Anguillosyllis aciculata, Maciolek, 2020

Maciolek, Nancy J., 2020, Anguillosyllis (Annelida: Syllidae) from multiple deep-water locations in the northern and southern hemispheres, Zootaxa 4793 (1), pp. 1-73 : 25-27

Anguillosyllis aciculata n. sp.

Figures 5–6

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Material examined. (1 specimen) South China Sea, off Brunei. Coll. P. Neubert, Chief Scientist. Sta. SA 5, 29 Jun 2011, 5°36′56.59222″N, 113°41′07.37801″E, 2162 m, holotype ( MCZ 147935 ) .

Description. Body with 11 setigers ( Fig. 5A ), arched dorsally; 2.9 mm long, width 0.6 mm at setiger 5 without parapodia, 1.0 mm with parapodia but without setae, ca. 1.6 mm with setae, Palps slim, elongated, bean-shaped, appear free to base on dorsal surface but connected by membrane on ventral surface; tips of palps retain MB stain. Prostomium roughly circular ( Figs. 5A , 6A ); eyes lacking; no antennae or remnants of antennae seen, presumed lost. Prostomium and peristomium with glands on medial dorsal surface. Nuchal patches obvious, lateral, between prostomium and peristomium; division between pro- and peristomium otherwise not clear. Peristomium with two small, oval tentacular cirri.

Proventricle in three setigers, elongated heart shape, rounded anteriorly, tapered at posterior end ( Figs. 5A , 6 A–C); muscle rows not clearly defined, visible in mid-region in high-contrast light as thin dark bands; post-ventricle caeca with dorsal gland cells lacking or not retaining MB stain.

Dorsum uniannulate, a few median setigers with slight wrinkling or indication of biannulation. Elongate tubes and clusters of cells numerous, extending across dorsum on all setigers, round glands similar to those noted on prostomium and peristomium ( Figs. 5B , 6A, C ). Parapodia uniramous, shortest and nearly square on setiger 1, becoming longer, slimmer, rectangular over subsequent setigers; with small but obvious translucent triangular anterior lobe on setigers 2–6, largest on setigers 3 ( Fig. 5D ) and 4; posterior lobe lacking; dorsal lobe small, rounded, glandular, obvious only on setigers 1–3. Parapodia with smooth elongate internal glands associated with external clusters of tightly packed cells ( Figs. 5 D–E, 6D–E), distal end of tube narrowing and exiting through dorsal lobe or surface of parapodium, glands becoming more numerous progressing posteriorly, last few setigers packed with glands. Venter of setigers 1–5/6 with scattered glands. Dorsal cirri lost, cirrophores seen on some setigers. Ventral cirri small, slim, with wider base tapering to narrower tip, inserted midway on parapodia; cirri with glands retaining MB stain ( Fig. 6B ).

All setae compound with heterogomph shafts, with short to long blades; falcigers 40–80 µm long, with serrated blades, dark blunt tip; spiniger-like blades up to 350 um long, serrated along length, with plain fine tips; setae numbering up to 10 long-bladed and 30 short-bladed setae in setiger 1, fewer short-bladed setae in setigers 2–3; setae reduced to ca. 20 in setigers 5–11; most setae emerging from distal end of parapodium, cluster emerging from ventral face Up to four aciculae per parapodium: two anterior aciculae thin, one with distal end bent at nearly right angle, other pointed; two posterior aciculae large, stout, pointed; tips of all aciculae emerging from tissue of parapodium ( Fig. 5 D–E).

All anal cirri lost.

No eggs seen.

Remarks. Anguillosyllis aciculata n. sp. is unique in having up to four emergent aciculae in each parapodium (setiger one appears to have only two aciculae whereas the remaining setigers have 4; Fig. 5C shows only one acicula). The distal tip of the anteriormost acicula is bent at an angle; the posteriormost acicula is especially large and stout. In A. acsara n. sp., the tip of one anterior acicula was seen to be minimally emergent from the parapodium, and in A. hessleri n. sp., the tips of some aciculae emerge from the body wall, but in all other known species of Anguillosyllis , the aciculae are not emergent.

The single specimen available appears to have glands on the surface of the prostomium rather than being smooth; antennae and insertions for antennae were not seen. It would be expected that this species would have three antennae as do all other species in the genus, but because of the limited amount of material, the nature of the prostomium could not be further understood.

This species is similar to A. palpata and A. hadra n. sp. in having 11 setigers and clearly separated palps, but differs in the number and nature of the setae and in lacking posterior lobes on the parapodia; the dorsal lobes in A. aciculata n. sp. are much smaller than those observed in either A. palpata or A. hadra n. sp. Both A. palpata and A. aciculata n. sp. have a cordate proventricle that is narrowly tapered at the posterior end; in A. hadra n. sp. the proventricle is shaped differently and is only slightly tapered at the posterior end.

The areas of A. aciculata n. sp. that stain deeply with MB include the tips of the palps, the tentacular cirri, the ventral cirri, the glands in the distal portion of the parapodia, and the clusters of glands on the lateral edges of the dorsum. This pattern differs from that seen in other Anguillosyllis species, which do not retain stain on the tips of the palps but, unlike A. aciculata n. sp., do retain stain in the dorsal cells of the post-ventricle gland that wraps around the posterior end of the proventricle (see, for example, A. palpata above).

Etymology. From Latin acus meaning needle or small pin, the root of the term aciculum, in reference to the large emergent aciculae of this species.

Records. South China Sea, off Brunei, 2162 m.

Figures

FIGURE 5. Anguillosyllis aciculata n. sp. Holotype (MCZ 147935): A, entire specimen, dorsal view; B, external glands, inset not to scale. C, setiger 1; D, setiger 3; E, setiger 10. Abbreviations: acic—acicula, aL—anterior lobe, dC—dorsal cirrus, dL—dorsal lobe, ExGl—external gland, InGL—internal gland.

FIGURE 6. Anguillosyllis aciculata n. sp. Holotype (MCZ 147935): A, entire specimen, dorsal view; B, entire specimen, ventral view; C, setigers 3–7, left side; D, setiger 9, right side; E, setigers 5–6, right side. A, C: arrows indicate external glands.