BULLETIN DE L'INSTITUT ROYAL DES SCIENCES NATURELLES DE BELGIQUE, BIOLOGIE, 73: 107 -11 3, 2003 BULLETIN VAN HET KONINKLIJK BELGISCH INSTITUUT VOOR NATUURWETENSCHAPPEN, BIOLOGIE, 73: 107- 11 3,2003

Vestigial structures in pontoporeiid and stegocephalid amphipods (Crustacea, , ) by Cedric d' UDEKEM d' ACOZ & J0rgen BERGE

Abstract pereiopod in the () and that of a rudimentary mandibular palp in stegocephalid Two kinds of previously overlooked ves ti gial structures in amphipods. Those structures, w hi ch have previously been amphipods are here described and illustrated by SEM overl ooked, are described here for the first time. photographi es. A rudimentary dactylu s, reduced to a tiny bud termi­ nated by a seta has been detected on th e second and the fifth pereiopod in Bathyporeia spp. (Pontoporeiidae), and a minute The dactylus of the second and fifth pereiopod in seti form stru cture representing the remn ant of th e mandibular palp Bathyporeia spp. (Pontoporeiidae) has been observed in most stegocephalid genera. Thei r evoluti onary significance is briefly di scussed. The very homogeneous genus Bathyporeia LiNDSTRO M, Key words : Bathyporeia, Pontoporeiidae, Stegocephalidae, 1855 includes about 20 species li ving in sandy intertidal and Eualus, Caridea, mandibular palp , dac tylus, vestigial, morphology. coastal bottoms in the A tl antic and the Mediterranean Sea (D' UDEKEM D' Acoz, submitted). Their antennae, pereiopods and uropods are deeply modified (G.O. SARS, 1891) in direct Resume relationship with their fossorial habits (NICOLAISEN & K ANNEWORFF, 1969). Previous authors such as e.g. G.O. Deux types de structures vestigiales presentes chez certains amphi­ SARS (1891) concluded that the dactylus was Jacking on the podes sont decrits ici pour Ia premi ere fo is, et illustres par des pho­ second and the fifth pere iopods, and indeed at first glance tographies en microscopie electronique a balayage. Un dactyle mi­ they seem to be absent. However, when studying the tax­ nu scul e et rudimentaire prolonge par un e so ie a ete detecte sur le onomy. of the northwestern European species under a high second et le cinquieme pereiopode de Bathyporeia spp. power light microscope, the first author had the surprise to (Pontoporeiidae). De meme, une tres petite stru cture .setiforme re­ detect minute structures between the apical propodal setae of presentant l'ultime vestige d' un palpe mandibulaire a ete observe chez Ia plupart des Stegocephalidae. Leur signification evolutive est the second and the fifth pereiopods, which are obviously ves­ brievement discutee. tigial dactyli. They were ob se ~;ved in all northwestern Euro­ pean Bathyporeia species: B. elegans W ATK IN , 1938; B. gra­ Mots des : Bathyporeia , Pontoporeiidae, Stegocephalidae, Eualus, cilis G.O. SARS, 189 1; B. guilliamsoniana (BATE, 1857); B. Caridea, palpe mandibulaire, dactyle, vesti gial, morphologie. nana TOULMOND, 1966; B. pelagica (BATE, 1856); B. pilosa LINDSTROM, 1855; B. sarsi W AT KI N, 1938 and B. tenuipes MEINERT, 1870, as well as in the northeastern American B. Introduction parkeri BOUSFIELD, 1973, and that dispositio n is presumably characteristic of the w hole genus. A closer examinatio n in As a conseque nce of evolutionary pressure, some append­ scanning electron microscopy (SEM) revealed that the rudi­ ages or structures may regress and finally disappear. Such mentary dactylus of the second pereiopod, w hich arises from regressive processes are usuall y gradual, and vestigial rem­ the ventral surface of the propodus, consists of a discoid tiny nants of these structures often persist fo r very lo ng periods bud fused to the propodus. erminated in a longer, strongly before their complete di sappearance. During our respective setulose seta (Fig. 1). Despite its very small size, the fifth studies on pontoporeiid and stegocephalid amphipods, both d actylus appears to be in a less advanced stage of morpho­ authors independently discovered two kinds of vesti gial logical regression. 1t consists of a minute cylinder, distinctly structures, which are here presented in a j o int paper: the oc­ articulated w ith the anteroventral part of the propodus and currence of a rudimentary dactylu s on the second and fifth terminated in a scarcely setulose seta (Fig. 2). I I

108 CEDRIC D' UDEKEM D' ACOZ & J0RGEN BERGE

Fig. I. Bathyporeia guilliamsoniana (BATE, 1857), male, the Netherlands, second pereiopod. A, carpus and propodus; B, D, tip of propodus +vestigial dactylus; C, vesti gial dactylus. On fig. D , the apical seta of the vestigial dactylus has been rubbed off during the removal of the propodal marginal setae. ·

In related genera like Pontoporeia and Amphiporeia, the dac­ Bathyporeia (P2 and .PS modified, both with very reduced tylus of the second pereiopod, although not always large, re­ dactyli). mains well developed and fonns a subchela with the propodus (e.g. G .O. SARS, 189 1; SHOEMAKER, 1933; BOUSFIELD , 1973; GLENNON, 1979). In contrast, Bathy­ The stegocephalid mandible and its vestigial palp poreia possesses an elongate and deeply modified propodus with a vesti gial bud-like dactylus. So far, all authors dealing with either the morphology and/or the of the amphipod family Stegocephalidae As concerns the fifth pereiopod, its general shape remains D ANA, 1852 have concluded that the mandible of the family basal in Pontoporeia, whilst in Amphiporeia it is hjghly is always devoid both of palp and molar process; see espe­ m odified, with a blade-like merus, and morphologically very cially BERGE & V DER (200 1) in their recent revision of the close to that of Bathyporeia. However both in Pontoporeia family. However, a careful examination of representatives of and An;phiporeia, the dactylus of the fifth pereiopod, albeit all five subfamilies of the Stegocephalidae: Andaniexinae, small , remains conspicuous and is much bigger than in Andaniopsinae, Bathystegocephalinae, Parandaniinae and Barhyporeia. So, if the second and the fifth pereiopod are Stegocephalinae in SEM has revealed the existence of a tiny, considered alone, there is apparentl y a kind of evolutionary more or less setifom1 structure at the exact position where a gradation : Pontoporeia (P2 and PS basal)> Amphiporeia (P2 palp does occur in other amphipod families. That structure is basal; PS modified but with conspicuous dactylus) > herein interpreted as a rudimentary palp. ''

Vestigial structures in amphipods 109

Fi g. 2. Bat hyporeia gu illiamsoniana (BATE, I 857), male, the Netherl and s, fift h pereiopod. A, meru s to ti p; 8 , propodus + scarcely di stinct dactylus; C, tip of propodus + ves ti gial dactylu s. I I

110 CEDRIC D'UDEKEM D' ACOZ & J0RGEN BERGE

Fi g. 3. A, 8 : Stegonomadia biofar (BERGE & V ADER, 1997), Iceland; C, 0 : Parandania gigantea (STEBB ING, 1888), Southern Ocean, E, F: Bathystegocephalus globosus W ALKE R, 1909, Indian Ocea n. A, C, E, mandible and oral field; 8 , D, F, vestigial mandibular palp. Vestigial structures in amphipods 111

Fig. 4. A, B: Andaniopsis nordlmzdica (BOECK, 187 1), Northern No rway; C, 0 : Andaniotes linearis K .H. BARNARD, 1930, Southern Ocean; E: Eualus occultus (LEBOUR, 1936), female, NW France, lie Callot; F: Eualus cranchii (LEACH, 18 17), female, Belgium, Zeebrugge. A, C, mandible and oral field; B, D, vestigial mandibular palp; E, F, left mandible (respectively with and without palp). II

112 CEDRIC D'UDEKEM D' ACOZ & J0RGEN BERGE

Andaniexinae Stegonomadia biofar (Fig. 3 A-B). However, within the clade consisting of the four genera Austrophippsia, Phippsia, Schellenbergia and Tetradeion, it seems that most species in fact do not possess any palp, but that it has been retained in Andaniopsinae some Tetradion species.

Thus, it seems that within the three most basal stegocephalid subfamilies (Fig. 5), a rudimentary palp is present in all spe­ cies (at least, al l species examined hitherto have been ·con­ firmed to possess a palp), whereas the homologous feature is - Stegocephalinae not present in all species of the two more derived subfamilies (Andaniopsinae and Stegocephalinae, see Fig. 5).

Bathystegocephalinae Discussion and conclusion

Parandaniinae Interestingly, both in the case of the vestigial dactyli and in that of the mandibular palp, a hair-like element is present. Indeed the dactyli of spp. consist of a bud-like Fi g. 5. Phylogeneti c relationships among the subfamilies of Bathyporeia Stegocephalidae as hypothesised by BERGE & VADER structure terminated by a proportionately large seta, and the (200 1) . stegocephalid palp as a whole is setifonn. M aybe, the stegocephalid condition is a more advanced stage or regres­ sion. This is supported by the fact that the vestigial condition is the rule in the family, whilst various character states are Its distribution across all five subfamilies clearly indicates found amongst Pontoporeiidae. this being a plesiomorphic character state. Indeed, all mem­ bers of the two most plesiomorphic subfamilies (Bathystego­ Although, in the cases described above, the regression ap­ cephalinae and Parandaniinae, see Fig. 5), which together pears to be a gradual process, with a long-persisting vestige, consist of merely 4 species (Bathystegocephalus globosus there are probably exceptions to that rule in . Re­ W ALKER, 1909, Parandania boecki (STEBBI NG , 1888), P cently, we have examined the mandible of the caridean gigantea (STEBB ING, 1888) and P ·nonhiata ANDRES, 1985), shrimp Eualus cranchii (LEACH, 1817) which was also sup­ possess a rudimentary palp (Fig. 3 C-F), as do all examined posed to be devoid of a mandibular palp . Scanning electron species of the subfamily Andaniexinae (Andaniexis lupus microscopy examination confinned that it was completely BERGE & VADER , 1997, Andaniotes linearis K.H BARNARD, absent as previously stated, without any vestigial remnant 1930, A. pseudolinearis BERGE, 2001 , Glorandaniotes eilae (Fig. 4 F). Very closely related species such as Eualus BERGE & VADER , 1997, Mediterexis mimonectes (RUFFO, occultus (LEBOUR, 1936) exhibit a well-developed palp (Fig. 1975), and Stegosoladidus simplex (K.H. BARNARD , 1930)), 4 E). Because of the great similarity between the two species, here represented by Andaniotes linearis (Fig. 4 C-D). In all . it is li kely that the regressive process has been very fast, un­ these three subfamilies, the palp remnant consists of a rela­ like in Stegocephalidae. tively elongated structure, very similar to a long simple seta, but eventually with a sli ght basal thi ckening (Figure 3 B). In Finally, our observations clearly demonstrate that very care­ the m ajority of the Andaniopsinae (Andaniopsis nordlandica ful examination is necessary before claiming the complete (BOECK, 187 1), Andaniopsis sp. nov, BERGE in press and disappearance of a s"tructure, and it would not be surprising if Steleuthera maremboca BARNARD, 1964) a rudimentary other supposedly lacking dactyli, palps or spines will prove palp, similar to that of Andaniopsis nordlandica (Fig. 4A-B), to have persisted in a vestigial condition in other crustaceans. is present. However, among the remaining three Andanio­ psinae species, two (Andaniopsis pectinata G.O. SARS, 1883 and Steleuthera africana BERGE, DE BROYER & VADER , Acknowledgments 2001) are shown to have no palp at all , whereas the corre­ sponding character state is still unknown fo r the last The authors are grateful to Pro f Wim VADER (Troms0 Mu­ Andaniopsinae species, Andaniopsis in.tegripes (BELLAN­ seum) for his help with earlier drafts of the manuscript, and SANTINI & LEDOYER , 1986). to Tom lvar EILERTSEN (Troms0 University), Chris JONES In the fifth stegocephalid subfamily, the Stegocephalinae, at and Prof. Geoff uXS HALL (The Natural History Museum in least six genera are known to possess a rudimentary palp London) for their help and support in preparing the SEM pic­ (Austrocephaloides australis (K.H. BARNARD, 1930, Pseudo tures, and Dr. David M. KNOTT, Southern Regional Taxo­ bioice (BERGE & V ADER, 1997), Stegocephalina wagini nomic Center, Charleston for providing us w ith material of (GURJANOVA, 1936), Stegocephalus inflatus KR0YER, 1842, Bathyporeia parkeri BOUSFIEL D, 1973. Stegonomadia biofar (BERGE & V ADER, 1997) and The second author was funded by the Norwegian Research Tetradeion crassum (CH ILTON , 1883), herein represented by Council, project number 145384/432. Vestigial structures in amphipods 11 3

References SHOEMAKER , C. R., 1933. A new amphipod of the genus Amphiporeia from Virginia. Journal of the Washington Academy of BERGE, J. & W. VADER , 2001. Revision of th e amphipod (Cmsta­ Sciences, 23(4): 212-216. cea) famil y Stegoceph alidae. Zoological Journal of the Linnean UDEKEM D' Acoz, C. d', submitted. The genus Bathyporeia Society, 133:53 1-592. LI NDSTROM, 1855 in Western Eu rope (Crustacea, Amphipoda, BOUSFIELD , E.L. , 1973. Shall ow-water gamm aridean Amphi poda Pont oporeiidae). Zoologische Verhandelingen, Leiden of New England. Comstock Publishing Associates, a di vision of Cornell Uni versity Press, Ithaca & Lo ndon: 1 frontispiece + i- xii + l-312. GLENNON, T.A. , Jr. , 1979. Descripti on of the Male of Amphiporeia Cedric o ' UDEKEM D'ACOZ gigantea BOUSFIELD (Amphipoda, Haustoriidae). Crusraceana, Troms0 Museum (Department of Zoology) 37 (3): 304-310. University of Trom sl!) NICOLAISEN, W. , & E. KANNEWORFF, 1969. On the burrowing and 9037 Troms0, Norway fee ding habits of the amphipods Bathyporeia pilosa LINDSTROM E-mail: cdudekem @tmu.uit.no and Bathyporeia sarsi WALK ER. Ophelia, 6: 23 1-250. J¢rgen BERGE SARS , G.O., 1890-1 895. An accoun t of the Crustacea of Norway, with short descri ptions and figures of all th e species. Vol. l . Associate Professor, M arine Biology Amphi poda. Christi ana and Copenh agen, published by Alb. UNIS, Pb 156 CAMMERM EYER (reprinted 1966 by Uni versitetsforlaget, Bergen 9 171 Longyearbyen, Norway and Oslo): l-7 11 + pl. 1-240 + pl. i-viii. E-mail : j orgen.berge@ unis. no