Review of the Symbiotic Genus Haplosyllides (Polychaeta: Syllidae), with a Description of a New Species

Nygren²,

Hjelmstedt

et al. 2015

Zool J Linn Soc

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The hesionid genus Parasyllidea differs from Oxydromus in lacking median antennae. It was originally described to include a single species, P. humesi, known only from its original description. This was based on specimens from mangrove swamps at Pointe-Noire (Republic of Congo, West Africa), living endosymbiotically with the bivalve Tellina nymphalis. Lately, the genus included P. blacki and P. australiensis. A new population of P. humesi was recently found at the upper intertidal level of Rio San Pedro salt marsh in Cádiz Bay (eastern Atlantic, Iberian Peninsula). It was also living endosymbiotically, but with another bivalve, Scrobicularia plana. Some Iberian and Congolese specimens revealed the presence of a small papilla-like central antenna associated with the prostomial median ridge, which raised some doubts on the validity of the genus Parasyllidea. A phylogenetic analysis based on the mitochondrial COI and 16S and the nuclear 18S and 28S genes confirms Parasyllidea as a junior synonym of Oxydromus. Therefore, in this paper, P. humesi is fully re-described as Oxydromus humesi comb. nov. The worm has never been reported as free-living. Previously, the association appeared to be an obligate symbiosis, closer to parasitism, as infested hosts had lower relative biomasses than non-infested ones and the worm did not occur locally inside any other bivalve co-habiting the intertidal salt marsh. The finding of a highly infested population (> 85% in the specimens longer than 20 mm) of a new host at the lower subtidal part of Rio San Pedro mouth, the bivalve Psammotreta cumana, led us to discuss the host-specificity of O. humesi. In addition, the observation of living specimens during sampling and laboratory handling enabled detailed observations of the host-entering behaviour of the specimens living with S. plana, which are also described and illustrated. Living, uninfested specimens of P. cumana have not been obtained, preventing us from checking the host-entering behaviour in the new host. The significance of the intraspecific attacks observed in experimental conditions is also discussed.

Section: Symbiotic Behaviourmentioning

confidence: 76%

On the enigmatic symbiotic polychaete ‘Parasyllidea’humesi Pettibone, 1961 (Hesionidae): taxonomy, phylogeny and behaviour

Nygren²,

Hjelmstedt

et al. 2015

Zool J Linn Soc

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“…Among polychaetes, many taxonomically robust morphological characters may be defined by measurements and/or proportions, some of them being size-dependent (Ben-Eliahu, 1987;Fauchald, 1991;Sigvaldadóttir and Mackie, 1993). This approach has been used independently of molecular analyses to successfully resolve the taxonomy of several sibling species complexes, often leading to the description of new species (Orrhage and Sundberg, 1990;Fauchald, 1991;Blake, 2000;Martin et al, 2003Martin et al, , 2006Martin et al, , 2009Ford and Hutchings, 2005;Garraffoni and de Garcia Camargo, 2006;Glasby and Glasby, 2006;Lattig et al, 2007;Hernández-Alcántara and Solís-Weiss, 2014;Coutinho et al, 2015). However, Ford and Hutchings (2005) were the first to consider the use of the statistical dissimilarities derived from the SIMPER routine of the PRIMER software (Clarke and Warwick, 2001;Clarke and Gorley, 2006), based on a matrix of morphometric measurements, as a robust support to distinguish between morphologically close species.…”

Section: Morphometry and Taxonomymentioning

confidence: 99%

Another brick in the wall: population dynamics of a symbiotic species of Oxydromus (Annelida, Hesionidae), described as new based on morphometry

Meca

Gil

et al. 2017

CTOZ

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Oxydromus humesi is an annelid polychaete living as a strict bivalve endosymbiont (likely parasitic) of Tellina nymphalis in Congolese mangrove swamps and of Scrobicularia plana and Macomopsis pellucida in Iberian saltmarshes. The Congolese and Iberian polychaete populations were previously considered as belonging to the same species, the latter showing regular distribution, intra-specific aggressive behaviour, and complex hostentering behaviour. The fresh Iberian samples enabled us to undertake consistent morphometric analyses, as well as to further analyse the characteristics of the association and the population dynamics of the Iberian population hosted by S. plana. Among the morphological differences between the Congolese and Iberian specimens, leading to the description of the latter as Oxydromus okupa sp. nov., the most important are: 1) longer cephalic appendages, 2) greater distance between the eyes, 3) larger dorsal cirrostyle in relation to the corresponding dorsal lobe and cirrophore. Moreover, dorsal and ventral lobes are similar in length, with the tip of the former reaching the tip of the latter in O. okupa sp. nov., while the dorsal lobe is much shorter than the ventral one in O. humesi. Mature adults of O. okupa sp. nov. occurred during the whole study period, with a higher percentage of ripe females in spring and, particularly, in summer. Numerous host specimens showed the symbiont’s most preferred shell length (>26 - 36 mm). However, the prevalence was very low (usually <5%) and showed a clear seasonal pattern, being lower during spring/summer. This suggests that males are able to leave their hosts during this period, most likely to improve fertilization by directly entering or approaching a host occupied by a ripe female, while females usually remain inside. Based on the new results, the current knowledge of symbiotic Hesionidae and their relationships with invertebrate hosts is updated and discussed.

“…Host tissue overgrowths are limited to small tube-like protuberances at the gallery exits, from where the worms supposedly feed by stealing food from the nearby host polyps (Martin et al, 2002). Polychaete sponge borers are mainly syllids (e.g., Haplosyllis , Haplosyllides ), which may either inhabit the aquiferous channels of the sponge or excavate their own galleries inside the host tissues (Martin & Britayev, 1998; Martin, Aguado & Britayev, 2009; Lattig & Martin, 2011). …”

Section: Discussionmentioning

confidence: 99%

Proceraea exoryxaesp. nov. (Annelida, Syllidae, Autolytinae), the first known polychaete miner tunneling into the tunic of an ascidian

Nygren²,

Cruz‐Rivera

2017

PeerJ

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While studying organisms living in association with the solitary tunicate Phallusia nigra (Ascidiacea, Ascidiidae) from a shallow fringing reef at Zeytouna Beach (Egyptian Red Sea), one of the collected ascidians showed peculiar perforations on its tunic. Once dissected, the perforations revealed to be the openings of a network of galleries excavated in the inner tunic (atrium) by at least six individuals of a polychaetous annelid. The worms belonged to the Autolytinae (Syllidae), a subfamily that is well known to include specialized predators and/or symbionts, mostly associated with cnidarians. The Red Sea worms are here described as Proceraea exoryxae sp. nov., which are anatomically distinguished by the combination of simple chaetae only in anterior chaetigers, and a unique trepan with 33 teeth in one outer ring where one large tooth alternates with one medium-sized tricuspid tooth, and one inner ring with small teeth located just behind the large teeth. Male and female epitokes were found together with atokous individuals within galleries. Proceraea exoryxae sp. nov. constitutes the first known miner in the Autolytinae and the second species in this taxon known to live symbiotically with ascidians. The implications of finding this specialized parasite are discussed considering that Phallusia nigra has been introduced worldwide, in tropical and sub-tropical ecosystems, where it has the potential of becoming invasive.