A new species and nine new records of Syllidae (Annelida) from the Socotra Archipelago (Indian Ocean) Author Rodríguez, Yolanda Lucas Author Martín, Guillermo San Author Fiege, Dieter text Zootaxa 2019 2019-08-05 4651 2 235 258 journal article 26091 10.11646/zootaxa.4651.2.2 1184b85a-5699-4722-968e-58834f3c1273 1175-5326 3363175 A90D52DC-727E-4723-B205-47B3C4F0C3A7 Megasyllis heterosetosa ( Hartmann-Schröder, 1991 ) Figures 1–3 Typosyllis ( Typosyllis ) heterosetosa Hartmann-Schröder, 1991: 30 , figs. 30–35. “ Typosyllis ” heterosetosa (sic) Licher 1999: 298 , fig. 115. Megasyllis heterosetosa San Martín et al . 2008: 8–11 , figs. 9, 10. Material examined. Socotra , N coast, 12º36.369N 54º19.751E , intertidal, 09.02.1999 , 1 specimen (including 4 permanent slides of parapodia) ( SMF 24978) . Description. Specimen difficult to examine, strongly coiled, hardened and fragile. Body long, broad and strongly built, cylindrical ( Fig. 1A ), ventrally flattened; about 27 mm long (including stolon), 1.3 mm wide, about 75 segments plus incomplete stolon; yellowish, opaque in alcohol. Prostomium small, short, oval to bilobed, strongly contracted and difficult to observe. Four small orange eyes in trapezoidal arrangement. Antennae shorter than combined length of prostomium and palps; lateral antennae inserted on anterior margin of prostomium, slightly shorter than median antenna; median antenna inserted near posterior margin. Palps large, broad, divergent, basally fused, similar in length to prostomium, ventrally orientated. Peristomium similar in length to subsequent segments; most anterior segments short, sub-divided into 2–3 rings. Median segments inflated, with segmental rings slightly marked ( Fig. 1A ). Tentacular cirri longer than antennae, dorsal ones slightly shorter than half peristomial width and longer than ventral ones. Antennae, tentacular and dorsal cirri appearing smooth, unarticulated under low magnification; under high magnification irregularly articulated, with indistinct articles ( Fig. 2 A–C). Dorsal cirri inserted on cirrophores. Parapodial lobes short, triangular, ( Fig. 2 A–C). Ventral cirri digitiform, similar in length or slightly shorter than parapodial lobes ( Fig. 2 A–C). Dorsal cirri pseudo-articulated, alternating long cirri, inserted more dorsally (shorter than half of body width) and short cirri, approximately half the length of the long ones, inserted more ventrally; parapodial lobes short, triangular. Compound heterogomph falcigers with subdistal spines, more marked on anterior and dorsal chaetae ( Fig. 3A, C ); bidentate blades, with short, straight spines on margin, subdistally longer and curved upwards, extending beyond proximal tooth; dorsal and anterior chaetae with both teeth similar, teeth becoming dissimilar progressively along body, more marked on ventral chaetae ( Fig. 3A, C ); posteriormost ventral compound chaetae with proximal tooth distinctly longer and thicker than distal tooth, with distinctly curved blades and longer subdistal spines. About 14 chaetae anteriorly per parapodium, with elongated blades, progressively reduced to 11 on midbody parapodia ( Fig. 3A, C ), with dorsoventral gradation in length, changing from anterior (53– 33 μm) ( Fig. 3A ) to midbody segments (49–42 μm) ( Fig. 3C ). From midbody backwards, compound chaetae less elongated, with shorter and wider blades, dorso-ventral gradation in length, changing from anterior to posterior, respectively; blades more strongly bidentate, becoming shorter and wider within fascicle ventrally and posteriorly, with proximal tooth becoming larger and more triangular more posterior and ventral ( Fig. 3A, C ). Dorsal and ventral simple capillary chaetae not seen. Anterior and midbody parapodia with five to six aciculae each, with short, slightly oblique tips ( Fig. 3B, D ). Pharynx very contracted, about 0.90 mm long, 0.54 mm wide; pharyngeal tooth on anterior margin, surrounded by crown of approximately 10 soft papillae ( Fig. 1B ). Proventricle, about 2.40 mm long, 1.84 wide, with about 30 muscle cell rows. FIGURE 1. Megasyllis heterosetosa ( Hartmann-Schröder, 1991 ) (SMF 24978); A complete specimen, lateral view; B pharynx and proventricle dissected (arrows showing detail of pharyngeal papillae); C oocyte with nucleus (arrow). FIGURE 2. Megasyllis heterosetosa ( Hartmann-Schröder, 1991 ) (SMF 24978); A anterior parapodium; B midbody parapodium; C stolon parapodium completely filled with oocytes (arrows). FIGURE 3. Megasyllis heterosetosa ( Hartmann-Schröder, 1991 ) (SMF 24978); compound chaetae A anterior; C midbody; aciculae, B anterior; D midbody. Reproduction. In members of Megasyllis , sexual reproduction occurs by means of scissiparous schizogamy ( San Martín et al . 2014 ). An incomplete female dicerous stolon was observed attached to the specimen, with approximately 28 segments, yellowish, opaque in alcohol; four orange eyes observed; segments completely filled with yellowish spherical oocytes ( Fig. 2C , arrows), about 121 μm in diameter ( Fig. 1C ), nucleus can be observed ( Fig. 1C , arrow). Cirri from stolon thinner and shorter than those of stock. Habitat. Coralline and muddy sand, seagrasses; intertidal to shallow depths ( San Martín et al. , 2008 ). Distribution. Originally described from Queensland ( Australia ) ( Hartmann-Schröder, 1991 ); San Martín et al . (2008) recorded this species also in New South Wales ( Australia ). First record from the Indian Ocean.