AÇOREANA, 2021, Suplemento 11: 141-150 FIRST REPORT OF MESOPSAMMIC NEMERTEA FROM THE AZORES Jon L. Norenburg1, Irina A. Cherneva2, Christina I. Ellison3 & Freya E. Goetz1 1 Department of Invertebrate Zoology, Smithsonian National Museum of Natural History, Washington, DC, USA 20560 E- mail: norenbur@si.ed 2 Lomonosov Moscow State University, Leninskie gory 1/12, Moscow, Russia 119234 3 Oregon Institute of Marine Biology, University of Oregon, Charleston, OR, USA 97420 ABSTRACT Whereas a few macrofaunal nemerteans were described previously from the Azores islands of Faial and Pico, a survey of marine meiofauna from littoral and shallow sublittoral sediments sampled at São Miguel Island and Santa Maria Island in the Azores yields this first report of Nemertea for those two islands, with 55 specimens, whereas a search for littoral mesopsammic Nemertea on Pico Island was fruitless. Based on morphology, specimens were initially thought to comprise twelve morpho-species: four morphs of Cephalothrix Örsted, 1843, accounted for 43 specimens; three morphs of Ototyphlonemertes Diesing 1863, accounted for five specimens; one specimen of Lineus cf. sanguineus (Rathke, 1799), one of Zygonemertes Montgomery, 1897, and two unknown species (one a juvenile) of Eumonostilifera were associated with the sediments; one specimen of Baseodiscus cf. delineatus (Delle Chiaje, 1825) was retrieved from an incidental algal sample. The Cephalothrix morphs collected at São Miguel Island resemble C. rufifrons and C. simula; whereas the morph collected at Santa Maria Island has the habitus “typical” for mesopsammic species of the genus. One of the Ototyphlonemertes morphs has a combination of discrete characters that appears to make it an undescribed species endemic to the Azores. All specimens were preserved for genetic analyses, which will be reported as they are completed. RESUMO Embora alguns nemertinos da macrofauna já tivessem sido descritos anteriormente nas ilhas dos Faial e do Pico, um levantamento da meiofauna marinha de sedimentos litorais e sub-litorais de baixa profundidade amostrados nas Ilhas de São Miguel e Santa Maria, nos Açores, constitui este primeiro trabalho de Nemertea para essas duas ilhas, com 55 exemplares, ao passo que a procura de Nemertea mesopsâmmicos no litoral da Ilha do Pico foi infrutífera. Com base na morfologia, os espécimes foram inicialmente alocados a doze morfo-espécies: quatro formas de Cephalothrix Örsted, 1843, representadas por 43 espécimes; três formas de Ototyphlonemertes Diesing 1863, responsáveis por cinco espécimes; um espécimen de Lineus cf. sanguineus (Rathke, 1799), um de Zygonemertes Montgomery, 1897, e duas espécies desconhecidas (uma juvenil) de Eumonostilifera foram associadas aos sedimentos; um espécime de Baseodiscus cf. delineatus (Delle Chiaje, 1825) foi recuperado de uma amostra de algas. As formas de Cephalothrix recolhidos na Ilha de São Miguel assemelham-se a C. rufifrons e C. simula; já aquele coletado na Ilha de Santa Maria tem habitus “típico” para espécies mesopsâmicas do género. Uma das formas de Ototyphlonemertes tem uma combinação de caracteres que parece torná-la candidata a espécie endémica dos Açores, a descrever. Todas as amostras foram preservadas para análises genéticas, que serão reportadas assim que forem concluídas. 142 AÇOREAN A 2021, Suplemento 11: 141-150 INTRODUCTION and Pico Islands (Strand, 2002) and one additional subtidal macrofaunal Members of the approximately species from Pico Island (Wirtz, 1,300+ accepted species (Gibson, 2009). There also are several reports 1995; Kajihara et al., 2008; Norenburg and references to Azorean terrestrial et al., 2021a) of Nemertea range widely Nemertea (see Herrera-Bachiller et al., in size, with lengths of gonad-bearing 2015). There are no reports of marine adults ranging from 1 mm (JLN, mesopsammic Nemertea from the unpubl. obs.) to a reported approximate Azores. This contrasts with the relatively 50 m (McIntosh, 1873-74). They also well-known mesopsammic nemertean are extremely elastic; adults of many faunae of the eastern and western nemertean species are capable of passing continental margins of the temperate or squeezing through a 0.5 mm mesh, and tropical North Atlantic Ocean and perhaps a majority can pass through (Kirsteuer, 1971; Norenburg, 1988a, b; a 1 mm mesh, therefore meeting both Envall & Norenburg, 2001; Tulchinsky size criteria for characterizing animals et al., 2011; Leasi et al., 2016). Hence, as meiofauna (Higgins & Thiel, 1988; marine mesopsammic Nemertea of the Giere, 2009). However, historically, for Azores are of particular biogeographic Nemertea, the term meiofauna has been interest, and sediments with potential applied primarily to species whose for harboring them were the focus of this adults are mesopsammic, also referred survey but several non-mesopsammic to as interstitial. Whereas meiofauna are Nemertea were encountered as well and characterized by size and, in principle, provide new records for the Azores. are not restricted as a group by habitat, The genus Ototyphlonemertes Diesing, mesopsammic Nemertea are restricted as 1863, is the most iconic group of adults to the aqueous interstitial space of mesopsammic Nemertea. The genus marine sediments, through which they is known almost exclusively from the move without needing to displace the interstitial pore space of moderately sediment (Norenburg, 1988a, b). Most but coarse littoral and relatively shallow not all mesopsammic Nemertea display sublittoral marine sediments. Its species a suite of morphological and life-history are characterized by presence of a characteristics (e.g., adhesive properties, pair of statocysts, one resting on each elaborated sensory cilia, modified of the two ventral ganglia (Kirsteuer, reproductive biology, elongated body 1971). The group currently comprises and cephalic region, sometimes presence 33 accepted species (Norenburg et of statocysts, and often loss of eyes) al., 2020) but molecular data suggest considered to be adaptive to a physically that there are many more cryptic dynamic existence in the aqueous pore species, with geographic ranges that space among marine sediment particles differing widely (Leasi et al., 2016). (Kirsteuer, 1971; Norenburg, 1988a, b). Other Nemertea that can be considered Many of these features also characterize typically mesopsammic are relatively soft-bodied mesopsammic members of rare (Norenburg, 1988a, b). Some are other phyla (Swedmark, 1964). monotypic and some are placed in genera The only two first-hand taxonomic comprising mostly species generally not accounts of marine Nemertea from the treated as meiofauna (regardless of size). Azores document 11 species of littoral Among these latter are the species of macrofaunal nemerteans from Faial Cephalotrhix Örsted, 1843, encountered NORENBURG ET AL.: MESOPSAMMIC NEMERTEA FROM THE AZORES 143 in the present survey. Other marine of Natural History (USNM accession mesopsammic Nemertea are addressed 2087187). Morphs of Ototyphlonemertes by Kirsteuer (1971), Norenburg (1988a, b) are characterized in accord with the and von Döhren & Bartolomaeus (2020); “phylomorphs” suggested by Envall & none were encountered in the present Norenburg (2001). survey. RESULTS MATERIAL AND METHODS Nemertea were obtained from 15 Sites on São Miguel Island were (Table 1, Figure 1) of approximately sampled 14-23 July 2019, as part of 65 marine benthic collecting events a meiofauna workshop comprising (including one algal washing) on São a diverse assemblage of meiofauna Miguel Island, representing seven of researchers and students, as detailed in 18 marine benthic localities sampled the introduction to this issue by Jörger by the workshop (for details of all et al. (2021). Additional stations were collecting events see Jörger et al., 2021). sampled by JLN on Santa Maria Island, Nemerteans were not abundant in any 26-31 July 2019, as described by Curini- of the samples, whether moderately Gallettti (2021). JLN surveyed the shore coarse sediment from high-energy of Pico Island 1-15 August 2019, for littoral sites or relatively silt-less suitable sampling sites. Living specimens medium-to-coarse sediment from were extracted with seawater or MgCl2 sublittoral sites. These samples yielded decantation through a 63 µm mesh five specimens of Ototyphlonemertes and sieve (for details, see Jörger et al., 2021). 42 specimens of Cephalothrix (Figure 1A, Nemerteans were examined alive and B). The Ototyphlonemertes included three annotated by JLN, IC, or CE by use of a specimens of an O. cf. duplex morph Leica M3Z binocular stereo microscope (Figure 1C, D) and one specimen each of and facilitated by narcotizing specimens two morphs of O. cf. macintoshi (Figure 1E, in MgCl2 isotonic with seawater and then F) (Table 1). The Cephalothrix specimens diluted 1:1 with seawater. Specimens were assigned initially to a single morph were placed in a drop of this solution resembling Cephalothrix rufifrons (1643, on a microscope slide and then lightly Table 1), which accounted for 43 of 55 compressed under a coverslip floated specimens processed. The only evident on this drop. They were examined variable in our field observations for the and photographed by use of a Leitz Cephalothrix cf. rufifrons specimens was a Laborlux-12 trinocular microscope fitted subtle difference in color at the cephalic with a C-mounted Canon EOS 70D camera tip (Table 1): 28 red, one yellow, and one operated in tether mode via Canon EOS orange; two specimens had yellowish- Utility 2 software. Subsequently, each green epidermal globules, and a color, specimen was individually preserved if present, was not recorded for nine in 0.5 ml Autogen M2 lysis buffer in a specimens. Several other nemerteans, 1.4 ml Matrix™ alphanumeric storage possible juveniles and not members tube (Thermo Scientific) and stored at of the permanent meiofauna, were approximately 4 ºC (except for a few hours recovered from the sediment samples: each day during 10 days of the workshop two unknown eumonostiliferans, one and while traveling) and deposited Zygonemertes sp., and one Lineus cf. in the Smithsonian National Museum sanguineus (Figure 1 G). Even adult 144 AÇOREAN A 2021, Suplemento 11: 141-150 Lineus sanguineus can become very thin TABLE 1. Stations with Nemertea. For station and easily pass through a 0.5 mm mesh details see Jörger et al. (2021) and Curini- and often are found in littoral sediments Galletti (2021) for station MCG6. Snout color with significant organic particulate noted for Cephalothrix 1643 morphs: “?”= color loads (JLN, unpubl. obs.). One specimen not recorded. of the circumglobally distributed Baseodiscus cf. delineatus was recovered from algal washings. About two liters of sublittoral shelly sediment collected at one site, at 10 m depth, off Santa Maria (St. 6, Curini- Galletti, 2021) yielded two Cephalothrix specimens, as well as flatworms and mollusks characteristic of a mesopsammon assemblage that typically would also include Ototyphlonemertes, but none were found. The two Cephalothrix specimens fit the unique mesopsammic morphotype or habitus described by Gerner (1969), which is found in relatively coarse sediments and shell hash and characterized by small size, relatively non-contractile and almost nematode-like body shape (JLN, unpubl. obs.). One author (JLN), over the course of a week, explored the shoreline of Pico Island, which is known for its mostly steep rocky shoreline and having very few areas of littoral sediment accessible from the shore or even by wading or snorkeling. Five sites were sampled but it was immediately evident that these accessible sediments were too fine and/ or too silty (e.g., Madalena harbor, the “natural pools” at Ponta de Fonte and São Roque do Pico) to be suitable for mesopsammic Nemertea. Indeed, no Nemertea were found at these sites. It was evident, however, that storm activity deposits much shelly sediment on high ledges along the rocky shore, which indicates significant potential for sublittoral deposits of shelly sediment conducive to harboring a diverse mesopsammic meiofauna and worthy of a diver expedition (JLN, unpubl. obs.). NORENBURG ET AL.: MESOPSAMMIC NEMERTEA FROM THE AZORES 145 FIGURE 1. A-G. Photomicrographs of living Nemertea collected at São Miguel Island. A, Prebuccal region of Cephalothrix sp. 1643 without colored snout; B, Prebuccal region of Cephalothrix sp. 1643 with reddish snout; C, Ototyphlonemertes cf. duplex sp. 1644, entire specimen; D, Ototyphlonemertes cf. duplex sp. 1644, cephalic region; E, Ototyphlonemertes cf. macintoshi sp. 1647, cephalic lobe; F, Ototyphlonemertes cf. macintoshi sp. 1647, central stylet region; G, Lineus sanguineus, anterior region. Scale bars = 250 µm, except F = 50 µm. 146 AÇOREAN A 2021, Suplemento 11: 141-150 DISCUSSION mens were retrieved, representing three morphs: two specimens from a single Kirsteuer (1971) suggested that swash zone sample and three from marine mesopsammic Nemertea are diver or snorkel samples (Table 1). We relatively non-diverse systematically expected, based on isolation distance of (i.e., genera, families), an assessment the islands and nature of the sediments that continues to be true (Envall & sampled, to encounter one to three Norenburg, 2001; von Döhren & morphs of Ototyphlonemertes but with Bartolomaeus, 2020). However, multiple much higher numbers of specimens. studies of mesopsammon in general and In contrast, the number of Cephalothrix mesopsammic Nemertea in particular morphs encountered in this survey, from have demonstrated high numbers of relatively few sample sites, is a surprise cryptic species (Leasi & Norenburg, 2014; with respect to comparable sampling Leasi et al., 2016; Martínez et al., 2019 elsewhere in the world (JLN, unpubl. and references therein). Though there obs.). We expected only one or two has been minimal previous sampling species. It is not unusual for Cephalothrix for Nemertea in the Azores (Strand, to be abundant in sampled sublittoral 2002; Wirtz, 2009), the littoral nemertean coarse sediments and shell hash, species diversity of the Azores, thus alongside or as part of the mesopsammon far, appears depauperate relative to or psammophilic community, as was eastern and western Atlantic continental the case in the present survey, with 37 coastlines; whereas there are virtually no Cephalothrix retrieved from samples data to judge for sublittoral Nemertea. collected by diver or snorkeler, and six The diversity of morpho-species of from submerged sediment in a littoral littoral mesopsammic Nemertea reported but permanent rock pool. In contrast here is similar to what is observed on littoral Cephalothrix when associated other isolated islands in the world, such as with sediments usually are on, not in, Hawai’i, French Polynesia, and Fernando sediments under rocks (JLN, unpubl. do Noronha (Brazil) (JLN, unpubl. obs.). obs.). It is unknown at this time whether Islands close to continental margins, such sublittoral psammophilic Cephalothrix, as the Caribbean islands, Okinawa, and when in situ, actually are in or at the islands in the Gulf of Chiriquí (Panama) surface of sediments collected in this yield greater systematic diversity survey or elsewhere in the world. and larger numbers of species as well São Miguel has perhaps the greatest as specimens (ibid.). The number of number and diversity of beaches specimens per unit collecting effort in the among the Azores islands, and many Canary islands was higher but species- of the habitats sampled, especially level diversity of littoral mesopsammic sublittoral ones, in this survey yielded Nemertea was similar (JLN, unpubl. good numbers and broad phyletic obs.; Martinez et al., 2019). Though diversity of typical mesopsammon, such isolation distance is an evident factor in as Proseriata (Curini-Galletti, 2021), accounting for differences in richness Annelida (Martínez et al., 2021), Mollusca of local faunae, sediment characteristics (Neusser et al., 2021) that commonly also comprise important factors related co-occur with Ototyphlonemertes to diversity of mesopsammic Nemertea elsewhere in the world (JLN, unpubl. (JLN, unpubl. obs.). obs.). In light of the diversity of other Only five Ototyphlonemertes speci- mesopsammon encountered in the NORENBURG ET AL.: MESOPSAMMIC NEMERTEA FROM THE AZORES 147 present survey, the paucity of Nemertea the mesopsammon more frequently. observed was surprising. This may In addition, Nemertea may have reflect biogeography and/or lack of ideal more stringent biological constraints habitat – i.e., suitably coarse clean sand (especially with respect to carnivorous and shell hash. In addition, in the context feeding), some of which may be further of this workshop, Ototyphlonemertes and constrained by granulometry and similarly sized Nemertea were effectively hydrodynamics. Non-mesopsammic camouflaged among large numbers of meiofaunal Nemertea (those able to pass similar appearing flatworms in many of through 1 mm sieve mesh) comprise a the sorting dishes; therefore, nemerteans large proportion of the phylum’s species could easily have been overlooked by and phyletic diversity (JLN, unpubl. inexperienced workshop participants. obs.); size alone is not sufficient for As noted by Curini-Galletti (2021), successful mesopsammic existence. shelly sand is particularly favorable Curini-Galletti (2021) points out habitat for Proseriata; and the same that Azorean meiofauna likely has is true for Ototyphlonemertes but such experienced poor faunistic connectivity sand is rare along the São Miguel coast. with the rest of the Macaronesia islands Sampled littoral sediments of São Miguel similar to what has been documented for and Pico are predominantly volcanic in macrofauna (Freitas et al., 2019). Lack of origin, which tends to generate finer and or short duration of a pelagic larval phase more uniform granularity than more characterizes most marine meiofauna and irregular biogenic calcareous sediments generally is expected to inhibit dispersal that Ototyphlonemertes favor elsewhere (Giere, 2009). Geophysical, biological, in the world. This also is observed with and historical variables combine to create volcanically derived sediments sampled dispersal possibilities and probabilities on the Canary islands (Martinez et al., unique to species, clades and 2019), Hawai’i and French Polynesia assemblages of meiofauna (Giere, 2009; (JLN, unpubl. obs.). Santa Maria had Cerca et al., 2018, Martínez et al., 2020). a few beaches with large stretches of Marine shipping, which for the Azores “white” sand but that sand mostly was would be principally with Southern and not sorted and too fine for mesopsammic Western Europe, often is invoked as an Nemertea. There also were some gravel anthropogenic variable that enhances beaches exposed to significant wave long-distance transport of marine action but that gravel was too coarse invertebrates with low innate dispersal and probably would not sustain stable potential. Though Ototyphlonemertes populations of mesopsammic Nemertea, very occasionally are locally abundant especially with no proximate sources for at particular sites, suitable sites are rare, recruitment. Overall global taxonomic discontinuous, often small, and widely diversity of mesopsammic Nemertea is dispersed, and mesopsammic Nemertea considerably less than for mesopsammic generally are low in numbers at most Acoela, Platyhelminthes, Nematoda sites where they are found (JLN, unpubl. and Annelida. With respect to the first obs.). Given the former conditions three groups this probably reflects a and, particularly, the relatively narrow much more recent evolutionary history sediment requirements of mesopsammic and diversification as mesopsammon, Nemertea (clean, dynamic and relatively whereas Annelida are phyletically coarse littoral and shallow sublittoral more diverse overall and have invaded sediments), the probability seems low 148 AÇOREAN A 2021, Suplemento 11: 141-150 that these worms will be present in ballast and perhaps two of the Cephalothrix water or sediments acquired by ships in morphs found in the present study environmentally inhospitable harbors. appear to be endemic to the Azores, However, recent evidence for a rich which strengthens the perception that the diversity of meiofauna on the carapaces Azores are relatively isolated with respect of sea turtles (Ingels et al., 2020), is of to dispersal by mesopsammic Nemertea. special relevance to the Azores because Furthermore, though Leasi et al., (2016) its rich turtle fauna presents intriguing found Ototyphlonemertes genetic species potential for transport of mesopsammic to have a wide range of distribution Nemertea, given that some sea turtles limits, from hundreds to thousands of deposit eggs in beaches suitable for kilometers, none traversed deep ocean Ototyphlonemertes (JLN, unpubl. obs.) basins, such as bracket the Azores. We are and, conceivably, could carry worm- undertaking DNA analyses of specimens bearing sand back to sea. No Nemertea collected in the present survey to test were reported from sea turtles by for the presence of endemic species and Ingels et al. (2020) but they did report genetically isolated populations of large numbers of “turbellaria” visually mesopsammic Nemertea in the Azores. sorted from the preserved samples. Preserved meiofaunal Nemertea would ACKNOWLEDGEMENTS be mostly indistinguishable among these “turbellaria” even to an expert observer We thank Ana Cristina Costa (JLN, unpubl. obs.), so would be likely to and Katharina Jörger for organizing be missed in visual sorting. Regardless, the workshop and coordinating the field experience shows that despite collecting, and the workshop participants mechanisms for adhering to sediment for providing specimens. We are particles, mesopsammic Nemertea especially grateful to Katharina Jörger for readily release from these particles after her collecting efforts and for heroically a few seconds (JLN, unpubl. obs.) and managing sediment samples faced with likely would be washed off a swimming the onslaught of many eager hands once turtle. Though Ototyphlonemertes species in the laboratory. JLN is grateful to Marco have a short (1-3 days?) larval phase, Curini-Galletti for undertaking a mini- transport of adults entrained in the water expedition to Santa Maria Island with column – e.g., as the result of vigorous him and for making two diver samples hydrodynamic disturbance of sediments from which he recovered two specimens or being washed off a turtle or other sand- of mesopsammic Cephalothrix. bearing flotsam – has been proposed as a potential source of dispersal for these Author contributions worms (Tulchinsky et al., 2012; Leasi All authors participated in field work, et al., 2016). 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