Anguillosyllis hessleri, 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 : 59-60

Anguillosyllis hessleri n. sp.

Figures 29–30A urn:lsid:zoobank.org:act:04177057-7E4B-49C7-91DD-14A880E9BB1D

Material examined. (3 specimens from 3 stations, 3 samples) Abyssal Pacific Ocean, Clarion-Clipperton Fracture Zone. NOAA DOMES Site C , coll. R.R. Hessler, ECHO I, sample H353, Sandia box corer, 18 June 1983, 14 o 42.09ʹN, 125 o 24.27ʹW, 4516 m, 1 specimen, damaged ( LACM-AHF Poly 10171 ) ; sample H356, Sandia box corer, 21 June 1983, 14 o 42.45ʹN, 125 o 24.27ʹW, 4518 m, holotype ( LACM-AHF Poly 10169 ) ; sample H362, Sandia box corer, 18 June 1983, 14 o 42.08ʹN, 125 o 25.86ʹW, 4480 m, paratype ( LACM-AHF Poly 10170 ) .

Description. Body with 11 setigers (holotype and paratype) ( Figs. 29A , 30A ), third specimen smaller, damaged, with 10 setigers, colorless, opaque; holotype complete, 3.8 mm long without anal cirri, 0.5 mm wide without parapodia, 1.2 mm wide with parapodia but excluding setae; paratype 2 mm long, appearing linear or rectangular in overall shape. Palps elongated, completely fused, anterior margin bluntly rounded with small medial indentation, median furrow faintly visible ( Figs. 29A , 30A ); prostomium dome-shaped, demarcation with peristomium indistinguishable, both appearing as one large dome-shaped unit ( Figs. 29A , 30A ); one antenna present, others presumably lost; eyes lacking; peristomium with two oval tentacular cirri. Small nuchal patches between prostomium and peristomium seen with Shirlastain A and MG as area staining darker than surrounding tissue. Proventricle in two setigers, blocky and bluntly barrel-shaped, occupying width of body ( Figs. 29A , 30A ), rows of muscle cells at least 10, but mostly obscured by opaque body wall; post-ventricle caeca with dorsal circlet of cells retaining MG stain ( Fig. 30A ).

Parapodia uniramous, shortest on setigers 1 and 2, longer, rectangular, with truncate distal margin on setigers 3–10, becoming slightly shorter on setiger 11; anterior lobe from setiger 1, obvious in anterior setigers, becoming reduced or absent in posterior setigers ( Fig. 29 B–G); posterior lobe absent; dorsal lobe or hood low, not obvious. Internal parapodial glands noticeable from setiger 2, elongated, sac-like, becoming larger, through setiger 9, numbering 3–5 per parapodium, wrapped around posterior aciculae ( Fig. 29 C–G). Dorsal cirri filiform, retained only on setiger 1 ( Fig. 30A ). Ventral cirri slim, digitiform, inserted in middle of parapodium, may extend beyond parapodium ( Fig. 29E ). Small, rounded external structures, possibly glands, on anterior and posterior margins of parapodia near body wall; tiny on setiger 1–5, larger on setiger 6, largest on setiger 8.

All setae compound with heterogomph shafts, those with shortest blades emerging from ventral face of parapodium between insertion of ventral cirrus and distal tip, remaining setae emerging from distal tip of parapodium; all blades with fine proximal serrations, short falcigers terminating in narrow pointed tips ( Fig. 29H ), longer spinigerlike setae terminating in fine elongated tips. Setigers 1–3 with ca. 26 setae, blades ranging from 30–120 µm long in setigers 1–2, setiger 3 with longest blades reaching 240–300 µm. Setigers 4–10 with 14–16 setae, shortest blades 38–50 µm, longest blades 240–360 µm. Setiger 11 with slightly fewer setae (ca. 12), with slightly shorter blades ranging from 50 µm to 195 µm. Parapodia with four aciculae, two anterior and two posterior; posteriormost acicula heaviest, golden, pointed; upper posterior acicula slimmer, may move to middle of parapodium in posterior setigers ( Fig. 29E ); aciculae in anterior of each parapodium slimmer, pointed, less obvious and sometimes not seen; tips of posterior aciculae emergent ( Fig. 29 B–G), those of anterior aciculae usually not emergent.

Pygidium with two ventromedial, filiform cirri and two lateral cirri with stalk or base measuring ca. 35 µm long, ending in very large (0.2 mm long), distal oval portion ( Figs. 29H , 30A ).

Remarks. Anguillosyllis hessleri n. sp. is one of several species that have 11 setigers, most of which have palps that are entirely or at least dorsally free (i.e., A. aciculata n. sp., A. hadra n. sp., A. hampsoni n. sp., A. palpata , and A. truebloodi n. sp.) unlike A. hessleri n. sp., which has bulky palps that are fused for their entire length with only a small medial dimple on a wide anterior margin. Anguillosyllis capensis , which most likely also has 11 setigers, has palps that are not completely fused, but have a clear separation of the tips (fide Day 1963; Aguado & San Martín 2008).

The prostomium and peristomium of A. hessleri n. sp. appear completely fused from the dorsal side. Staining with Shirlastain A and examination at 1000x revealed only the faintest suggestion of demarcation between the two, with the peristomium appearing as long as the prostomium. Two small patches that stain more deeply than the surrounding tissue may represent nuchal patches just at the line between prostomium and peristomium, but no separate cilia could be seen, even at 1000x (SEM may reveal cilia in this area).

The aciculae in the posterior part of the parapodia of A. hessleri n. sp. also appear to differ from those of most other species in being much heftier and of a darker golden color, and especially in having protruding pointed tips rather than being fully enclosed in tissue. A. aciculata n. sp. has four emergent aciculae in each parapodium, but that species has palps that are not fused.

The small external structures on the margins of the parapodia of A. hessleri n. sp. are similar to those seen on A. elegantissima n. sp. and described for A. lanai ; in A. hessleri n. sp. they are larger on the posterior rather than the anterior edges of the parapodia.

The lateral anal cirri differ from those seen in the other Anguillosyllis species in that they are much larger and have a base or stalk connecting the expanded oval portion to the pygidium. The stalk measured one-quarter the length of the expanded oval portion, which appears to have some internal structure but does not stain with MG.

Etymology. This species is named for Dr. Robert R. Hessler, Scripps Institute of Oceanography, Co-Chief Scientist on the survey to the Clarion-Clipperton Fracture Zone in 1983 on which these specimens were collected, in recognition of his considerable contributions to the study and understanding of deep-sea benthos.

Records. Abyssal Pacific, Clarion-Clipperton Fracture Zone, 4480–4518 m.

Figures

FIGURE 29. Anguillosyllis hessleri n. sp. Holotype (LACM-AHF Poly 110169): A, entire specimen, dorsal view. Paratype (LACM-AHF Poly 110170): B, setiger 1; C, setiger 2; D, setiger 3; E, setiger 5; F, setiger 7; G, setiger 9; H, falcigers from setiger 1; I, pygidium and anal cirri. A–G, I, dorsal view. Abbreviations: aCF—filiform anal cirrus, aCL— lateral anal cirrus, aL—anterior lobe, base aCL—basal portion of lateral anal cirrus, ExGl—external glands, InGl—internal gland, MGst—cells stained with Methyl Green, SeSac—setal sac, vC—ventral cirrus.

FIGURE 30. Anguillosyllis hessleri n. sp. Holotype (LACM-AHF Poly 110169): A, entire specimen, dorsal view.—Anguillosyllis sepula n. sp. Holotype (MCZ 150582): B, entire specimen, dorsal view.