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Zookeys
2025 Mar 05;1230:25-36. doi: 10.3897/zookeys.1230.140329.
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Ambusher in sponge: a new species of Eunice (Annelida, Eunicidae) commensal within deep-sea Farreidae (Porifera, Hexactinellida) on northwest Pacific seamounts.
Zhou Y
,
Zhang R
,
Shen C
,
Mao Q
,
Zhang M
,
Zhang D
.
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Deep-sea sponges create complex biogenic structures and attract a wide array of deep-sea organisms, including symbionts. In this study, we describe Eunicesiphoninsidiator sp. nov., a new eunicid species living in the central cavity of deep-sea farreid glass sponges found on northwest Pacific seamounts. The new species closely resembles the Atlantic Eunicenorvegica both morphologically and molecularly, but it differs in the relative length of palp compared to peristomium, starting points of subacicular hooks, and shape of pectinate chaetae. A 13% COI genetic distance between the two species further supports the establishment of E.siphoninsidiator as a distinct species. Gut content analyses reveals fragments of barnacles and brittle stars, suggesting a carnivorous diet and a sit-and-wait predatory strategy. The eunicid gains protection from living inside the sponge, which consistently harbored the polychaete in all specimens examined, while the sponge benefits from the cleaning of epibionts, pointing to a potentially mutualistic relationship.
Figure 1. Map of sampling locations (A–D) and in situ images of farreid glass sponges captured during the Jiaolong dive JL230 (E) and JL233 (F) B DD Seamount C O-Hakucho Guyot D Albo Guyot.
Figure 2. Eunicesiphoninsidiator sp. nov. A paratype (RSIOPOLY80002) commensal within a farreid sponge collected during the dive JL233 B anterior part of paratype (RSIOPOLY80002), anterior-ventral view C paratype (RSIOPOLY80002, before fixation), lateral view D holotype (RSIOPOLY80001, before fixation), dorsal view E anterior end of holotype, dorsal view (fixed in 100% (v/v) ethanol) F detail of anterior end of holotype, lateral view (fixed in 100% (v/v) ethanol) G location of eye in the paratype, dorsal view (fixed in 100% (v/v) ethanol) H anterior end of paratype, frontal view (fixed in 100% ethanol) I mandible of paratype, ventral view J maxillae apparatus of paratype (RSIOPOLY80002), frontal view (before digestion with Proteinase K) K maxillae apparatus of paratype (RSIOPOLY80002), dorsal view (after digestion with Proteinase K). Scale bars: 1 cm (A–D); 1 mm (E, F); 0.5 mm (G, J); 1 mm (I, K).
Figure 3. Eunicesiphoninsidiator sp. nov. A middle frontal segments of holotype, lateral view (right side) B middle segments of paratype in lateral view (right side) C posterior end of holotype, lateral view (left side) D right parapodium of chaetiger 4 of paratype (RSIOPOLY86005, frontal view) E right parapodium of chaetiger 30 of holotype (frontal view) F right parapodium of chaetiger 44 of holotype (frontal view) G right parapodium of chaetiger 103 of paratype (RSIOPOLY86005, frontal view) H limbate chaetae on chaetiger 30 I pectinate chaetae on chaetiger 64 of paratype (RSIOPOLY86005) J compound falcigers on chaetiger 54 of paratype (RSIOPOLY80002) K compound falcigers on chaetiger 30 of paratype (RSIOPOLY80002) L subacicular hooks on a posterior chaetiger of paratype (RSIOPOLY80002) M subacicular hooks on chaetiger 50 of paratype (RSIOPOLY80002). Scale bars: 1 mm (A–D); 0.5 mm (E, F); 0.2 mm (G); 0.1 mm (H, J–L); 50 μm (I).
Figure 4. Gut contents of paratype A–D fragments of stalked-barnacle ctenopod cirri E, F fragments as brittle star arm spines. Scale bars: 0.1 mm (A–F).
