ZOOLOGIA 30 (1): 88–96, February, 2013 http://dx.doi.org/10.1590/S1984-46702013000100011 First record of Thylaeodus (Gastropoda: Vermetidae) from the Equatorial Atlantic Ocean, with the description of a new species Paula Spotorno1 & Luiz Ricardo L. Simone2 1 Museu Oceanográfico “Prof. Eliézer de Carvalho Rios”, Universidade Federal do Rio Grande. 96200-580 Rio Grande, RS, Brazil. E-mail: [email protected] 2 Museu de Zoologia da Universidade de São Paulo. 04299-970 São Paulo, SP, Brazil. E-mail: [email protected] ABSTRACT. The vermetid Thylaeodus equatorialis sp. nov. is endemic to the São Pedro and São Paulo Archipelago, located at the mid equatorial Atlantic Ocean. The species is closely related to Thylaeodus rugulosus (Monterosato, 1878), as indicated by similar shell characters, coloration of the soft parts, and feeding tube scars. However, T. equatorialis sp. nov. mainly differs from T. rugulosus in the operculum/aperture diameter ratio (~79% versus 100%), by having well developed pedal tentacles and fewer egg capsules in brooding females. In addition, the new species has the following unique characteristics: size almost twice as large (shell, tube aperture, erect feeding tube, protoconch and egg capsules) as the other Atlantic species; unusual method of brooding egg capsules; radula with prominent and more numerous flanking cusps; and small pustules following the suture of the protoconch. A detailed discussion on the taxonomy and biology of vermetid Thylaeodus and allies is also presented. KEY WORDS. Mollusca; São Pedro and São Paulo Archipelago; taxonomy; anatomy Thylaeodus equatorialis sp. nov.; vermetid. Vermetids are sessile gastropods characterized by an un- tion between the Brazilian and West African faunal provinces coiled shell attached to or buried in hard substrates. Their pe- and the archiplepelago’s small area (EDWARDS & LUBBOCK 1983b). culiar shells grow irregularly, adapting to the substratum (KEEN The archipelago has been visited by scientific expeditions since 1961, SAVAZZI 1996), and individuals are mobile only in the early 1799 (EDWARDS 1985) and some publications on the marine bi- stages after hatching (KEEN 1961). Additional data and a com- ology and ecology of ASPSP have been published. Literature plete description of the family can be found elsewhere (KEEN data indicates that Dendropoma sp. is the only vermetid record 1961, MORTON 1965, HADFIELD 1970, KELLY 2007). in the species checklist (EDWARDS & LUBBOCK 1983a, EDWARDS Brazilian reef-building vermetids are found mainly on 1984). the Northeast and Southeast coasts, between 3°S (northern coast The present contribution is part of a research program of Ceará) to 22°S (northern coast of Rio de Janeiro) (SOARES- initiated several years ago, and which investigates the ASPSP GOMES et al. 2001) including the Brazilian oceanic islands marine molluscan fauna (SPOTORNO-OLIVEIRA et al. 2003). So far, (LABOREL & KEMPF 1965). An assembly of six vermetid gastropod a total of 48 mollusk taxa have been recorded from tide pools species occurs along the Brazilian coast, from states of Amapá and rocky shores in the Belmonte Islet, ASPSP (SPOTORNO-OLIVEIRA to Santa Catarina – Dendropoma irregulare (d’Orbigny, 1842); et al. 2009), and five recently described species (SIMONE 2008, Dendropoma sp.; Petaloconchus erectus (Dall, 1888); P. myrakeenae 2009a,b), two of which are considered endemic (SIMONE 2008, Absalão & Rios, 1987; P. varians (d’Orbigny, 1841), and 2009a). Thylacodes decussatus (Gmelin, 1791) (LABOREL & KEMPF 1965, The ASPSP vermetids are distributed along the intertidal LABOREL 1977, RIOS & BARCELLOS 1979, 1980, BARCELLOS et al.1989, shoreline and down in tide pools, which are often flushed with LEAL 1991, RIOS 1994, SPOTORNO-OLIVEIRA 2009). Nevertheless, the seawater when the tide is high (EDWARDS & LUBBOCK 1983a,b, Brazilian vermetids are remarkably numerous, and the total EDWARDS 1984). Two vermetid taxa have been recorded from number of known taxa has increased to 16 (SPOTORNO et al. 2012). this locality (SPOTORNO-OLIVEIRA et al. 2009), one of which is The Archipelago of São Pedro and São Paulo (also known herein described as new. as St. Paul’s Rocks, abbreviated ASPSP) is the smallest Brazilian The genus Thylaeodus Mörch, 1860, type species Bivona oceanic archipelago, located at the mid equatorial Atlantic contorta Carpenter, 1857 (SD by KEEN 1961: 191), from Tropical Ocean (00°55’02"N 29°20’42"W), about 1,010 km off the Bra- West America, is characterized by shells of moderate to small zilian coast and 1,824 km off the African coast. The marine diameter, feeding tube scars present in most specimens, oper- flora and fauna of ASPSP are of considerable biogeographic culum slightly overlapping foot (though not reaching the di- interest because of their isolation, ASPSP’s intermediate loca- ameter of the aperture, with less than 3/4 the diameter of the © 2013 Sociedade Brasileira de Zoologia | www.sbzoologia.org.br | All rights reserved. First record of Thylaeodus from the Equatorial Atlantic Ocean, with the description of a new species 89 aperture), operculum with a central spiral lamina in the upper following suture. Soft body coloration overall milky-white, with surface of 1.5 whorls, and inner shell surface lacking longitu- some red bands in head-foot. Operculum with ~79% of aper- dinal columellar lamellae (KEEN 1961, 1971, MORTON 1965). ture diameter. Radula with strong prominent flanking cusps; Thylaeodus was believed to be absent from the mid equatorial lateral tooth with 7-9 flanking cusps on outside; outer mar- Atlantic Ocean and the species described herein is the first ginal tooth (second marginal) with 7-10 flanking cusps on in- record of the genus for that region. ner side. Mantle border of brooding females with deep incision along midline. Brooding egg capsules both freely in interior of MATERIAL AND METHODS mantle cavity and attached to inner shell surface by stalks; up to three egg capsules, containing 2-6 embryos. Males with Samples were removed from the rock using hammer and mantle border thickened. chisel. Specimens were fixed and preserved in 80 to 100% etha- Description. Holotype: part of cluster of specimens; con- nol and deposited in MORG and MZSP malacological collec- sisting of isolated tube. Aperture diameter: 1.5 mm; length 6 tions. Soft parts were removed after crushing the shell with a mm. Shell. Protoconch (Fig. 1): barrel-shaped, slender and small lathe. Anatomy, shells, radula, protoconch and opercula stretched, buried by teleoconch whorls; with 2.5 whorls. were studied and photographed with a Canon Power Shot S45 Protoconch average length: 1.43 ± 0.05 mm (range 1.3 to 1.6 camera connected to a binocular stereomicroscope Leica mm, n = 7); width: 0.77 ± 0.04 mm (range 0.7 to 0.9 mm, n = 7). MZ125. The dissections were performed by standard techniques, At attachment, protoconch positioned on side with outer with specimens immersed in fixative under a stereo-microscope. apertural edge against substrate. Pre-attachment protoconch with For detailed examination, some shells, protoconchs and radu- slightly wavy surface, subsequent protoconch whorls smooth- lae samples were mounted on stubs, coated with a gold-palla- surfaced, translucent, color light amber with dark brown at su- dium alloy and observed under scanning electron microscope ture; small pustules following suture after first half-whorl. in the Laboratório de Microscopia Eletrônica of the Museu de Teleoconch (Figs 2-6 and 18): 3 to 5 loops of tubular teleoconch Zoologia, Universidade de São Paulo (MZSP). coiled in variable shapes; length averages 9.06 ± 0.55 mm (range Institutional abbreviations are as follows: (MORG) Museu from 7 to 11 mm, n = 7). Early whorls piled up attached to sub- Oceanográfico “Prof. Eliézer de Carvalho Rios”, Universidade strate, arranged into irregular stack or expanding laterally, rarely Federal do Rio Grande, Brazil; (MZSP) Museu de Zoologia da forming open loops; last whorl becoming emergent above sub- Universidade de São Paulo, Brazil; (MNRJ) Museu Nacional, strate. First whorls thicker, color pink or translucent-brown, be- Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil; coming paler or translucent-white next to aperture. Emergent (USNM) National Museum of Natural History, Smithsonian tube (or feeding tube) with average of 7.42 ± 1.90 mm (from 3 to Institution, Washington, D.C., United States. 13 mm, n = 5), forming erect tube above substrate, thin walled, white-light or pink in color, section rounded, narrower and more TAXONOMY finely ridged than first whorls of teleoconch. Aperture circular with average diameter of 1.71 ± 0.14 mm (range from 1.1 to 2.2 Thylaeodus equatorialis sp. nov. mm, n = 7). Early post larval sculpture of axial ribs, subsequent sculpture of axial growth lines, without longitudinal (spiral) Figs 1-18 sculpture. Most specimens with remnants of earlier feeding tubes, Vermetidae sp.: Spotorno-OLIVEIRA et al., 2009: 180. i.e, feeding tube scars (Figs 2, 4, and 6: fc). Inner shell surface Thylaeodus sp.: Spotorno et al., 2012: 06. smooth, color usually light brown, sometimes paler. Longitudi- nal columellar lamellae lacking. Head-foot (Figs 7 and 10): Head Type locality. BRAZIL, Pernambuco: São Pedro e São Paulo not especially broad, bulbous, about a half of foot length. Snout Archipelago (Belmonte Inlet, Enseada, 00°55’01"N-29°20’44"W, large and cylindrical, with mouth as vertical slit in ventral-ter- 3-10 m), , 7.xi.2007, Simone & Cunha leg. minal surface. Cephalic tentacles elongated, emerging laterally Type material. Holotype MORG 51621. Paratypes from from snout base, weakly longer than snout. Eyes small, black, the type locality: MORG 50785, 10 spm, vii.2005; MORG 51296, immersed in ventral region of tentacles’ base. Color overall milky- 1 spm, iii.2005, both Spotorno leg.; MORG 51622, 3 spm, white, with some red pigmented band in some specimens. Foot 07.xi.2007; MZSP 82314, 5 spm, iii.2005; MZSP 86531, 3 spm, occupying ~1/2 of total head-foot volume.