Pherusa hobsonae, Salazar-Vallejo, 2014

Salazar-Vallejo, Sergio I., 2014, Revision of Pherusa Oken, 1807 (Polychaeta: Flabelligeridae), Zootaxa 3886 (1), pp. 1-61 : 19-21

Pherusa hobsonae n. sp.

Figure 5

Type material. Northeastern Pacific Ocean. Washington, U.S.A. Holotype ( USNM 43803 ) and paratype ( USNM 1131565 ) complete, Seal Rock , Neah Bay, 7 Jul. 1940, M.H. Pettibone, coll., id. as Pherusa plumosa (paratype dissected for anterior end details, tunic detached in several areas, posterior end regenerating; 58 mm long, 6 mm wide, cephalic cage broken, 8 mm long, 58 chaetigers; chaetiger 10 with 2 transverse rows of papillae, others scattered not arranged in a row, 5 notochaetae and 2 neurohooks per bundle).

Description. Holotype (USNM 43803) complete, pale; body cylindrical, slightly tapered posteriorly, medially broken ventrally, gonads exposed ( Fig. 5A ); 29.5 mm long, 5 mm wide, cephalic cage broken, 8 mm long, 51 chaetigers. Body papillae short, rounded, clean, without sediment, arranged in 2–3 transverse rows in medial chaetigers, a single row with larger papillae on anterior chaetigers, dorsally ( Fig. 5B, D ) and ventrally ( Fig. 5C ); tunic thin, detached, lost from some areas.

Cephalic hood not exposed, palps slightly exposed (anterior end details observed in paratype). Prostomium low cone; eyes not visible. Caruncle short, greyish ( Fig. 5E ), other details not seen. Palps twice as thick as, and longer than branchiae (left palp in regeneration); palp keels low. Lateral lips compressed, large lobes, dorsal and ventral lips reduced.

Branchiae cirriform, arranged into two groups, four filaments forming a continuous row, proximal filaments in two lateral groups, each with two filaments. Longer branchiae shorter than palps. Nephridial lobes short, whitish, between proximal branchiae.

Cephalic cage chaetae variably covered by epibionts, as long as ¼ body length, or less than twice as long as body width. Chaetigers 1–3 forming cephalic cage; chaetae arranged in short series, dorsal in chaetiger 1, dorsolateral in chaetigers 2–3. Chaetiger 1 with 14 noto- and 6 neurochaetae, chaetiger 2 with 9 noto- and 6 neurochaetae, chaetiger 3 with 8 noto- and 5 neurochaetae per side.

Anterior dorsal margin of chaetiger 1 with a bifid projection, without papillae. Chaetigers 1–3 decreasing in length posteriorly. Chaetal transition from cephalic cage to body chaetae abrupt; anchylosed, falcate blunt neurohooks start from chaetiger 4. Gonopodial lobes not seen.

Parapodia poorly developed, chaetae emerge from body wall. Parapodia lateral, medial neuropodia ventrolateral. Noto- and neuropodia without projected lobes or long papillae, but some postchaetal or interramal papillae slightly longer in posterior chaetigers than anterior ones.

Medial notochaetae arranged in short, transverse series; all notochaetae multiarticulated capillaries, articles short basally, medium-sized medially, long distally ( Fig. 5F ); 5–6 notochaetae per bundle, half as long as body width, becoming as long as body width posteriorly. Neurochaetae multiarticulated capillaries in chaetigers 1–3; anchylosed, falcate neurohooks from chaetiger 4, arranged in transverse series, two hooks in anterior chaetigers, three in medial and posterior regions ( Fig. 5G ), two in pre-pygidial chaetigers.

Posterior end with long chaetae; pygidium with anus terminal, without anal cirri.

Etymology. This species is named after the late Dr. Katherine D. Hobson, in recognition of her publications about polychaetes and especially because of her two books about British Columbian polychaetes, both made with Dr. Karl Banse, which are very useful and widely employed beyond the Canada-USA Pacific border. The epithet is a noun in the genitive case.

Type locality. Seal Rock, Neah Bay, Washington, U.S.A. No further field data or details; perhaps living in intertidal to shallow subtidal, rocky or mixed shores.

Remarks. Pherusa hobsonae n. sp. groups with P. affinis , P. mikacae n. sp., P. moorei n. sp., P. papillata ( Johnson, 1901) , and P. rullieri because they have sediment-free papillae. It has been indicated that P. affinis is unique because it has neurohooks from chaetiger 5, instead of starting from chaetiger 4 as in the other species. With falcate medial and posterior neurohooks, P. hobsonae n. sp. is more similar to P. mikacae n. sp. and P. papillata . However, P. hobsonae n. sp. can be easily distinguished as it has only 2–3 transverse series of papillae, and 2–3 neurochaetae in medial chaetigers, whereas the other two species, P. mikacae and P. papillata , have 10 or more transverse series of papillae, and 3–5 neurohooks.

The reduction in the number of transverse series of papillae is unexpected in Pherusa , but this is common in Semiodera Chamberlin, 1919 ( Salazar-Vallejo 2012c). The latter includes species with a dorsal shield made of cemented sediment particles, and in comparison to Pherusa species , their papillae are reduced in size; Pherusa and Semiodera also differ in the number of transverse rows of papillae per segment. Most Semiodera species bore calcareous substrates or consolidated muds (pers. obs.), where they build galleries and only expose their long cephalic cage or occasionally the posterior end for defecation. Their body sometimes resembles sabellariids by having a long, thin posterior region for this purpose. Regretfully, there is no further information about the ecology of P. hobsonae ; because of reductions in papillae size and number of transverse rows, it can be hypothesized that it lives in rocky shore interstices. The broken cephalic cage might indicate that the specimens were gathered by breaking rocks. The possibility that members of the species actually bore into calcareous substrates, or even only furnish a gallery inside them, deserves closer study.

Distribution. Only known from the type locality, probably living in intertidal rocky or mixed bottoms.

Figures

FIGURE 5. Pherusa hobsonae n. sp. A. Holotype (USNM 43803), lateral view. B. Anterior end, dorsal view. C. Same, right side, ventral view. D. Paratype (USNM 1131565), anterior end, dorsal view, tunic removed. E. Same, head, frontal view (branchiae and palps removed; BS: branchial scar, NL: nephridial lobe, PS: palp scar). F. Paratype, chaetiger 12, right parapodium, notochaetae (inset: basal and distal regions). G. Same, chaetiger 12, right parapodium, neurochaetae (one not shown). Scale bars: A: 3 mm, B: 2.2 mm, C: 1.7 mm, D: 1 mm, E: 0.5 mm, F: 0.25 mm, G: 45 µm.