Goniadella bobrezkii ( Annenkova , 1929 ) ( Annelida , Polychaeta ) : first record in the Italian waters

Goniadella bobrezkii (Annenkova, 1929) is a small goniadid worm identifiable by the number of anterior uniramous parapodia and by the position of the posterior spine-like notochetae arising dorsal to dorsal cirri. Although it was already reported in the Mediterranean Sea, it has never been found in the Italian waters. This study represents the first generic and specific record of G. bobrezkii along Italian coasts. A total of 25 specimens were collected in a Posidonia oceanica (L.) Delile bed, depth of 7 m, off Civitavecchia (Rome).


Introduction
The family Goniadidae Kinberg, 1866 (Annelida, Phyllodocida) includes 11 genera and 73 species (Read and Fauchald 2018a).The members of this family are represented by errant polychaetes occurring from intertidal to abyssal depths (Böggemann 2005).The goniadids are characterized by an annulated conical prostomium ending in 2 pairs of appendages, and by a long eversible pharynx densely covered by papillae.The proboscis is armed with 2 types of paragnaths (macro-and micrognaths), arranged in a dorsal and in a ventral arc, and they may also have 2 lateral rows of horizontal V-shaped chevrons near pharynx base.The body of the goniadids is usually divided into an anterior region, with uniramous parapodia, and a following region with biramous or sub-biramous parapodia (Böggemann 2005, Böggemann andPurschke 2006).

Methods
Specimens of Goniadella bobrezkii were collected off Civitavecchia (Rome), near the harbor (Fig. 1).Sampling SCUBA surveys were performed during 2015 and 2016 in different months (October, March, May and August) on some sandy pools located among shallow waters in Posidonia oceanica meadow.Samples were collected by means of corers.After Gambi et al. (1998) and Buia et al. (2003), each PVC tube corer was 10cm in diameter and 25 cm long (surface area = 78.5 cm 2 ), with a 0.4 mm mesh net on top.Corers were plunged into the sediment to a depth of 20 cm.At each sampling date, 5 replicates were collected and each sample was sieved with a mesh size of 0.5 mm, the retained fraction of sediment was preserved in 4% buffered formalin.In the laboratory, all organisms were sorted and identified to the finest taxonomic level possible (i.e.species), and subsequently preserved in 75% ethanol.The morphological features and the diagnostic characteristics of G. bobrezkii specimens were examined following Hartman (1950) and Böggemann (2005).The material was deposited in the marine invertebrate collection of Laboratory of Experimental Oceanology and Marine Ecology, University of Tuscia (Civitavecchia, Roma).
Environmental characteristics.At the study site, the bed of P. oceanica occurs at depths between 3 m and about 18 m, and its architecture shows a fragmented coverage that is characterised by the presence of several circular sandy patches and mixed rocks.Living P. oceanica covered 69% of the bottom, and its density did not vary over the year, remaining quite constant (260-312 shoots m -²) (Paladini De Mendoza et al. 2018).In the sampling site, the bed sediment is composed by gravelly coarse sand; the gravel fraction (19-60%) mainly consisted in bioclasts composed by skeletal fragments and shells.The coastal site has moderate to high wave conditions with seasonal oscillation of wave intensity, with the maximum intensity in autumn and winter (1.5-3 m) and minimum in summer (0.5-1.5m) (Paladini De Mendoza et al. 2018).
Identification.The specimens were assigned to the genus Goniadella based on the following morphological characteristics: prostomium annulated with 8 rings; trior quadriarticulated appendages on tip; proboscis with a few different types of papillae and with macrognaths and dorsal and ventral micrognaths; chevrons present; first segment with only a pair of small lateral cirri; anterior chaetigers with uniramous parapodia, following chaetigers with biramous or sub-biramous parapodia.Notochaetae acicular in anterior to posterior parapodia; neurochaetae compound falcigers and spinigers on all parapodia (Böggemann 2005).The specimens were subsequently identified as G. bobrezkii on the basis of the number of uniramous anterior parapodia (21-24) and of the position of the posterior acicular notochetae arising dorsal to dorsal cirri (Hartman 1950, Böggemann 2005).
During the year, no significant variation in the morphological features and in the diagnostic characteristics of the specimens were observed.
Most of the specimens were collected in August and May, months characterised by maximum leaf length of P. oceanica and minimum wave intensity.Conversely, only 3 individuals were collected in the cold months, when the sediment resuspension was maximum.The analysis of the macrozoobenthic fauna associated with the sandy patches revealed that polychaetes were the dominant taxon, mostly represented by the onuphid Aponuphis brementi (Fauvel, 1916), and by the phyllodocid Pseudomystides limbata (de Saint-Joseph, 1888).In addition, the detritivorous amphipod Gammarella fucicola (Leach, 1814), and the ophiuroid Amphipolis squamata (Della Chiaje, 1828) were also well represented in the benthic community.

Discussion
This study represents the first record of Goniadella bobrezkii (as well as the first record of the genus Goniadella) in the Italian coastal waters and the second record of this species in the Mediterranean waters.According to the literature, in the Mediterranean Sea, the species has been only reported in Greek waters (Arvantidis 2000, Costello et al. 2001, Faulwetter et al. 2017).In the European waters, this species is commonly distributed in the Black Sea (Annenkova 1929, Böggemann 2005) and around the North Eastern Atlantic coasts, England, France, Belgium and North Sea (Wolff and Stengega 1975, Kirkegaard 2001, Böggemann 2005, Read and Fauchald 2018b).
Goniadella bobrezkii shows some morphological similarities with the congeneric species G. galaica (Rioja, 1923), as described by Gil (2011) and remarked by Moreira and Parapar (2015), but G. galaica was only reported in the Galicia and in the Atlantic coast of Portugal.As suggested by above-mentioned authors, a direct comparison between the 2 species is necessary to determine their effective synonymy and their correct distribution in the European waters.
In our specimens, no significant variation in the morphological features and in the diagnostic characteristics of the specimens was observed during the year, while the analysis of the abundance revealed an increase in the number of individuals from October to August.However, the lack of variation in morphological features could be related to the selectivity of the mesh size used during the sampling, which failed to retain intermediate and juvenile stages.
As for the ecology of G. bobrezkii, our work represents the first record of this species in association with the shallow water P. oceanica beds.In previous studies (Arvanitidis 2000, Böggemann 2005), this species has always been related to sandy substrates (fine, medium coarse sand and coarse sand with gravel).In agreement, our individuals were collected on gravelly coarse sand with high percentage of shells and skeletal fragments.
This work increases the knowledge about the distribution and ecology of this species, highlighting the need for a re-analysis of available collections in order to better clarify the taxonomic status of the genus Goniadella and consequently the real geographical distribution of G. bobrezkii.

Figure 1 .
Figure 1.Map of the study area with location of sampling site (SCI: Site of Community Importance "Posidonia oceanica meadows").