Iphitime nubila Hookabe, Yamamori, Ogawa, Jimi, Kohtsuka & Rouse, 2025, sp. nov.

Iphitime nubila sp. nov. (Figs 3–5) Japanese name: unryû-mino-isome. ZooBank: urn:lsid:zoobank.org:act: 55B4F2D2-FD69-43E9-96 DE-3DCAD7BE9FAD. Materials examined: Holotype (NSMT-Pol H-986): female, fixed/preserved in 5% formalin in seawater, collected off Minabe, Wakayama, Japan, on 2 December 2021 from Dardanus crassimanus with a shell of Tutufa bufo (Röding, 1798) (Fig. 3A, B) caught with a gill net at depths of 5–50 m; several branchiae were fixed and preserved in 99% ethanol. Paratype 1 (NSMT-Pol P-987): male, fixed/preserved in 10% formalin in seawater, collection date, location, and host individual same with the holotype. Paratype 2 (NSMT-Pol P-988), female, fixed/preserved in 70% ethanol, collected off Minabe, Wakayama, Japan, on 9 December, from D. crassimanus with a shell of T. bufo caught with a gill net at depths of 5–50 m; Paratype 3 (NSMT-Pol P-989), female, fixed/ preserved in 70% ethanol, collected off Minabe, Wakayama, Japan, on 9 December, from Dardanus pedunculatus with a shell of Charonia lampas (Linnaeus, 1758) caught with a gill net at depths of 5–50m; Paratype 4 (NSMT-Pol P-990), female, fixed/preserved in 70% ethanol, collected off Minabe, Wakayama, Japan, on 9 December, collected from D. pedunculatus with a shell of Tonna luteostoma (Küster, 1857) caught with a gill net at depths of 5–50m, head region dissected for observation of jaw morphology. Exact coordinates of sampling localities unavailable. Diagnosis: Prostomium with two antennae protruding forward. Branchiae cirriform without branching, present from chaetiger 1, and inserted dorsally.Parapodia uniramous with 3–5 supraacicular simple chaetae, 6–10 subacicular compound chaetae, and 1 or 2 slender capillary chaetae. Pygidium with two cirri. Sex dimorphism present; female jaws P-type; male jaws K-type. Description: Body flattened, tapered in posterior region (Fig. 3C, D). Prostomium rounded without eyespots. Two digitiform antennae dorsally protruding forward on prostomium; mature female antennae long, extending beyond prostomium (Fig. 3E); male antennae short, not extending beyond prostomium (Fig. 3D). Peristomium represented by two apodous achaetous rings, 1st ring slightly longer than 2nd ring (Fig. 3D, E). Palps absent. Chaetae present at first segment after peristomium (Fig. 3E). Branchiae cirriform inserted dorsally (Fig. 3F) and present from chaetiger 1 (Fig. 3E). Parapodia uniramous with a rounded acicular lobe and papilliform dorsal cirri (Fig. 4A, B). Three kinds of chaetae present; 3–5 supraacicular simple chaetae with hook-shaped tips (Fig. 4D, F); 7–10 subacicular compound chaetae slightly serrated (Fig. 4E, G); at ventralmost, 1–3 slender capillary chaetae curved up dorsally or just extending laterally (Fig. 4A, B). Paired pygidial cirri digitiform shorter than antennae (Fig. 3G). Female (holotype): 10.6 cm in length, 3.0 mm in maximum width for 403 chaetigers (Fig. 3C). Two long digitiform antennae 2.1 mm in length, extending beyond prostomium (Fig.3E). Branchiae first digitiform, tapering and becoming longer in mid-body but shorter in the posterior 20 segments (Fig. 3C). Chaetae comprising of 3 supraacicular simple, 9 or 10 subacicular compound, and 1–3 slender capillary chaetae (Fig. 4A, C–E). Subacicular compound chaetae more dorsally socketed in posterior part of body. Paired short pygidial cirri about 0.9 mm in length (Fig. 3G), shorter than antennae (Fig. 3E). Mandibles lost during preparation. P-type maxillae 490 μm in length with six pairs of denticles fused with each other; maxilla I with at least eight teeth, maxilla II with at least six teeth, and maxilla III with at least six coarse teeth variously developed (Fig. 5A, B). The posteriormost denticles (maxillae III–VI) fused with each other (Fig. 5A, B). Eggs about 120 μm diameter found between the branchiae (Fig. 3C). Male (paratype 1): 4.0 mm in length, 1.2 mm in maximum width for 79 chaetigers (Fig.3D). Two short digitiform antennae 0.5 mm in length, without extending beyond prostomium (Fig.3D). Branchiae first digitiform, tapering and becoming longer in mid-body but shorter in the posterior 20 segments (Fig. 3D). Chaetae comprising of 5 supraacicular simple, 6 subacicular compound, and 1 or 2 slender capillary chaetae (Fig. 4B, F, G). Pygidial cirri lost. Rod-like mandibles 350 μm in length, strongly sclerotized, comprising of two shafts distally widening and smooth; distal cutting edge without serration (Fig. 5C, D). K-type maxillae 600 μm in length, with smooth ice tong-shaped forceps and at least one free-denticle (Fig. 5C, D). Distribution and habitat: The species is found inside the apex of shells carried by hermit crabs (D. pedunculatus and D. crassimanus) with small amounts of mud possibly host faeces (Fig. 3A, B). They are only known from the type locality, off Minabe, Wakayama, Japan, at depths of 5– 50m. Two to four worms were found in a single shell, including a large female and multiple smaller males. Etymology: The specific epithet originates from the Latin word for ‘cloudy’ or ‘foggy’, inspired by the Cloud Dragon painting ‘Unryû-zu’ on the ceiling of Tenryu-ji Temple in Kyoto, Japan. It describes the species’ prominent dorsal branchiae, reminiscent of dragon scales, and their attachment to the ventral surface inside their host hermit crab shells, reminiscent of the painting. Remarks The new species can be distinguished from other described species by combination of several morphological characters. The prostomium has two antennae protruding forward, in contrast to several dorvilleids. The branchiae are cirriform and lack branching, unlike I. cuenoti, I. doederleini, and I. loxorhynchi, which have branched branchiae. Additionally, the branchiae are present from chaetiger 1, whereas in I. paguri, I. loxorhynchi, I. holobranchiata (possible junior synonym of I. loxorhynchi; see below), Iphitime sartorae de Paiva & Nonato, 1991, and I. hartmanae, branchiae appear chaetigers 2–5. The branchiae are inserted dorsally, distinguishing the new species from I. cuenoti, I. doederleini, I. loxorhynchi, and I. holobranchiata, where the branchiae are inserted dorsolaterally. The number of chaetae, pygidium cirri, and the presence of sex dimorphism further differentiated the new species from the congeneric species. Iphitime nubila resembles I. paguri from Europe, though they are not closely related suggesting that having hermit crab hosts has evolved twice (Figs 1, 2). Both species have cirriform unbranched branchiae, exhibit sexual dimorphisms in jaw morphology, and utilize hermit crabs as hosts. However, I. nubila can be distinguished from I. paguri by the insertion position of the branchiae (Fig. 3E); in I. nubila, they insert from chaetiger 1 (Fig. 3E), whereas in I. paguri, they are present from chaetiger 4–5 (HØisaeter and Samuelsen 2006). The ML tree topology inferred that I. nubila was sister to I. loxorhynchi fromsouthernCalifornia(Fig.1), althoughthesupportvalue was quite low.The two species can be distinguished by the insertion position of the branchiae (chaetiger 1 in I. nubila vs. 2 in I. loxorhynchi), and the numbers of supraacicular simple chaetae (3–5 in I. nubila vs. 20 in I. loxorhynchi) and subacicular compound chaetae (6–10 in I. nubila vs. 20 or more in I. loxorhynchi) (Hartman 1952). Furthermore, the branchiae of I.nubila are entirely cirriform without distal branching as reported in I. loxorhynchi (Hartman 1952).