Megasyllis heterosetosa ( Hartmann-Schröder, 1991 )

Rodríguez, Yolanda Lucas, Martín, Guillermo San & Fiege, Dieter, 2019, A new species and nine new records of Syllidae (Annelida) from the Socotra Archipelago (Indian Ocean), Zootaxa 4651 (2), pp. 235-258 : 237-241

publication ID	https://doi.org/ 10.11646/zootaxa.4651.2.2
publication LSID	lsid:zoobank.org:pub:A90D52DC-727E-4723-B205-47B3C4F0C3A7
DOI	https://doi.org/10.5281/zenodo.5241228
persistent identifier	https://treatment.plazi.org/id/03F187B1-FFF2-242A-FF6F-A687FAD6FE14
treatment provided by	Plazi
scientific name	Megasyllis heterosetosa ( Hartmann-Schröder, 1991 )
status

Treatment

Megasyllis heterosetosa ( Hartmann-Schröder, 1991) View in CoL

Figures 1–3 View FIGURE 1 View FIGURE 2 View FIGURE 3

Typosyllis (Typosyllis) heterosetosa Hartmann-Schröder, 1991: 30 View in CoL , figs. 30–35. “ Typosyllis View in CoL ” heterosetosa View in CoL (sic) Licher 1999: 298, fig. 115.

Megasyllis heterosetosa San Martín et al. 2008: 8–11 View in CoL , 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) GoogleMaps .

Description. Specimen difficult to examine, strongly coiled, hardened and fragile. Body long, broad and strongly built, cylindrical ( Fig. 1A View FIGURE 1 ), 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 View FIGURE 1 ). 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 View FIGURE 2 A–C). Dorsal cirri inserted on cirrophores. Parapodial lobes short, triangular, ( Fig. 2 View FIGURE 2 A–C). Ventral cirri digitiform, similar in length or slightly shorter than parapodial lobes ( Fig. 2 View FIGURE 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 View FIGURE 3 ); 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 View FIGURE 3 ); 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 View FIGURE 3 ), with dorsoventral gradation in length, changing from anterior (53– 33 μm) ( Fig. 3A View FIGURE 3 ) to midbody segments (49–42 μm) ( Fig. 3C View FIGURE 3 ). 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 View FIGURE 3 ). 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 View FIGURE 3 ). 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 View FIGURE 1 ). Proventricle, about 2.40 mm long, 1.84 wide, with about 30 muscle cell rows.

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 View FIGURE 2 , arrows), about 121 μm in diameter ( Fig. 1C View FIGURE 1 ), nucleus can be observed ( Fig. 1C View FIGURE 1 , 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.