Dipolydora walkerae, Blake, 2025

Dipolydora walkerae new species

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Figures 1–2 View FIGURE 1 View FIGURE 2

Material examined. Gulf of Mexico, off Louisiana, continental slope, BOEM Green Canyon Lease Block 234 , HOV Johnson Sea Link Dive 2059 , June 1987, coll. WR Callender; worms removed from burrows in the columella of the gastropod Kanoia meroglypta collected from the mussel bed with a scoop sampler, 27.733°N, 91.253°W, 617 m, holotype ( FMNH 223654 ), GoogleMaps 1 paratype ( MCZ IZ 173000 ). GoogleMaps

Description. Body elongate, slightly wider anteriorly; holotype complete with 60 setigers, 8.4 mm long and 0.7 mm wide anteriorly, 0.4 mm wide posteriorly; paratype larger, also complete but damaged and not as well preserved, with 85 setigers, 17 mm long, 0.8 mm wide anteriorly, 0.5 mm wide posteriorly. Color in alcohol: light tan; only pigment from two large, curved reddish-colored peristomial glands lateral to oral vestibule.

Prostomium narrow, distinctly rounded on anterior margin ( Figs. 1A View FIGURE 1 , 2B–C View FIGURE 2 ), posteriorly extending to anterior border of setiger 1 as a caruncle ( Fig. 1A View FIGURE 1 ); occipital antenna absent; eyes absent. Palps thick, relatively short when preserved, only about as long as first 4–5 setigers ( Fig. 2A View FIGURE 2 ); each palp with narrow ventral groove lined with short cilia; cilia not observed on dorsal surface. Peristomium wide and long, rounded anteriorly and laterally ( Fig. 1A View FIGURE 1 ), interrupted dorsally by caruncle ( Fig. 1A View FIGURE 1 ) and ventrally by oral vestibule ( Fig. 2C View FIGURE 2 ).

Setiger 1 with capillary setae and postsetal lamellae in both rami; lamellae short, rounded on setigers 1–4 ( Fig. 1A View FIGURE 1 ); notosetae of setiger 1 shorter, fewer (4–5) than on setigers 2–5 (8–10); neurosetae of setiger 1 as long those on setiger 2, but fewer (6–8) than on setigers 2–4 (8–10). Posterior to setiger 5, notopodia with a row of 8–10 moderately long capillaries continuing posteriorly; these replaced in last 11–12 setigers by 6–8 long, narrow acicular spines arranged in a rosette and producing a distinct spinous appearance to the posterior end of body ( Fig. 1B View FIGURE 1 ). Each spine narrowing to pointed tip ( Figs. 1I View FIGURE 1 , 2G–H View FIGURE 2 ).

Setiger 5 twice as large as setigers 4 and 6, with 5–6 dorsal superior capillaries, six large falcate spines arranged in an oblique row, and 7–8 capillaries ventral to major spines ( Fig. 1A View FIGURE 1 ); companion setae absent between falcate spines. Dorsal superior and ventral capillaries geniculate, winged with crest of short fibrils along one edge ( Fig. 1F View FIGURE 1 ); these capillaries shorter and fewer than on setigers 4 and 6. Distal convex sides of falcate spines surmounted by a distinct dorsal crest formed by numerous fibrils ( Figs. 1C–E View FIGURE 1 , 2E View FIGURE 2 ).

Hooded hooks in neuropodia from setiger 7, up to 6–8 in a row, accompanied by 1–3 inferior winged capillaries. Hooks bidentate, with slightly recurved shaft without constriction and with wide angle between shaft and main fang in hooks from anterior and middle segments ( Fig. 1G–H View FIGURE 1 ); posterior hooks with more acute angle between teeth ( Fig. 2F View FIGURE 2 ).

Branchiae from setiger 7, full-sized from setiger 8 ( Fig. 1A View FIGURE 1 ), absent from posterior setigers from about setiger 30 in holotype and setiger 40 in paratype, or about mid-body; branchiae arising from base of notopodial postsetal lamellae, flattened, directed toward dorsal midline, but not reaching entirely across dorsum ( Fig. 1A View FIGURE 1 ); each branchia broad, with distinct blood loop ( Fig. 1A View FIGURE 1 ).

Pygidium with four large lobes ( Figs. 1B View FIGURE 1 , 2D View FIGURE 2 ), surface covered with numerous papillae; a rounded medial lobe also present between the dorsal lobes, dorsal to anal opening ( Fig. 1B View FIGURE 1 ).

Due to opaque nature of body, internal morphology not visible; thus neuropodial glandular pouches, nephridia, and digestive system not observed.

Methyl green staining. Anterior ventral and lateral border of anterior setigers retaining stain; rest of body with no staining reaction.

Remarks. Dipolydora walkerae sp. nov. belongs to a group of species having the modified spines of setiger 5 with an apical cloak or crest of fibrils and acicular spines in posterior notopodia ( Blake 1996). In D. walkerae sp. nov., the posterior acicular spines are uniquely arranged in a rosette and provide a spinous appearance to the posterior end of the body. Only two other species of Dipolydora have a similar configuration: D. armata ( Langerhans, 1880) and D. paracaulleryi Meissner, Bick, Guggolz & Götting, 2014 .

Dipolydora armata is a widespread shallow-water tropical and sub-tropical coralline boring species ( Woodwick 1964; Blake & Kudenov 1978; Blake 1983, 1996; Radashevsky & Nogueira 2003). Dipolydora walkerae sp. nov. differs from D. armata in that the major spines of setiger 5 have a shaft that curves apically to a narrowly pointed tip that is surmounted by a distinct crest formed of bristles or fibrils; the posterior notopodial spines are narrow with a pointed tip and the pygidium has four large papillated lobes and a fifth medial dorsal lobe. In contrast, D. armata has major spines with a main fang, a large lateral tooth and wide cowling or third tooth, all of which are covered with a cloak of bristles, the posterior spines that form the rosette are thick and awl-shaped, and the pygidium is a simple cup that opens dorsally.

Dipolydora paracaulleryi is known from the Meteor Seamounts west of the Canary Islands in the North Atlantic Ocean, dredged from coral and crushed shell gravel at a depth of 300 m ( Meissner et al., 2014). This species is similar to D. walkerae sp. nov. in having curved major spines on setiger 5 with pointed tips surmounted by a bristled crest and with a narrow prostomium, but this is weakly incised on the anterior end rather than entire. In addition, the prostomium of D. paracaulleryi continues posteriorly as a caruncle over setigers 1–2 instead of bluntly ending anterior to setiger 1 as in D. walkerae sp. nov. Ventrally, the peristomium of D. paracaulleryi continues posteriorly over several anterior setigers as a ventral ridge whereas a posterior extension is absent in D. walkerae sp. nov. Both species have four pygidial lobes, but these are distinctly unequal in D. paracaulleryi with the dorsal lobes being smaller; whereas in D. walkerae sp. nov. all four lobes are of an equivalent size and there is, in addition, a fifth medial lobe dorsal to the anal opening. While the posterior notopodial spines of D. walkerae sp. nov. form a rosette, these are few in D. paracaulleryi and are arranged in a curved row. Dipolydora paracaulleryi also has a distinctive methyl green staining pattern on the venter of setigers 6–7 where stained glands are concentrated medially from which a pair of bands extends laterally.

Biology. Dipolydora walkerae sp. nov. was found boring in the shells of the gastropod Kanoia meroglypta collected from mussel beds in methane seep habitats off Louisiana at an upper continental slope depth of 617 m. MacDonald et al. (1990a: fig. 4) and (1990b: fig. 2A) illustrated mussels with attached specimens of the gastropod K. meroglypta on their shells. The mussels were likely Gigantidas childressi ( Gustafson, Turner, Lutz & Vrijenhoek, 1998) , originally described in the genus Bathymodiolus .

In a letter to the author dated 05 June 1992 regarding the availability of the worms described here that were collected in June 1987, Dr. Sally E. Walker stated that “ the spionid is large in comparison to the living snail. It has burrowed through the protoconch, then, through the columella and umbilicus. ” Warén & Bouchet (2001: 133) later stated “ Several specimens ( of Kanoia meroglypta ; then in the genus Cataegis ) from the Bush Hill Seep (off Louisiana) had the shell tunneled by polychaetes of the subfamily Polydorinae , in one case so wide a tunnel that both the in and outside of the shell had been broken through. Usually the tubes were restricted to the umbilicus of the shell.” These observations suggest that D. walkerae sp. nov. is likely widespread in upper slope depths across the northern Gulf of Mexico where the gastropod, K. meroglypta is present. The degree of infestation of D. walkerae sp. nov. on these gastropods and other molluscs is unknown.

Fragmented egg capsules were present with yellow eggs and early 4-cell cleavage stages; eggs measured 138– 143 µm in diameter. Although the capsules are broken into separate pieces, they appear to have an elongate tubular shape rather than as strings of beads; attachment threads were not evident.

Etymology. This species is named for Dr. Sally E. Walker, Professor of Paleontology, University of Georgia, Athens, Georgia, USA. Dr. Walker initially discovered and removed these worms from their burrows and identified them as spionids. Having known Dr. Walker from her student days, she notified me of their availability.

Distribution. Gulf of Mexico, off Louisiana, in deep-water methane seep habitats, a borer in shells of the gastropod, Kanoia meroglypta , 617 m.