Addition to the knowledge on Acromegalomma messapicum (Giangrande & Licciano, 2008) (Annelida: Sabellidae)

The genus Acromegalomma has been recently introduced as nomen novum for the polychaete genus Megalomma. Recently specimens of A. messapicum were collected from the coastal area of Civitavecchia (Tyrrhenian Sea, Italy) and re-collected from the type locality (Brindisi, Adriatic Sea, Italy) allowing us to examine additional fresh material and to add some useful morphological and biological information to the original description. The present data widens the distribution of the species. The possibility to examine several specimens of A. messapicum collected in different areas allowed us to state with certainty the absence of variability as concerns both the distribution of the radiolar eyes and the collar shape. The new findings revealed a colouration pattern present in the thorax and in the branchial crown, as well as the presence of large pygidial eyes previously not reported. Specimens have very broadly hooded chaetae, especially at the beginning of the abdomen, becoming more slender and therefore narrowly hooded, proceeding towards the end of the abdomen. This could explain the incorrect statement in the original description, of the presence of narrowly hooded abdominal chaetae as characterising A. messapicum. The present data also allowed some biological observations. Acromegalomma messapicum is gonocoric with eggs measuring about 120 mm in diameter. Most of the specimens were collected in cold months but ripe specimens were found in warm months. In addition a scheme of groups of Acromegalomma species modified from that previously proposed by different authors is given, where some taxa have been moved to different groups on the basis of a new interpretation of the collar features.