Raphidrilus hawaiiensis Magalhães, Bailey, Brock & Davenport, 2011, sp. nov.
Creators: name: Magalhães, Wagner F.
name: Bailey, Julie H.
name: Brock, -
name: Davenport, Jennifer S.
Publisher: name: Zenodo
Year: 2011
Subjects: Biodiversity
Taxonomy
Animalia
Annelida
Polychaeta
Terebellida
Ctenodrilidae
Raphidrilus
Raphidrilus hawaiiensis

description: Raphidrilus hawaiiensis sp. nov.
Figures 4 (A–C), 5 (A–F), 6 (A–F) and 7 (A–F)
Material examined. Holotype: Kaimana Beach, Waikiki, south shore of Oahu, Hawaii, 21°15ʹ45ʹ 157°49ʹ19ʹ, collected from mud adhering to branches of the brown alga Gracilaria salicornia (C. Agardh), coll. W. Magalhães, Oct/09 (USNM 1150465); Paratypes: same location, date and collector as holotype (8, BPBM-R3434; 5, USNM 1150466; 5, BMNH 2011.2–6). Non– type material: Kaimana Beach, Waikiki, Oahu, Hawaii, on Gracilaria salicornia 21°15ʹ50ʹ 157°49ʹ21ʹ, coll. C. Moody, Jan/09 (42); July/2008 (8); coll. W. Magalhães, Oct/09 (10); Sand Island outfall, off Honolulu, Oahu, Hawaii, station D6R1, 2004, 50 m (9); Barbers Point outfall, off Honolulu, Oahu, Hawaii, 66 m, station HB1R5, 2004 (6), station HB3R5, Jan/10 (1); Sand beach 1000 m west from Paiko Lagoon Sanctuary, south shore of Oahu, Hawaii, 21°16ʹ47ʹ 157°43ʹ45ʹ, collected on Avrainvillea amadelpha (Mont.) A. Gepp & E. Gepp, station A7R3, coll. W. Magalhães, Mar/10 (4).
Description. Specimens 2–3 mm long, 0.1–0.2 mm wide for 12–26 chaetigers. Body elongated, cylindrical, and indistinct posteriorly (Fig. 4 A). First four chaetigers (thorax) and last few wider than long (Figs. 4 A; 5F); abdominal chaetigers as long as wide, sometimes sub–moniliform. From chaetiger 5 to posterior end 10–20 sub– annulations present per segment (Fig. 6 B). Branchiae scarce in adults, frequently broken off, present on variable number of anterior chaetigers. Color in alcohol light yellow; few specimens yellow to dark brown; internal structures observed through transparent body wall. Color in life not observed.
Prostomium as long as two anterior chaetigers, pear–shaped, with pair of nuchal organs located near postero– lateral border (Fig. 5 A–C). Nuchal organs oval ciliary patches (8–10 µm wide) with long cilia, situated in a shallow pit (2–3 µm deep) (Fig. 5 D). Peristomium consisting of single achaetous segment not clearly distinct dorsally from prostomium (Fig. 5 A–C); ventral proboscis with numerous basal bar–like papillae (Fig. 5 E). One (N=38) or two (N=5) achaetous segments biannulated dorsally; one specimen with three achaetous segments but third one not biannulated. First four chaetigers short, with 4 notochaetae and 4 neurochaetae in each fascicle; subsequent chaetigers with 1–2 chaetae per fascicle. Heart body always on chaetiger 4; sac–like, anteriorly directed, extending to middle of chaetiger 3 (Fig. 4 B). Digestive tube divided in three parts; cylindrical esophagus enlarges at chaetiger 5 in all specimens where inflated stomach begins (Fig. 4 A, B); posterior third of the body with curled digestive tube (Fig. 4 A); number of segments with inflated stomach and curled intestine variable.
Branchial filaments postero–dorsal to notochaetae (Fig. 6 A). Serrate capillary chaetae throughout (Fig. 6 C, D), emerging directly from the body wall (Fig. 6 A). Chaetae few or absent on far posterior chaetigers. Fibrils along the capillary edge with distance between the insertion point of two capillary fibrils approximately the same as half the width of a single fibril.
Anal aperture dorsal on elongated pygidial segment, covered by fields of long cilia (Fig. 6 E, F).
Biology. Raphidrilus hawaiiensis sp. nov., is usually found in low abundance (10–70 ind./m², Ambrose et al. 2010) adjacent to ocean outfalls in sandy bottoms and in high abundance (1125 ind./m², C. Moody, unpublished data) on the invasive alga Gracilaria salicornia, which is a successful invader on Oahu’s south shore reef flats. Few specimens were found inhabiting branches of the green invasive alga Avrainvillea amadelpha. Raphidrilus hawaiiensis sp. nov., has been collected with a fine sediment coating of unknown function, but this sediment coat (mostly composed of fragments of diatoms, radiolarians, and clay particles) may protect the worms against the adhesive properties of algal mucilage and abrasion.
Raphidrilus hawaiiensis sp. nov., reproduces asexually and maybe sexually. Some specimens, even one regenerating fragment (Fig. 7 F), had what may be larvae in the coelom, but no larval chaetae or segmentation were observed, so this might be intracoelomic parasites (Fig. 4 C). If these small worm–like individuals are indeed larvae, it might indicate that this species is a viviparous hermaphrodite with larvae exiting the body as juvenile worms as reported for R. nemasoma (Monticelli 1910b, Sokolow 1911a). Several specimens of R. hawaiiensis sp. nov., were found with regenerating anterior and/or posterior ends (Figs. 7 A–F). Worm fragments as small as four chaetigers seem to be capable of regenerating a whole worm. These regenerating fragments most likely belong to mid– body chaetigers due to the enlarged digestive tube seen through the transparent body wall. If the anterior and posterior ends begin regeneration simultaneously, the posterior end appears to regenerate faster than in the anterior end as there are a greater number of posterior segments. This could be due to the increment of new segments from the growing zone in the newly regenerated pygidium. Further experimental studies are necessary to fully understand the process of regeneration in this species.
Etymology. This species is named after the type locality.
Distribution. Known from shallow subtidal to 66 m off south shore of Oahu Island, Hawaii; on shallow reefs they inhabit the invasive algae Gracilaria salicornia and Avrainvillea amadelpha.
Remarks. Raphidrilus hawaiiensis sp. nov., differs from R. harperi sp. nov., and R. nemasoma by the presence of numerous bar–like papillae in the ventral proboscis, one or two dorsally biannulated achaetous segment between peristomium and chaetiger 1, and digestive tube clearly divided in three parts with a bottle–neck from chaetiger 4 to 5. The shape and arrangement of fibrils along the capillary chaetal blades in R. hawaiiensis sp. nov., is very similar to R. harperi sp. nov., by being thicker and having less space in between the fibrils in comparison with R. nemasoma.
description: Published as part of Magalhães, Wagner F., Bailey, Julie H., Brock, - & Davenport, Jennifer S., 2011, On the genus Raphidrilus Monticelli, 1910 (Polychaeta: Ctenodrilidae) with description of two new species, pp. 1-14 in Zootaxa 2804 on pages 9-12, DOI: 10.5281/zenodo.277061