Kirkegaardia araiotrachela Blake, 2016, new species

Kirkegaardia araiotrachela new species

Figure 28

Material examined. Pacific Ocean, Western South America, off Peru, west of Trujillo, La Libertad Province, R/ V Anton Bruun Sta. 85, 14 Oct 1965, 07°53′S; 80°30′W, 520 m, Menzies trawl, holotype (USNM 1013893); South of Lima, R/ V Anton Bruun, Cruise 17, Sta. 660-A, 12°27′S, 077°16′W, 805 m, coll. 25 Jun 1966, Campbell grab, 1 specimen (USNM 1407135).

Description. Holotype posteriorly incomplete, with about 75 setigers, 22 mm long; width variable depending upon body region: 0.4 mm wide across peristomium and some anterior setigers, 1.0 mm wide at enlarged area between setigers 18–30, and 0.6–0.7 mm wide in middle posterior segments, (Fig. 28 A). Specimen from off Lima, Peru smaller, 9 mm long, 0.5 mm wide across thorax, 1.4 mm wide across expanded mid-body region, for 43 setigerous segments. Color in alcohol: light tan.

Body narrow over first 15–16 setigers comprising a thoracic region with narrow segments about 3.5x wider than long, then followed by expanded anterior abdominal section with segments 5.5x as wide as long over next 10 setigers (Fig. 28 A), then narrowing again in middle and posterior abdominal segments; these becoming longer, about 1.5x as long as wide. Venter with prominent groove from end of thoracic region to end of fragment.

Prostomium narrow, triangular, tapering to pointed anterior tip; eyes absent, nuchal organs not observed. Peristomium with one large and two narrow annular rings with groove visible only laterally, not cutting across smooth dorsum; first ring a large inflated annulus followed by two narrower annulae (Fig. 28 A) appearing to be two achaetous segments; dorsum of peristomium smooth, rounded. Dorsal tentacles short, possibly regenerating, arising from second annular ring and well anterior to setiger 1 (Fig. 28 A). First pair of branchiae from posterior border of third annular ring and anterior to setiger 1; second pair of branchiae on posterior border of setiger 1, dorsal to notosetae; subsequent branchiae arising in a similar location; branchiae rarely observed in posterior segments.

Parapodia reduced to low ridges; lacking postsetal lamellae; notosetae thick, with thick brown bases and include smooth to finely denticulated capillaries, with short, pointed denticles most visible in setae of middle body segments (Fig. 28 B). Anterior neurosetae including fascicles of thin, broad-bladed capillaries, with sharply tapering tips; in middle body setigers, these setae with fine denticles or serrations at point of abrupt tapering (Fig.

28C–D); these broad-bladed pointed setae transitioning to sharply pointed spines and then blunt-tipped spines (Fig. 28 E) in posterior segments from about setiger 68, both types of setae in same fascicle, alternating with narrow, smooth capillaries (Fig. 28 F). Non-type specimen with many setae sheared off along body precluding confirmation of all setal observations made on holotype; however, neurosetae with serrations at point of abrupt tapering present on next to last segment of smaller specimen; spines not present on this fragment.

Pygidium not observed.

Etymology. Araiotrachela is from the Greek: araios for narrow, thin; trachelos for neck. The name is suggested by the narrow neck-like region of the anterior end that precedes the enlarged, fusiform expanded section.

Methyl Green stain. Prostomium retaining light green stain; peristomium and rest of body not retaining stain after differentiation.

Remarks. There are many unusual features of Kirkegaardia araiotrachela n. sp. suggesting that a further evaluation of its generic status is warranted. The occurrence of the paired dorsal tentacles on the middle annular ring of the peristomium is unusual in being so far anterior on the peristomium. The occurrence of branchiae on the last annular ring suggests this might be an achaetous segment rather than part of the peristomium. The denticulate capillaries found in middle body notopodia are typical of those found in several species of Kirkegaardia, but these are normally in the neuropodia as well, rather than limited to the notopodia. The heavy, thickened, pointed neurosetae with denticles or serrations evident at the point of narrowing begin from setigers 5–6 and transition to spines having either long, tapering tips or shorter blunt tips; in posterior setigers both types of spines intergrade within a single neuropodium and alternate with long, slender capillaries; damage to the notosetae in the second specimen precludes confirmation of these observations on another specimen. For this reason it is difficult to confirm the distribution of the different forms of spines observed on the holotype except that the blunt-tipped spines are first observed from setiger 68, with their homologues beginning in anterior setigers. This type of setal transition appears to be unique among the bitentaculate cirratulids studied to date. The alternation of thin capillaries and spines in the neuropodia, as occurs in K. araiotrachela n. sp., also occurs in related bi-tentaculate species of Chaetozone. However, Chaetozone species also have these spines and capillaries in the notopodia which together with the neuropodial spines form posterior cinctures with a distinct armature (Blake 2015). Heavy spines are absent in notopodia of K. araiotrachela n. sp. and true cinctures are not developed. There are no known species of Chaetozone that have denticulate or serrated setae. Setae with serrations evident only at the point of narrowing were illustrated by Eliason (1962) for a cirratulid from the Skagerrak off Sweden that he named Caulleriella serrata. It is likely that upon re-examination Eliason’s species will be referred to Kirkegaardia. However, C. serrata does not have the more typical denticulated setae as in K. araiotrachela n. sp. or other species of the genus.

Biology. The inflated portion of the body of K. araiotrachela n. sp. is possibly related to sexual maturity because sperm packets are present in the coelom of the holotype. No other information is available relative to the habitat or associated organisms.

Distribution. Known only from off Peru in 520– 805 m.