Kirkegaardia luticastella ( Jumars, 1975 ) Jumars, 1975

Blake, James A., 2016, Kirkegaardia (Polychaeta, Cirratulidae), new name for Monticellina Laubier, preoccupied in the Rhabdocoela, together with new records and descriptions of eight previously known and sixteen new species from the Atlantic, Pacific, and Southern Oceans, Zootaxa 4166 (1), pp. 1-93 : 37-38

Kirkegaardia luticastella ( Jumars, 1975) new combination

Figure 17

Tharyx luticastellus Jumars, 1975: 341 –348, figs. 1–2.

Monticellina luticastella: Blake 1996: 322 –323, fig. 8.23.

Material examined. California continental slope, west of Farallon Islands, San Francisco Deep Ocean Disposal Site (SF-DODS) September 2006 monitoring survey, R/ V Point Sur, Sta. 57, 37º42.946′N, 123º32.947′W, 2637 m , 24 Sep 2006, coll. J.A. Blake, 1 specimen (LACM-AHF Poly 8929).

Description. Farallons specimen complete, in two parts, 6 mm long, 0.7 mm wide across the thorax for about 30 segments. Thoracic region expanded, with seven setigerous segments followed by moniliform abdominal segments ( Fig. 17 A). Thoracic setigers all similar, short, dorsally elevated over midline forming shallow groove ( Fig. 17 A); these abruptly transitioning to anterior abdominal segments each about as long as wide, distinctly moniliform ( Fig. 17 A–B). Posteriormost segments becoming narrow, more crowded, terminating in simple pygidium with ventral lobe ( Fig. 17 B).

Pre-setigerous region enlarged, bulbous, as wide as long, together with thick thoracic region forming enlarged, thickened anterior end ( Fig. 17 A). Prostomium broadly triangular, narrowing to rounded anterior margin ( Fig. 17 A); posterior dorsal margin merging indistinctly with peristomium; nuchal organs not observed; eyes absent. Mouth large, with emerging bulbous proboscis ( Fig. 17 A), surrounded by thick lateral peristomial lips. Peristomium smooth dorsally, weak lateral groove dividing peristomium into two annular rings, apparent only laterally and not prominent ( Fig. 17 A). Dorsal tentacles arising from between posterior margin of peristomium and anterior border of setiger 1 ( Fig. 17 A); first pair of branchiae arising lateral to dorsal tentacles on posterior margin of peristomium; second pair of branchiae arising from posterior margin of setiger 1, with subsequent thoracic branchiae in similar position ( Fig. 17 A). Branchiae of abdominal segments evident on a few moniliform segments, arising laterally, dorsal to notosetae; all branchiae thin, relatively short, most missing.

Parapodia of thoracic region small mounds from which setae arise. Notosetae elongate, smooth capillaries throughout, numbering 12–15 per notopodium in thoracic region, same in abdominal segments, reduced to 8–10 in posterior segments. Neurosetae similar in number and appearance in thoracic segments; transitioning to short, denticulated capillaries on setigers 9–10 ( Fig. 17 A). Denticles of neurosetae very fine, visible at 400x, but with details apparent only at 1000x, each seta observed to have numerous curved and pointed denticles along one narrow margin ( Fig. 17 C–D).

Methyl Green stain. Some stain retained on anterior margin of prostomium and on the posterior borders of the first and second peristomial rings; retention is weak.

Remarks. A single complete specimen of Kirkegaardia luticastella was collected on the continental slope west of San Francisco , California as part of a long-term monitoring effort at SF-DODS. K. luticastella was the first mud ball worm to be described and this represents the first record of the species since the original collection from the San Diego Trough ( Jumars 1975). The specimen is smaller than reported for the types by Jumars (1975) and Blake (1996), being only 6 mm long and 0.7 mm wide instead of 15–30 mm long and 2 mm wide and with only 30 setigerous segments instead of 48–69. In addition, the Farallons specimen has only seven thoracic segments instead of 10–11 as in the type specimens. The position of the first pair of branchiae on the peristomium, recorded here for the northern California specimen, differs from the descriptions by Jumars (1975) and Blake (1996), which were based on the type collection from southern California . The branchiae were described as first occurring on setiger 1; however, Shirlastain A was used with the new material but not on the type specimens. It is likely that the same presetiger branchiae will be found on the type specimens when they are rechecked using the stain as they are present in both K. jumarsi n. sp. and K. olgahartmanae n. sp., two new mud ball worms reported in this study.

Despite these differences in size, numbers of segments, and location of the first pair of branchiae, the main features described for the species by Jumars (1975) and Blake (1996) are consistent. The prostomium is bluntly rounded on the anterior margin and the peristomium is relatively short, being generally wider than long, for a species of Kirkegaardia. Jumars (1975) illustrated a distinct groove in the peristomium producing two annular rings; Blake (1996) illustrated only a weak lateral groove on the holotype; a more prominent lateral groove on the Farallons specimen produces a lateral separation of the peristomium into two more-or-less equal annular rings. However, peristomial rings are often more or less prominent depending on contraction during preservation; often the grooves that define annular rings can be observed only with stains such as Shirlastain A or with SEM.

The species most similar to K. luticastella is K. jumarsi n. sp. described in this paper from the Peru-Chile Trench. The two species are compared below in the K. jumarsi n. sp. description. A third species, K. olgahartmanae n. sp., from off the Antarctic Peninsula is also closely related to both of these species and is treated separately below.

Biology. The species is known only from muddy sediments in offshore basins and slope depths. At the Farallons location, K. luticastella was found only once, and in an environment with fine silty sediments dominated by numerous polychaetes of the families Paraonidae , Spionidae , Cossuridae , and Cirratulidae (mainly species of Chaetozone ) (Blake et al. 2009).

Distribution. San Diego Trough off Southern California, 1200 m in soft sediments; continental slope off northern California, 2637 m in muddy sediment.

Figures

FIGURE 17. Kirkegaardia luticastella (Jumars, 1975): A, anterior end dorsal view; B, posterior end, right lateral view; C – D, denticulated neurosetae. (LACM-AHF Poly 8929).