Kirkegaardia jumarsi Blake, 2016, new species

Kirkegaardia jumarsi new species

Figure 30

Material examined. Pacific Ocean, off Western South America, Peru-Chile Trench, R/ V Anton Bruun, Cruise 17, Sta. 664-C, 13°41′S, 077°50′W, Menzies trawl, 5430 m, coll. 29 Jun 1966, holotype (USNM 1407135).

Description. Holotype incomplete, well-preserved but fragile, 21 setigerous segments breaking into two parts during handling, collectively 7.6 mm long, 0.8 mm wide across expanded thoracic region.

Head or pre-setigerous region as wide as long and with thoracic segments forming thick, bulbous, expanded anterior region. Prostomium broadly triangular, with anterior end apically rounded and turned up dorsally (Fig. 30 A–B); nuchal organs narrow slits; eyes absent. Mouth large, with emerging bulbous proboscis, surrounded by thick lateral peristomial lips (Fig. 30 B); peristomium divided into two more or less equal annular rings; anterior ring with smooth, dorsal dome and thick lateral lips surrounding mouth; second ring with relatively smooth dorsum, laterally subdivided into 2–4 narrow lateral rings (Fig. 30 A–B).

Thorax expanded, with only seven setigerous segments, narrowing to four moniliform abdominal segments that twist sharply at setiger 12, with posterior abdominal segments 12–21 forming a right angle to anterior segments 1–11. Figures (30B–D) show a numerical sequence and shape of first 19 setigers.

Dorsal tentacles arising from peristomium mid-dorsally near border with setiger 1 (Fig. 30 A). First pair of branchiae short, located on posterior margin of peristomium in groove anterior to setiger 1 and lateral and dorsal to tentacles (Fig. 30 A); second pair of branchiae and following thoracic branchiae located on posterior edge of each parapodium overlying mid-dorsal groove (Fig. 30 A); most branchiae missing, but scars evident. Branchiae of abdominal segments not readily evident, but a few segments with short branchiae intact arising near notosetae (Fig. 30 D).

Thoracic segments short, about 6x as wide as long, anterior and posterior margins of each thoracic segment with thickened borders, parapodia dorsally elevated forming shallow dorsal groove (Fig. 30 A). Segmental boundaries of thoracic segments visible on dorsal surface with distinct lines demarking each segment (Fig. 30 A). Setigers 1–7 all similar, but with setigers 1–3 swollen ventrally (Fig. 30 B); thoracic setiger 7 followed abruptly by four moniliform abdominal setigers 8–11 (Fig. 30 B–C); abdominal setigers 9–11 about as long as wide, distinctly moniliform (Fig. 30 C); setigers 12–13 elongate and narrow about 2x as long as wide (Fig. 30 D); setigers 14–17 then becoming shorter, about 2.5x as wide as long (Fig. 30 D); setiger 18 and rest of holotype with long, narrow segments.

Parapodia of thoracic region well developed, with distinct tori from which setae arise. Notosetae elongate, smooth capillaries throughout, numbering 12–15 per notopodium in thoracic region, continuing in abdominal segments, reduced to 8–10 in posteriormost notopodia. Neurosetae similar in number, elongate smooth capillaries to setiger 13, then abruptly transition to 14–16 short, broad-based denticulated setae arranged in two rows. Denticles visible at 400x, but details apparent only at 1000x where numerous pointed denticles along one narrow margin observed (Fig. 30 E), with crease of each set of denticles extending entirely across spine, almost forming spiral pattern.

Far posterior segments and pygidium unknown.

Methyl Green stain. No stain retained on holotype.

Etymology. This species is named for Dr. Peter Jumars, deep-sea biologist and benthic ecologist, who described the first species of the unusual mud-ball worms from off southern California.

Remarks. With the description of K. jumarsi n. sp. and K. olgahartmanae n. sp. (see below), there are now three species of unique deep-water mud ball worms, K. luticastella being the first described. All three species have an expanded, modified thoracic region followed by a narrow, twisted abdominal region that conforms to the shape of its tube within a hardened mud ball.

Kirkegaardia jumarsi n. sp. appears to be most similar to K. luticastella in having short thoracic parapodia that are elevated sufficiently high to overlie a relatively smooth dorsal surface. In K. luticastella n. sp., this dorsal thoracic surface is smooth, whereas that of K. jumarsi n. sp. is cut with thin lines demarking each segment. The pre-setigerous region of both species is short, enlarged, and about as long as wide, which together with the expanded thoracic region provides both species with an enlarged and thickened anterior end to the body. Although of similar size and shape, details of the pre-setigerous area of the two species differ considerably. In K. luticastella the entire peristomium is relatively smooth and only incised by a single groove to varying degrees. In larger specimens the groove is barely evident, in smaller specimens such as the one from off northern California (Fig. 17 A), the lateral groove is prominent. In K. jumarsi n. sp., on the other hand, the main lateral groove divides the peristomium such that the anterior half laterally and ventrally forms large lateral lips around the mouth and is overlaid with a rounded dorsal crest or dome. The second half of the peristomium, while smooth dorsally, is divided laterally into at least four narrow ridges (Fig. 30 A–B). Comparison of these two species with the third mud ball species, K. olgahartmanae n. sp., is discussed below.

Biology. The shape of the body with an expanded, almost bulbous, anterior end followed by a narrow twisted abdominal region is similar to that of two other species of mud ball worms. It is here postulated that K. jumarsi n. sp. produces and inhabits mud balls similar to those described for K. luticastella by Jumars (1975) and K. olgahartmanae (see below). Although all mud ball worms to date are from deep-water, K. jumarsi n. sp. is the first to be reported from abyssal depths greater than 5000 m.

Distribution. Known only from the Peru-Chile Trench off Peru in 5430 m.