Redescription and designation of a neotype for Caecum floridanum (Littorinimorpha, Truncatelloidea, Caecidae) with a characterization of the protoconch and growth stages

Abstract After an extensive search for the type specimens of Caecum floridanum Stimpson, 1851, we believe that these specimens may have been either lost or destroyed in the Chicago fire (1871). This paper presents a redescription of the species and a neotype is designated based on material from the type locality (Florida). Protoconch and growth stages of Caecum floridanum are described and illustrated herein. The teleoconch IV of Caecum floridanum is characterized by strong, wide, low, rounded, closely arranged axial ribs, except last three to four preceding the aperture, which are larger and more widely separated. Caecum compactum Dall, 1892 is here synonymized under Caecum floridanum. Caecum annulatum Emmons, 1858 and Caecum dux Folin, 1871 are not considered synonyms of Caecum floridanum in this report.


Introduction
described the marine gastropod Caecum floridanum from specimens collected on the coast of Florida (USA). Stimpson's description for this species is brief, with no illustration and no information on the type material, depository institution(s) or habitat.
According to Dance (1966: 302), shells studied by Stimpson were deposited in the Chicago Natural History Museum (CNHM), currently called the Field Museum of Natural History (FMNH), Illinois, Chicago, USA, and destroyed in the Chicago fire (1871). However, the institution destroyed was the Chicago Academy of Sciences (CAS), where Stimpson had stored the malacological material studied (Hendrickson and Beecher 1972). According to Bartsch et al. (1946: 10) and Warén (1980), types described by Stimpson were deposited in the "J.G. Jeffreys" collection and Zoological Museum of the University of Copenhagen (ZMUC), respectively. However, Cernohorsky (1974) and Dr Ole S. Tendal (Curator of Mollusca -personal communication, June 2008) found no specimens of C. floridanum in the ZMUC collection. Moreover, a number of years after Jeffreys death, his conchological collection was given by Dall to the U.S. National Museum of Natural History (USNM, Smithsonian Institution) (Dance 1966: 289-290, Warén 1980. Some years later, a part of the material collected during the Lightning, Porcupine and Triton expeditions was given to BMNH (actually NHMUK) (Warén 1980: 4). However, based on information from the respective curators, no type material for C. floridanum was found in either institution. Thus, we conclude that all types of this species were deposited in the CAS and lost or destroyed in the Chicago fire.
Caecum floridanum is a shallow water species widespread throughout the Western Atlantic and associated with a variety of ecosystems and biotopes (Abbott 1974, Vokes and Vokes 1983, Leal 1991, Lightfoot 1992, Diaz and Puyana 1994, Bandel 1996, Rios 2009, Tunnell et al. 2010, Redfern 2013, Lima et al. 2015. The present study provides a detailed re-description for Caecum floridanum based on a large number of specimens studied from the Western Atlantic and the designation of a neotype for the species based on a specimen from the type locality (Florida). In addition, the protoconch and all growth stages of this species are described and figured here based on scanning electron microscopy.

Materials and methods
Identification of the material was performed under a stereomicroscope. Specimens were also studied based on photographs taken with scanning electron microscopy (SEM), at the Electron Microscope Laboratory of the "Museu Nacional do Rio de Janeiro (MNRJ)".
Growth stages in shells were recognized based on truncation regions characterized herein as strangulation (Fig. 2C), suture (Fig. 2G), pronounced increase in diameter ( Fig. 3A), or with an interface of sculpture patterns (3)(4). Roman numerals discriminate and arrows delimit each growth stage. Some growth stages were characterized together (e.g., Fig. 2D: II-III) due to the lack of a distinct truncation region [see approach originally proposed in Lima et al. (2013)].
The following standard measures are based on Lima et al. (2013) and were taken using a stereomicroscope with an eyepiece micrometer: total length (Tol), length from the aperture to the point of maximum arc (Larc), maximum arc (Arc), diameter of aperture (Da), diameter of posterior extremity (Dpe), length of mucro (Lm) and width of mucro (Wm). Only undamaged shells were measured. Simple descriptive statistics were performed to determine the range of meristic and morphometric variables. Other abbreviations used: number (N), mean (M), range (R), standard deviation (SD). The number inside brackets indicates the number of specimens in each lot.
Diagnosis. Teleoconch with strong, wide, low, rounded, closely arranged axial ribs, except last three to four preceding the aperture, which are larger and more widely separated.

Discussion
The brief original description (without illustration) and the loss of the types does not permit recognition of the morphotype originally proposed for Caecum floridanum. These issues are more than sufficient to make the taxon a nomen dubium. However, since 1892 a typical morphotype, which is not in agreement with the conchological characters described by Stimpson (1851) (see also Jong and Coomans 1988: 35, C. irregulare) has been universally accepted for C. floridanum in the vast majority of taxonomic and ecological papers. Although the original description is brief, we can recognize that there are considerable discrepancies between the morphotype of the original description and that universally accepted for C. floridanum. Stimpson described this species as having "thirty-two sharp elevated ribs much narrower than the interspaces", while the most papers recognize that the taxon has 22 to 33 low, rounded, closely arranged axial ribs and very narrow and shallow axial interspaces, except the last one preceding the aperture. Dall (1892: 298) was the first to characterize this species in disagreement with the original proposition based on C. irregulare Folin, 1867 (Fig.  4D), which was included as a synonym in the author's study, without, however, giving any reasons for such an action. Thereafter, a new concept of C. floridanum sensu Dall was established and followed by practically all authors addressing the taxon (Rehder 1943, Olsson and Harbison 1953, Olsson and McGinty 1958, Moore 1970: fig. 2, Abbott 1974, Vokes and Vokes 1983, Leal 1991, Lightfoot 1992, Diaz and Puyana 1994, Bandel 1996, Gomes and Absalão 1996, Lee 2009, Rios 2009, Tunnell et al. 2010, Redfern 2013, Lima et al. 2015. Caecum floridanum cannot be identified accurately based on Stimpson's description, which is too vague and might be applied to various Caecum taxa from the Western Atlantic. Therefore, any nomenclature decision regarding this taxon (e.g., description of the taxon as a new species or validating its synonym C. irregulare, making C. floridanum a nomen dubium) will cause instability, inconsistency and taxonomic confusion (unless some type material is found).
Thus, we believe that the best course is to designate a neotype for Caecum floridanum based on a specimen deposited at the ANSP (International Commission on Zoological Nomenclature, 1999: art. 75.3.7.) and collected from the type locality (ICZN 1999: art. 76.3.) due to the rather vague original description (in our view, an exceptional need before the ICZN 1999: art. 75.3.). This neotype replaces the lost or destroyed original type material (ICZN 1999: art. 75.3.4, see Introduction to review the steps taken to trace the type material) and clarifies inconsistencies between the concepts put forth by Stimpson (1851) and subsequent authors (ICZN 1999: art. 75.3.1.), conserving the current usage of the name and the universally accepted morphological concept of the species (as have been used in most of the literature) beyond doubt (ICZN 1999: art. 75.3.5.). Vokes and Vokes (1983: 120, fig. 12) recognized a hypotype for Caecum floridanum, but this nomenclatural type does not appear in the ICZN (1999) and has no scientific value.
The characterization of teleoconch II presented herein for Caecum floridanum is consistent with that of Lightfoot (1992: 179). Bandel (1996) recognized four to five growth stages in the ontogeny of this species, but did not describe each stage separately. Thus, reconstruction of the stages presented by him is an assumption not supported with clear data. Still according to Bandel (1996), a varix is seen on the penultimate and last growth phases, but it is characterized here only at the end of the last stage.
Ms Andreia Salvador for relaying information on Caecidae deposited in their respective institutions; to Mr Philippe Maestrati and Ms Virginie Héros (MNHN) for providing the MNHN number and sending photos of C. irregulare and C. phronimum; Ms Yolanda Villacampa for sending photos of Caecum compactum; to Dr Gregory P. Dietl (Director of Collections, PRI) and Dr Judith Nagel-Myers (Collections Manager, PRI) for loan of type material (C. puntagordanum); to Mr Colin Redfern (USA), Dr Harry Lee (USA), Mr Marien Faber (Netherlands) and anonymous referees for the valuable comments on the manuscript; our best thanks to Dr Ulisses Caramaschi (MNRJ) for the critical review of this study, especially the case of designation of a neotype; to Dr Helena P. Lavrado (IBUFRJ, Department of Marine Biology) for providing the stereomicroscope with an ocular micrometer; to Dr Christian Betzler (Universität Hamburg, Germany) who kindly allowed us to use two figures published in Mitteilungen des Geologisch-Paläontologischen Instituts der Universität Hamburg.