First records of two Cuthona species (Gastropoda: Nudibranchia) in the Adriatic Sea 
 
 
 
Lovrenc LIPEJ1, Borut MAVRIČ1, Domen TRKOV2 
 
 
1Marine Biology Station, National Institute of Biology, Fornace 41, 6330 Piran, Slovenia; E-mail: lipej@mbss.org 
2Biodiva – Conservation Biologist Society, Kettejeva 1, SI-6000 Koper, Slovenia 
 
 
 
Abstract. Authors are reporting on the first records of two nudibranch species of the genus Cuthona in the Slovenian part of the Adriatic Sea. In the period from September 2014 to March 2015, specimens of Cuthona genovae and C. miniostriata were found at different localities in the mediolittoral and upper infralittoral belts. The findings of both Cuthona species represent the first records in the Adriatic Sea. 
 
Key words: first records, Cuthona genovae, Cuthona miniostriata, Gastropoda, Nudibranchia, Adriatic Sea 
 
 
Izvleček. Prvi zapis o pojavljanju dveh vrst iz rodu Cuthona (Gastropoda: Nudibranchia) v Jadranskem morju – Avtorji poročajo o prvi najdbi dveh vrst polžev gološkrgarjev iz rodu Cuthona v slovenskem delu Jadranskega morja. V obdobju od septembra 2014 do marca 2015 so bili v mediolitoralu in zgornjem infralitoralu na različnih lokalitetah najdeni primerki vrst Cuthona genovae in C. miniostriata. To je tudi prvi zapis o pojavljanju obeh vrst iz rodu Cuthona v Jadranskem morju. 
 
Ključne besede: prvi zapisi, Cuthona genovae, Cuthona miniostriata, Gastropoda, Nudibranchia, Jadransko morje 
 
Introduction 
 
 
The marine opisthobranch fauna of Slovenia gained increased scientific attention only during the last few decades when first checklists of this particular group were published by  De Min & Vio (1997). The first checklist of opisthobranchs in the area was presented by Turk (2000). This list was further complemented by later works of Turk (2005a, b), Lipej et al. (2008, 2012), Mavrič & Lipej (2012), Lipej et al. (2014) and Zenetos et al. (2015a). Certain species, such as Cumanotus beaumonti (Turk 2005a, b) and Piseinothecus sphaerifera  (Mavrič & Lipej 2012), had previously been found only in very few cases in the Mediterranean and other parts of world oceans.  
 
This paper deals with two nudibranch species (Gastropoda: Heterobranchia) found in the coastal waters of Slovenia. They represent new records for the entire Adriatic Sea in general. 
 
 
 
Material and methods 
 
 
The nudibranchs of the genus Cuthona were found while inspecting the samples of low vegetation belt (known as turf) in the mediolittoral and infralittoral belts from different localities along the Slovenian coastline (Gulf of Trieste, northern Adriatic) (Fig. 1). The specimens were measured alive and photographed under the stereomicroscope Olympus SZX16. Afterwards, the nudibranchs were identified with the help of the determination keys for opisthobranchs (Pruvot-Fol 1954, Barletta 1980, Schmekel & Portmann 1982,  Bielecki 2011, Trainito & Doneddu 2014). Specialized web sites such as www.seaslugforum.net were helpful as well. The taxonomy and nomenclature are in accordance with the World Register of Marine Species (WoRMS; www.marinespecies.org/). Subsequently, the specimens were fixed in 70% alcohol solution and deposited in the collection of the Marine Biology Station (MBS) of the National Institute of Biology. 
 
 

Figure 1. Study area with localities where nudibranchs Cuthona genovae (black circles) and C. miniostriata (black square) were recorded for the first time in the Adriatic Sea. 
Slika 1. Zemljevid obravnavanega območja z lokalitetami, na katerih so bili prvič v Jadranskem morju najdeni gološkrgarji Cuthona genovae (črni krogci) in C. miniostriata (črni kvadrat). 
 
 
Results 
 
 
Cuthona genovae (O'Donoghue, 1928)  
 
Material:  
. 24. 9. 2014, 2 specimens, Fiesa, 1 m depth, on Cystoseira barbata;  

. 5. 10. 2014, 2 specimens, Atlantida – Izola, 1 m depth, on turf; 

. 19. 1. 2015, 2 specimens, under Piran church, Piran, 1 m depth, algal belt; 

. 3. 2. 2015, 1 specimen, Port of Koper, Koper, 1 m depth, algal belt; 

. 19. 2. 2015, 1 specimen, Morgan, Piran, 1 m depth, turf on rocks; 

. 3. 3. 2015, 2 specimens at 2 m depth and 7 specimens at 3 m depth, in front of the Marine Biology Station of the National Institute of Biology, Piran. 


 
The specimens were recognized by parallel orange lines running from oral tentacles to rhinophores and to the base of the first cerata, forming a rhomboid shape on the head. Additional orange line is evident between the oral tentacles. Another characteristic is a yellow band running from rhinophores back to the heart (Schmekel & Portmann 1982, Rudman 2008, Trainito & Doneddu 2014). The body is more or less transparent, whereas up to seven groups of cerata are brownish.  
 
Up to date, the species has been recorded in the entire Mediterranean Sea and British waters (Picton & Morrow 2010), Portugal (Calado et al. 1999), in waters off the Canarian Archipelago and in the Caribbean (Ballesteros et al. 2012-2015). In the Mediterranean Sea, it has been recorded in Genoa (locus typicus), more or less along the whole Mediterranean coast of Spain and along the Balearic Islands (Cervera et al. 2004) and in the waters off Malta (Sammut & Perrone 1998, Sammut 2011-2014a). 
 
Cuthona miniostriata Schmeckel, 1968  
 
Material:  
. 3. 2. 2015, 1 specimen, Port of Koper, Koper, 1 m depth, algal belt. 


 
The main distinguishing character of this species is the orange line on the backside of rhinophores, which extends to the eyes. Rhinophores are smooth and somehow longer than oral tentacles. The body is whitish and translucent, whereas the 5 or 6 groups of thin cerata are brownish at the base and white on the top. The distal part of the cerata is rounded. According to Sammut & Perrone (1998), some specimens have a large amount of white pigment, especially on the cerata. 
 
This species was found within a turf microhabitat in the mediolittoral belt (< 1 m depth). Samut & Perrone (1998) mentioned this species as fairly common on algae in shallow waters. Up to date, the C. miniostriata has been considered an endemic species in the Mediterranean Sea. It has been recorded in waters off the eastern Spanish coast (Cervera et al. 2004), Maltese Islands (Sammut & Perrone 1998, Sammut 2011-2014b) and in the Gulf of Naples (Schmekel & Portmann 1982), where it was described from. 
 

Figure 2. Nudibranchs Cuthona genovae and C. miniostriata, both recorded in the algal belt of the mediolittoral zone on 3. 2. 2015 in the Port of Koper (photo: B. Mavrič). 
Slika 2. Polža gološkrgarja Cuthona genovae in C. miniostriata, najdena v algalni zarasti bibavičnega pasu v koprskem pristanišču 3. 2. 2015 (foto: B. Mavrič).  
 
 
 
Discussion 
 
 
Both species of the genus Cuthona were found in mediolittoral and infralittoral zones on turf or algal belts. Their small size (both species ± 5 mm in length) and peculiar habitat type in which they are living are probably the main reasons why these species have been overlooked in many Mediterranean areas (sensu Sammut 2011-2014a, b). So far, 5 species of the genus Cuthona have been recorded in the Adriatic Sea: C. caerulea, C. foliata, C. ocellata, C. gymnota and C. perca (sensu Zenetos et al. 2015b). 
 
Although the coastal sea of Slovenia constitutes only a very small portion of the Adriatic Sea, at least 75 opisthobranch species (nudibranchs and other seaslug groups) have been recorded in this area (see Lipej et al. 2014). However, the checklist of opisthobranch fauna should be considered far from complete, since many species found in the Italian part of the Gulf of Trieste have not yet been confirmed in the Slovenian part of the Gulf (see Graeffe 1902, Zenetos et al. 2015b). In addition, certain habitat and microhabitat types were poorly studied. Interstitial habitats have not been studied at all, while muddy areas are probably hiding many not yet recorded fossorial opisthobranchs. Among the poorly studied habitats is also the low vegetation in shallow coastal areas (known as turf).  
 
 
During sampling in specific habitat and microhabitat types in different seasons, certain rare or less known opisthobranchs were detected for the very first time in Slovenian coastal waters and adjacent areas along the west Istrian coasts. For instance, recent findings of Aplysiopsis elegans (Mavrič et al. 2014) and Thordisa filix (Zenetos et al. 2015a) represent the first Adriatic records for both species. Taking into consideration such records of small and thus easily overlooked opisthobranch species, it seems possible that the list of seaslugs will probably be enlarged even more in the near future. 
 
 
 
Povzetek 
 
 
Avtorji poročajo o prvi najdbi dveh vrst polžev gološkrgarjev iz rodu Cuthona v slovenskem delu Jadranskega morja. Vrste iz tega rodu so navadno majhne, zato jih je v njihovem okolju težko opaziti. V obdobju od septembra 2014 do marca 2015 so bili v različnih predelih slovenskega dela Jadrana najdeni primerki vrst Cuthona genovae in C. miniostriata. Prva vrsta je bila najdena na šestih različnih lokalitetah (Bernardin, Piran, med Piranom in Fieso, Fiesa, Izola, pristanišče Koper) v mediolitoralu (bibavičnem pasu) in infralitoralu do 3 m globine. Vsi primerki te vrste so bili najdeni v blazinasti algalni obrasti (turf) in na manjših algah. Druga vrsta, C. miniostriata, je bila najdena le v enem primeru februarja 2015 v koprskem pristanišču, in sicer v algalni zarasti bibavičnega pasu (±1 m globine).  
 
Pričujoči prispevek je prvi zapis o pojavljanju obeh vrst iz rodu Cuthona v Jadranskem morju. Tudi sicer ni veliko znanih zapisov o pojavljanju teh vrst v Sredozemskem morju, prav vsi pa izvirajo iz njegovega zahodnega dela. Vrsta C. genovae se poleg Sredozemskega morja pojavlja še v severnem delu vzhodnega Atlantika in v Karibskem morju, vrsta C. miniostriata pa je endemit Sredozemskega morja. 
 
 
 
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