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© Biodiversity Heritage Library, http://www.biodiversitylibrary.org/; www.zoologicalbulletin.de; www.biologiezentrum.at Bonnerzoologische Beiträge Band 55 (2006) Heft 3/4 Seiten 301-310 Bonn, November 2007 Exploring Cerebral Features in Acochlidia (Gastropoda: Opisthobranchia)* Timea P. Neusser, Katharina Jörger & Michael Schrödl" 'Zoologische Staatssammlung München, Munich, Germany ' *Paperpresented tothe 2nd hiternational Workshopon Opisthobranchia, ZFMK, Bonn, Germany, September20th to 22nd, 2006 Abstract. Histological semithin sections ofthe marine acochlidian speciesHedylopsisspiciilifera (Kowalevsky, 1901), H. ballantineiSommerfeldt& Schrödl,2005,Microhedyleremand(Marcus, 1953)andAsperspiiuimiirmanica(Kudins- kaya&Minichev, 1978)andofthe limnic Tantulum elegansRankin, 1979 were(re)examinedfordifferentcerebral features: 1) the number ofcerebro-rhinophoral connectives, 2) the presence ofHancock s organs, 3) the relative position andsizeoftheeyes,thelengthanddiameteroftheopticnerve,andthepresenceofanopticganglion,and4)cellularag- gregates attached to the cerebral ganglia. We describe novel structures such as double cerebro-rhinophoral connectives in T. elegans.and"lateralbodies" inH. spicnlifera,H. ballantineiandA. mwnianica. Cerebral featuresarediscussedas apromisingadditionalsetofcharactersforphylogeneticanalysis.However,(ultra)structuralcomparisonsofacochlidians withbasal opisthobranchsandpulmonates areoverdue. Keywords. Cerebral nerves, "lateral bodies'", dorsal bodies, Hancock'sorgan,optic ganglion. INTRODUCTION 1. Acochlidianopistobranchgastropodsshow high morpho- be trusted (seeNeusser & Schrödl 2007). Furthermore, logical andbiological diversity. However, the number of very few studies give data about cerebral nerves and sen- useful characters for phylogenetic analyses is still limit- sory organs reflecting the coinplexity ofthe acochlidian edbythepaucityofcomparative dataavailable. Thecen- ens. Huber (1993) gave a detailedoverview ofthe ens in tralnervoussystem(ens)ofseveral euthyneuroustaxawas marineheterobranchsanddetemiinedthe numberofcere- described(e.g. Haszprunar&Huber 1990; Huber 1993; bral nerves inAcochlidiato onlytwo (the labiotentacular MlKKELSEN2002), comprisingdataaboutcerebral nerves nerveandtheproximallyjointoral andrhinophoralnerve) and sensory organs. The value ofthese data in phyloge- plus the static nerve. Sommerfeldt & Schrödl (2005) netic studies is evident (Dayrat & Tillier 2002; confirmed these three nerves plus optic nerves forHedy- MlKKELSEN 1996). In contrast, several of the species lopsisspiculifera andH. ballantinei. The authors empha- (re)descriptions in Acochlidia do not include any infor- sized the presence of large rhinophoral ganglia, from mation on the ens (e.g. Haynes & Kenchington 1991; which thejoint oral and rhinophoral nerve arise, and that Hughes 1991; Kirsteuer 1973; Marcus & Marcus was overlooked in H. spicuHJeiri by Huber (1993). The 1955, 1959; Salvini-Plawen 1973; Wawra 1979, 1980, terminology and the homology ofthe different cerebral 1988). Otherauthors limited theirdescriptions ofthe ens nerves in Acochlidia are still uncetlain. totheinaingangliaonthe(pre)phai7ngeal nerveringand thevisceralnervecord(e.g. Bergh 1895; BUcking 1933; Dataaboutsensoryorgansaresparse, oftenconsistingon- Challis 1968, 1970; Doe 1974; Hertling 1930; ly intheaffirmationofpresenceorabsenceofeasily iden- Kowalevsky 1901; Kudinskaya & Minichev 1978; tified structures, such as eyes (e.g. Challis 1970; Mar- Küthe 1935; Marcus 1953; Marcus & Marcus 1954; cus 1953; Marcus & Marcus 1955; Westheide & Morse 1976; Swedmark 1968; Wawra 1989; Westhei- Wawra1974). Hancock's organs, the primary chemosen- de & Wawra 1974). Unfortunately, the identification of soiy organs in architectibranchs and cephalaspideans the small and hardly separated ganglia on the visceral (MlKKELSEN 1996, 2002), were thought to be absent in nerve cord is problematic. Even detailed histological de- Acochlidia (e.g. Neusser et al. 2006; Sommerfeldt & scriptions, such as that of Tantulum elegans by Rankin Schrödl 2005; Wawra 1987). However, Hancock's or- (1979), can be considerably misleading and thus cannot gans likestructureswerereportedfromMiavhedyleglan- © Biodiversity Heritage Library, http://www.biodiversitylibrary.org/; www.zoologicalbulletin.de; www.biologiezentrum.at 302 Timea P. Neusseret al.: Cerebral features inAcochlidia Table I . Comparison ofcerebral features in different acochlidian species. +: present,-: absent, ?: not detected. species feature Hedylopsis Hedylopsis Asperspina Tantuhtm Microhedyle spiciilifera ballantinei mwmanica elegaijs Double cerebro- rhinophoral connective Hancock's organ Eyes + pigmented + pigmented + reduced unpigmented Eyes externally visible dorsal and lateral dorsal and lateral not visible well visible hardly visible Eyes position posterior to the slightly posterior slightly anterolateral rhinophores to the rhinophores to the cerebral (in some distance) (at theirbase) ganglion Eye size in diameter 25 |.im 30 \xm 20 urn Optic nerve long, undulated long, undulated short, not undulated Optic nerve diameter 6-7 |jm 6-7 |.im 3 |am Optic ganglion (diameter) - + (18 um) Lateral bodies + Cells above cerebral ? commissure diilifera (Kowalevsky, 1901 ) and Pontohedyle milasche- September 2005) and one paratype series (section thick- witchii (Kowalevsky, 1901) by Edlinger (1980a, b), and ness: 2 \xm)ofHedylopsissiiecica Odhner, 1937, Swedish recently confirmed for P. milaschcwitchii (Jörger et al. Museum ofNatural History, SMNH N° 27211; H siieci- inpress).Additionally,ourre-examinationofTantiilum el- ca was considered as a synonym of H. spiciilifera by egaiis revealed the presence ofa small Hancock's organ Wawra (1989) and confirmed by Sommerfeldt & in this species too (Neusser & Schrödl 2007). Schrödl (2005). Five paratype series (section thickness: 2 um) of Hedylopsis ballantinei. ZSM N° 20004766/1, Amongrepresentativesoffourtraditional acochlidian fam- 20004767, 20004768,20004769andN°26X(Dahab,Gulf ilies(Hedylopsidae,Asperspinidae,Tantulidaeand Micro- ofAqaba, northern Red Sea, October 1999). Six series hedylidae), thepresent study(re)investigatesanumberof (section thickness: 1.5 |nm) ofMicrohedylerenianei.ZSM special cerebral nervous features using histological sec- N° 20070079,20070080,20070081,20070082,20070083 tions. As far as information is available, these characters and 20070084 (southwest ofCastle Roads, Bennuda Is- arecompared with otheracochlidian species andareeval- lands, July 1999). Fourseries (section thickness: 1.5 ¡.im) uated as a possible set ofcharacters for future phyloge- ofAsperspinaniiirnianica,ZSM N°20062163, 20062164, netic analysis. 20062165 and20062167 (YamyshnayaBay, Barents Sea, Russia,August 2005). Fouroriginal paratype series (section thickness: 3 ¡xm) andtworecently preparedparatype MATERIAL 2. series (section thickness: 1.5 j.im) of Tantiilwn elegans. Royal Ontario Museum, Canada, ROM N° 8EI and 2F0 Serial semi-thin sections of five different acochlidian (Golden Grove, St. Vincent, West Indies, July 1972). All species were available for re-examination by light mi- sections, except theoriginal paratype seriesofT. elegans. croscopy: oneseries(sectionthickness: 1.5 |im)ofHedy- were stained with methylene blue-azure II according to lopsisspicidifera. ZoologischeStaatssammlungMünchen, Richardson et al. (1960). ZSMN° 20070391 (Secchedella Meloria, Livomo, Italy, 8 . © Biodiversity Heritage Library, http://www.biodiversitylibrary.org/; www.zoologicalbulletin.de; www.biologiezentrum.at Bonnerzoologische Beiträge 55 (2006) 303 3. CEREBRAL FEATURES EXAMINED just posterior to the rhinophores (Fig. 2C). The optic nerves show approx. 6-7 |Lim in diameter in both species 3.1. Rhinophoral ganglia and cerebro-rhinophoral (Fig. 3A, B). They arise from therhinophoral gangliaand connectives arehighly undulated.Anopticganglion isabsentinH. spiculifera as well as in H. ballantinei. In contrast, Tantu- A comparative overview ofall examined features in the liim elegansdevelopsaveryshortandthinopticnerve(ap- different species is given in Table 1 prox. 3 \im in diameter) leading to a reduced unpigmented eye ofapprox. 20 |im in diameter (Figs. 1, 3C). The All species re-examined herein, except Micwhedyle re- opticnervearisesfromasmall optic ganglion (approx. 1 mauei, have a pair oftrue rhinophoral ganglia, i.e. large |am in diameter) that is subdivided into the outer cortex gangliaseparated into a nuclei-free medulla and a cortex and the innermedulla (Fig. 3D). It is attached laterally to composed ofcell bodies. The rhinophoral ganglia ofA/. the cerebral ganglion, both ofwhich are suiToundcd by a remanei are not subdivided into cortex and medulla; in- thin layer ofconnective tissue (Fig. 3D). No nerves can stead the nuclei are distributed homogeneously all over be detected by light microscope examination connecting theganglion(seeNeusseretal. 2006, fig. 3d). Serial sec- the cerebral with the optic ganglion. tions ofHedylopsisspiciilifera, H. ballantinei and M. remanei show only a single nerve (approx. 5-10 jam in di- 3.3. Aggregates attached to the cerebral ganglia ameter) that connects the cerebral ganglion to the 3.3.1. "Lateral bodies" rhinophoralone. InonespecimenoíTantuliim elegansex- amined,wefoundtwonervesconnectingthecerebral ganglion with the rhinophoral ganglion (Fig. 1 ). Both nerves A "lateral body" as defined herein consists ofa more or are thin (approx. 7 [im in diameter) and lie close togeth- lesshemispherical clusterofcellsthatis lyinglaterallyon er(distancebetweenthemapprox. 3¡im). Nevertheless,the the surface ofeach cerebral ganglion. Under a light mi- transition between the cerebral ganglion and the croscope, the cells ofthe "lateral bodies" cannot be dis- rhinophoral ganglion is well identifiable due to the pres- tinguished from the neuron bodies situated in the cortex ence ofdark stained fibres (Fig. 1A, D). ofthecerebral ganglion. Each "lateral body" is surrounded by a separate, relatively thin sheath ofconnective tis- 3.2. Sensory organs sue and together with the cerebral ganglion by a second common and thick one. "Lateral bodies" are present in 3.2.1. Hancock's organ and nerve Hedylopsisspiculifera (Fig. 4A),H. ballantinei(Fig. 4B) andAsperspina murmanica (Fig. 4C). The"lateral body" Paired, small and ciliated invaginations posterior to the lacks any subdivision. The nuclei are more or less uni- head appendages and innervated by cerebral nerves are fomilydistributedovertheentire"lateralbody".Thereare present in Tcmtulum elegans (see Neusser & Schrödl no nerves visible under the light microscope connecting 2007, flg. 4b).Neithersuchorgansofsimilarshapecould the cerebral ganglion with the "lateral body", and there be detected in Hedylopsis spiciilijera, H. ballantinei and are no nerves arising from the latter. None ofthe speci- Micwhedyle remanei, or cerebral nerves innervating the mensexaminedofMicrohedyleremaneiand Tantulum el- region where Hancock's organs are present in other egans had "lateral bodies". acochlidian species. 3.3.2. Cells near the cerebral commissure 3.2.2. Eyes, optic nerves and optic ganglia Additionally, we could findseveral cellsofuncertain ori- AsperspinamurmanicaandMicrohedyleremaneiareeye- gin and function dispersed intheconnectivetissue above lessandlackanyopticnerveoropticganglion. BothHedy- the cerebral commissure inAsperspina murmanica (Fig. lopsis specieshavepigmentedlens eyes(Fig. 3A, B)that, 4D). In contrasttothe "lateral bodies", these cells arenot however, differ in size and relative position. The eyes of tightly attached to each other, and are not enclosedby an H. spiculifera are clearly visible externally (Fig. 2A, B) individual sheath ofconnective tissue. No data about the from dorsal and lateral and reach up to 25 |im in diame- presence orabsence ofthesecells canbegiven forHedy- ter (Fig. 3A). They are located on the rather lateral side lopsis spiculifera, H. ballantinei and Tantulum elegans, ofthe head (Fig. 2B), and are in some distance posterior due to very compressed tissue layers. to the rhinophores (Fig. 2A, B) and anterior ofthe cerebral ganglia. In contrast, the eyes of H. ballantinei are hardly detectableby external view (Fig. 2C) even though theyare slightly larger(approx. 30 fxm indiameter) (Fig. 3B). Furthennore,theyaresituatedclosertogetherandare © Biodiversity Heritage Library, http://www.biodiversitylibrary.org/; www.zoologicalbulletin.de; www.biologiezentrum.at 304 Timea P. Neusser et al.; Cerebral features inAcochlidia Fig. 1. Doublecerebro-rhinophoralconnectivein Tantulumelcgaiis. FourconsecutivecrosssectionsofseriesROMN°8E1,3.sli- de, 6. ribbon, section N° 17-20. A: section N° 17, first cerebro-rhinophoral connective. B and C: section N° 18 and 19, respectively, without connective. D: section N° 20, second cerebro-rhinophoral connective, eg cerebral ganglion; ey eye; rhgrhinophoral ganglion; arrow, indicates fibres ofthe cerebro-rhinophoral connective. Scale barsA-D; 15 [im. 4. DISCUSSION nei(seeSommerfeldt& Schrödl2005),Microhedylere- manei (see Neusser et al. 2006), T. elegans (see Neuss- 4.1. Rhinophoral ganglia and number of er & Schrödl 2007) and Pontohedyle milascheMitchii cerebro-rhinophoral connectives (seeJörgeretal. in press). Duetotheirpositionanterodor- sally ofthe cerebral ganglia andtheir similar innervation The presence of rhinophoral ganglia were reported for the homologyofthe rhinophoral gangliacanbeassumed Hedylopsisspiciiliferiiand Tantuliint clegans(see Rankin for all acochlidian species studied herein. In contrast to 1979; Wawra 1989), butboth descriptions lack histolog- Hedylopsisspecies,Asperspiiuiiminuanicaand T. elegans., icaldataoftherhinophoralganglia. Recently,rhinophoral rhinophoralgangliaofP. milaschewitehiiandM. vemanei ganglia were described in detail for Hedylopsis hallauti- are not separated into medulla and cortex. The presence © Biodiversity Heritage Library, http://www.biodiversitylibrary.org/; www.zoologicalbulletin.de; www.biologiezentrum.at Bonnerzoologische Beiträge 55 (2006) 305 Fig. 2. Positionofeyes in different acochlidian species, external view.A; Hedylopsisspiculifeni. dorsal view, length 3.5 mm. B: Hedylopsisspiculifera, lateral view, length 3.5 mm. C: Hedylopsis ballantinei, lateral view, length 5 mm. D: Pontohedyle luila- schewitchii, dorsal view, length 2.5 mm. ey eye; It labial tentacle; rh rhinophore. of rhinophoral ganglia within P. milaschewitchii that is tive has been identified by the presence ofdark stained lacking any rhinophores might be explained by a modi- fibres. Haszprunar (1985, figs. 19, 20) described simi- fied, e.g. neurosecretory function. Microhedyle remanei, lar fibres occuiring at the transition between two differ- however,possessesrhinophoresandcell bodiesevenlydis- entganglia inDiscotectouicadiscus Philippi, 1844.Adou- tributed within the rhinophoral ganglia. ble cerebro-rhinophoral connective has also been found inPontohedylemilaschewitchii(seeJörgeretal. inpress); Ofall the specimens here studied, the double connection both nerves are even thinner than those in T. elegans. between the cerebral ganglia and rhinophoral ganglia There is no reliable data on further acochlidians. could onlybe detected in one specimen of Tantidum elegans, and is only clearly visible on the right side ofthe Haszprunar & Huber (1990) described a double cere- nervous system. Unfortunately, the identificationofthese bro-rhinophoral connective for the enigmatic opistho- thinnervesdependscriticallyuponpreservationandstain- branchs Rhodope veranii Kölliker. 1847 and Rhodope ingconditionsaswell asonthecuttingplane. Tinynerves trcinstrosa Salvini-Plawen, 1989, aswell asadoublecon- can thus be overlooked and easily misinterpreted, or be nective attaching the cerebral ganglion with the procere- invisibleevenon semi-thinserial sections. While"detect- brum in thepulmonateSineagolinanneringiClimo, 1980. ed"usuallymeans"presenf,"notdetected"doesnotnec- In fact, the double cerebro-rhinophoral connective ofthe essarilymean "absenf'.Thecerebro-rhinophoral connec- acochlidian ens resembles the general pulmonate condi- © Biodiversity Heritage Library, http://www.biodiversitylibrary.org/; www.zoologicalbulletin.de; www.biologiezentrum.at 306 Timea P. Neusser et al.; Cerebral features inAcochlidia Fig. 3. Eyes and optic ganglion (cross sections). A: Pigmented eye in HedylopsisspiciiJifera ZSM N° 20070391. B; Pigmented eye in Hedylopsis hallantinei ZSM N° 20004766/1. C: Unpigmented eye in Tantulum elegans ROM N° 8E1. D: Optic ganglion attached lothecerebral ganglion in Tantulum elegans ROM N° 8E1. egcerebral ganglion; ey eye; ogoptic ganglion; onoptic nerve; rhg rhinophoral ganglion. Scale barsA-D: 15 [im. tion (Van Mol 1967). Therefore, the potential homology eleganswhichshowsapairofepidemial foldsonthe side ofacochlidian rhinophoral ganglia to the procerebrum of ofthehead (Neusser& Schrödl 2007). Such foldswere pulmonates should be investigated in detail. reportedforPontohedyleluilaschewitchiiandMicrohedyle glandulifera and regarded as Hancock's organs by 4.2. Sensory organs Edlinger (1980a, b), i.e. as tine homologues ofthe pri- maxy chemosensoiy organs in architectibranchs and 4.2.1. Hancock's organ cephalaspids (see Mikkelsen 1996). According to their similarposition,cerebral inneiA'ation. (althoughmoretiny) WewerenotabletodetectanyHancock'sorgan likestruc- structure, andprobablesensoiy function, ageneralhomol- tures in the species examined herein except for Taiitiiliini ogy can be suspected. Some doubts persist, such as the . © Biodiversity Heritage Library, http://www.biodiversitylibrary.org/; www.zoologicalbulletin.de; www.biologiezentrum.at Bonnerzoologische Beiträge 55 (2006) 307 B cg Ib cg cg cc cg f? Ib »VW 9 Fig. 4. AggregatesattachedtothecerebralgangliWa(crosssections).A:"Lateralbody"inHedvlopsisspkiiliferaZSMN°20070391 B: -Lateralbody"inHedvlopsisballantineiZSM 20004766/1. C: "Lateralbody"inAsperspinamwmanicaZSMN°20062163. D: Cells abovecerebral commissure inAsperspina munnanica ZSM N° 20062163. cc cerebral commissure; cgcerebral ganglion; lb "lateral body"; arrow, cells nearcerebral commissure. Scale barsA-D: 15 \im. yetunclearhomologyofeuthyneurancerebralnerves,the sensoryorgans. EyesareabsentinallAsperspina species, unknownoriginoftheAcochlidiaandreportsofacochlid- Microhedyle reinanei, Ganitiis evelinae Marcus, 1953, ian "Hancock's organs" from only a few and supposedly ParagcinitusellynnaeChallis, 1968 andPontohedylever- derived microhedylid species, i.e. P. milaschewitchii and rucosa Challis, 1970 (see Challis 1968, 1970; Kudin- M. glandulifera, and the enigmatic T. elegans. SKAYA & MiNiCHEV 1978; Marcus 1953; Morse 1976; Salvini-Plawen 1973; Swedmark 1968). Our results 4.2.2. Eyes, optic nerves and optic ganglia show that the position, size and development ofeyes in Acochlidia examined herein differ considerably. In the past, thedescription ofacochlidian eyes often was limited to the affirmation ofpresence orabsence ofthese © Biodiversity Heritage Library, http://www.biodiversitylibrary.org/; www.zoologicalbulletin.de; www.biologiezentrum.at 308 Timea P. Neusser et al.: Cerebral features inAcochlidia The eyes oíHedylopsisspiciilifera are clearly visible ex- The eye size differs within the species: whereas eyes of ternally from a dorsal and lateral view. In the freshwater Hedylopsisspiciilifera andH. ballantineimeasureapprox. acochlidian species Stnibelliaparadoxa (Strubell, 1892) 25 and30 |iin,respectively, eyesinPontohedylemilasche- andAcocliliiliumfijieiiseHaynes& Kenchington, 1991 the witchii reach approx. 20 [im (Jörger et al. in press). The eyes are clearly observable only in lateral view (unpubl. largesteye sizeknown fromanacochlidianspecies is0.52 mm data ofMS). In contrast, the eyes ofthe marine Micro- and was reported for the limnic Pallioliedyle weberi hedyleglandulifera (see Kowalevsky 1901; Marcus & (see Bergh 1895). Marcus 1955; Odhner 1952), Hedylopsis ballantinei (Fig. 2C) and Pontohedyle milaschewitcini (Fig. 2D) are Theopticganglionin Tantuliim eleganswasfirstdescribed externallynotthatclearlyvisible throughthe head tissue. by Neusser & Schrödl (2007) and is regarded to be a Westheide & Wawra (1974) observed that eyes of true ganglion with subdivision into cortex and medulla Parliedyle ciyptophthalma (Westheide & Wawra, 1974) (seeNeusseretal. 2006). More specifically, itisenclosed were not visible externally in living specimens, and only in a thin layer ofconnective tissue together with and at- as two small pigmented spots in preserved specimens. tached to the cerebral ganglion. This feature should not Eyes inPseudimelaconiiita(Challis, 1970) arepoorlyde- beconfusedwiththe"lateralbodies"describedinthepres- veloped and not visible externally (Challis 1970, as ent study, since the latter are lying inside the thick layer Hedylopsis coruuta). ofconnective tissue from the cerebral ganglion (see be- low). So far there are only two reports ofganglia being The eyes oíHedylopsisspiciilifera andH. liallautineiare surrounded by a common layerofconnective tissue with both located dorsolaterally in the body cavity; while the thecerebral ganglia: therhinophoralgangliaofT. elegans eyes of H. Ixillantinei are situated at the base of the (seeNeusser& Schrödl2007), andtherhinophoral gan- rhinophores, in H. spiciilifera they are somewhat more glia of Pontohedyle milaschewitcliii (Jörger et al. in posteriorly.Asimilardorsolateral eyeposition atorclose press). to the base ofthe rhinophores is already known from the limnic acochlidian species Acoclilidiiini amhoineiise The presence ofan optic ganglion only in T. elegans is Strubell, 1892, Pallioliedyle weberi (Bergh, 1895) and surprising, since eyes are unpigmented in this species, Stnibellia paradoxa (see Bfrgh 1895; Bücking 1933; while for species possessing more well-developed eyes Küthe 1935). In contrast, the eyes ofPontohedyle mi- (e.g. bothHedylopsis species andPontohedylemilasche- laschewitchii are located more posteriorly and closer to- witchii)thischaracteris lacking. Eithertherearesomeun- gether(Fig. 2D). Westheidf & Wawra (1974) described known sensory abilities involved in at least one ontoge- asimilareyeposition inthemarineacochlidianParliedyle netic stage, or both eyes and optic ganglia are evolution- cryplophtluihua. ary remnants oforgans in the process ofbeing reduced. The optic ganglia of Tantiiliiin do no inore fuse with the Theopticnerve isshortinStnibelliaparadoxa (see Küthe rhinophoral ganglia, as may be the case in bothHedylop- 1935). The well-devclopcd eyes of Acoclilidiiini ani- sis species with large rhinophoral ganglia bearing optic boinense, Pallioliedyle weberi and S. paradoxa were de- nerves. Weurgentlyneedontogenetic evidenceforthede- scribedasattachedanterodorsallytoanterolatcrallyonthe velopment ofacochlidian central nervous structures. cerebral ganglia (Bergh 1895; BUcking 1933; Küthe 1935), thus the optic nerves are probably short as well. Thepresenceofoptic ganglia, theorigin and length ofop- The eyes ofPontohedyle milascliewitchii are directly at- tic nerves, eye position in tenns ofsituation and proxim- tached to the cerebral ganglia (Jörger et al. in press), as ity to the cerebral ganglion, as well as eye size and struc- are the eyes ofParliedyle ciyptophthalma, Microliedyle ture should be reinvestigated in all acochlidian species, M iiahantensis(Doe, 974), glanduliferaandM. odhiieri since these may be easily accessible and phylogenetical- 1 (Marcus, 1955) (see Doe 1974; Marcus& Marcus 1955; ly infonnative characters (see Mikkelsen 1996). Westheide & Wawra 1974). The optic nerve is moder- ately long but thin in Tantitliiin elegans, while long and 4.3. Aggregates attached to the cerebral ganglia thick in both Hedylopsis species. The long optic nerves 4.3.1. "Lateral bodies" observed herein may be phylogenetically informative in Acochlidia. Sommerfeldt& Schrödl (2005)described"dorsal bod- All eyes described forAcochlidia are pigmented, except ies" attached to the cerebral ganglion in the acochlidian those of Taiituliim elegans (present study) and ofMicro- Hedylopsis ballantinei. We herein confirm the presence liedyle nahantensis (see Doe 1974). The "poorly devel- ofsuch organs for both Hedylopsis species and A. niur- oped" eyes ofPseudimela corniita describedby Challis manica. Theirposition is,however,morelateralthandor- (1970) should be reinvestigated. sal. We thus propose to use the tenn "lateral bodies" for © Biodiversity Heritage Library, http://www.biodiversitylibrary.org/; www.zoologicalbulletin.de; www.biologiezentrum.at Bonnerzoologische Beiträge 55 (2006) 309 such acochlidian structures until more detailed and com- 4.3.2. Cells near the cerebral commissure parativedataareavailabletoassesstheirhomologytopul- monate dorsal bodies. For the first time in an acochlidian species we describe several cellsthatare looselydispersed within the connec- The "lateral bodies" of the re-examined acochlidian tive tissue above the cerebral commissure in Asperspina speciesarecharacterizedbyagroupofneuronal cellsthat munnanica. Dueto itsposition such acell aggregation re- are enclosedwithin the thick connective tissue layersur- sembles the dorsal bodies of stylommatophoran pul- rounding the cerebral ganglion. The dorsal bodies ofba- monates (e.g. Tliebapisana Mueller, 1774, Helix asper- sommatophoran pulmonates consist ofa pair of similar sa Mueller, 1774 and Achatina fúlica Femssac, 1821) neuronalcellclustersthatare,however,enclosedinathin which were described as diffusely scattered cells within sheath ofconnective tissue, and are situated dorsally on the connective tissue sheath ofthe cerebral ganglion and thecerebral ganglia. Basommatophorandorsalbodiescan located near the cerebral commissure (Saleuddin 1999; lie close together and appear as one group in Helisoma Saleuddin et al. 1997; Takeda & Ohtake 1994). The Swainson, 1840andPlauorbariitsDuméril, 1806,orthey presence, structure, origin and function ofthese cells in canbe distinguished as two separate tissue masses, as in acochlidianscannotberevealedbylightmicroscopyalone Ancylus Mueller, 1774, Lymnaea Lamarck, 1801 and but requires ultrastiiictural studies. Siphonaria Sowerby, 1823 (Saleuddin 1999; Saleuddin et al. 1997; Takeda & Ohtake 1994). Acknowledgements. We thank the Royal Ontario Museum (Canada)andtheSwedishMuseumofNatural Histoiy(Sweden) SOMMERFELDT & ScHRÖDL (2005) described the "lateral forproviding material forre-examination. Gerhard Haszpnmar bodies" ofHedylopsis spiciilifera andH. ballantinei be- (ZSM)isthankedforhelpfuldiscussions. Wearegrateful to Liz ing subdivided into an outer cortex and an inner medul- Atwood(UniversityofWashington) forimprovingthe English. Two anonymous referees provided helpful comments on the la. According to Saleuddin (1999), most of the dorsal manuscript. Thisstudy wassupportedbytheGentian Research bodies ofbasommatophoran pulmonates develop a cor- Foundadon (DFG grant SCHR 667-4 to MS). tex with nuclei and an inner medulla with cell processes that lieveryclose to the cerebral ganglia. In "lateralbodies"ofH. spiciilifera,H. ballantineiandAsperspiiia nnir- REFERENCES manica, no suchclearsubdivision intocortex and medul- lawasfound; insteadallnuclei aredistributedmoreorless Bergh, R. 1895. Die Hedyliden, eine Familie derkladohepati- uniformly. Similarly, the basommatophoran pulmonate schen Nudibranchien. Verhandlungen der Kaiserlich König- lichen Zoologisch-Botanischen Gesellschaft Wien 45: 4-12. Siphonariapectinata Linnaeus, 1758 is described to pos- BüCKiNG, G. 1933. 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