Polydora mohammadi Radashevsky, Al-Kandari, Malyar & Pankova, 2024, sp. nov.

Polydora mohammadi sp. nov. http://zoobank.org/ urn:lsid:zoobank.org:act: 2132ECD6-381C-4010-898B-15E84F2B0A9F Figures 4–9 Polydora hoplura (?): Mohammad 1971: 296. Not Claparède 1868. Polydora aff. hoplura: Al-Kandari et al. 2019: 9. Not Claparède 1868. Material examined. Arabian Gulf, Kuwait: Kuwait Bay, 29.333ºN, 48.0947ºE, st. 5, coll. Mohammad, M.-B.M., 1968, NHMUK 1969.230 (3 paratypes). Failaka Is., 29.3916ºN, 48.3989ºE: 25 Dec 2014, coll. Grintsov, V.A., in shell limestone, MIMB 42192 (1 paratype); 11 Feb 2020, coll. Radashevsky, V.I., in shell of razor clam Pinna bicolor Gmelin, MIMB 42696 (15 paratypes), MIMB 42697 (1 paratype), MIMB 42698 (holotype). Al-Judailiat, 29.377ºN, 47.759ºE, 4 Feb 2015, coll. Radashevsky, V.I., MIMB 33067 (1 paratype). Auha Is., 29.3764ºN, 48.4391ºE, coll. Radashevsky, V.I.: 10 Feb 2016, in shell of spiny oyster Spondylus spinosus Schreibers, MIMB 33068 (1 paratype); 13 Feb 2020, in shell of pearl oyster Pinctada margaritifera (Linnaeus), MIMB 42695 (5 paratypes). Ras Ajuza, Kuwait City, 29.3913ºN, 47.9967ºE, in shell limestone, coll. Radashevsky, V.I.: 6 Jan 2015, MIMB 42693 (2 paratypes); 13 Mar 2017, MIMB 42694 (4 paratypes). Adult morphology. Adults up to 30 mm long, 1.6 mm wide for 140 chaetigers; holotype 26 mm long, 1.0 mm wide at chaetiger 7 for 132 chaetigers. Body pale to light tan in life; with numerous glandular cells on dorsal side from chaetigers 10–12 onwards giving dorsum whitish appearance in life (Fig. 4A). A pair of rounded whitish spots (gatherings of glandular cells) present on ventral side of chaetiger 7. Up to 11 paired black bands (10 in holotype) present on palps on sides of frontal ciliated groove in individuals with more than 100 chaetigers (Fig. 5A, B); smaller worms without pigment on palps. Small spots of ochre pigment scattered on dorsal side of chaetigers 4 and 5 in individuals of all sizes in life (Figs 4B, 6A); a few spots present also on chaetigers 3 and 6 in some individuals; ochre pigment on anterior chaetigers absent in fixed specimens. Paired patches of small spots of dark ochre pigment present on dorso-lateral sides of 10–30 posterior chaetigers in formalin-fixed specimens with more than 50–60 chaetigers (Fig. 7H, I); in some specimens ochre pigment arranged in transverse bands across dorsal side of chaetigers (Fig. 7D, E). Prostomium anteriorly rounded to blunt, with frontal margin entire to weakly incised, posteriorly extending to end of chaetiger 3 as a low caruncle, shorter in small individuals (Fig. 8A). Short occipital antenna present on prostomium between palp bases in individuals with more than 50 chaetigers (Fig. 5C), absent in smaller worms; antenna easily broken during treatment and fixation of specimens.Two to four black eyes usually present, occasionally eyes absent. Palps as long as 15–20 chaetigers, with frontal longitudinal groove lined with numerous short cilia, fronto-lateral motile compound cilia, and small papillae with short non-motile compound cilia arranged on sides of frontal groove in 2–3 rows and also individually scattered on lateral and abfrontal palp surfaces (Fig. 6C). Chaetiger 1 with short capillaries in neuropodia and small postchaetal lamellae in both rami; notochaetae absent. Notopodia of 7–20 posterior chaetigers with two kinds of heavy spines in addition to 2–6 slender capillaries. Those comprising slender, slightly curved awl-like spines, and larger, heavily recurved sickle-shaped spines (Figs 4C, 6D, F–H). Awl-like spines usually present in notopodia (from chaetiger 117 in holotype) a few chaetigers after posterior branchiate chaetiger (chaetiger 116 in holotype), and 1–8 chaetigers before beginning of large sickle-shaped spines (chaetiger 118 in holotype); occasionally absent in some notopodia. In large individuals, spines beginning from more posterior notopodia (Fig. 8B). Chaetiger 5 twice as large as chaetiger 4 or 6, dorsally overlapping chaetiger 6, with up to five dorsal superior winged geniculate capillaries, seven heavy falcate spines arranged in a slightly curved diagonal row and alternating with pennoned companion chaetae, and seven ventral winged capillaries (Figs 4B, 5E–G, 6A, B, 7C). Dorsal superior and ventral capillaries shorter and fewer than those on chaetiger 4 or 6. In small individuals with up to 40– 60 chaetigers, falcate spines with lateral tooth connected by thin sheath to main shaft on one side and a small spur on another side (Fig. 5E). In larger individuals, lateral spur usually not seen; lateral tooth with sheath partly broken (especially in anterior older spines) and appearing as a thin semioval or subtriangular structure (Fig. 5F, G). Hooded hooks in neuropodia from chaetiger 7, up to ten in a series, not accompanied by capillaries. Hooks bidentate; shaft slightly curved, with constriction in upper part (Fig. 6E). Branchiae from chaetiger 7 through most of body (Figs 4A, 5C, 8B), full-sized from chaetigers 9–11, gradually diminishing in size along posterior half of body. Branchiae flattened, with surfaces oriented parallel to body axis, free from notopodial postchaetal lamellae, with longitudinal band of cilia along inner surface. Nototrochs from chaetiger 7 onwards, each composed of one row of short cilia in both sexes, on branchiate chaetigers extending onto branchiae. Pygidium cup-shaped to disc-like with dorsal gap to incision, white due to numerous fusiform glandular cells with striated content (Figs 4A, C, 6D, 7E, I). Glandular pouches in neuropodia from chaetiger 7, large in chaetigers 7–9, diminishing in size in succeeding chaetigers. Digestive tract without ventral buccal bulb and gizzard-like structure. Nephridia from chaetiger 7 onwards, opening to exterior dorsally via two separate nephridiopores on each chaetiger. In gravid females, ascending lateral and dorsal parts of nephridia in fertile chaetigers easily absorbing MG dye and thus marking fertile chaetigers (Fig. 5D). Methyl green staining. All type specimens (31 complete worms and anterior fragments) originally fixed in formalin and then transferred to 70% ethanol were stained with MG. Thirty specimens showed the same pattern of staining, including intensely stained paired blotches (dense gatherings of stained individual cells) on the dorsal side from chaetigers 9–10 onwards (Fig. 7A–C, F–I), and narrow transverse bands on the anterior and posterior edges on the ventral side from chaetiger 7 to chaetigers 20–40. Prostomium, peristomium and the anterior chaetigers (8–9 chaetigers on dorsal side and 6 chaetigers on ventral side) did not absorb the dye. One specimen (MIMB 33068 = VIR 19861), in addition to dense dorsal staining from chaetiger 10 onwards, was densely stained on the prostomium, peristomium and dorsal and ventral sides of chaetigers 1–4 in the same pattern as illustrated above for P. hoplura (Fig. 3A–F). However, genetically this specimen was identical to other worms from Kuwait (Fig. 1). Habitat. Adults of P. mohammadi sp. nov. were found in the intertidal and shallow water boring in shells of the pearl oyster Pinctada margaritifera (Linnaeus), the spiny oyster Spondylus spinosus Schreibers, the razor clam Pinna bicolor Gmelin, and shell and coral limestone. Worms were relatively rare and did not form numerous colonies. Up to three individuals were found in one shell. The U-shaped burrows of the worms were similar to those previously illustrated for P. hoplura (Radashevsky et al. 2023a: fig. 4G). Reproduction. Polydora mohammadi sp. nov. is dioecious. Of the 11 sexually mature individuals studied, seven were males and four were females. The smallest mature worms had about 50 chaetigers. In both females and males, gametes develop from chaetigers 20–35 to chaetigers 22–115 (Fig. 11C) in gonads on blind extensions (genital vessels) of segmental blood vessels. The holotype is a male with sperm present in chaetigers 35–115. Spermatogonia proliferate in testes; spermatogenesis occurs in the coelomic cavity. Spermatids, each 3–4 µm in diameter, were interconnected in octads (Fig. 9A). Spermatozoa were introsperm less than 1 µm in diameter, with pointed acrosome about 3 µm, nucleus 5 µm, midpiece 4 µm (head + midpiece about 12 µm), and a flagellum about 50 µm long (Fig. 9B). Oogenesis is intraovarian. Developed oocytes accumulate in the coelomic cavity prior to spawning (Fig. 9C). Females lay eggs into thin transparent capsules joined to each other in a string and each attached by two thin stalks to the inner wall of the burrow (Figs 4D, E, 9E). Large females deposit up to 70 eggs in one capsule, up to 81 capsules and 4500 eggs in one brood; small females deposit smaller broods. Eggs were slightly oval, 105–112 µm in diameter, with smooth envelope less than 1 µm thick (Fig. 9D). Embryonic and larval development were not observed, thus it remains unknown if all the eggs develop into larvae or if some are nurse and consumed by the developing larvae. Females brooding egg capsules in burrows had the next generation of oocytes developing in the ovaries. Thus, each female probably raises several broods over a long breeding period. Egg capsules in burrows were found in the Arabian Gulf in February 2020. Remarks. Worms like those described herein as P. mohammadi sp. nov. were collected “on rocks” (station 5) in Kuwait City and assigned to P. hoplura by Mohammad (1971: 296). Mohammad’s material is deposited in the Natural History Museum, London (NHMUK 1969.230) and contains three large individuals in pieces in very good condition, including two anterior fragments, two middle fragments, three posterior fragments, and one almost complete specimen (about 1.3 mm wide, 25 mm long for 112 chaetigers) without pygidium. Most likely, Mohammad collected worms that were boring into shell/coral limestone, which is common in Kuwaiti intertidal and shallow water. During our research, we also found worms of the same morphology in this habitat. Polydora mohammadi sp. nov. shares habitat and main morphological characters