JOURNAL OF CRUSTACEAN BIOLOGY, 35(2), 191-201, 2015

ARCHAEOSTRACAN (PHYLLOCARIDA: ARCHAEOSTRACA) ANTENNULAE AND ANTENNAE: SEXUAL DIMORPHISM IN EARLY MALACOSTRACANS AND CERATIOCARIS M’COY, 1849 AS A POSSIBLE STEM EUMALACOSTRACAN

Wade T. Jones 1,∗, Rodney M. Feldmann 1, and Donald G. Mikulic 2

1

Department of Geology, Kent State University, Kent, OH 44242, USA Downloaded from https://academic.oup.com/jcb/article-abstract/35/2/191/2547904 by guest on 22 April 2019 2 Illinois State Geological Survey, 616 East Peabody, Champaign, IL 61820, USA

ABSTRACT Although there is a relatively robust fossil record of archaeostracan phyllocarids, preserved antennulae and antennae are rare. Few examples have been described. A review of archaeostracans with preserved antennulae and antennae is provided, as well as a description of a specimen of Ceratiocaris cf. macroura Collette and Rudkin, 2010, with preserved antennae, and a detailed description of a specimen of Ceratiocaris papilio Salter in Murchison, 1859, from the Silurian of Scotland. The presence of antennulae with two subequal length rami in Rhinocaridina and Echinocaridina supports previous assertions that possessing biramous antennulae is a malacostracan synapomorphy. An antennal scale in Ceratiocaris, in contrast to those of Rhinocaridina and Echinocaridina, but consistent with eumalacostracans, suggests that ceratiocarids could represent stem eumalacostracans. Hooked antennae in C. papilio, similar to copulatory clasping antennae of Nebaliopsis typica G. O. Sars, 1887, are interpreted to represent the earliest evidence of sexual dimorphism in malacostracans. KEY WORDS: antenna, antennule, Archaeostraca, Malacostraca, Paleozoic, Phyllocarida, sexual dimor- phism DOI: 10.1163/1937240X-00002328

INTRODUCTION mous antennae with an elongated exopod and that Cerati- ocaris exhibited biramous antennae with the exopod rep- We review cases of preserved antennulae and antennae of resented by an antennal scale. As such, it is hypothesized archaeostracan phyllocarids; describe a specimen of Cera- that Ceratiocaris spp. might represent stem lineage eumala- tiocaris cf. macroura Collette and Rudkin, 2010 with ex- costracans and that the ancestral condition within Malacos- ceptionally preserved antennae from the Wenlock (Middle traca is the retention of two, elongated antennal rami, rather Silurian) Racine Dolomite, IL, USA; explore what general- than uniramous antennae, or antennae with an exopod scale. izations can be made about antennulae and antennae in Cera- It is additionally postulated that the paucity of stem lin- tiocaridina, Echinocaridina, and Rhinocaridina; and explore possible sexually dimorphic and phylogenetic implications eage eumalacostracan fossils might be the result of reten- of preserved archaeostracan antennulae and antennae. tion of phyllocarid-like features, i.e., seven pleomeres, phyl- Antennular morphology has important phylogenetic im- lopodous thoracopods, and styliform caudal furcae. plications in malacostracan higher taxa. For example, eu- Although archaeostracan phyllocarids have a relatively carids and some amphipods retain two antennular rami; robust fossil record, especially in the Paleozoic, the rarity isopods exhibit uniramous antennulae; hoplocarids and some of specimens with preserved antennulae and antennae leaves carideans exhibit triramous antennulae; and leptostracans researchers with an incomplete understanding of cephalic exhibit biramous antennulae, with the exopod represented by appendage morphology in that group. Because of light scle- a scale – an apparent autapomorphy. Our results support hy- rotization, preserved crustacean antennulae and antennae are potheses (Richter and Scholtz, 2001) that retention of two rare in the fossil record, commonly occurring only in cases equal-to-subequal length antennular rami is a malacostra- of exceptional preservation. Despite this, a number of pre- can synapomorphy and further suggests that malacostracan served archaeostracan antennulae and antennae have been antennular morphologies differing from this are autapomor- described or figured (Salter, 1860: Fig. 3g; Rolfe and Beck- phic or homoplasic. ett, 1984; Bergström et al., 1987, 1989; Briggs et al., 2004) Antennal morphology is apparently equally phylogenet- and researchers can begin making generalizations about an- ically significant, with leptostracans exhibiting uniramous tennular and antennal morphology in that group. antennae, and most eumalacostracan taxa exhibiting bira- Because males of the living leptostracan phyllocarids of- mous antennae with the exopod represented by an anten- ten exhibit sexually dimorphic antennae encompassing a nal scale. The results presented here indicate that represen- range of morphologies (Song et al., 2013), one would pre- tatives of Rhinocaridina and Echinocaridina exhibited bira- dict that sexual dimorphism might be recognizable in ar-

∗ Corresponding author; e-mail: [email protected]

© The Crustacean Society, 2015. Published by Brill NV, Leiden DOI:10.1163/1937240X-00002328 192 JOURNAL OF CRUSTACEAN BIOLOGY, VOL. 35, NO. 2, 2015 chaeostracan specimens. This issue is complicated by an in- of the thoracomeres and at least the four anteriormost complete understanding of the range of antennal morpholo- pleomeres. As such, the flagellum is approximately 2/3 to gies exhibited by archaeostracans and by the possibility that 3/4 the total body length. The flagellum gradually tapers archaeostracan species exhibited sexually dimorphic charac- in width from the basis to an acute distal termination. In ters that differed greatly from those of extant leptostracans. high magnification, it can be observed that the flagellum Examination of Ceratiocaris papilio Salter in Murchison, exhibits a fibrous, pitted structure (Fig. 1H); the pits are 1859, specimen GLAHM 2244 has provided the oldest evi- paired and span the entire length of the flagellum. These pits dence of sexual dimorphism in Malacostraca in the form of are interpreted to represent setal articulations, suggesting apparent copulatory clasping antennae similar to those of the that the antennae exhibited dense setation that is not well extant species Nebaliopsis typica G. O. Sars, 1887. preserved on the specimen. The following abbreviations indicate the repositories of The antennal exopod is positioned lateral to the endopodal specimens we studied: GLAHM, Hunterian Museum, Uni- flagellum (Fig. 1A-D, C). The exopod is slender throughout

versity of Glasgow, Glasgow, UK; ISGS, Illinois State Ge- its length and narrows abruptly to a bluntly acuminate Downloaded from https://academic.oup.com/jcb/article-abstract/35/2/191/2547904 by guest on 22 April 2019 ological Survey, Champaign, IL, USA; UWGM, University termination. On the part (Fig. 1A, C), the distal component of Wisconsin Geology Museum, University of Wisconsin at appears to be slightly damaged. However, on the counterpart Madison, Madison, WI, USA. (Fig. 1B, D, G) the exopod appears to terminate naturally. As such, the exopod is interpreted to have been much shorter FOSSIL PHYLLOCARID ANTENNULAE AND ANTENNAE than the endopod, unlike in rhinocarids and Cinerocaris magnifica Briggs, Sutton, Siveter, and Siveter, 2004, the only in Ceratiocaridina Clarke Zittel, 1900 echinocarid with known antennal morphology. Although it Ceratiocarididae Salter, 1860 is possible that the short scale-like nature of the antennal Ceratiocaris M’Coy, 1849 exopod of ISGS 100P-22A was the result of biostratinomic Ceratiocaris macroura Collette and Rudkin, 2010 breakage of an elongated antennal exopod, the apparent Source.—This paper (previously undescribed specimens natural termination of the exopod on the counterpart is ISGS 100P-22A and UWGM 1906). inconsistent with this interpretation. Occurrence.—ISGS 100P-22A occurred in the Middle Sil- Based on its length, lateral relationship to the endopod, urian (Wenlock, “Lecthaylus beds”), Upper Racine Dolomi- and abrupt but apparently unbroken termination, the anten- te, 24 m north of 142nd Street, 82 m west of Mackinaw Av- nal exopod is interpreted as an antennal scale. Although the enue, Burnham, Cook County, IL, USA. UWGM 1906 oc- exopod appears to be approximately equal in width to the an- curred in the Middle Silurian (late Llandovery to early Wen- tennal flagellum, this is not entirely inconsistent with its in- lock), Waukesha Biota, Brandon Bridge Formation, Wauke- terpretation as a scale. Because leptostracan phyllocarids ex- sha, WI, USA. hibit an autapomorphic, uniramous antenna, a modern phyl- locarid could not be used for comparison. Eumalacostracans, Background.—The specimens newly described here were however, do exhibit an antennal scale (Calman, 1904). The held in the collections of Donald Mikulic, Illinois State Geo- antenna of a preserved specimen of Procambarus cf. clarkii logical Survey, now deposited at the Illinois State Geological (Girard, 1852), from the Kent State University Department Survey (ISGS 100P-22A), and the University of Wisconsin of Geology Spirit Collection was excised and examined for at Madison Geology Museum (UWGM 1906). The Illinois comparative purposes (Fig. 1E, F). Study of the P. clarkii specimen occurred as part and counterpart from a split core antenna revealed that the antennal scale is composed of a from the Calumet System of the Water Reclamation District relatively narrow dorsal keel (Fig. 1E) with a ventrally posi- of Greater Chicago’s Tunnel and Reservoir Plan. The an- tioned, roughly triangular flap-like element (Fig. 1F). In the tenna preserved on UWGM 1906 is too incomplete to con- case of P. clarkii, the antenna is oriented such that the flap tribute much to understanding the antennal morphology of is positioned medially to the antennal endopod. The anten- C. macroura. nal exopod of the ISGS 100P-22A is interpreted to represent Antennule.—The antennulae are present but too poorly the dorsal keel of an antennal scale, the flap-like element preserved for any meaningful morphological elements to be of which would likely have been positioned laterally to the interpreted. endopod. The implications of the antennal scale will be dis- cussed below. Antenna.—The antennae exhibit a short, stout basis (Figs. 1A-D, G and 2A, B). The number of basal articles Ceratiocaris papilio Salter in Murchison, 1859 is unclear, however, it appears that there are at least two or Source.—Rolfe and Beckett (1984); this paper (restudy of three. Lateral to the exopod and emanating from the basis is a previously figured specimen; new specimens: GLAHM a poorly preserved, apparently branched or biramous struc- 2149, 2244). ture (Fig. 1A, C). This structure does not appear to be the Occurrence.—Middle Silurian (Llandovery), Jamoytius lo- exopod, as the exopod is well-preserved and in a more me- cality, Logan Water, Lesmahagow, Lanarkshire, Scotland. dial position. We interpret the feature to represent antennal setae, or some poorly preserved element unrelated to the an- Background.—Understanding of the antennal morphology tenna. of C. papilio has a long, strange history beginning with The endopod consists of a thin, multiarticulate flagellum the reconstruction of that species figured by Salter (1860, (Fig. 1A-D). The flagellum is slightly longer than the Fig. 3g) (Fig. 2C). The figured reconstruction, although carapace, which in archaeostracans generally contains all correct with respect to the relative position of the carapace, JONES ET AL.: FOSSILIZED ANTENNULE DIMORPHISM IN ARCHAEOSTRACANS 193 Downloaded from https://academic.oup.com/jcb/article-abstract/35/2/191/2547904 by guest on 22 April 2019

Fig. 1. Ceratiocaris cf. macroura Collette and Rudkin, 2010. A, ISGS 100P-22A part, scale bar = 10 mm; B, ISGS 100P-22A counterpart, scale bar = 10 mm; C, D, line drawings of A and B; BW, body wall; LCM, lateral carapace margin; Ma, mandible; Se, setae; Al, antennule; AnEn, antennal endopod; AnEx, antennal exopod; PD, preparation damage; E, F, dorsal and lateral view of Procambarus cf. P. clarkii (Girard, 1852) antennal scale, scale bar = 5 mm; G, close up of C. macroura antennal basis and scale, corresponding to A, scale bar = 1 mm; H, SP = setal pit, close up of C. macroura flagellar endopod, corresponding to A, scale bar = 1 mm. thoracomeres, pleomeres, and mandibles, was reconstructed distal ends and apparent scale-like exopods. This will be with the rostral plate protruding anteriorly from the carapace discussed in more detail below. and what were interpreted as questionable antennae or Antennule.—The antennular morphology of C. papilio is thoracic appendages positioned anterior to the carapace. still unknown. Only one actual photograph of a specimen of C. papilio, Antenna.—The antenna exhibits a relatively long basis, GLAHM 2244, with antennae has been published (Rolfe approximately 1/3 the length of the whole antenna, and and Beckett, 1984: Fig. 3). This specimen exhibits some an endopodal flagellum that comprises approximately 2/3 similarity to that figured by Salter (1860); however, the the total length (Fig. 3A, B). The number of basal articles antennae exhibit flagella with posteroventrally recurved is unclear, however, it appears that two articles could be 194 JOURNAL OF CRUSTACEAN BIOLOGY, VOL. 35, NO. 2, 2015 Downloaded from https://academic.oup.com/jcb/article-abstract/35/2/191/2547904 by guest on 22 April 2019

Fig. 2. Ceratiocarid antennulae and antennae. A, B, Ceratiocaris macroura UWGM 1906 with line drawing; C, reconstruction of Ceratiocaris papilio Salter in Murchison, 1859, modified from Salter (1860: Fig. 3g); D, Ceratiocaridina ? (family and genus indeterminate), modified from Bergström et al. (1989: Fig. 2f). An, antenna; Al, antennule; VCM, ventral carapace margin; Ma, mandible; Pl, pleonite. present (Fig. 3A, B). The flagellum is approximately as the leptostracan species Nebaliopsis typica G. O. Sars, 1887, wide as the basis, and it appears to have been relatively or a “distally excavated but blind eye-stalk such as occurs rigid and robust. Whether the flagellum was antennulate is in some deep-sea isopods, or that used for ploughing the unclear. The number of flagellar articles is also unclear, as no substrate by some living phyllocarids.” Distally excavated, evidence of individual articles is preserved. The distal-most blind eyestalks are present in some leptostracan species, portion of the flagellum is posteriorly recurved and hook- such as Dahlella calderiensis Hessler, 1984, Sarsinebalia ty- like (Fig. 3A, B). phlops (G. O. Sars, 1870), and species of Nebaliella Thiele, The antennal exopod is preserved on two of the specimens 1904. Examination of figured specimens of D. calderiensis, examined, GLAHM 2149 and 2244. GLAHM 2244 bears an S. typhlops, and Nebaliella cabotti indicates that blind eye apparent scale-like exopod superimposed over the right an- stalks of those species are variable in length and robustness tennal endopod and basis, as well as a similar structure in (Hessler, 1984; Mauchline, 1984). However, such eyestalks association with the left antenna – the left antennal basis and are consistently much shorter than the appendages figured in endopod being superimposed over it (Fig. 3C-E). Examin- Salter (1860) and are not posterodorsally recurved like those ing GLAHM 2244 alone, it is unclear whether the exopod appendages. As such, the suggestion of Rolfe and Beckett is scale-like or a short, slender ramus that is posteriorly re- (1984) that the appendages figured in Salter (1860) repre- curved or bent posteriorly (Fig. 3A). GLAHM 2149 exhibits sent blind eye stalks seems improbable. a similar structure impressed over a faintly preserved anten- The suggestion that the appendages represent copulatory nal basis; however, this structure is demonstrably a com- clasping antennae merits investigation. Examination of high plete scale-like exopod (Fig. 3C, D). Thus, examination of resolution photographs of GLAHM 2244, the specimen fig- GLAHM 2149 confirms that the antennal exopod of C. pa- ured by Rolfe and Beckett (1984) indicated that the anten- pilio, like that of C. macroura, was scale-like, not elongated nae of C. papilio do resemble the appendages figured in like those of rhinocarids and Cinerocaris magnifica. As such, Salter (1860: Fig. 3g) (Fig. 2A). However, the appendages of the antennal exopods of Ceratiocaris spp. appears to have GLAHM 2244 are strongly posteroventrally recurved, rather been a scale-like exopod, as in eumalacostracans, rather than than posterodorsally. The posteroventrally recurved anten- an elongated expodal ramus, as in other archaeostracans. nae of GLAHM 2244 are much more consistent with cop- Remarks.—Rolfe and Beckett (1984: 31) suggested that the ulatory, clasping antennae characteristic of sexually dimor- appendages figured by Salter (1860: Fig. 3g) might repre- phic males of N. typica (Fig. 3F); indeed they exhibit enough sent copulatory clasping antennae, such as those found in similarity to clasping antennae of those species that arguing JONES ET AL.: FOSSILIZED ANTENNULE DIMORPHISM IN ARCHAEOSTRACANS 195 Downloaded from https://academic.oup.com/jcb/article-abstract/35/2/191/2547904 by guest on 22 April 2019

Fig. 3. Ceratiocaris papilio Salter in Murchison, 1859. A, GLAHM 2244, scale bar = 10 mm. Af, antennal flagellum; Ab, antennal basis; Sc, scale; B, Explanatory line drawing. C, D, GLAHM 2149, close up of antennal scale and basis with line drawing; ACM, anterior carapace margin. E, GLAHM 2149, box indicates position of C. F, copulatory clasping antenna of Nebaliopsis typica G. O. Sars, 1887, modified from Thiele (1904: Fig. 44). 196 JOURNAL OF CRUSTACEAN BIOLOGY, VOL. 35, NO. 2, 2015 for an alternative function seems unwarranted (Fig. 3A, B, similarity to the legs of the fossil pycnogonid Palaeoiso- F). We suggest that the antennae of GLAHM 2244 represent pus problematicus Broili, 1928 and that structures inside the copulatory clasping antennae. Hence, males of C. papilio ap- carapace valves could represent the rest of the body of the parently exhibited sexually dimorphic antennae – the oldest pycnogonid. As such, summarizing the antennal morphol- potential record of sexual dimorphism in Malacostraca. ogy of this indeterminate ceratiocaridine cannot be under- That posteroventral curvature of the antennae of GLAHM taken with certainty. If the structures occupying the proba- 2244 represents biostratinomic alteration is a possibility that ble position of antennae are indeed antennae, then antennae must be evaluated. Unfortunately, specimens of C. papilio of this specimen are wide and paddle-like with a blunt distal with preserved distal antennae, other than GLAHM 2244, termination and stout basis approximately the same length are not available for examination because the only other as the flagellum (Fig. 2D). This would not be consistent with report of preserved antennae on C. papilio (Salter, 1860: known antennae of any archaeostracan phyllocarid. Hence, Fig. 3g) included neither specimen numbers, nor repository the interpretation of Bergström et al. (1989) that the structure

information. Thus, we had no additional specimens to use is a pycnogonid leg seems most probable. Downloaded from https://academic.oup.com/jcb/article-abstract/35/2/191/2547904 by guest on 22 April 2019 for comparison and potential support of the sexual dimor- Remarks.—This indeterminate specimen of Bergström et al. phism hypothesis. Despite this, a biostratinomic origin for (1989: Fig. 2a, f) is problematic in terms of its placement the curvature does not seem to be the most parsimonious ex- within Archaeostraca. The elongated, styliform telson ex- planation. The right and left antennae of GLAHM 2244 ex- hibiting much greater length than the caudal furcae and the hibit almost exactly the same degree of curvature. Addition- presence of a raised ventral carapace border are consistent ally, curvature is restricted to the distalmost antennomeres with its placement in Ceratiocaridina (Rode and Lieberman, (Fig. 3A, B), similar to the curvature of clasping antennae of 2002; Collette and Hagadorn, 2010). Bergström et al. (1989) Nebaliopsis typica (Fig. 3F), and the curvature of the right additionally asserted that the specimen lacked evidence of and left antennae is consistently posteroventral. It is unlikely a medial dorsal plate and mesolateral carina, features char- that curvature resulting from biostratinomic alteration would acteristic of Rhinocaridina, the latter more specifically of have resulted in such consistency in the degree, direction, Rhinocarididae (Rode and Lieberman, 2002; Collette and and point of flexure in both the right and left antennae. Hagadorn, 2010). The appendages figured in Salter (1860, Fig. 3a-g) are cor- However, the radiograph of the specimen figured by rectly positioned to be antennae, despite the aforementioned Bergström et al. (1989: Fig. 2a, f) is not entirely consistent differences between them and GLAHM 2244. The assertion with the claim that the specimen lacks a medial dorsal plate of Salter (1860) that the specimen depicted (his Fig. 3a-g) and mesolateral carina. The right and left carapace valves was a specimen “with all parts in situ” suggests that the ap- of the specimen appear to be widely separated; furthermore, pendages were part of that specimen. However, there is no it appears that there is a structure reminiscent of a medial indication that the appendages actually articulate with the dorsal plate (Bergström et al., 1989: Fig. 2a). There is also cephalon of the specimen. It is possible that the appendages a feature present on the right carapace valve consistent with represent antennae of another individual that happened to the position and shape of a mesolateral carina. Hence, we be- be preserved near the anterior of that figured by Salter. It is lieve placement of the specimen within Rhinocaridina seems also possible that the appendages represent the antennae of as likely as its placement in Ceratiocaridina. Unfortunately, that specimen but that they were distorted, or that the speci- Bergström et al. (1989) were only able to study radiographs men was a female or sexually immature male. Location and of the specimen. Location and restudy of the specimen might restudy of the specimen could resolve this issue, although it someday resolve these issues. seems improbable given that no repository information was If the specimen does prove to be a ceratiocarid, however, made available. it is the only specimen figured with preserved antennulae. Ceratiocaridina (family and genus indeterminate) In exhibiting two slightly subequal flagellar rami, the an- tennulae of the specimen are consistent with rhinocarid and Source.—Bergström et al. (1989). echinocarid species with known antennular morphology. If Occurrence.—Lower Devonian (early Emsian), Hunsrück the specimen is a ceratiocarid, it suggests that ceratiocarid Slate, southern Rhenish Massif, Germany. antennular morphology was similar to that of the rhinocarids and echinocarids. Background.—The specimen attributed to Ceratiocaridina was figured and described in the restudy of the Hunsrück Echinocaridina Clarke in Zittel, 1900 Slate phyllocarids by Bergström et al. (1989). Their de- Cinerocaris magnifica Briggs, Sutton, Siveter, and scription was based on radiographs produced by Walter M. Siveter, 2004 Lehmann, and that was the only material available for study Source.—Briggs et al. (2004). (Bergström et al., 1989). Occurrence.—Middle Silurian (Wenlock), Herefordshire Antennule.—The antennulae are composed of a short ba- Biota, Herefordshire, UK. sis and two short, slender, multiarticulate flagella. The flag- ella are approximately three times the length of the basis Background.—Briggs et al. (2004) described a single spec- (Bergström et al., 1989: Fig. 2a, f) (Fig. 2C). imen of Cinerocaris magnifica from the Middle Silurian (Wenlock) Herefordshire Biota of Herefordshire, UK. These Antenna.—Bergström et al. (1989) remarked that the struc- specimens are unique in that they are studied by serially ture in the expected position of the antenna exhibited great grinding, scanning, and creating a computerized reconstruc- JONES ET AL.: FOSSILIZED ANTENNULE DIMORPHISM IN ARCHAEOSTRACANS 197

pace node and purported appendage position cannot be ac- complished using Cinerocaris magnifica, however, because the carapace of this species is not strongly regionalized. Although sweeping conclusions about echinocarid anten- nular and antennal morphology cannot be made based on a single species, the gross morphology of those limbs is con- sistent with that of rhinocarids whose antennular and an- tennal morphology is known (Bergström et al., 1987, 1989; Bergman and Rust, 2014). This is discussed in more detail below.

Rhinocaridina Clarke in Zittel, 1900

Rhinocarididae Hall and Clarke, 1888 Downloaded from https://academic.oup.com/jcb/article-abstract/35/2/191/2547904 by guest on 22 April 2019 Nahecaris stuertzi Jaekel, 1921 Source.—Rolfe (1981); Bergström et al. (1987). Occurrence.—Lower Devonian (early Emsian), Hunsrück Slate, southern Rhenish Massif, Germany. Background.—Bergström et al. (1987) figured and redescri- bed N. stuertzi based on 40 specimens from the early Emsian Fig. 4. Cinerocaris magnifica Briggs, Sutton, Siveter, and Siveter, 2004. Hunsrück Slate. Museum numbers for specimens examined Al, antennule; AnEn, antennal endopod; AnEx, antennal exopod. Modified from Briggs et al. (2004: Fig. 1a). are included therein. Nearly all figured specimens exhibited exceptionally preserved antennulae and antennae, permitting tion of the fossils (Sutton et al., 2001). The computer gen- relatively detailed examination of the antennular and anten- erated rendering is a three-dimensional representation of the nal morphology of those species, including ventral, dorsal, specimen that exhibits remarkable morphologic detail, in- and lateral views. Rolfe (1981) also figured a ventrally pre- cluding soft parts, and delicate appendages with otherwise a served N. stuertzi with preserved antennulae and antennae low potential for preservation. The reconstruction of Cine- in his evaluation of phyllocarids and malacostracan origins rocaris magnifica includes most details of the antennulae (Fig. 5A). and antennae, however, very fine details, such as individual Antennule.—The antennulae exhibit a basis with two or podomeres, are not well resolved. three articles, and two slender, multiarticulate flagellar rami, Antennule.—The antennular peduncle is shorter than the one apparently positioned above the other. The lower ramus flagellum, oval in cross section, and expands distally to a is thickened proximally and slightly longer to approximately circular cross-section. The distal flagellum is slightly longer 30% longer than the upper ramus. than the medial flagellum. Both rami are assumed to have Antenna.—The antenna is more robust than the antennule. been antennulate (Briggs et al., 2004) (Fig. 4). The endopod bears a basis composed of two exceptionally Antenna.—The antenna is larger than the antennule with a long, robust articles; the second article is much longer than basis that is oval in cross-section and tapers slightly to the the first. The antennal flagella are setose, the endopodal point at which the flagellar rami attach. The distal ramus is a flagellum being densely setose. The exopodal flagellum is short, slender flagellum. The medial ramus has a short, broad narrower than the endopodal flagellum, and emanates from base that tapers abruptly into a flagellum (Fig. 4). a basal article shared by the antennal rami. The exopod is multiarticulated throughout its length, and evenly tapering Remarks.—Cinercaris magnifica is the only described echi- (after Bergström et al., 1987). nocarid with preserved antennulae and antennae. Attempts have been made to interpret the position of cephalic ap- Remarks.—See below. pendages of Echinocaris Whitfield, 1880 based on the size and position of dorsal carapace nodes (Beecher, 1902). For Oryctocaris balssi (Broili, 1930) example, Beecher demonstrated that the largest cephalic lobe of Echinocaris socialis corresponds to the position of Source.—Bergström et al. (1989); Bergman and Rust (2014). the mandible, and suggested that the anterior dorsal lobe Occurrence.—Lower Devonian (early Emsian) Hunsrück corresponds to the antennule, the lobe posterior to that rep- Slate, southern Rhenish Massif, Germany. resents the antenna, and the double node next to the nuchal furrow represents the maxillae. These assertions, with the Background.—Oryctocaris ballsi was originally described exception of the relationship of the largest cephalic node by Broili (1930) and was attributed to Nahecaris.The and mandibles, cannot at present be verified. However, the species was redescribed in the restudy of Hunsrück phyl- position of these appendages on Cinerocaris magnifica,as locarids by Bergström et al. (1989). Bergman and Rust figured by Briggs et al. (2004), does correspond to the po- (2014) undertook a detailed restudy of O. balssi, removed sition of the carapace lobes of more advanced echinocarids O. balssi from Nahecaris, and placed it in Oryctocaris,a (Beecher, 1902; Eller, 1935). Definitive correlation of cara- new monospecific genus. 198 JOURNAL OF CRUSTACEAN BIOLOGY, VOL. 35, NO. 2, 2015 Downloaded from https://academic.oup.com/jcb/article-abstract/35/2/191/2547904 by guest on 22 April 2019

Fig. 5. Rhinocarid antennulae and antennae. A, Nahecaris stuertzi Jaeckel, 1921, modified from Rolfe (1981: Fig. 2); B, Oryctocaris balssi (Broili, 1930), modified from Bergman and Rust (2014: Fig. 2); C, Oryctocaris balssi (Broili, 1930), after Broili (1930); D, Rhinocaridina family and genus indeterminate, modified from Bergström et al. (1989: Fig. 4e). Al, antennule; AnEn, antennal endopod; AnEx, antennal exopod; LM, labrum; Pe, pereiopod.

Antennule.—The antennulae of O. balssi exhibit two slen- Antennule.—The antennulae exhibit bases with at least two der, multiarticulate flagella emanating from a stout, three- articles, which are much longer than those of N. stuertzi,a article basis. One flagellum is positioned dorsal to the other. similar rhinocaridid species from the Hunsrück Slate. Both The proximal basal segment is the longest, and the next two antennular rami are equal in length and width and appear to are shorter and subequal in size. The flagella are approxi- taper anteriorly to an acuminate termination. The antennulae mately equal in length and width (Bergman and Rust, 2014) are approximately 3/4 the length of the antennae and bear no (Fig. 5B, C). visible setae (Bergström et al., 1989) (Fig. 5d). Antenna.—The antennae exhibit a broad anterior flagellum Antenna.—The antennae exhibit a long, stout endopod emanating from the front of the second basal article and a and short, slim exopod, emanating from a short basis of narrow posterior flagellum emanating from the first basal apparently two articles. The endopodal and exopodal flagella article. The posterior flagellum is approximately one quarter appear to have been annullated throughout their length. The to one half the length of the anterior flagellum. The margin endopod was described as being densely setose, with longer of the anterior flagellum is fringed by a range of setae (after setae on one side than the other, but this was not reflected in Bergman and Rust, 2014) (Fig. 5B, C). the explanatory drawing of Bergström et al. (1989: Fig. 4e- Rhinocarididae? (genus and species indeterminate) f) and is not clearly visible in photographs of the specimen (Bergström, 1989: Fig. 4a-c). Source.—Bergström et al. (1989). Remarks.—Because rhinocarids are apparently rather con- Occurrence.—Lower Devonian (early Emsian) Hunsrück sistent in their antennular and antennal morphology. Rhino- Slate, southern Rhenish Massif, Germany. caridina which preserve these limbs exhibit biramous anten- Background.—Bergström et al. (1989, Fig. 4a-f) figured and nulae with flagellar rami of equal to slightly subequal length; described specimen WS 11709, which they attributed to the antennae also exhibit well-developed endopodal and ex- Rhinocarididae. Based on their figures, the specimen does opodal rami, although the length of the exopod relative to appear to be a rhinocaridid as diagnosed by Rode and Lieber- that of the endopod is apparently variable. The antennal ex- man (2002) based on the presence of a relatively broad, flat opods of rhinocarids are consistently shorter and more slen- telson, broad furcal rami longer than the telson, and a me- der than the endopods, and in O. balssi and the indetermi- dian dorsal plate separating the carapace valves. The meso- nate rhinocarid of Bergström et al. (1989) are reduced to lateral carina and carapace ornament, if present, are poorly as little as one quarter the length of the endopodal flagel- preserved. Thus, we agree with Bergström et al. (1989) that lum. This differs from the condition seen on N. stuertzi,in the specimen is likely attributable to Rhinocarididae. which the exopodal flagellum is much more slender, but only JONES ET AL.: FOSSILIZED ANTENNULE DIMORPHISM IN ARCHAEOSTRACANS 199 slightly shorter than that of the endopod. Moreover, the well- Scholtz, 2001). Richter and Scholtz (2001) considered bi- developed antennal exopod of rhinocarids differs from the ramous antennulae to be a key character in support of mala- scale-like antennal exopod of ceratiocarids and is very much costracan monophyly, despite the aforementioned variation. consistent with the well-developed, but slightly reduced, ex- The consistent presence of two well-developed flagellar rami opodal flagellum of Cinerocaris magnifica. The implications on archaeostracan antennulae supports the idea that posses- of this are discussed below. sion of biramous antennulae is a malacostracan synapomor- phy, and further suggests that variations from that condition DISCUSSION are autapomorphic or homoplasic. The presence of a scale-like antennal exopod has long Sexual Dimorphism in Fossil Phyllocarids been considered a synapomorphy of Eumalacostraca (Cal- Males of many leptostracan species exhibit sexually dimor- man, 1909). Schram and Hoff (1998) included two char- phic antennae. In Nebalia and Sarsinebalia, the antennal acter states for the antennal scale, the first possessing a

flagellum of the male exhibits extreme elongation, in many separate basal segment, as in stomatopods, and the second Downloaded from https://academic.oup.com/jcb/article-abstract/35/2/191/2547904 by guest on 22 April 2019 cases being as long as the entire body (Dahl, 1985; Song lacking the basal segment as in most other eumalacostra- et al., 2013). Males of Nebalia can also display antennal cans (Schram and Hoff, 1998; Richter and Scholtz, 2001). flagella that are distinctly anteriorly directed, with numer- Richter and Scholtz (2001), however, considered the exo- ous flagellar articles or distinct setation (Haney and Martin, pod scale to be homologous in stomatopods and other eu- 2000, 2005; Moreira et al., 2007; Lee and Bamber, 2011; malacostracans. A scale-like exopod is absent from the an- Song et al., 2012, 2013). As we noted above, males of tennae of nearly all isopods and thermosbaenaceans (Br- Nebaliopsis typica exhibit posteroventrally recurved copu- usca and Wilson, 1991; Wagner, 1994; Richter and Scholtz, latory clasping antennae (Thiele, 1904; Rolfe and Beckett, 2001), an apparent autapomorphy. In contrast to eumalacos- 1984), which are grossly similar to the antennae of C. pa- tracans, leptostracan phyllocarids exhibit uniramous anten- pilio-specimen GLAHM 2244 described herein (Fig. 3A, D). nae (Richter and Scholtz, 2001; Walker-Smith and Poore, For the reasons discussed above, a taphonomic origin of the 2001). The presence of a scale-like exopod, rather than an curvature of the distal antennae of GLAHM 2244 can be dis- elongated exopodal flagellum on both species of Ceratio- carded. caris with known antennal morphology is intriguing. As can The issue of sexual dimorphism is complicated in fos- be seen, this character differs from both leptostracans and sil phyllocarids, since there is little basis for recognizing other archaeostracans. The presence of an elongated exopo- dimorphic characters with the exception of drawing analo- dal flagellum in all archaeostrans, except Ceratiocaris, sug- gies from extant species. Because it is unknown whether ar- gests that retention of a well-developed exopodal flagellum chaeostracans exhibited sexually dimorphic characters not is the ancestral ground plan in Malacostraca. seen in the leptostracans, dimorphism in some archaeostra- The presence of an antennal exopod scale in Ceratiocaris can species might be unrecognizable. However, as has been spp. intimates that ceratiocarids might represent stem lin- demonstrated here, dimorphic characters are possible to rec- eage eumalacostracans. The lack of generally eumalacostra- ognize in rare instances when the antennae are preserved. As can-like characters, such as the thoracic stenopodia, cari- was demonstrated by Song et al. (2013) in their description doid pleon, and characteristic eumalacostracan caudal fan in of Nebalia pseudotrocosoi Song, Moreira, and Min, 2013, Ceratiocaris makes such an hypothesis somewhat less com- new expressions of sexual dimorphism in lepstostracans are pelling, as was recognized by Hessler and Schram (1984) still being recognized. Recognition of new forms of sexual in their discussion of leptostracans as ‘living fossils.’ De- dimorphism in leptostracans could lead to the recognition of spite this, the antennal scale appears to be a rather robust dimorphism in more fossil phyllocarids in the future. character in eumalacostracans; it is present in all repre- sentatives of that group other than thermosbaenaceans and Phylogenetic Considerations some isopods. Worthy of note is that no other definitive All representatives of Echinocaridina and Rhinocaridina eumalacostracan character has been recognized in fossil or possess antennulae with two rami of equal or slightly sube- living phyllocarids, implying that vast gaps must exist in qual length. This differs from leptostracan phyllocarids, that our knowledge of the apparent phyllocarid-eumalacostracan have antennulae with a single flagellar ramus and an anten- transition. The antennal scale in ceratiocarids represents the nular scale, an apparent autapomorphy (Hessler and Schram, only concrete morphological evidence of such a phyllocarid- 1984; Oleson, 1999; Walker-Smith and Poore, 2001). Eu- eumalacostracan transitional form, albeit only a single char- malacostracans exhibit variations in antennular morphology, acter. with eucarids and some amphipods exhibiting an antennule In considering this critical transition, the issue arises of with two rami; Richter and Scholtz considered biramous what the stem lineage of Eumalacostraca actually might have antennulae to be the ground plan for Amphipoda. Anten- looked like. Much discussion of early eumalacostracan evo- nulae in isopods have variously been considered to be bi- lution has focused on Calman’s (1904, 1909) concept of the ramous or uniramous (Brusca and Wilson, 1991; Richter caridoid (Schram, 1969, 1973; Dahl, 1983; Hessler, 1983), and Scholtz, 2001). Stomatopods and early fossil hoplo- which is not surprising given that all eumalacostracan lin- carids, as well as some carideans, exhibit triramous anten- eages retain arguably caridoid morphological aspects and nulae (Schram and Hoff, 1998; Richter and Scholtz, 2001; even Paleozoic eumalacostracans not attributable to any liv- Davie, 2002). Bathynellaceans exhibit biramous antennu- ing eumalacostracan taxon, such as belotelsonids and an- lae with an endopodal scale (Siewing, 1959; Richter and thracophausiids, are markedly and recognizably caridoid. In 200 JOURNAL OF CRUSTACEAN BIOLOGY, VOL. 35, NO. 2, 2015 addition to this, crown-group Eumalacostraca, as evidenced the Lower Devonian Hunsrück Slate (Germany). Journal of Systematic by Devonian decapods and stomatopods, appear in the fos- Palaeontology 12: 427-444. sil record with no apparent precursor stem lineage (Schram Bergström,J.,D.E.G.Briggs,E.Dahl,W.D.I.Rolfe,andW.Stürmer. 1987. Nahecaris stuertzi, a phyllocarid crustacean from the Lower et al., 1978; Feldmann and Schweitzer, 2010; Jones et al., Devonian Hunsrück Slate. Paleontologische Zeitschrift 61: 273-298. 2014). , , , ,and . 1989. Rare phyllo- Given the presence of apparent eumalacostracan charac- carid crustaceans from the Devonian Hunsrück Slate. Paleontologische ters in hoplostracan phyllocarids (Schram, 1969, 1973), the Zeitschrift 63: 319-333. presence of a scale-like antennal exopod in Ceratiocaris Briggs, D. E. G., M. D. Sutton, D. J. Siveter, and D. J. Siveter. 2004. A new phyllocarid (Crustacea: Malacostraca) from the Silurian fossil – spp., and the remarkable lack of evidence of a stem lineage Lagerstätte of Herefordshire, UK. Proceedings of the Royal Society of eumalacostracan, the possibility must be considered that ev- London. Series B: Biological Sciences 271: 131-138. idence of eumalacostracan origins lies within the known Pa- Broili, F. 1928. Crustaceenfunde aus dem rheinischen Unterdevon. I. leozoic phyllocarid fossils; such stem-forms may have re- Über Extremita¨tenreste. der Bayerischen Akademie der Wissenschaften, Mathematisch-Naturwissenschaftliche Abteilung 1928: 197-201.

tained phyllocarid characters, including phyllopodous tho- Downloaded from https://academic.oup.com/jcb/article-abstract/35/2/191/2547904 by guest on 22 April 2019 . 1930. Ein neuer Nahecaride aus den Hunsrückschiefern. Central- racopods, seven pleomeres, and uniramous, styliform furcal blatt für Mineralogie, Geologie, und Paläontologie B: 247-251. rami. As has remained the case for as long as malacostracan Brusca, R. C., and G. D. F. Wilson. 1991. A phylogenetic analysis of phylogeny has been studied, hypotheses about eumalacos- the Isopoda with some classificatory recommendations. Memoirs of the tracan origins raise more questions than they answer. The Queensland Museum 31: 143-204. possibility must be explored, however, that stem lineage eu- Calman, W. T. 1904. On the classification of the Crustacea Malacostraca. Annals and Magazine of Natural History 7: 144-158. malacostracans have remained so enigmatic because they are . 1909. Crustacea. In, E. R. Lankester (ed.), A Treatise on Zoology a lineage shrouded in furcae and phyllopods. 7. Adam and Charles Black, London. In conclusion, we wish to state that based on our analysis Colette, J. H., and J. W. Hagadorn. 2010. Early evolution of phyllo- of previously described archaeostracan antennulae and an- carid arthropods: phylogeny and systematics of Cambrian-Devonian ar- tennae, as well as description of newly available specimens chaeostracans. Journal of Paleontology 84: 795-820. , and D. M. Rudkin. 2010. Phyllocarid crustaceans from the (ISGS 100P-22A and UWGM 1906) and re-description of Silurian Eramosa lagerstätte (Ontario, Canada): taxonomy and functional GLAHM 2244, some generalizations can be made about the morphology. Journal of Paleontology 84: 118-127. morphology of these limbs. Although antennulae are un- Dahl, E. 1983. Malacostracan phylogeny and evolution, pp. 189-212. In, known from ceratiocarid specimens, the presence of two F. R. Schram (ed.), Crustacean Phylogeny. Crustacean Issues 1. A. A. equal, to subequal, length antennular rami in Rhinocaridina Balkema, Rotterdam. . 1985. Malacostraca mistreated – the case of the Phyllocarida. and Echinocaridina seconds the idea that this was the an- Journal of Crustacean Biology 7: 721-726. cestral ground plan for malacostracan antennulae; variations Davie, P. J. F. 2002. Crustacea: Malacostraca: Phyllocarida, Hoplocarida, from this pattern in other malacostracan clades are either au- Eucarida (Part 1). In, A. Wells and W. W. K. Houston (eds.), Zoological tapomorphic, or homoplasic. The presence of an elongated Catalogue of Australia 19.3A. CSIRO Publishing, Melbourne, VIC. antennal exopod in Rhinocaridina and Echinocaridina im- Eller, E. R. 1935. New species of Echinocaris from the Upper Devonian, of Alfred Station, New York. Annals of the Carnegie Museum 24: 263-274. plies that this was the ancestral condition in Malacostraca; Girard, C. 1852. 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