Parahesione dudahamra sp. nov.

Zoobank LSID: urn:lsid:zoobank.org:act: 41B7FC87-5648-4843-B3DC-3E4DEF4647E6

(Figs. 1–5)

Diagnosis. Lateral antennae simple, without distinct ceratophores; palps biarticulate, with style abruptly narrowing to thin distal half. Eight pairs of tentacular cirri; longest dorsal cirri reaching chaetiger 12, longest ventral cirri reaching chaetiger 4. Dorsal foliose lobes of parapodia without projections, with bluntly pointed tips.

Type material. Holotype FLMNH UF 12510, Saudi Arabia, Makkah Governate, Thuwal, KAUST, King Abdullah Monument, 22.340608°N 39.087519°E, sandflat adjacent to mangroves, suction pump, in burrow near mangrove roots, depth 0.3–0.5 m at low tide; leg. A. Anker, V. Syomin, G. Kolbasova, 1 March 2025 [fcn KSA_ 42858]. Originally complete specimen with regenerating left parapodium in chaetiger 16. Body 32 mm long, with 51 chaetigers. Maximum body width 2 mm without parapodia, 5 mm with parapodia. Pharynx not everted. Fixation: 4% formalin, transferred to 70% ethanol. Parapodia from chaetigers 16 to 18 (left side) dissected for DNA extraction and fixed with 96% ethanol. Parapodia of chaetigers 1 and 19 (left side) dissected and mounted on slides for study under compound microscope.

Description. Body depressed, tapering posteriorly (Fig. 2). Prostomium rectangular, wider than long (Fig. 3A). Lateral antennae as long as prostomium, cylindrical, with narrow tips, simple, inserted directly on minute elevations on prostomium (Fig. 3C). Palps slightly longer than antennae, biarticulate; style basally thick, abruptly narrowing to thin distal half. Palpophore as long as half of style. Eyes brownish, two pairs of equally sized spots (Fig. 3A).

Pharynx not everted in holotype. Elongated cirri in segments 1–5: 8 pairs of tentacular cirri in segments 1–4 and elongated dorsal parapodial cirri in segment 5 (i.e., chaetiger 1). Tentacular cirri smooth. Ventral pair in segment 3 considerably shorter and thinner than in other segments. Cirrophores of tentacular cirri cylindrical, basally fused, without aciculae. Longest dorsal tentacular cirri reaching chaetiger 12; longest ventral tentacular cirri reaching chaetiger 4.

Segments 1–4 without chaetae; 1 st chaetiger is segment 5. Parapodia of chaetiger 1 uniramous. Dorsal cirrus reaching chaetiger 5, with cylindrical cirrophore, smooth cirrostyle, without notoaciculum. Neuropodium underdeveloped compared to subsequent parapodia, posterodorsal projection short (Fig. 4A); with about 15 heterogomph chaetae, superior ones regular, coarsely serrated spinigers (Fig. 4B). Length and shape of blades gradually changing in ventral direction. Inferior neurochaetae 3–4.6 times shorter than superior ones; length to width ratio of blades decreasing from 23 to 4, accordingly; medium neurochaetae with fine serrations along their entire length (Fig. 4C, D); inferior neurochaetae with faint serrations only in basal part (Fig. 4E). All chaetae variable in shape within same type; true falcigers absent.

All subsequent parapodia biramous. Notopodia small, bluntly conical, with about 60 simple capillary notochaetae, each serrated along most of their length; notoaciculum single, not protruding, transparent in fixed specimen (Fig. 5A); each notopodium with dorsal foliose lobe (Fig. 3B, D, E). Lobes narrow, with fringed edge from base to approximately 1/4 of parapodial length, usually marked by noticeable notch (Fig. 3E); gradually broader and gaining asymmetrical leaf-like shape from 2 nd quarter of parapodial length; each lobe partially covering subsequent parapodium; lobe tips rounded or bluntly pointed, without digitiform projection. In anterior third of body, from chaetiger 6, all lobe tips with compact glands in form of swellings with granulose contents, barely seen in living animal (Fig. 2), more distinct after fixation (Fig. 3B, D, E); in anteriormost 5 chaetigers and second third of body, glands occurring randomly in about half of lobes on either side of body; posterior third of body without glands. Posterior margin of each lobe edged by row of regularly spaced ciliary tufts (Fig. 3D), latter less numerous and not forming regular row, or absent, in posterior third of body. Dorsal cirrophores cylindrical, fused with dorsal foliose lobe (Fig. 5A); dorsal cirrostyle tapering, smooth; its length slightly exceeding that of parapodium.

Neuropodia large, truncate, longer than wide, with distinct prechaetal lobe, smaller postchaetal lobe, and digitiform posterodorsal projection (Fig. 5A). In most chaetigers except chaetiger 1, each neuropodium with about 15 supraacicular spinigers and 30 subacicular falcigers, all heterogomph with unidentate blades, their length within bundle decreasing 3.8–4.9 times from superior spinigers to inferior falcigers, along with slightly increasing thickness of chaetae (Fig. 5B–E). Spinigers coarsely serrated along their entire length (Fig. 5B). Blades of superior falcigers as long as those of medium spinigers, with fine but distinct serrations in proximal 1/2–2/3 of length (Fig. 5C). Towards middle of bundle, serrations becoming barely distinguishable, occupying less than half blade length, or absent; inferior falcigers with smooth blades (Fig. 5D, E). Neuroaciculum single, not protruding, with transparent sheath and dark core. Ventral cirrophores fused to parapodium; ventral cirrostyles short, extending beyond neuropodial lobes, conical, smooth.

Pygidium with 2 smooth anal cirri as long as 12 posterior chaetigers, mounted on massive cirrophores.

Colour: body bright red in life (Fig. 2), pale beige-orange after fixation (Fig. 3B); foliose parapodial lobes transparent, barely visible in living worms (Fig. 2C), opaque whitish with chalk-white tips after fixation (Fig. 3B, E), each lobe with central dark spot composed of granules of brown pigment (Figs. 2, 3B, D); bases of dorsal cirrophores of segments 4 and 5 with brown spots (Fig. 2B).

Etymology. The specific epithet “dudahamra ” stands for “red worm” in Arabic language (دودة حمراء = dudat hamra’ or, simplified, duda hamra), referring to the bright red colour of the new worm species; used as a noun in apposition.

Distribution. North-western Indian Ocean: presently known only from the type locality in the central Red Sea (Thuwal, north of Jeddah, Saudi Arabia).

Ecology. The holotype was extracted from a burrow of an unknown host; the burrow entrance was a small hole in muddy sand close to mangrove roots, at a depth of 0.3–0.5 m. The rich burrowing infauna of the type locality, which is still being studied taxonomically, included acorn worms, echiurans, sipunculids, various polychaetes and decapod and stomatopod crustaceans. Among the burrowing decapods, five species of snapping shrimps (Alpheus spp.) and at least eight species of ghost and mud-shrimps in the families Callichiridae (3 species), Callianassidae (2 species), Eucalliacidae (1 species) and Laomediidae (2 species) were identified (Anker, in prep.), including a large callichirid species preliminarily identified as Neocallichirus cf. vigilax (De Man, 1916). Since the two species of Parahesione described by Jimi et al. (2023) were coinhabiting burrows of callichirids (Neocallichirus jousseaumei, Glypturus armatus) and upogebiid (Upogebia sp.), it is possible that P. dudahamra sp. nov. is associated with one of the Red Sea species of Neocallichirus, such as N. cf. vigilax or N. jousseaumei, or with Glypturus laurae (de Saint-Laurent in de Vaugelas & de Saint-Laurent, 1984). Within the studied area, P. dudahamra sp. nov. appears to be very rare: a considerable sampling effort to collect additional specimens of the new species (specifically targeting possible ghost-shrimp burrows but also other burrows) was unsuccessful.

Remarks. Parahesione dudahamra sp. nov. belongs to the same species group as the two species described by Jimi et al. (2023), viz. P. apiculata and P. pulvinata, characterised by eight pairs of tentacular cirri. The most reliable difference of the new species from the Red Sea from the two western Pacific species is the absence of distinct ceratophores in the lateral antennae. In P. dudahamra sp. nov., the lateral antennae are attached directly to minute elevations of the prostomium, which could represent rudimentary ceratophores fused to the prostomium. Other diagnostic features of P. dudahamra sp. nov. include the higher number of chaetae per parapodium, around 60 notochaetae and 45 neurochaetae in the new species vs. about 40 notochaetae and 30 neurochaetae in P. apiculata and P. pulvinata; the relatively longer dorsal tentacular cirri, the longest reaching chaetiger 12 in the new species vs. reaching chaetiger 8 in P. apiculata and P. pulvinata; the relatively shorter ventral cirri, reaching chaetiger 4 in the new species vs. reaching chaetigers 7 and 5 in P. apiculata and P. pulvinata, respectively; and the presence of granulose swellings on the tips of foliose dorsal parapodial lobes in the new species, which are more distinct after fixation, and which are absent in both western Pacific species (cf. Fig. 3; Jimi et al. 2023: figs. 3A, C and 7A, C, E). Results of the phylogenetic analysis of Parahesione are discussed below.

The holotype of P. dudahamra sp. nov., with full body length 32 mm and 51 chaetigers, is larger than any of the specimens reported in Jimi et. al. (2023), with the longest specimens measuring 19.5–20 mm for 45–48 chaetigers. Since the number of chaetae per parapodium can be a size-dependent feature, it cannot be used for distinguishing the new species from its congeners until its variability is known for smaller individuals. On the other hand, while the dorsal cirri in the holotype of P. dudahamra sp. nov. are longer than in P. apiculata and P. pulvinata, its ventral ones are shorter than in the previously described species. Therefore, this character can be used as a secondary diagnostic feature to distinguish the new species from P. apiculata and P. pulvinata, in addition to the absence of ceratophores in the lateral antennae. The granulose swellings in the tips of dorsal foliose lobes are absent in the western Pacific species (Jimi et al., 2023; N. Jimi, pers. comm.). It is possible that this character emerges only in mature individuals; therefore it can be used as a secondary diagnostic character for large specimens, but its inclusion in the diagnoses requires additional material of different sizes.