Capitella singularis ( Fauvel, 1932 ) Fauvel, 1932

Magalhães, Wagner F. & Bailey-Brock, Julie H., 2012, Capitellidae Grube, 1862 (Annelida: Polychaeta) from the Hawaiian Islands with description of two new species, Zootaxa 3581, pp. 1-52 : 14-16

Capitella singularis ( Fauvel, 1932) comb. nov.

Figures 3 A–B, 9 A–D, 10 A–F

Branchiocapitella singularis Fauvel, 1932: 197 , pl. VII, figs. 9–14.

Branchiocapitella singularis .— Fauvel 1953: 371 –372, fig. 193a–f. Pillai 1965: 157 –160, fig. 19a–f.

Material examined. Oahu Island: Mamala Bay, underneath threadfin mariculture cages, Sta. UR3, 21°17ʹ17.7ʺ N, 158°00ʹ26.5ʺ W, 40.2 m, Feb. 2004 (2, 1 on stub; 1, BPBM R3581).

Description. Two complete specimens 20 and 26 mm long, 0.5 mm wide for about 120–130 chaetigers. Third specimen largest one but lacking posterior-most segments, 70 mm long, 0.8 mm wide for about 91 chaetigers. Body elongate, wider on mid-thoracic chaetigers, gradually narrowing before pygidium; rounded dorsally and with shallow ventral groove beginning after chaetigers 7–8. Color in alcohol pale yellow or brownish orange.

Prostomium conical, as long as wide, with rounded tip ( Figs 9 A, 10A, B); nuchal organs and eyespots not observed. Peristomium distinct from prostomium as a complete ring, dorsally as wide as chaetiger 1 but shortens ventrally surrounding mouth ( Figs 9 A, 10A, B). Proboscis partially everted in largest specimen and apparently smooth.

Thorax with 10 segments, one achaetous peristomium and nine chaetigers. Anterior thoracic segments biannulate, after chaetiger 4 segments may appear tessellated with sub–annulations ( Figs 9 A, 10A); first chaetiger biramous, chaetigers 1–7 with 12 short bilimbate capillaries per fascicle. Males with chaetigers 8–9 enlarged, muscular with notopodia replaced by embedded genital hooks ( Fig. 9 B); hooks overlapping each other, from chaetiger 8 directed posteriorly and chaetiger 9 directed anteriorly. Neuropodia of chaetiger 8 with five hooded hooks, neuropodia of chaetiger 9 with 10 similar hooks. Abdominal segments multiannulated, more strongly after chaetiger 14 ( Fig. 10 C); noto- and neuropodia with well separated glandular tori pads ( Fig. 10 D); abdominal chaetae with hooded hooks throughout, anteriorly 12 hooks, reduced to 4–6 posteriorly. Lateral organs and genital pores not observed.

Genital spines with different configuration in two large specimens; one specimen apparently without exposed spines on chaetiger 8 (but with groove) and two robust embedded spines on chaetiger 9, directed anteriorly; largest specimen with two sets of 3–4 spines on chaetiger 8 facing next chaetiger and two robust spines on chaetiger 9 facing anteriorly ( Fig. 9 B).

Noto- and neuropodial hooks similar; hoods short, not extending beyond main fang. Hooks with moderate anterior shaft, slight node and multiple teeth, with two rows of teeth in frontal view (4–6 teeth in basal and 7–8 in superior row), although superior row may not be seen with light microscopy ( Fig. 10 F).

Branchiae present after chaetiger 30, present throughout posterior end of body; 1–4 digitiform branchial filaments arising below neuropodial lobes ( Fig. 10 D); number of filaments increasing posteriorly ( Fig. 10 E). Pygidium simple with terminal anus.

Methyl green staining pattern. All specimens male, with same staining reaction. Anterior end and thoracic region staining light green; second half of segments from chaetiger 5–9 with dark speckles ( Fig. 3 A). Abdomen stained darker than thorax; anterior five segments with two rings formed on second half of segments by staining of pre- and post-chaetal tori; posteriorly, stain only retained on pre- and post-chaetal region, with a light green band circling dorsum and no stain ventrally ( Fig. 3 B). Pygidium not stained.

Distribution. Indian Ocean ( Fauvel 1932), Indonesia ( Pillai 1965) and newly recorded from Hawaii in the northwestern Pacific Ocean.

Remarks. The specimens from Oahu, Hawaii agree well with the original description but differ in that the branchial filaments are positioned ventrally and not dorsally as stated and illustrated in Fauvel (1932, 1953). However, preserved specimens usually have the abdomen deformed in a way that is difficult to ascertain noto- and neuropodial orientations. Pillai (1965) reports specimens with ventral branchiae and points out that Fauvel’s drawing was upside down. Examination of the holotype is necessary to verify if the branchiae are dorsal or ventral.

The peristomium of Capitella singularis comb. nov., forms a complete ring (assumed to be fused in Warren (1976) but specimens examined herein and drawings in Fauvel (1932) show otherwise), as opposed to being partly or completely fused with the prostomium as in other Capitella species (exception of Capitella minima ). The anterior thoracic chaetigers may be multiannulated in C. singularis comb. nov. and seem to be always biannulated in other Capitella species. Fauvel (1932, 1953) states that the thorax has only seven chaetigers, not considering the modified segments as being thoracic. Female individuals were not described in Fauvel (1932, 1953) nor were they found in the Hawaiian material; therefore, hermaphroditism may occur in C. singularis comb. nov. as well.

Figures

FIGURE 3. Capitella singularis comb. nov.: A, MGSP of anterior end; B, MGSP of abdominal segments showing staining on parapodial tori and presence of branchial filaments. Capitella giardi: C, preserved specimen with brown pigmentation on anterior end and abdominal parapodial tori; D, MGSP of anterior end in lateral view; E, MGSP of anterior end in dorsal view; F, MGSP of posterior end and pygidium.

FIGURE 9. Capitella singularis comb. nov.: A, anterior end, lateral view; B, end of thoracic region in dorsal view showing genital spines; C, branchial tufts; D, posterior end in lateral view.

FIGURE 10. SEM of Capitella singularis comb. nov.: A, anterior end and thoracic region in dorso-lateral view; B, anterior end, lateral view showing distinction between prostomium, persitomium and chaetiger 1; C, anterior multi-annulated abdominal segments; D, posterior abdominal segments showing beginning of branchiae with a single filament; E, posterior abdominal segment with well-developed branchial tufts; F, detail of an abdominal hooded hook.