Cainozoic Research, 2(1-2) (2002), pp. 163-170, October 2003 Notes on the systematics, morphology and biostratigraphy of fossil holoplanktonic Mollusca, 13. Considerations on a subdivision of Thecosomata, with the classification of Limacinidae emphasis on genus group Arie+W. Janssen Nationaal Natuurhistorisch Museum (Palaeontology Department), P.O. Box 9517, NL-2300 RA Leiden, the Netherlands: current address: 12, Trig tal’ Hamrija, Xewkija VCT 110, Gozo, Malta; e-mail: [email protected] Received 11 June 2003; revised version accepted 15 June 2003 The families Limacinidae, Cavoliniidae and Peraclididae (Gastropoda, Thecosomata) are raised in rank to Limacinoidea, Cavolinioidea and and subfamilies Peraclidoidea, respectively, currently recognised ofthe Cavoliniidae are given full familial status, viz. Creseidae, Cuvierinidae, Clioidaeand Cavoliniidae.A is preliminary genus group classificationof the Limacinidae proposed, mainlyon morphological shell features; a new genus, Currylimacina n. gen., is introduced. KEY WORDS: Mollusca, Gastropoda, Thecosomata, Euthecosomata, Limacinidae, pteropods, new genus, taxonomy. Introduction Systematics of Thecosomata Currently, holoplanktonic gastropods, usually referred to as In the present paper, the systematics of Thecosomata, and of ‘Pteropoda’, are subdivided into two orders, Thecosomata the Limacinidae in particular, is considered. The currently and Withinthe Thecosomata suborders Gymnosomata. two applied taxonomy is almost entirely based on the relatively are recognised, namely Euthecosomata and Pseudothe- few, extant species. From the fossil record, however, numer- cosomata. ous taxa are known which cannot always be incorporated in The Euthecosomata comprises three families, Limacini- the existing systematic framework satisfactorily. Cavoliniidae and all of soft of Recent dae, Sphaerocinidae, representatives Although part anatomy most representa- which are shelled in the adult state. Both Limacinidae and tives of the Euthecosomata has been studied extensively, Cavoliniidae are known from the fossil the earliest identification of taxa is record, species group predominantly based occurrence being Late Paleocene, and are still extant; on shell morphology. Limacinidae differfrom Cavoliniidae known fossils. Withinthe in Sphaerocinidae are exclusively as basically possessing an ultra-dextrally coiledshell which, Pseudothecosomata three families is illustrated are distinguished, namely however, usually as being sinistral. In the Peraclididae(adult specimens are shell bearing), Cymbulii- Cavoliniidae, the shell is not coiled, but either coni- dae shell shed, but adult individuals with (larval a cartilagi- cal/cylindrical (Creseinae, Cuvierininae) or bilaterally sym- so-called and with ventral and dorsal shell nous pseudoconcha) Desmopteridae (adult metrical, parts more or less animals shell The latter lacking or pseudoconcha). family, distinctly separated (Clioinae, Cavoliniinae). The Sphaero- unknown from the fossil record to date, is occasionally cinidae differ from both in showing cavoliniid larval shell considered to belong to the Gymnosomata (van der Spoel, features and secondary dorso-ventralcoiling ofthe shell. 1976, p. 45). Differences between Limacinidae on the one hand and In the five larval Cavoliniidae+ Gymnosomata, containing families, only Sphaerocinidae on the other, taken together shells These shed are present. are shortly after hatching, the with a large data set for fossil members, have led me to adult ‘naked’. few of these larval consider these specimens being Only two groups as superfamilies rather than fami- shells have been described which so far, explains why little lies. This point of view is also based on the fact that both is known about fossil which date back the and fossil representatives, to Recent pteropods apparently comprise far more Miocene. taxa at the species level than previously assumed. Examples - 164- of this are given by e.g. van der Spoel et al. (1993) and In accepting a superfamily Cavolinioidea, the next logical views would consider the subfamilies Janssen (in press); the observation is also supported by step be to existing (Cresei- Norris The of fossil Clioinae and families. A expressed by (2000, p. 254). study nae, Cuvierininae, Cavoliniinae) as representatives also yields a more reliable insight into the similar argumentation appears valid for the Pseudothecoso- subdivision of evolutionary development of this group, which may be mata, which leads to the following (Table 1) from the the Thecosomata. The ofthe is expected to be far more complex than judged authorship new higher taxa relatively few Recent species alone. attributed according to the Principle ofCo-ordination(ICZN, also advisable rank the In this context, it might be to art. 36.1, p. 45). Sphaerocinidae as a superfamily. However, for the time To my knowledge, DNA structures of extant Thecoso- such studies being I prefer to retain it as a family within the Cavolini- mata have not yet been studied. I expect that would additional criteria which will either confirm oidea, in view ofthe fact that but very few species are known yield or to ofwhich has been described far. refute considerations this outlinedhere. date, only one so my on subject as Order Thecosomata de Blainville, 1824 Suborder Euthecosomata Meisenheimer, 1905 Superfamily Limacinoidea Gray, 1847 Family LimacinidaeGray, 1847 Superfamily CavolinioideaFischer, 1883 Family Creseidae Rang, 1828 Family Cuvierinidae van der Spoel, 1967 Family Clioidae van der Spoel, 1967 Family CavoliniidaeFischer, 1883 Family Sphaerocinidae Janssen & Maxwell in Janssen, 1995 Suborder Pseudothecosomata Meisenheimer, 1905 Superfamily Peraclidoidea Tesch, 1913 Family Peraclididae Tesch, 1913 Family Cymbuliidae Cantraine, 1841 Subfamily Cymbuliinae Cantraine, 1841 Subfamily Glebinae van der Spoel, 1976 ?Family Desmopteridae Chun, 1889 Table 1. Proposed subdivision ofthe Thecosomata. outlined here did mine. A taxonomy which is comparable to the one as Fortunately, Jeffery permitted me to publish has recently been proposed by Jeffery (2003). Jeffery consid- my results independently. ered the Thecosomataand Gymnosomata to be suborders; the Euthecosomataand Pseudothecosomatain his scheme are ofThecosomata. The subdi- Genus level of Limacinidae infraorders Gymnosomata are taxonomy vided into the infraorders Gymnosomata and Gymnoptera. Within the Euthecosomata, however, Jeffery distinguished The systematics ofthe Limacinidae are here enlarged upon three based shell from but a single superfamily (Limacinoidea), comprising further, mainly on morphology as gleaned families, namely Cavoliniidae, Limacinidae and Sphaero- existing literature and available collections. No attempt has but been made unravel in detail the cinidae. I have no opinion on the rank of the higher taxa, yet to undoubtedly quite consider the Limacinoidea and Cavolinioidea to be more complex evolutionary history of this family. This may be lead natural subdivision. than sufficiently differentto represent separate superfamilies. expected to eventually to a more I have contacted Paul Jeffery on this subject; he informed me The application of subgeneric names in RecentLimacina is the lack of data. that his relative ranking of the Thecosomata as given in his frequently seen, despite any phylogenetic In the result of overall in the of of trends in the website was an adjustment anticipation an analysis evolutionary genus inclined ranking of the superorders Heterobranchiaand Caenogas- Limacina, I am now to use only generic names. in tropoda, thus subunits ofthe Euthyneura were changed rank (generally reduced, actually). The scheme on his Limacinidae (revised diagnosis) — Marine, holoplanktonic Soft dextral, shell webpage arose largely as a matter of systematic conven- euthyneuran gastropods. part anatomy of Thecosomata, coiled in an ultra-dextral thin- ience and not from any special study the (seemingly sinistral) spiral, - 165 - conical-almost with walled,ranging in form from discoidal to high or a subperipheral thickened zone projecting as a ros- Larval shell Surface the Umbilicus from wide in cylindrical. not clearly separated. orna- trum at aperture. ranging very ment usually absent, but a divaricate or collabral micro- some discoidal forms, to very narrow in high-conical species, ornament is found in some forms. In the normally smooth or even entirely absent. The columella is simple, sometimes forms occasionally a weak spiral or collabral striation may with a weak central fold, twisted, or with a three-dimensional occur as a senile characteristic. Aperture either simple or torsion. Stratigraphical range: Late Paleoceneto Recent. widened, with an internally or externally reinforced margin, Name Type species Designation Altaspiratella Korobkov, 1966 elongatoidea Aldrich, 1887 original Chaduma Korobkov, 1966 chadumica Korobkov, 1966 original ChadumellaKorobkov, 1966 planorbella Korobkov, 1966 original Crino Gistel, 1848 arctica Fabricius, 17801780 monotype Embolus Jeffreys, 1869 rostralis Souleyet in Eydoux & Souleyet, 1840 original Heliconoides d’Orbigny, 1836 inflata d’Orbigny, 1836 Herrmannsen, 1846 Heterofusus Fleming, 1823 retroversus Fleming, 1823 Gray, 18471847 Limacina Bose, 1817 helicina Phipps, 1774 monotype this Munthea van der Spoel, 1967 trochiformis d’Orbigny, 1836 paper ?PakistaniaIPakistaria Lames,Eames, 19521952 antirotataFames,Eames, 1952 monotype Planorbella Gabb, 1873 nonnon Haldeman, 1843 imitans Gabb, 1873 monotype Plotophysops Curry, 19811981 bearnensis Curry, 1981