Sphaerosyllis isabellae, Nogueira, 2001

Nogueira, J. M. De M., 2001, Description of ® ve new species of Exogoninae Rioja, 1925 (Polychaeta: Syllidae) associated with the stony coral Mussismilia hispida (Verrill, 1868) in SaÄo Paulo State, Brazil, Journal of Natural History 35, pp. 1773-1794 : 1777-1779

Sphaerosyllis isabellae n. sp.

(®gure 1)

? Sphaerosyllis sp. Temperini, 1981: 20 , ®gures 38±42.

Material examined

Holotype and two paratypes from Ilha dos Alcatrazes . Holotype (MHN-BPO 70-0): incomplete specimen in good condition, with 24 chaetigers, lacking posteriormost chaetigers and pygidium, 1.8 mm long, 0.22 mm wide. Paratype 1 (MHN- BPO 70-1): juvenile, incomplete, with six chaetigers, 0.1 mm wide; paratype 2 (MHN- BPO 70-2): complete specimen, in poor condition, with 21 chaetigers, 0.16 mm wide.

Description

Body short, relatively broad, without colour patterns, dorsal and ventral surfaces covered by numerous small papillae. Prostomium rectangular; two pairs of large lensed eyes in rectangular arrangement close to each other on each side, and two ocular spots on anterior margin. Antennae very short, with bulbous bases (ceratophores) and short rounded tips (ceratostyles); lateral antennae inserted on anterior margin of prostomium, just behind eyespots; median antenna originating on posterior margin. Palps completely fused, nearly rectangular, densely papillated. Peristomium large, well de®ned, dorsally and laterally covering the posterior part of the prostomium; tentacular cirri similar to antennae, but even smaller (®gure 1A). Dorsal cirri mammiform, with a long proximal part and short, button-like, retractile, globular tips; base with several iridiscent glands (®gure 1B). Parapodia conical, papillated, from midbody, each with about ®ve to six heterogomph compound chaetae with smooth shafts, blades all of similar length; in anterior parapodia, blades of uppermost falcigers about 9.5 m m in length, median, 9 m m, and the lowest, 8 m m; from midbody, all chaetae are about 9 m m long, although there still exists some slight dorsoventral gradation. Blades strongly curved, unidentate, with shortly spinulated cutting edges that become smooth from midbody (®gure 1C, E). Solitary dorsal simple chaetae from chaetiger 1 on holotype and paratype 2, slightly thicker than compound chaetae, especially from midbody segments, with pointed tip and very short spines on margin (®gure 1D); solitary ventral simple chaetae, only seen on last chaetiger of holotype and on four posteriormost chaetigers of paratype 2, much thinner, smooth and with more curved tip than dorsal ones (®gure 1F). Solitary aciculum per parapodium, with a subdistal enlargement and acuminate tip (®gure 1G). Pharynx long and wide extending through four to ®ve chaetigers, with a small triangular tooth placed on its anterior third, and one pair of large brown glands on posterior part of chaetiger 1; proventriculum large and wide, through about three or four chaetigers, with 32±36 muscle cell rows (®gure 1A).

Etymology

The given name is a homage to Isabella Nogueira de Matos Ferreira, niece of J. M. M. N.

Discussion

This species is characterized by: (1) bulbous antennae, and tentacular and dorsal cirri, articulated, with an elongate proximal part and a retractile globular tip; (2) palps fused and densely papillated; and (3) blades of compound chaetae very short, nearly smooth, with slight gradation in length. Sphaerosyllis ranunculus Kudenov and Harris, 1995 diOEers from Sphaerosylli s isabellae n. sp. in having: (1) palps much less papillated, almost smooth; (2) nuchal lobes present; (3) pharyngea l tooth placed close to the margin of pharynx; (4) proventriculum with fewer rows of muscle cells, 19±22 rows against 32±36 rows in Sphaerosyllis isabellae n. sp.; (5) absence of pharyngeal glands on chaetiger 1; (6) blades of anterior compound chaetae proportionally longer, slender, with marked dorsoventral gradation in length, dorsal ones with cutting edges more spinulated; and (7) dorsal cirri digitiform after midbody (see Kudenov and Harris, 1995). Sphaerosyllis xarifae Hartmann-SchroÈder, 1960 has very similar dorsal cirri, but diOEers from S. isabellae because it has: (1) palps less papillated; (2) longer pharyngeal tooth, placed more posteriorly, on the midpharynx; (3) pharynx without glands on chaetiger 1; (4) proventriculum with only 17±21 rows of muscle cells; (5) from midbody, dorsal cirri with longer basal part; (6) six compound chaetae on anterior parapodia, against four in Sphaerosyllis isabellae n. sp.; and (7) blades of compound chaetae much longer, slender, with long spines on the base and strong dorsoventral gradation (see Hartmann-Schr oÈder, 1960; San MartõÂn, 1984a). Sphaerosylli s brandhorst i Hartmann-Schr oÈder, 1965 diOEers from S. isabellae n. sp. in having: (1) palps not densely papillated; (2) pharyngeal tooth much closer to the margin of pharynx; (3) pharynx without glands on chaetiger 1; (4) acicula only slightly bent, with rounded tip and lacking subdistal enlargement; (5) blades of compound chaetae slender and with conspicuous spinulation (see Hartmann-SchroÈder, 1965). Probably the species most similar to S. isabellae n. sp. is S. brevicirra Hartmann-SchroÈder, 1960, but they are easily distinguished because the latter has: (1) palps not so densely papillated; (2) pharynx lacking glands on chaetiger 1; (3) acicula with rounded tip, instead of acuminate; and (4) blades of compound chaetae markedly stouter (see Hartmann-SchroÈder, 1960; AloÂs, 1988). Sphaerosyllis palpopapillata Hartmann-SchroÈder, 1992 is another species provided with numerous papillae on palps, however its antennae and dorsal cirri are longer and not mamillate (see Hartmann-SchroÈder, 1992a).