Strepternos Watson Russell, 1991

Watson, Charlotte & Faulwetter, Sarah, 2017, Stylet jaws of Chrysopetalidae (Annelida), Journal of Natural History 51 (47 - 48), pp. 2863-2924 : 2888-2890

Genus Strepternos Watson Russell, 1991

( Figure 15a–f ; Tables 1, 2)

Type species: Strepternos didymopyton Watson Russell, 1991

Material examined

Two specimens Strepternos didymopyton, NTM W. 26327, Bahamas, Tongue of The Ocean, West Atlantic Ocean (mCT-00023; mCT-00101)

Distribution

Strepternos is a deep-water taxon found in the West Atlantic . It has been examined from sites along the eastern seaboard of the Americas, ~ 40°N to ~ 25°S, including off Massachusetts , two sites in the Caribbean Sea ( Bahama Islands and St. Croix, Virgin Islands) and most recently from Brazil (Shimabukuro, pers. comm.) .

Habitat

Strepternos has been collected solely from ‘wild’ and experimental wood habitats, ~ 1800– 4000 m depth, which are colonized primarily by the wood-boring molluscs Xylophaga Turton, 1822 and Xyloredo Turner, 1972 ( Turner 1978; Watson Russell 1991, 1997).

General morphology

Strepternos didymopyton is a large polychaete with a distinctive broadened anterior end and a pair of pale golden-coloured notochaetal paleal fans that cover most of the

dorsum. Main paleae are symmetrical with slightly raised ribs; the median fascicle is lacking, leaving a mid-dorsal bare section on the anterior body ( Figure 15a ). Sensory structures include a very small prostomium fused with anterior segments and capable of being completely retracted ( Watson Russell 1997, figure 7A); simple eyes present in larvae and juveniles (absent in adults), broad, elongate-ovate palps and a relatively small nuchal fold. Dorsal styles appear partly retractile within the large cirrophores ( Watson Russell 1991). Larval and juvenile morphology has been documented during settlement and metamorphosis ( Watson Russell 1991, 1997).

Pharynx and jaws

Strepternos possesses a relatively short, broad proboscis and an undifferentiated, broad pharynx with posterior large caeca ( Figure 15b–d ). The pair of jaws are broad, robust and heavily calcified. The anterior halves diverge, turning outwards, the posterior halves of each jaw are set close together with the basal-most cross sections indicating interlinking of jaws ( Figure 15f ). The jaws possess a pronounced mid-way projection on the outer jaw margin that flares out in the form of a ‘shelf’, marked by a distinct raised, horizontal ridge; the interior groove is very wide ( Figure 15e, f ). The thick distal jaw tips are serrated on the convex margin when viewed under a compound microscope ( Watson Russell 1991, p. 291, figure 4 Y2).

Figures

Figure 15. Anterior end of Strepternos didimopyton (mCT-00101), imaged through micro-CT and rendered in 3D. (a) dorsal view; (b) dorsal view with lowered opacity to show position of jaws; (c) dorsal view, virtually dissected to expose pharyngeal structures; (d) lateral view, virtually dissected to expose pharyngeal structures; (e and f) jaws of Strepternos didimopyton (mCT-00023), (e) anterior view; (f) dorsal view and cross sections through the jaw along its length.