INTRODUCTION
While the European Register of Marine Species (ERMS) project compiled a list of marine species in Europe, it quickly became obvious that our knowledge of the fauna of the European seas remains patchy. This is particularly so for some groups of small animals, such as Rotifera (Costello et al., Reference Costello, Bouchet, Emblow and Legakis2006). A recent detailed analysis of literature data on the global distribution of rotifers in the sea confirmed this suggestion (Fontaneto et al., Reference Fontaneto, De Smet and Ricci2006), and pointed out a strange inconsistency between the number of faunistic studies and species richness from different European areas: more than 100 taxa are listed in only five studies on the Black Sea, yet the 25 studies on the Mediterranean only reported 90 rotifer taxa. The aim of this study is to address this inconsistency by sampling an area in the Mediterranean.
We selected the Northern Adriatic, as it is illustrative for the paradox: it is one of the most studied areas in all the Mediterranean, with extensive studies of diverse habitats, yet only 32 rotifer species belonging to 14 genera are recorded (Pasquali, Reference Pasquali1940; Wulfert, Reference Wulfert1942; Rubino et al., Reference Rubino, Belmonte, Miglietta, Geraci and Boero2000).
MATERIALS AND METHODS
Samples were collected from 28 June to 6 July 2006 in the Northern Adriatic (Table 1). Plankton samples were collected using a plankton net with 50 µm mesh; other samples were directly collected with plastic bottles of 250 ml capacity. Samples were immediately brought to the laboratory located at the Foce dell'Isonzo Natural Park at Isola della Cona, Staranzano, GO, Northern Italy.
Table 1. Number of individuals of species of rotifers collected during the survey in the Northern Adriatic Sea (*: new to the Northern Adriatic; unidentified species reported as genus sp. refer to unrecognized species, but not to those already known in the area).
Living animals were extracted under a dissecting microscope while samples were washed with filtered saltwater collected directly in the field. Specimens for identification were fixed in ethanol, anaesthetizing them with a 0.5% marcaine solution when appropriate. Permanent glycerine slide mounts were prepared for all species and Giulio Melone at the University of Milan kept stubs with trophi prepared for scanning electron microscopy (SEM) observation. Trophi were prepared for SEM by sequentially dissolving tissues in 5% NaOCl solution on a circular cover slip, and rinsing with distilled water (Segers, Reference Segers1993; De Smet, Reference De Smet1998).
RESULTS
We obtained 47 samples from plankton, periphyton on rocks, sandy bottom, algae and gravel littoral, at depths ranging from 0.2 m to 38 m. We obtained rotifers from 31 of these samples. A total of 545 specimens belonging to 20 taxa were found (Table 1), 12 of these have not been recorded from the region before. Species richness varied from 1 to 7, and abundance of individuals varied from 1 to 85 per sample.
Two of the samples contained specimens of a hitherto unnamed species, which we describe here. In addition, we illustrate some other species recorded by SEM pictures of their trophi (Figure 1).
Fig. 1. Scanning electron microscopy pictures of trophi of marine rotifer species collected during the survey in Northern Adriatic. (A&E) Lecane grandis, sample F22; (B&F) Pleurotrocha atlantica, sample F28; (C&G) Colurella colurus, sample F25; and (D&H) Proales similis, sample F22. (A–D) Ventral view. (E–H) Dorsal view. Scale bar = 10 µm.
TYPE LOCALITY
Open sea part of outlet of the Isonzo River, sandy bottom, -0.5 m, Foce dell'Isonzo Natural Park at Isola della Cona, Staranzano, GO, Friuli Venezia Giulia, Northern Italy, salinity 30‰, collected on 30 June, 2006; approximate coordinates 45° 43′ 23′′ N, 13° 33′ 36′′ E.
TYPE MATERIAL
Holotype: a single specimen in glycerine permanent slide mount, deposited in the Royal Belgian Museum of Natural Sciences, Belgium, catalogue number IG30743, RIR 169, from the type locality.
Paratypes: three specimens in a glycerine permanent slide mount each, deposited in the Royal Belgian Museum of Natural Sciences, Belgium, catalogue number IG30743, RIR 170–172, from the type locality. One stub with 5 trophi prepared for SEM, deposited in the collection of G. Melone at the University of Milan, Department of Biology.
ADDITIONAL MATERIAL
Ten specimens from the type locality preserved in ethanol in an Eppendorf vial, and another two from a sample a few metres from the type locality, but at 2 m depth, preserved in ethanol in an Eppendorf vial, all kept in the collection of G. Melone at the University of Milan, Department of Biology.
ETYMOLOGY
This species is named after its type locality, the beautiful Natural Park Isola della Cona.
DIFFERENTIAL DIAGNOSIS
The new species is unmistakable by the presence of unique bifid, anterolateral projections on the ventral lorica plate, and by a pair of series of smaller projections on the anterolateral parts of the dorsal lorica plate (Figure 2). In fully extended and living animals these features may be hidden, but proper contraction of the body inside the lorica immediately reveals these species-specific features. Using the key by Segers (Reference Segers and Dumont1995), the species will key out to L. hastata (Murray, 1913) or L. rhenana Hauer, 1929, depending on whether the toe tips are interpreted as true claws or pseudoclaws, but neither of these has the unique disposition of anterolateral spines on the lorica.
Fig. 2. Lecane insulaconae sp. nov., habitus. (A) Dorsal view; and (B) ventral view. Scale bar = 50 µm.
DESCRIPTION
Body loricate (Figure 2), but lorica relatively soft, easily deformed; anterolateral projections on the ventral plate well developed, bifid and acutely pointed; anterolateral parts of dorsal plate with series of 2 to 4 minute, acute projections. Dorsal head aperture margin clearly protruding, both ventral and dorsal margins nearly straight; ventral plate almost parallel-sided, anteriorly wider, medially narrower than dorsal plate. Posterior margin of dorsal and ventral plate convex, without projections. Lateral sulci indistinct. Ventral plate with a weak, incomplete transverse fold, no longitudinal folds. Foot pseudosegment slightly longer than wide, diverging to terminally, scarcely projecting. Prepedal fold broad, rounded posteriorly. Coxal plates present. Two completely separated toes, with rather straight inner and curved external edge. Toe tips with a weak terminal bulb and incompletely separated claws.
Trophi modified malleate (Figure 3). Fulcrum a wide and rather short lamina, terminally truncated. Rami weakly asymmetrical; right and left ramus with rounded alulae. Unci slightly asymmetrical, with one major ventral, and three or four minor teeth dorsally. Manubria elongate, posterior chambers extend up to the curved tips.
Fig. 3. Scanning electron microscopy pictures of trophi of Lecane insulaconae sp. nov. (A) Ventral view. (B) Ventral–caudal view. (C) Dorsal view. Scale bar = 10 µm.
Measurements (average (range)). Body (N = 5): total length (without toes) 75 µm (68–85), maximum width 60 µm (59–62), toe length 25 µm (23–27). Trophi (N = 5): manubrium 24 µm (23–25), uncus 10 µm (9–11).
DISTRIBUTION AND ECOLOGY
Lecane insulaconae sp. nov. have been found only in the open sea part of the outlet of the Isonzo River. The sandy bottom sample of the type locality, at 0.5 m depth contained numerous specimens, whereas a few animals were found a few metres further, at a greater depth of 2 m. None of the other samples collected in the Northern Adriatic contained the species. Whereas the outlet of the Isonzo River could be considered brackish, because of the high supply of freshwater by the river, the salinity in both samples, at about 30‰, clearly indicated marine conditions. No other ecological data are available for this new species.
The most recent estimate of diversity in the genus Lecane reports 200 different species-level taxa (Segers, Reference Segers2007a, Reference Segersb). The genus is predominantly freshwater, with few brackish water species (e.g. L. grandis (Murray, 1913) and L. punctata (Murray, 1913)) but without any exclusively marine representative. Lecane insulaconae sp. nov. is the first, and probably not the last, truly marine Lecane.
DISCUSSION
This survey of the marine rotifers of the Northern Adriatic confirms the low diversity of rotifers, both in terms of specimens and species, in the marine environment, when compared to the diversity of phylum Rotifera in freshwater habitats (Wallace et al., Reference Wallace, Snell, Ricci, Segers and Dumont2006). Nevertheless, we add 12 taxa to the 32 already recorded from the Northern Adriatic, and describe a new species. Both the increase in species diversity on record for the region and the new species, suggest that our knowledge of marine rotifer diversity is far from being exhaustive, and that more sampling and taxonomic efforts are needed, even in well studied areas such as the Mediterranean. Therefore, the inconsistency between number of studies and richness of species lists of rotifers from different marine areas may be an artefact, due to the low number of comprehensive studies available, rather than being a feature of marine rotifer diversity.
Acknowledgements
We thank the Foce dell'Isonzo Natural Park at Isola della Cona for its hospitality and logistic support. We thank Miramare Marine Natural Reserve for sampling permission, and Wim De Smet for his help in rotifer identification. This research has been conducted within the framework of the project BIOIMPA (Biodiversity of Inconspicuous Organisms in Italian Marine Protected Areas), and benefited from a MIUR grant PRIN-2004 to Giulio Melone (‘Contributo della meiofauna alla biodiversità marina italiana’ [Contribution of meiofauna to Italian marine biodiversity]. We thank all the researchers involved in the project BIOIMPA for the nice samplings season. Scanning electron microscopy was done at CIMA.
