Six sediment samples weighing between 224–735 g were collected in June of 2016 from Cayo Nuevo reef, located at the Campeche Bank, southern Gulf of Mexico. Samples were collected by SCUBA diving, from were two stations at depths of 7.6 and 18.2 m. Sediment was sieved and molluscs (adults and micromolluscs ≤ 10 mm) were sorted, examined, and identified to the lowest taxonomic level. A total of 1,347 specimens was found, of which 224 shells were dead and 1,123 were alive. Thirty-four families, 53 genera, and 67 species were identified. The most abundant families were Chamidae and Arcidae for the Bivalvia class, and Caecidae and Tornidae for the Gastropoda class. The vertical range of Bentharca sp. was extended.

baseline, inventory, Campeche Bank, Gulf of Mexico, micromolluscs

Frequently, species molluscan biodiversity accounts are incomplete because of the lack of some groups such as sea slugs and micromolluscs. Compared with macromolluscs, the study of micromolluscs is still in its infancy, which is probably due not to the difficulty involved in obtaining samples, but difficulties in identification of such small animals and the time-consuming process required to separate specimens from sand or other substrates (e.g., algae or rocks), and photography. In order to get a more realistic picture of the biodiversity for different habitats, micromolluscs should be incorporated into the different studies (Sasaki 2008, and pers. obs.).

The term micromollusc has been applied in arbitrary and non-standardised ways. Micromolluscs are molluscs not visible without some type of artificial assistance, such as a microscope or magnifying glass. The most restrictive definition, or sensu stricto, stated that micromollusc size should be less than 5 mm as an adult (Narciso 2005, Geiger et al. 2007). Other authors considered micromolluscs as specimens smaller than 10 mm as an adult (Barrera and Tunnell 2001). Finally, the wider definition of micromollusc, or sensu lato, includes molluscs whose size is typically less than 10 mm as an adult and also included juvenile representative of macromolluscs (Moore 1964; García-Cubas 1970; Tunnell 1974; Kay 1980; Vokes and Vokes 1983).

Barrera (2001) stated that within Texas and Mexico, the majority of the studies involved macromolluscs. In Mexico, more than 4,643 species of marine molluscs have been recorded, and approximately 2,067 of them inhabit the Gulf of Mexico (GoMx) and the Mexican Caribbean Sea (Castillo-Rodríguez 2014). Unfortunately, Castillo-Rodríguez did not state which of them were micromolluscs. Important molluscan compilations focusing on these groups include publications by García-Cubas and Reguero (2007) and Vokes and Vokes (1983), although only a few publications have addressed the micromolluscan fauna specifically such as García-Cubas (1963, 1970 and 1971) for lagoons in the Gulf of Mexico and Hicks et al. (2001) at Alacranes reef.

The Campeche Bank is located at the southern GoMx and is composed of several emergent and submerged coral reefs (Tunnell et al. 2010). One of the smaller and most remote reefs is Cayo Nuevo, located between Arenas and Triángulos reefs (190 km offshore) in the GoMx (Fig. 1). Studies on this reef are almost non-existent with the exception of polychaetes (Granados-Barba et al. 2003).

Figure 1. 

Map of the Gulf of Mexico, with the largest reef in the GoMx and sampling locations where micromolluscs have been documented in the literature and this study (adapted from Felder and Camp 2009).

The present work focuses on the molluscs of the Cayo Nuevo sandy bottoms, Gulf of Mexico. In this substrate we could find micromolluscs sensu stricto and juveniles of macromolluscs species that inhabit the interstitial as but also empty shells that could be carried by external factors such wind and currents.

Using SCUBA gear, six sediment samples of coarse sand to fine gravel weighing 224–735 g each were collected by hand at 7.6 and 18.2 m on 19 June 2017 at Cayo Nuevo reef (Table 1). Each sample was sieved by pouring water through six differently sized sieves (2 mm, 1.4 mm, 1 mm; 710 µm, 500 µm, and 250 µm) (Table 2) and sorted dry using a dissecting Nikon SMZ800 microscope. Specimens were picked out using soft forceps and 000 fine paint brushes. Molluscs were placed into 2 mm tubes and micromolluscs were placed into PCR tubes, both with 70% ethanol for long-term storage. Identification of specimens to species level was based on Abbott (1974), Tunnell et al. (2010) and Redfern (2013). Whenever possible, at least one specimen of each species or morphotype was photographed. All the specimens were deposited at the “Colección de Moluscos de la Peninsula de Yucatán” (CMPY), Unidad Multidisciplinaria de Docencia e Investigación Campus Sisal, Universidad Nacional Autónoma de México.

The nomenclature of the species listed was assigned according to Bouchet and Rocroi (2010) for Bivalvia, Bouchet et al. (2017) for Gastropoda, and Kaas and Van Belle (1985) for Polyplacophora, due to the variability of some categories we only present the Linnaean ones. Abundance categories were assigned following Hicks et al. (2001): Abundant ≥ 50 (A); Common = 6–49 (C); Uncommon = 2–5 (UC), and Rare = 1 (R). Juvenile species are denoted by an asterisk (*).

The results from the analysis of the sediment from Cayo Nuevo reef revealed 67 species of molluscs, from which 50 species are gastropods, 14 species are bivalves and three are chitons. These species belong to 38 different families.

Phylum Mollusca Linnaeus, 1758

Class Polyplacophora Gray, 1821

Polyplacophora sp. 1 * (R) (Fig. 2–1)

Figure 2. 

Polyplacophora1–3: 1Polyplacophora sp. 1, dorsal view, scale bar 0.5 mm 2Polyplacophora sp. 2, dorsal view, scale bar 1 mm 3 Ischnochiton sp., dorsal view, scale bar 0.5 mm. Bivalvia4–15: 4Arcidae sp., dorsal view, scale bar 0.5 mm 5 Arca imbricata 5a ventral view 5b dorsal view, scale bar 1 mm 6 Barbatia domingensis 6a ventral view 6b dorsal view, scale bar 1 mm 7 Barbatia sp. 7a ventral view 7b dorsal view, scale bar 1 mm 8 Bentharca sp. 8a ventral view 8b dorsal view, scale bar 1 mm 9 Anomia sp. 9a ventral view 9b dorsal view, scale bar 1 mm 10 Carditopsis smithii 10a ventral view 10b dorsal view, scale bar 1 mm, 11Lucinidae sp., ventral view, scale bar 0.5 mm 12 Chama sinuosa 12a ventral view 12b dorsal view, scale bar 0.5 mm 13Chamidae sp. 13a ventral view 13b dorsal view, scale bar 1 mm, 14 Crassinella lunulata 14a ventral view 14b dorsal view, scale bar 1 mm 15 Semele bellastriata 15a dorsal view 15b lateral view, scale bar 1 mm. Gastropoda16–23: 16Gastropoda sp., ventral view, scale bar 0.5 mm, 17 Diodora minuta, ventral view, scale bar 0.25, 18 Diodora listeri 18a ventral view 18b dorsal view, scale bar 1 mm, 19 Scissurella redferni 19a ventral view 19b dorsal view, scale bar 1 mm 20 Synaptocohlea picta 20a ventral view 20b dorsal view, scale bar 1 mm 21 Lodderena ornata 21a ventral view 21b Apical view, scale bar 0.5 mm 22 Cerithium sp. 1 22a ventral view 22b dorsal view, 1 scale bar 1 mm 23 Cerithium sp. 2 23a ventral view 23b dorsal view, scale bar 1 mm.

Polyplacophora sp. 2 * (R) (Fig. 2–2)

Order Chitonina Thiele, 1909

Family Chitonoidea Rafinesque, 1815

Genus Ischnochiton Gray, 1847

Ischnochiton sp. * (UC) (Fig. 2–3)

Class Bivalvia Linnaeus, 1758

Order Arcida Stoliczka, 1871

Family Arcidae Lamarck, 1809

Arcidae sp. (UC) (Fig. 2–4)

Genus Arca Linnaeus, 1758

Arca imbricata Bruguière, 1789 * (UC) (Fig. 2–5a, b)

Genus Barbatia Gray, 1842

Barbatia domingensis * (Lamarck, 1819) (UC) (Fig. 2–6a, b)

Barbatia sp. * (C) (Fig. 2–7a, b)

Genus Bentharca Verrill & Bush, 1898

Bentharca sp. (R) (Fig. 2–8a, b)

Order Mytilida Férussac, 1822

Family Mytilidae Rafinesque, 1815

Genus Crenella T. Brown, 1827

Crenella sp. (R)

Order Pectinida Gray, 1854

Family Anomiidae Rafinesque, 1815

Genus Anomia Linnaeus, 1758

Anomia sp.* (R) (Fig. 2–9a, b)

Order Cardita Bruguière, 1792

Family Carditidae Férussac, 1822

Genus Carditopsis E. A. Smith, 1881

Carditopsis smithii (Dall, 1896) (C) (Fig. 2–10a, b)

Order Lucinida Gray, 1854

Family Lucinidae J. Fleming, 1828

Lucinidae sp. * (UC) (Fig. 2–11)

Order Venerida Gray, 1854

Family Chamidae Lamarck, 1809

Chamidae sp. (UC) (Fig. 2–12a, b)

Genus Chama Linnaeus, 1758

Chama sinuosa Broderip, 1835 * (A) (Fig. 2–13a, b)

Family Galeommatidae Gray, 1840

Galeommatidae sp. (R)

Order Carditida Dall, 1889

Family Crassatellidae Férussac, 1822

Genus Crassinella Guppy, 1874

Crassinella lunulata (Conrad, 1834) * (R) (Fig. 2–14a, b)

Order Cardiida Férussac, 1822

Family Semelidae Stoliczka, 1870 (1825)

Genus Semele Schumacher, 1817

Semele bellastriata (Conrad, 1837) * (UC) (Fig. 2–15a, b)

Class Gastropoda Cuvier, 1795

Gastropoda sp. * (R) (Fig. 2–16)

Order Lepetelloidea Dall, 1882

Family Fissurellidae Fleming, 1822

Genus Diodora Gray, 1821

Diodora minuta (Lamarck, 1822) * (UC) (Fig. 2–17)

Diodora listeri (d’Orbigny, 1847) (R) (Fig. 2–18a, b)

Family Scissurellidae Gray, 1847

Genus Scissurella d’Orbigny, 1824

Scissurella redferni (Rolán, 1996) (C) (Fig. 2–19a, b)

Order Trochida Rafinesque, 1815

Family Trochidae Rafinesque, 1815

Genus Synaptocochlea Pilsbry, 1890

Synaptocochlea picta (d’Orbigny, 1847) (A) (Fig. 2–20a, b)

Family Skeneidae W. Clark, 1851

Genus Lodderena Iredale, 1924

Lodderena ornata (Olsson & McGinty, 1958) (A) (Fig. 2–21a, b)

Family Cerithiidae Fleming, 1822

Genus Cerithium Bruguière, 1789

Cerithium sp. 1 (R) (Fig. 2–22a, 22b)

Cerithium sp. 2 (UC) (Fig. 2–23a, 23b)

Cerithium atratum (Borns, 1778) (R) (Fig. 3–1a, b)

Figure 3. 

Gastropoda1–26: 1 Cerithium atratum 1a ventral view 1b dorsal view, scale bar 1 mm 2 Alaba incerta 2a ventral view 2b dorsal view, scale bar 0.25 mm 3 Finella sp. 3a ventral view 3b dorsal view, scale bar 1 mm 4 Sansonia tuberculata 4a ventral view 4b dorsal view, scale bar 1 mm 5 Hipponix sp. 5a ventral view 5b dorsal view, scale bar 0.1 mm 6 Iniforis turristhomae 6a ventral view 6b dorsal view, scale bar 1 mm 7 Metaxia rugulosa 7a ventral view 7b dorsal view, scale bar 0.5 mm 8 Cerithiopsis sp. 8a ventral view 8b dorsal view, scale bar 1 mm 9Cerithiopsis cf. iuxtafuniculata9a ventral view 9b dorsal view, scale bar 1 mm 10Vermetidaeincertae sedis irregularis scale bar 1 mm 11 Dendropoma corrodens scale bar 1 mm 12 Vermetid sp. C, ventral view, scale bar 0.25 mm 13 Petaloconchus mcgintyi, ventral view, scale bar 0.25 mm 14 Thylacodes sp. scale bar 1 mm 15 Simulamerelina caribaea 15a ventral view 15b dorsal view, scale bar 1 mm 16 Schwartziella fischeri 16a ventral view 16b dorsal view, scale bar 1 mm 17 Zebina sp. 2 17a ventral view 17b dorsal view, scale bar 1 mm 18 Zebina sp. 2 18a ventral view 18b dorsal view, scale bar 0.5 mm 19 Truncatella sp. 19a ventral view 19b dorsal view, scale bar 0.5 mm 20 Caecum circumvolutum, lateral view, scale bar 0.2 mm 21 Caecum donmoorei 21a stage 1, lateral view, scale bar 0.2 mm 21b adult, lateral view, scale bar 0.2 mm 22 Caecum johnsoni, lateral view, scale bar 0.2 mm 23 Caecum pulchellum, lateral view, scale bar 0.2 mm 24 Caecum textile, lateral view, scale bar 0.2 mm 25 Caecum sp. B, lateral view, scale bar 0.2 mm 26 Meioceras nitidum, lateral view, scale bar 0.2 mm.

Family Litiopidae Gray, 1847

Genus Alaba H. adams & A. Adams, 1853

Alaba incerta (d’Orbigny, 1841) (C) (Fig. 3–2a, b)

Family Scaliolidae Jousseaume, 1912

Finella sp. (UC) (Fig. 3–3a, 3b)

Family Pickworthiidae Iredale, 1917

Subfamily Pickworthiinae Iredale, 1917

Genus Sansonia Jousseaume, 1892

Sansonia tuberculata (Watson, 1886) (R) (Fig. 3–4a, b)

Family Hypponicidae Troschel, 1861

Hipponix sp. (C) (Fig. 3–5a, 5b)

Family Triphoridae Gray, 1847

Genus Iniforis Jousseaume, 1884

Iniforis turristhomae (Holten, 1802) (UC) (Fig. 3–6a, b)

Genus Metaxia Monterosato, 1884

Metaxia rugulosa (C. B. Adams, 1850) (R) (Fig. 3–7a, b)

Family Cerithiopsidae H. Adams & A. Adams, 1853

Genus Cerithiopsis Forbes & Hanley, 1850

Cerithiopsis sp. (R) (Fig. 3–8a, 8b)

Cerithiopsis cf. iuxtafuniculata Rolán, Espinosa & Fernández-Garcés, 2007 (R) (Fig. 3–9a, b)

Family Vermetidae Rafinesque, 1815

Vermetidaeincertae sedis irregularis d’Orbigny, 1841 (Fig. 3–10)

Genus Dendropoma Mörch, 1861

Dendropoma corrodens (d’Orbigny, 1841) (R) (Fig. 3–11)

Vermetid sp. CRedfern 2013 (A) (Fig. 3–12)

Genus Petaloconchus Lea, 1843

Petaloconchus mcgintyi (Olsson & Harbison, 1953) * (C) (Fig. 3–13)

Genus Thylacodes Guettard, 1770

Thylacodes sp. * (R) (Fig. 3–14)

Family Rissoidae Gray, 1847

Genus Simulamerelina Ponder, 1985

Simulamerelina caribaea (d’Orbigny, 1842) (UC) (Fig. 3–15a, b)

Family Zebinidae Coan, 1964

Genus Schwartziella G. Nevill, 1881

Schwartziella fischeri (Desjardin, 1949) (UC) (Fig. 3–16a, b)

Genus Zebina H. Adams & A. Adams, 1854

Zebina sp. 1 (A) (Fig. 3–17a, 17b)

Zebina sp. 2 (C) (Fig. 3–18a, 18b)

Family Truncatellidae Gray, 1840

Genus Truncatella Risso, 1826

Truncatella sp. (R) (Fig. 4–19a, 19b)

Family Caecidae Gray, 1850

Genus Caecum Fleming, 1813

Caecum circumvolutum de Folin, 1867 (C) (Fig. 3–20)

Caecum donmoorei Mitchell-Tapping, 1979 (C) (Fig. 3–21a, b)

Caecum johnsoni Winkley, 1908 (A) (Fig. 3–22)

Caecum pulchellum Stimpson, 1851 (C) (Fig. 3–23)

Caecum textile de Folin, 1867 (UC) (Fig. 3–24)

Caecum sp. B sensuRedfern 2013 (C) (Fig. 3–25)

Genus Meioceras Carpenter, 1859

Meioceras nitidum (Stimpson, 1851) (UC) (Fig. 3–26)

Family Tornidae Sacco, 1896 (1884)

Genus Parviturboides Pilsbry & McGinty, 1949

Parviturboides sp. (C) (Fig. 4–1a, b)

Figure 4. 

Gastropoda1–18: 1 Parviturboides sp. 1a ventral view 1b dorsal view, scale bar 1 mm 2 Vitrinella sp. 2a ventral view 2b dorsal view, scale bar 0.5 mm 3 Gibberula lavalleeana 3a ventral view 3b dorsal view, scale bar 1 mm 4 Volvarina sp. 1 4a ventral view 4b dorsal view, scale bar 1 mm 5 Volvarina sp. 2 5a ventral view 5b dorsal view, scale bar 1 mm 6Columbellidae sp. 1 6a ventral view 6b dorsal view, scale bar 0.5 mm 7Columbellidae sp. 2 7a ventral view 7b dorsal view, scale bar 0.5 mm 8 Steironepion moniferum 8a ventral view 8b dorsal view, scale bar 1 mm 9 Phrontis sp. 9a ventral view 9b dorsal view, scale bar 0.5 mm 10 Trachypollia sp. 10a ventral view 10b dorsal view, scale bar 1 mm 11Turridae sp. 1 11a ventral view 11b dorsal view, scale bar 1 mm 12 Ammonicera lineofuscata, Apical view, scale bar 0.25 mm 13 Ammonicera minortalis 13a Apical view 13b ventral view, scale bar 0.1 mm 14 Rissoella galba 14a ventral view 14b dorsal view, scale bar 0.1 mm 15Pseudoscilla aff. babylonia15a ventral view 15b dorsal view, scale bar 1 mm.

Genus Vitrinella C. B. Adams, 1850

Vitrinella sp. (A) (Fig. 4–2a, b)

Family Cystiscidae Stimpson, 1865

Genus Gibberula Swainson, 1840

Gibberula lavalleeana (d’Orbigny, 1824) (UC) (Fig. 4–3a, b)

Family Marginellidae Fleming, 1828

Genus Volvarina Hinds, 1844

Volvarina sp. 1 (UC) (Fig. 4–4a, 4b)

Volvarina sp. 2 (R) (Fig. 4–5a, 5b)

Family Columbellidae Swainson, 1840

Columbellidae sp. 1 (UC) (Fig. 4–6a, b)

Columbellidae sp. 2 (R) (Fig. 4–7a, 7b)

Genus Steironepion Pilsbry & H. N. Lowe, 1932

Steironepion moniliferum (G. B. Sowerby I, 1844) (UC) (Fig. 4–8a, b)

Family Nassariidae Iredale, 1916 (1835)

Genus Phrontis H. Adams & A. Adams, 1853

Phrontis sp. (UC) (Fig. 4–9a, b)

Family Muricidae Rafinesque, 1815

Genus Trachypollia Woodring, 1928

Trachypollia sp. (R) (Fig. 4–10a, b)

Family “Turridae” H. Adams & A. Adams, 1853 (1838)

Turridae sp. 1 (R) (Fig. 4–11a, 11b)

Family Omalogyridae G.O. Sars, 1878

Genus Ammonicera Vayssière, 1893

Ammonicera lineofuscata Rolán, 1992 (A) (Fig. 4–12)

Ammonicera minortalis Rolán, 1992 (A) (Fig. 4–13a, b)

Family Rissoellidae Gray, 1850

Genus Rissoella Gray, 1847

Rissoella galba Robertson, 1961 (R) (Fig. 4–14a, b)

Order Aplysiida

Family Aplysiidae Lamarck, 1809

Genus Aplysia Linnaeus, 1767

Aplysia sp. (R)

Order Siphonarimorpha

Family Pyramidellidae Gray, 1840

Genus Pseudoscilla Boettger, 1901

Pseudoscilla aff. babylonia (C. B. Adams, 1845) (R) (Fig. 4–15a, 185b)

The most abundant families of gastropods were the Caecidae (456 specimens, seven species), Tornidae (221 specimens, two species), and Omalogyridae (132 specimens, two species). The most abundant families of bivalves were Arcidae (40 specimens, five species) and Chamidae (59 specimens, two species). The most abundant gastropod species were Caecum johnsoni (310 specimens), Vitrinella sp. (208 specimens), Vermetid sp. C (91 specimens), Lodderena ornata (71 specimens), and Caecum donmoorei (147 specimens). For the Bivalvia the most abundant species were Chama sinuosa (57 specimens), Barbatia domingensis (57 specimens) and Carditopsis smithii (12 specimens).

From the six sediment samples, the most commonly found molluscs were Lodderena ornata, Caecum johnsoni and Ammonicera lineofuscata, while other species appeared only once: Leptochiton sp., Arcidae sp., Bentharca sp., Crenella sp., Anomia sp., Chama sp., Galeommatidae sp., Chione elevata, Semele bellastriata, Cerithium sp. 1, Gastropoda sp., Diodora listeri, Cerithium atratum, Sansonia tuberculata, Iniforis turristhomae, Metaxia rugulosa, Cerithiopsis cf. iuxtafuniculata, Cerithiopsis sp., Vermetidaeincertae sedis irregularis, Dendropoma corrondens, Thylacodes sp., Finella sp., Caecum textile, Hipponix sp., Volvarina sp. 2, Columbellidae sp. 2, Aplysia sp., and Pseudoscilla aff. babylonia.

This new data becomes a taxonomic reference list for the molluscs that inhabit Cayo Nuevo, GoMx, including micromolluscs as well as juvenile macromolluscs. To place it within a useful context we mention other inventories made in this area: Felder and Camp (2009) recorded some 5,517 species of invertebrates in the GoMx, of which 2,455 were marine molluscs (Moretzsohn et al. 2009). González et al. (1991) recorded 298 species of molluscs and included 33 localities distributed around the coasts of the Yucatan Peninsula and adjacent coral reefs but did not mentioned Cayo Nuevo. García-Cubas et al. (1999) recorded 110 species of gastropods in the northern and northeastern regions of the Yucatan Peninsula. Rice and Kornicker (1962) recorded 130 species for Alacranes reef in the Campeche Bank and later, Hicks et al. (2001) recorded 215 species of molluscs on the same reef. Although earlier articles include reefs or sampling locations within the Bank of Campeche (e.g., Rehder and Abbott 1951, Springer and Bullis 1956, Kornicker et al. 1959), no mention of molluscs from Cayo Nuevo were found. Only Barrera (2001) study focuses on reef micromolluscs, recording 131 species from the East and West Flower Garden Banks (FGB).

The molluscan assemblage at Cayo Nuevo shares many species also present at the FGB (Barrera 2001) and Alacranes Reef (Hicks et al. 2001) (19 families/21 genera and 21 families/22 genera, respectively) (Table 3). The most diverse families recorded by Barrera (2001) and Hicks et al. (2001) were Caecidae (six genera and ten species) and Rissoidae (five genera and seven species) for Gastropoda and Arcidae (four genera and seven species) for Bivalvia.

Barrera (2001) most abundant gastropod species were Amphithalamus vallei (672 individuals) and cf. Vitrinella sp. (534 individuals); however, at Cayo Nuevo, 208 individuals of sf. Vitrinella sp., were found. Differences in the numbers of collected individuals can be explained by geography, but also by differences in the quantity of sediment collected and processed, fifteen sites with 300 ml sediment sampled at FGB and six samples of 224–735 g at Cayo Nuevo. Vitrinella sp. could not be identified to specific level due to the low similarity of characters shown with other described western Atlantic species. Barrera (2001) previously suggested that it could be an undescribed new species, but further detailed studies are required to establish its identity.

Regarding bivalves, the most abundant species reported by Barrera (2001) for the FGB were Gregariella coralliophaga (145 individuals) (summing nine identified as Barbatia domingensis (102 individuals) and eleven identified as Barbatia cancellaria (68 individuals, currently a synonym), and Carditopsis smithii (51 individuals). In comparison, 37 individuals of Barbatia domingensis and 12 Carditopsis smithii were collected at Cayo Nuevo and these were not the most abundant species.

It should come as no surprise that many organisms were not identified to species level (e.g., Leptochiton sp., Bentharca sp., Crenella sp., Anomia sp., Lottia sp., Diodora sp., Cerithium sp., Cerithiopsis sp., Thylacodes sp., Zebina sp. 1, Zebina sp. 2, and Phrontis sp.). We relied on regional and local literature that in fact was scarce. In the case of juveniles, shells within a genus are similar because they share many characters and the differential characters are difficult to discern even as adults and almost impossible in juveniles. Our specimens identified under the name of Gibberula lavalleeana could be considerate as a species complex, due to the evidence and description of new species in Cuban waters (Espinosa and Ortea 2007).

These faunistic results from Cayo Nuevo represent the first inventory of molluscs from this remote reef. These findings contribute to record expansions for the southern GoMx of Bentharca sp. This contribution highlights the importance of conserving small areas that can harbour a considerable diversity of organisms. Seasonal changes on the mollusc community assemblages were not evaluated but would be an interesting future project, as would collecting growth series of species to assist in confirming identifications. In 2004, González and Torruco stated the importance of the Campeche Bank’s reefs and proposed a marine reserve for the reefs located within this area, Cayo Nuevo included. However, this proposal never materialized and, up to now, only Alacranes reef has governmental protection under the status of marine reserve. Species checklists of micromolluscs, as well as other faunal groups, are of vital importance to serve as a baseline data set, due to the proximity to Mexico’s offshore oil production area within the GoMx. The soft benthic interstitial mollusc communities are diverse, and their monitoring could well represent ecological indicators of ecosystem health, especially in the light of potential future oil-spills.

We give our gratitude to the researchers from the Yucatan Marine Biodiversity Team (BDMY) who participated in the expedition on the boat “Isla Mujeres”, especially to P. Tapia Díaz who collected the samples. Thanks to M. Badillo Alemán and C. Galindo de Santiago for their general laboratory technical assistance and to B. Rodrigo Cobarrubias Contreras for his technical assistance with the granulometry analysis, all at the Unidad Académica Sisal, UNAM. Professor Fabio Moretzsohn kindly provided the base map. Financial support provided by the Harte Charitable Foundation, through the Harte Research Institute (Biodiversity of the southern Gulf of Mexico) and by the CONABIO NE018 Project (Update on the knowledge of the biodiversity of shallow water benthic marine invertebrate species (<50m) from the southern GoMx). First author received a postdoctoral grant from DGAPA-UNAM 2018-2019. We are grateful to Editor Nathalie Yonow for comments in the manuscript. We also thank the reviewer Dr. Henk Dekker and two other anonymous reviewers for their constructive comments and suggestions. We dedicate this work to our malacologist colleague, Dr. Wes Tunnell, who just left us. Dr. Tunnell was always curious for the Gulf of Mexico invertebrates and tireless promoter of marine biodiversity knowledge in the region.