Polydora mohammadi, Radashevsky & Al-Kandari & Malyar & Pankova, 2024

Radashevsky, Vasily I., Al-Kandari, Manal, Malyar, Vasily V. & Pankova, Victoria V., 2024, A twin of Polydora hoplura (Annelida: Spionidae) from the Arabian (Persian) Gulf, with review of primers used for barcoding of Spionidae, Zootaxa 5529 (2), pp. 245-268 : 252-258

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 with P. hoplura . Adults of both species bore in shells of molluscs and other calcareous structures and have palps with black bands, prostomium weakly incised anteriorly, caruncle extending to the end of chaetiger 3, short occipital antenna, and two kinds of heavy spines in the posterior notopodia. However, they differ in ochre pigment on the anterior chaetigers in life, a pattern of pigmentation after fixation in formalin, and a pattern of methyl green staining of fixed specimens. They also differ in the dimensions of mature spermatozoa. Moreover, P. hoplura is probably parthenogenic ( Radashevsky et al. 2023a), whereas P. mohammadi sp. nov. is likely dioecious with a sex ratio close to equal.

Although adult external morphology and black pigmentation, which is present in live individuals and remains after fixation, were described many times for P. hoplura from different localities by different authors, the post-fixation pigmentation and methyl green staining pattern in fixed specimens were never reported. Live individuals of P. mohammadi sp. nov. have ochre spots usually on the dorsal side of chaetigers 4 and 5 but occasionally from chaetiger 3 to chaetiger 6, while adult P. hoplura have no such a pigment. After fixation in formalin, paired patches or transverse bands of dark ochre pigment appear on the dorsal side of the posterior chaetigers in P. mohammadi sp. nov. In P. hoplura , paired patches of the same pigment of lower intensity appear only on the posterior branchiate chaetigers, but not on the postbranchiate chaetigers with heavy spines in the notopodia. The same ochre (brownishyellow or yellowish-orange) pigment appears in specimens of some other Polydora species after fixation with formalin. For example, the presence of an ochre pigment in fixed specimens of P. manchenkoi Radashevsky & Pankova, 2006 was used to distinguish them from those of P. calcarea , which appear very similar, but do not have such a pigment ( Radashevsky & Pankova 2006).

MG staining has been successfully used to distinguish similar adult annelids from different families (e.g., Hofsommer 1913; Banse 1970; Fitzhugh 1983; Winsnes 1985). Among spionids, adults of some species do not absorb the dye at all or are stained weakly and evenly, while others are stained in a specific pattern (e.g., Meissner & Hutchings 2003; Doner & Blake 2009; Simon et al. 2019; Radashevsky et al. 2021a). The case of P. mohammadi sp. nov. is somewhat confusing. While most of the specimens were stained only from chaetigers 9–10 dorsally and from chaetiger 7 ventrally, one specimen (genetically identical to the others) was stained according to the pattern characteristic of P. hoplura . This means that MG staining should be used with caution for identification purposes and, if possible, a large series of individuals should be stained to identify a species-specific pattern and its variability.

Etymology. The species is named after zoologist Murad-B. M. Mohammad who studied polychaetes of Kuwait from 1966 to 1981, described 24 new species, several new genera, and provided checklists of the polychaete fauna of Kuwait ( Mohammad 1971, 1980).

Distribution. Arabian Gulf, Kuwait.

Figures

FIGURE 1. Majority rule consensus tree of the Bayesian inference analysis of the combined COI (1134 bp), 16S (248 bp), 18S (1572 bp), 28S (228 bp), and Histone 3 (299 bp) sequences (3481 bp in total) of Polydora spp. rooted with sequences of Polydora brevipalpa Zachs, 1933. Posterior probabilities are shown on the branches.The numbers preceding collecting locations are unique numbers from the VIR database linking the individuals on the tree with the sampling data in Table 1; numbers of individuals/isolates are separated from sample numbers by dots.

FIGURE 3. Methyl green staining of Polydora hoplura (formalin-fixed specimens; palps missing). A, general view. B, anterior end, ventral view. C, anterior end, left lateral view. D, anterior end, curved. E, anterior end, dorsal view. F, middle chaetigers, dorsal view. Abbreviation: an = occipital antenna, br = branchiae, ch5 = chaetiger 5. Scale bars: A = 500 µm, B−F = 200 µm. A—Mar Grande of Taranto, Italy (MIMB 33029), B−F—Gulf of Naples, Italy (MIMB 28148).

FIGURE 4. Adult morphology and reproduction of Polydora mohammadi sp. nov. from the Arabian Gulf, Kuwait (in life). A, complete individual, dorsal view, showing white gatherings of glandular cells on dorsal side of median chaetigers. B, anterior end, dorsal view, showing small spots of ochre pigment on chaetigers 4 and 5. C, posterior end, dorsal view. D, E, part of egg capsules brooded by female inside burrow in a shell of the pearl oyster Pinctada margaritifera. Scale bars: A = 0.3 mm, B, C = 0.1 mm, D, E = 0.5 mm. A−E—MIMB 42695.

FIGURE 5. Adult morphology of Polydora mohammadi sp. nov. from the Arabian Gulf, Kuwait. A, B, palps with black bands on sides of frontal groove. C, anterior end, left lateral view.D, female fertile chaetigers, left lateral view, showing nephridia stained with MG (arrows). E, chaetiger 5 chaetae of a 33-chaetiger juvenile. F, G, chaetiger 5 chaetae of large mature individuals.Abbreviations: an = occipital antenna, br = branchiae, ch5 = chaetiger 5, co = bilimbate companion chaetae, fa = heavy falcate spines, su = dorsal superior capillaries, ve = ventral capillaries. Scale bars:A−C = 200 µm, D = 100 µm, E−G = 30 µm.A, C—MIMB 42698 (holotype), B—MIMB 42697, D−G—MIMB 42696. A−D—formalin-fixed specimens, C, D—stained with methyl green.

FIGURE 6. Adult morphology of Polydora mohammadi sp. nov. from the Arabian Gulf, Kuwait (in life).A, anterior end, dorsal view, showing small spots of ochre pigment on chaetigers 4 and 5. B, anterior end, ventral view. C, middle part of a palp, frontal view, showing ciliated groove bordered by low papillae bearing short non-motile cirri. D, posterior end, dorsal view. E, bidentate hooded hooks from a middle neuropodium. F, heavily recurved, sickle-shaped spines from posterior notopodia. G, right side of posterior postbranchiate chaetigers, dorsal view, showing notopodia with heavy spines in addition to slender capillaries. H, fragment of G, showing slender and slightly curved awl-like spine (aw) and heavily recurved sickle-shaped spine (si). Scale bars: A, B = 100 µm, C, E, G, H = 30 µm, D = 50 µm, F = 20 µm. A, D—MIMB 42695, B, C, E−H—MIMB 33067.

FIGURE 7. Post-fixation pigmentation and methyl green staining of Polydora mohammadi sp. nov. from the Arabian Gulf, Kuwait (formalin-fixed specimens).A, complete individual, dorsal view. B, anterior end, dorsal view. C, chaetigers 5–16, dorsal view. D, posterior branchiate chaetigers, dorsal view. E, H, I, posterior ends, dorsal view. F, G, middle chaetigers, dorsal view. Abbreviation: ch5 = chaetiger 5. Scale bars: A−E = 200 µm, F, I = 100 µm, G, H = 50 µm. A, B—MIMB 42694, C—MIMB 42696, D—MIMB 33068, E−H—MIMB 42695. A, C−E—in reflected light; B, F−I—in transmitted light; A−C, F−I—stained with methyl green; D, E—showing transverse bands of dark ochre pigment appeared after fixation in formalin; H, I—showing cells stained with methylene green and paired gatherings of dark ochre pigment appeared after fixation in formalin.

FIGURE 8. Adult morphology of Polydora mohammadi sp. nov. from the Arabian Gulf, Kuwait. A, relationships between length of caruncle (in chaetiger numbers) and total number of chaetigers in worm. B, relationships between arrangement of branchiae (referring to number of the last branchiate chaetiger), arrangement of spines in posterior notopodia (referring to number of the first chaetiger bearing awl-like and sickle-shaped spines) and total number of chaetigers in worm. C, relationships between arrangement of gametes (referring to number of the first and the last chaetiger with gametes) and total number of chaetigers in worm.

FIGURE 9. Reproductive biology of Polydora mohammadi sp. nov. from the Arabian Gulf, Kuwait (in life). A, B, coelomic sperm, showing diads of spermatocytes I, tetrads of spermatocytes II, octads of spermatids (A), and mature spermatozoa (B). C, coelomic oocytes. D, newly spawn eggs from egg capsule. E, part of egg capsules each attached by two stalks to wall of female’s burrow. Scale bars: A, B = 10 µm, C, D = 50 µm, E = 100 µm. A−E—MIMB 42696.