Syllidia hongkongensis, Ruta & Pleijel, 2006

Ruta, Christine & Pleijel, Fredrik, 2006, A revision of Syllidia (Psamathini, Hesionidae, Polychaeta), Journal of Natural History 40 (9 - 10), pp. 503-521 : 513-517

Syllidia hongkongensis , new species

( Figures 7 , 8 )

Material examined

Hong Kong: holotype ( MNHN POLY TYPE 1457), Lobster Bay, Cape d’Aquilar , 22 ° 12.49N, 114 ° 15.59E, 1 m, shell sand, gravel and stones with calcareous red algae ( Corallina sp.), snorkelling, collector FP, 10–23 July 1995; 18 paratypes ( MNHN POLY TYPE 1458–1472) , including three whole-mounted on slides ( MNHN POLY TYPE 1473–1475), same locality, data, and collector; five specimens mounted for SEM ( FP), same locality, data, and collector . USA, Hawaii, Pearl Harbor: two specimens ( BPBM-R 2213 ), West Loch, Walker Bay along shoreline, 0.5–1.5 m, 6 February 1996 ; four specimens ( BPBM-R 2231 ), north side of entrance channel, 0.5–3 m, 13 February 1996 ; seven specimens ( BPBM-R 2427 ), West Loch , mangrove area, 1 m, 16 April 1996 .

Apomorphies

Possibly the presence of neurochaetae on segment 3 (see Remarks).

Description

Holotype complete specimen, 5 mm long for 35 segments; see Figure 1 for further measurements. Body short, cylindrical, excluding parapodia, anteriorly truncate, posteriorly tapered; venter flattened without distinct median longitudinal furrow.

Prostomium rounded quadrangular, anteriorly straight, posterior incision weakly developed ( Figure 7A ). Small facial tubercle present ( Figure 7B ). Palpophores cylindrical, about as long as palpostyles; palpostyles tapered. Paired antennae elongated, tapering, as long as palps or slightly longer ( Figure 7A ). Anterior pair of eyes rounded to reniform, slightly larger than posterior pair and situated further apart, posterior pair rounded, both pairs with lenses. Nuchal organs lateral, mid-dorsally separated ( Figure 7A ). Distinct lip glands absent ( Figure 7B ). Non-everted proboscis reaching segments 7–10, with 10 terminal papillae, ventral incision present ( Figure 7C ). Proboscis with pair of ventro-lateral large, denticulate jaws with one dark pointed and one wing-like shaft and and serrated edges with about 10 teeth ( Figure 8B ); small unpaired stylet ( Figure 8B ) situated between jaws (may be difficult to detect). Segment 1 dorsally reduced, segment 2 fully developed. Dorsal cirri and cirrophores segments 1–5 enlarged and prolonged compared to following segments. Ventral cirri segments 1–3 enlarged and prolonged compared to following

Figure 9. Geographical distribution of Syllidia armata (., based on examined specimens; DZ, records from the literature), S. hongkongensis , new species (m, based on examined specimens), and S. liniata , nomen dubium (•, based on examined holotype).

segments, with well-developed cirrophores. Neuropodial lobes and neurochaetae absent on segments 1 and 2. All dorsal cirri distinctly annulated with basal rings as long as wide or longer, distal rings usually shorter. Elevated and prolonged dorsal cirri on segments 5, 8, 10, 12, 15, 17, 20, 22, 25, and every third segment thereafter, dorsal cirri of other segments shorter and more laterally orientated. Neuropodia of median segments with one or two aciculae and 20–30 compound chaetae ( Figure 8A ). Median neurochaetae with longer blades than dorsal and ventral ones; ventralmost ones shortest, length less than half of longest median ones. Chaetal shafts internally camerated. Several median chaetal blades with prolonged teeth. Blades with unidentate tips. Ventral cirri subdistally inserted on neuropodium, tapered, indistinctly annulated, cirrophores absent ( Figure 7D ). Pygidium with pair of cirri, similar to dorsal cirri. Small medio-ventral pygidial papilla present.

Colour

Live specimens opaque to transparent, unpigmented except for brown ventral longitudinal midline, usually on posterior part of body. Eyes red. Jaws dark brown, median stylet opaque. Preserved specimens yellowish with weak transverse darker pigmented bands.

Reproduction

Several sexually mature specimens observed, both from Hong Kong and Hawaii. Mature female from Hong Kong with egg diameter about 45 mm.

Habitat

At the type locality with shell sand, gravel, and stones with calcareous red algae ( Corallina sp.), low tide; down to 5 m depth in Hawaii.

Distribution

Presently known only from Hong Kong and Honolulu, Hawaii.

Remarks

Syllidia hongkongensis is clearly a member of Syllidia , as seen from the presence of paired, ventro-lateral jaws and a median stylet. Syllidia hongkongensis differs from all other Syllidia in the absence of neurochaetae on segments 1 and 2, rather than on segments 1–3. Hesionids go through a number of ontogenetic stages that involves reduction of chaetae and parapodial lobes on the anteriormost segments, such that most taxa have an adult condition with chaetae appearing first from segment 4 or 5 (see Pleijel 1998 and references within). It is therefore important to compare fully grown stages, and the adult status of our specimens of S. hongkongensis is evidenced by the presence of eggs and sperm in several of the animals. However, the unique presence of chaetae on segment 3 does not necessarily constitute an apomorphy for S. hongkongensis ; for example, it is instead a plesiomorphy if S. hongkongensis is the sister to remaining Syllidia . The most closely related taxa to Syllidia , according to Pleijel (1998), are the sister group Nereimyra and Bonuania , and then Sirsoe , and these taxa have members where the chaetae start on segment 4 ( Nereimyra ), but also on segment 2 or 3 ( Bonuania and Sirsoe ). Furthermore, if the presence of chaetae from segment 3 indeed is an apomorphy for S. hongkongensis , then we may instead lack diagnostic features for S. armata (and possibly also for the lesser well-known members of Syllidia ). Further characters are required to resolve these issues.

The specimens from Honolulu are in less good condition than those from Hong Kong. Nevertheless, they clearly are members of Syllidia as seen from, for example, the presence of similar jaws. Furthermore, all specimens from Honolulu, including mature ones, have chaetae present from segment 3, and based on this we refer them to S. hongkongensis .

Etymology

Named for the type locality, Hong Kong .

Figures

Figure 1. Relationships between number of segments and length in Syllidia armata (n) from Sweden and southern France and S. hongkongensi, new species (©) from the type locality.

Figure 7. SEM micrographs of Syllidia hongkongensis, new species. (A) Anterior end, dorsal view; (B) anterior end, ventral view; (C) distal proboscis ring with papillae embedded in cilia; (D) anteriormost segments, left side, lateral view; (E) median neuropodium, ventral view. Scale bars: 100 mm.

Figure 8. LM micrographs of Syllidia hongkongensis, new species. (A) Median parapodium; (B) jaws and median stylet. Scale bars: 200 mm (A); 100 mm (B).