycnogonid stem lineage. It probably lies between Palaeoisopus problematicus Broili, which has a lanceolate telson and the most trunk segments of any sea spider, and all other Silurian–Recent Pycnogonida. Our new material shows that at least two fossil pycnogonids retained a telson, albeit with very different morphologies, and further supports the idea that a greater diversity of body plans existed among the Palaeozoic pycnogonid taxa. Pycnogonida (sea spiders) are an enigmatic group basal Euarthropoda. Vilpoux and Waloszek (2003) further noted that the hatching protonymphon larva of pycnogonids, with three pairs of appendages, is shorter than the supposed ancestral condition for euarthropods, i.e. the ‘head larva’ sensu Walossek and Müller (1998) with its four pairs of appendages. This may imply that pycnogonids represent a more basal grade of organization. Molecular data are still somewhat equivocal and further work is clearly needed to resolve between these competing hypotheses. Fossil pycnogonids are extremely rare, with only five named species from three Palaeozoic localities. Stratigraphically, the oldest examples are several larval instars from the late Cambrian ‘Orsten’ of Sweden (Waloszek and Dunlop 2002). These are followed by a Silurian species from the Herefordshire Lagerstätte (Siveter et al. 2004). Both finds are remarkable for their three-dimensionality and completeness, the latter reconstructed from serial sections through the encasing nodules. An unnamed Jurassic pycnogonid from France was mentioned by Wilby et al. (1996), but occasional reports of Jurassic sea spiders from Solnhofen in Germany remain unconvincing (see, for example, Polz 1984). The best known fossil pycnogonids are three species from the Lower Devonian Hunsrück Slate of Germany: Palaeoisopus problematicus of arthropods, usually thought to be related to euchelicerates (i.e. arachnids, xiphosurans and the extinct eurypterids), together forming the traditional Chelicerata. Entirely marine, some 1163 living pycnogonid species in nine or ten families have been described, occurring from the shoreline down to deep water. Many aspects of their biology have been summarized by King (1973) and Arnaud and Bamber (1987), and the group as a whole is characterized by a suite of putative autapomorphies. These include a prominent food-gathering proboscis, modified egg-carrying limbs called ovigers, multiple genital openings on the proximal leg articles and a general trend towards either reducing organ systems or displacing them into the legs. Recent work has witnessed a renewed interest in pycnogonids and, in particular, their position within the Euarthropoda (Dunlop and Arango 2005, and references therein). In summary, their chelate chelifores composed of only a few articles (Waloszek and Dunlop 2002) and certain aspects of the reproductive (e.g. Miyazaki and Makioka 1992) and circulatory systems (Miyazaki and Pass 2004) support their traditional placement as basal Chelicerata. In contrast, their lack of a labrum, nephridia and intersegmental tendons (Edgecombe et al. 2000) supports the idea that pycnogonids may in fact be ª The Palaeontological Association Key words: Arthropoda, Pycnogonida, sea spider, morpho- logy, Emsian, Hunsrück, Bundenbach. 983 984 PALAEONTOLOGY, VOLUME 49 Broili, 1928, Palaeopantopus maucheri Broili, 1929 and Palaeothea devonica Bergström et al., 1980. The last is the most modern-looking of the three and has an unsegmented trunk end behind the last pair of walking legs. In contrast, P. problematicus and P. maucheri are of particular interest in that they were described as having the plesiomorphic character of a longer, segmented trunk end behind the legs. In P. problematicus this trunk is setose (Hartenberger 1995) and ends in a prominent, lanceolate telson bearing the anus midway along its length. An anus opening within the telson is another putative plesiomorphic feature for euarthropods (Walossek and Müller 1998, fig. 12.8). The Hunsrück fossils thus bridge the morphological gap between the extremely reduced bodies of living pycnogonids and what might be envisaged as a more ‘typical’ arthropod body plan; see also Vilpoux and Waloszek (2003, fig. 13). Here we describe a new fossil pycnogonid from the Hunsrück Slate. This remarkable specimen is characterized by an elongate, flagelliform telson, a unique structure not seen in any other sea spider. It was provisionally described and figured as part of the Nahecaris project by Poschmann (2004) and given the name ‘Flagellopantopus’, a nomen nudum lacking a diagnosis. We formally describe and name this specimen here and discuss both its systematic position and its probable mode of life. MATERIAL, METHODS AND TERMINOLOGY Drawings were made with the help of a camera lucida. The most satisfying photographs were obtained from a black-coloured plaster cast coated with MgO. The X-ray (WB702) was made under the direction of Prof. W. Blind at the Institute of Applied Geology in Gießen, Germany, using the X-ray equipment Kristalloflex II and the highresolution X-ray film Agfa-StructurixTM (for details, see Bartels and Blind 1995). In the application of morphological terms we mostly follow Brusca and Brusca (2003) and Dunlop and Arango (2005). All measurements are in millimetres. fossiliferous sequence exposed in this now abandoned quarry is attributed to the middle part of the Kaub Formation of the Lower Emsian Stage. An Early Emsian biostratigraphical age is largely consistent with a new absolute age obtained from intercalated volcaniclastics, yielding a U-Pb zircon age of 407Æ7 ± 0Æ7 Ma for the time of eruption of these pyroclastics (Kaufmann et al. 2005). Deposition took place at, or just below, the storm-wave base in an intrashelf basin with low-energy turbidity currents being a major source of clastic sediment (Sutcliffe et al. 1999, 2002). These fine-grained turbidites sometimes enclose exceptionally preserved fossils, remains of a diverse epifauna that flourished under well-oxygenated conditions at or above the sea-floor. MORPHOLOGICAL INTERPRETATION Unfortunately, parts of our fossil (Text-fig. 1), particularly the distal limb articles, have been damaged by crude preparation methods using wire brushes; see Glass and Blake (2004) for a discussion of appropriate methods. The transition region between the proboscis and the cephalosoma is also damaged and poorly resolved. About 7 mm from the distal tip of the proboscis there is a swelling in the anterior cephalosoma region. It is probably the remains of a dorsal ocular tubercle. Details of the cephalosoma are equivocal. Judging from the arrangement of the limb-bases the cephalosoma and limb-bearing part of the trunk was elongate to oval, rather than purely rod-shaped, with cylindrical lateral processes to which the most proximal articles of the limbs attached. Our fossil lacks tuberculated rings, which are present on the lateral body processes and proximal limb articles in Palaeoisopus and on the lateral body processes and the first segment of the trunk end in Palaeopantopus (e.g. Bergström et al. 1980). The body portion behind the last pair of walking legs consists of at least two, possibly three, larger, subrectangular trunk end segments. The exact position where the last pair of legs attaches is not very clear, thus the uncertainty. Behind these segments is a shorter, boss-like region. This is either an additional, terminal, body segment or, more likely, the enlarged basal article of the flagellum (see below). GEOLOGICAL SETTING Appendages The exact stratigraphical position of many Hunsrück Slate fossils is unknown owing to the fact that they were collected from loose blocks split for the production of roofslate. This is also the case with the new sea spider fossil. However, we can be sure that it originated from the Wingertshell Member (sensu Schindler et al. 2002) in the Obereschenbach quarry (H. Block, pers. comm. 2004), situated c. 1 km south-west of Bundenbach. The marine Chelifores are lacking in our fossil and so were probably highly reduced or absent in life. Even if damage during preparation is taken into account, we would expect some remains of the chelifores to be visible in this dorsally exposed fossil. Remains of two slender anterior pairs of appendages are interpreted here as representing palps and ovigers, respectively. Their exact article count remains P O S C H M A N N A N D D U N L O P : N E W S E A S P I D E R F R O M T H E D E V O N I A N H U N S R Ü C K S L A T E 985 C A B Flagellopantopus blocki gen. et sp. nov., holotype PWL 2004 ⁄ 5024-LS. A pycnogonid (sea spider) with a flagellate telson from the Early Devonian Hunsrück Slate of Bundenbach, Germany. A, X-ray WB702. B, photograph of whitened cast. C, camera lucida drawing (modified from Poschmann 2004). Roman numerals designate walking legs I–IV. Abbreviations: cx, coxa; et, eye tubercle; fb, basal article of flagellum; fe, femur; fl, flagellate telson; ov, oviger; pa, palp; pr, proboscis; ta, tarsus; te, trunk end; ti1, tibia 1; ti2, tibia 2. Scale bars represent 10 mm. TEXT-FIG. 1. 986 PALAEONTOLOGY, VOLUME 49 unknown. The putative palps lie laterally against the proboscis and are at least as long as the latter. Ovigers originate in the region around the first and second walking leg pairs. Metamerically they emerge behind the palps, but their coxae are often displaced underneath the body in extant taxa (e.g. Dunlop and Arango 2005, fig. 3d). The ovigers are a little longer than the palps and the left one shows the characteristic hook-like, curved distal portion, which presumably aided cleaning and egg carrying. Five articles can be counted, but their full number is unknown because the ovigers are proximally hidden beneath parts of the second walking legs and are not entirely preserved distally. Remains of four pairs of slender walking legs are preserved. Exact measurements and descriptions for the leg coxae cannot be given. The proximal tibiae (here treated as tibiae 1) show both a longitudinal furrow and a slight thickening about half-way along their length, possibly associated with some sort of gland. Cement glands are associated with femoral thickenings in extant male sea spiders. Only proximal parts of the tarsi are preserved and more distal joints are completely lacking. In cross-section the articles are not as flattened as in the distal parts of the limbs in Palaeoisopus. Telson The telson forms a long, thin, articulated flagellum. It is preserved at its presumed full length of around 66 mm, or about 2Æ5 times the length of the body. Individual articles are visible proximally while other regions exhibit a kind of artificial ‘pseudo-segmentation’, probably resulting from diagenesis and ⁄ or tectonic effects (cf. comments in Richter and Richter 1929). DISCUSSION Mode of life The long, essentially cylindrical walking legs indicate that our fossil was less well adapted for swimming than Palaeoisopus with its flattened distal leg articles. Evidence for the diet of Flagellopantopus is inconclusive. If it genuinely lacked chelifores, it may have been specialized on prey possessing a relatively hard periderm cover that could be attacked and sucked out without the use of chelifores (cf. Behrens 1984). Extant pycnogonids that lack chelifores normally feed only on sessile organisms (C. Arango, pers. comm. 2004). Unique among sea spiders is its possession of a long, thin, segmented telson or flagellum. Owing to its delicate construction it was probably unable effectively to withstand strong physical forces. Thus, it seems improbable that the flagellum was used as a steering device while the animal was swimming as assumed for the telson in Palaeoisopus (Bergström et al. 1980), nor could it have aided in righting overturned animals as in extant horseshoe crabs (Shuster and Anderson 2003) or served as a means of defence. More likely, the slender telson played a role in sensory perception. A similar function, facilitating orientation on a muddy sea-floor, has been tentatively ascribed to long flagelliform antenna-like structures in a number of other Hunsrück Slate arthropods, e.g. the ‘crustaceanomorph’ Cambronatus Briggs and Bartels, 2001. On the other hand, it is anatomically similar to the flagellum of whipscorpions (Uropygi) and palpigrades (Palpigradi) among the arachnids. Hairs are equivocal in the new fossil, but the whipscorpion flagellum bears many sensory setae (e.g. Moro and Geethabali 1985). In at least one extant desert species the whipscorpion flagellum also plays a role in (terrestrial) water balance and ion transport (Haupt et al. 1980). Affinities Poschmann (2004) provisionally placed our new Hunsrück fossil as sister-group to Pantopoda. Relationships within Pycnogonida have been investigated most recently by Munilla (1999) and Arango (2002, 2003). The name Pantopoda has been restricted to crown-group sea spiders (cf. Waloszek and Dunlop 2002), all of which were traditionally defined by the reduction of the body behind the last pair of walking legs to a tiny trunk end bearing the anus. Some (extant) families may not be monophyletic, while the general evolutionary trend implicit within the crown-group traditionally involved the successive reduction or loss of the anteriormost appendages (chelifores, palps and ovigers) in more derived clades. A simple phylogeny including the Hunsrück fossils was outlined by Bergström et al. (1980, fig. 32) and implied a successive reduction of the trunk and telson behind the last pairs of walking legs. This scheme has been incorporated into subsequent models involving extant taxa and was adopted and emended by Waloszek and Dunlop (2002) to incorporate their new Cambrian species, a larval instar, but still potentially the most basal taxon given its retention of gnathobases on the limbs. Siveter et al. (2004) scored their Silurian pycnogonid, Haliestes dasos Siveter et al., 2004, and the three Hunsrück species into the morphological dataset of Arango (2002). With respect to the number of trunk end segments (sensu Siveter et al. 2004; their character 36), i.e. the region behind the last pair of legs, Palaeoisopus has four post-appendicular trunk end segments, Palaeopantopus has three and Haliestes, which has three enigmatic trunk end ‘elements’ that may or may not be true segments, was scored as uncertain for this character. For a different character, the segmentation of the trunk (not P O S C H M A N N A N D D U N L O P : N E W S E A S P I D E R F R O M T H E D E V O N I A N H U N S R Ü C K S L A T E the trunk end) or limb-bearing region behind the cephalosoma, both Palaeopantopus and Haliestes were scored as having indistinct segmentation (their character 19; see also Arango 2002) and thus resolved as sister-taxa in the final cladogram. One further point of note is that Arango (2003) recovered some Austrodecus (an extant genus) species in a very basal position and indeed Siveter et al. (2004) provisionally recovered them within the fossil stem, which, if correct, would render Pantopoda sensu Waloszek and Dunlop (2002) paraphyletic. Our new fossil has at least two, perhaps three, trunk end segments behind the legs, depending on how some structures in this region (the flagellum base?) are interpreted. The flagelliform shape of the telson is autapomorphic for the species, but retention of a telson is plesiomorphic for euarthropods (cf. Walossek and Müller 1998, fig. 12.8) and suggests quite a basal position for the new fossil. Integrating it into the scheme of Siveter et al. (2004), we provisionally resolve this new fossil between Palaeoisopus and the remaining Siluro-Devonian–Recent pycnogonids (Textfig. 2). The Cambrian larvae are not included here, but the clade excluding Palaeoisopus can be defined by the reduction of the (adult) post-appendicular trunk end to three segments or fewer. The clade excluding Palaeoisopus and the new fossil can be easily defined by the complete loss of the telson. There are no apomorphies that appear to unite Palaeoisopus and the new fossil; thus, we suggest there was a paraphyletic grade of basal, telson-bearing pycnogonids in the mid Palaeozoic. Our new fossil also suggests a greater 987 disparity of body plans among the Devonian sea spiders than has been recognized previously. Finally, the apparent absence of chelifores in the new fossil is an apomorphic character that might predict a more derived phylogenetic position. However, Arango (2002, fig. 5A) criticized previous assumptions of a gradual trend towards successive limb reduction in pycnogonids. Her most parsimonious tree implied five independent losses of the chelifores, spread throughout the cladogram in various families. Given such homoplasy among the living sea spiders, a further independent loss in our new fossil is not necessarily inconsistent with a relatively basal position. SYSTEMATIC PALAEONTOLOGY Class PYCNOGONIDA Latreille, 1810 Genus FLAGELLOPANTOPUS gen. nov. Derivation of name. From the flagelliform telson and the name Pantopoda. Type species. Flagellopantopus blocki sp. nov., by monotypy. Diagnosis. Pycnogonid with an elongate, flagellate telson borne on a segmented trunk end behind the last pair of walking legs. T E X T - F I G . 2 . Suggested phylogenetic position of Flagellopantopus blocki gen. et sp. nov., partly after Siveter et al. (2004, fig. 2) for taxa known as adults. Fossil taxa are indicated in bold type. The new Hunsrück fossil is provisionally placed in a fairly basal position owing to its retention of a telson, yet it is probably more derived than Palaeoisopus, which also has a telson, but which preserves a longer trunk end region, closer to the expected ancestral condition. Principal apomorphies of clades and ⁄ or individual taxa are indicated on the diagram where known; see also Bergström et al. (1980) and Waloszek and Dunlop (2002) for further details. Characters supporting the basal position of the two extant austrodecids have not been elaborated upon. 988 PALAEONTOLOGY, VOLUME 49 Flagellopantopus blocki sp. nov. Text-figure 1 2004 Flagellopantopus Poschmann, p. 354, fig. 4. [nomen nudum] Derivation of name. In honour of Helmut Block (Erlangen), who generously donated the holotype to a public collection. Holotype and only specimen. PWL 2004 ⁄ 5024-LS (original collector’s number 2165), deposited at the Landessammlung für Naturkunde Rheinland-Pfalz, Mainz, Germany. Type locality and horizon. Wingertshell Member (sensu Schindler et al. 2002) of the now abandoned Obereschenbach quarry south-west of Bundenbach, Hunsrück, Germany. Lower Devonian, Lower Emsian, middle Kaub Formation, Hunsrückschiefer. Diagnosis. As for the genus. Description. Total body length, from tip of proboscis to base of telson, c. 26; transverse leg span c. 90. Integument covered with small pustules. Broad, sac-like proboscis directed anteriorly; length at least 6, proximal width 4. Chelifores absent. Pedipalps and ovigers present, slender; lengths up to 6 and 7, respectively. Four pairs of walking legs present. Leg articles elliptical or round in cross-section. Femora of legs 3 and 4 c. 9Æ1 long. Tibia 1 (respectively from legs 1–4) with lengths of 9Æ1, 10Æ6, 11Æ5 and 14Æ9. Slender tibia 2 (where visible) with lengths of 12Æ2 (leg 1) and 11Æ0 (leg 3). Two or possibly three subrectangular trunk end segments, length c. 2Æ9, maximum width 2Æ4, behind the last limb-bearing body segment followed by a shorter region, length 1Æ0; the latter is probably the basal article of the telson. Telson flagelliform, elongate, round to oval in cross-section, length 66, width 0Æ6 proximally, narrowing gradually to 0Æ2 distally. Individual articles in the first 15 mm c. 1Æ0 long and 0Æ5 wide, with thickened anterior and posterior margins. Acknowledgements. Many thanks are due to Helmut Block (Erlangen), who made this important fossil available to us. 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