Megasyllis, Martín & Hutchings & Aguado, 2008

Martín, Guillermo San, Hutchings, Pat & Aguado, María Teresa, 2008, Syllinae (Polychaeta, Syllidae) from Australia. Part. 2. Genera Inermosyllis, Megasyllis n. gen., Opisthosyllis, and Trypanosyllis, Zootaxa 1840, pp. 1-53 : 5-6

Genus Megasyllis n. gen.

Diagnosis. Body large (often greater than 30 mm), cylindrical, with numerous bi- or tri- annulated segments (sometimes more annuli per segment). Prostomium with 4 eyes, 3 antennae, 2 palps; and 2 prostomial lobes or cheeks. Palps fused basally, ventrally directed. Antennae, and tentacular (peristomial), anal and dorsal cirri with rugose epidermis, indistinctly articulated under high magnification, more distinctly articulated in juveniles, smoother on large specimens. Longer dorsal cirri arising more dorsally than shorter ones. Cirrophores distinct. Parapodia with prechaetal lobes. Ventral cirri triangular. Aciculae straight, sometimes protruding from parapodia. Compound heterogomph chaetae with two kinds of blades; few dorsal chaetae with slender, elongated blades, and numerous chaetae with shorter, broad blades with dorso-ventral gradation in size. Dorsal capillary and ventral simple chaetae present on posterior parapodia. Pharynx shorter than proventricle or almost equal in length, with an anterior tooth, surrounded by crown of numerous (around 15 or more) soft papillae. Two anal cirri. Reproduction by means of stolons.

Type-species. Megasyllis corruscans ( Haswell, 1885) , herein designated.

Remarks. The genus Megasyllis , n. gen., differs from all other genera of Syllidae in being of large size (> 30 mm in length, up to 140 mm), bright colour in life, opaque body wall (so that the digestive tract cannot be seen through it, as in almost all other members of the family), long and short dorsal cirri, originating at different levels (longer ones more dorsal), and segments with several annuli. Megasyllis appears to be morphologically similar to Pionosyllis Malmgren, 1897 , as re-defined by San Martín et al. (in press), since both typically have large, cylindrical bodies, cirri smooth in adults (articulated in juvenile individuals of species of Megasyllis ), distinct prechaetal lobes, and similar arrangement of chaetae on each parapodium. Some species previously identified as Pionosyllis in the AM collections belong in fact to this new genus. Pionosyllis does not have annulated segments, antennae, tentacular, anal, and dorsal cirri are smooth and distinctly long, and reproduces by epigamy. This character is diagnostic since Megasyllis reproduces by schizogamic scissiparity, which indicates that this genus is phylogenetically not related to Pionosyllis and instead belongs to the Syllinae , although some morphological characters suggest that it resembles Eusyllinae . Some species of Eusyllis Malmgren, 1897 (Malmgren 1897; San Martín 2003) do not have the incomplete trepan, which is characteristic of Eusyllis , but a single tooth and a crown of numerous soft papillae, indicating that they belong to Megasyllis . The type-species of the genus, Megasyllis corruscans , was originally described by Haswell as Syllis Lamarck, 1818 . Syllis species are typically much smaller than any species of Megasyllis , and they have simple, non-annulated segments, pharynx similar in size to proventricle or longer, and dorsal cirri originating all at the same level, both the long and short ones. The juveniles of Megasyllis are more similar to Syllis than are adult individuals. Haswell remarked, both in the original description (1885) and subsequently (1920), that “ Syllis corruscans was far from being a typical Syllis ” and how it resembled species of the subfamily Eusyllinae , but also noted that the species reproduced by schizogamy. Licher (1999) did not consider Syllis corruscans in his revision of Typosyllis , and named it as Odontosyllis (?) corruscans ( Haswell, 1885) comb. nov., species inquirenda. Aguado et al. (in press) also commented that there were clear differences between several species (considered herein as members of Megasyllis ) and the rest of the species considered as belonging to the genus Syllis . The new species these authors described is herein assigned to this new genus: Megasyllis multiannulata (Aguado, San Martín & Nishi, in press).

Etymology. From the Greek Mega - meaning “large, great” and the genotype of the family Syllidae (Syllis) .