First report of nematocysts fired at deep-sea hydrothermal vent nematodes
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OCEANARIUM
First report of nematocysts fired at deep-sea hydrothermal vent nematodes Daniela Zeppilli 1
&
Stefania Puce 2
Received: 23 April 2020 / Revised: 23 June 2020 / Accepted: 6 July 2020 # Senckenberg Gesellschaft für Naturforschung 2020
Fig. 1 Scanning electron micrographs of nematocysts on the cuticle of Oncholaimus dyvae. Scale bars: a 20 μm, b and d 10 μm, c 5 μm
Communicated by L. Menzel * Daniela Zeppilli [email protected]
1
IFREMER, Centre Brest, REM/EEP/LEP, ZI de la pointe du diable, 29280 Plouzané, France
2
Department of Life and Environmental Sciences, Polytechnic University of Marche, Via Brecce Bianche, 60131 Ancona, Italy
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Oncholaimus dyvae, a nematode recovered from the hydrothermal vent field of Lucky Strike (1700 m, Mid-Atlantic Ridge), previously reported as an Oncholaimus scanicus, was recently re-described in Zeppilli et al. (2019) and references therein. Scanning electron microscopy (SEM) revealed several discharged nematocysts piercing the nematode cuticle in the neck and mid-body region, likely resulting from contact with cnidarians (Fig. 1). Of the 17 specimens observed at the SEM, 5 (3 males and 2 females) were characterized by the presence of nematocysts. A total of 24 nematocysts, with a maximum of 12 on one single nematode, were observed. The nematocyst morphology is consistent with the microbasic eurytele type, whereby the shaft is slightly enlarged distally (Fig. 1b). Discharged capsules measure 4– 5.5 × 1.6–3 μm and the shafts are 4–4.5 μm long. The deepsea nematode O. dyvae is associated with the byssus of mytilid bivalve Bathymodiolus azoricus from hydrothermally active sites and it is associated with symbiotic sulfur-oxidizing bacteria (Zeppilli et al. 2019). Cnidaria can be found in deep-sea hydrothermal vents and several hydrozoan species have been reported from the studied area (Desbruyères et al. 2006), but the cnidome is described for few of them preventing any certain identification. However, the nematocysts reported here are similar in type and size to microbasic euryteles of Eudendrium planum sensu Calder and Vervoort (1998). At Lucky Strike, this species is attached to vent edges where B. azoricus also resides; therefore, a contact, even if accidental, is very likely. Although nematodes have been listed as preys for Eudendrium (Di Camillo et al. 2012), O. dyvae is likely too large for each single polyp. However, Bavestrello et al. (2000) observed in Perarella schneideri that polyps “cooperate” in capturing large meiobenthic organisms. They can also scratch organic matter from the host surface; therefore, bacteria on the nematode cuticle possibly represent a food source for Eudendrium polyps. We report here, for the first time, the evidence of nematocysts fired at nematodes that could represent a food source for vent-associated Cnidaria. Reliance on Cnidaria on nematodes as a regular source of food needs more extensive research, but these observations revealed another possible ecological interaction in this complex extreme ecosys
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