Lysippe nikiti, Jirkov, Igor A., 2016

Jirkov, Igor A., 2016, Lysippe nikiti sp. nov. (Polychaeta, Terebellomorpha) from the deep Pacific and Indian Oceans with an amendment to the generic diagnosis of Lysippe, Zootaxa 4117 (1), pp. 125-134 : 126-131

Lysippe nikiti sp. nov.

Type material. All from R/V Vitjaz. HOLOTYPE: cruise 39, station 5625, 45 °23' N 153°46' E, 6210 m, ‘Ocean’ grab, 1 specimen; PARATYPES: cruise 29, station 4158, 46 °56' N 143°58' W, 4653 m, ‘Ocean’ grab, 1 specimen, anterior fragment; cruise 31, station 4667, 8 °47' S 52°24' E, 4208 m, ‘Ocean’ grab, 1 specimen, anterior fragment; cruise 45, station 6136, 53 °25' N 163°28' W, 4260 m, ‘Sigsbi’ trawl, 3 specimens, two anterior fragments and one complete specimen retained as SEM stubs.

Description of holotype. ( Fig. 4 ). Complete specimen 30 mm in length with no evidence of reproductive material (macerated internally). Prostomium with median lobe encircled by surrounding lobe ( Fig. 4 A–C, E), without glandular ridges or eyespots but with a pair of large, brown pigmented spots. Buccal tentacles not observed (lost or retracted). Lower lip large, extends laterally (as is typical for Lysippe ), ventral surface with longitudinal furrows and ridges; ridges terminate in papillae. Paleal chaetae very small, 2 to 3 times shorter and thinner than notochaetae of second thoracic chaetiger. 3 pairs of branchiae in two transverse groups, separated by a gap that is wider than the diameter of single branchiophore; branchiae visible only as scars in holotype, branchiostyles lost. In each group, the second from the outermost branchiae originate from segment II, the outermost originate from segment III and the innermost originate from segment IV. Nephridial papillae or nephridiopores clearly visible: one pair on each of segments IV and V, dorsally from the notopodia, and a third behind the notopodia of segment VI ( Fig. 4 C). 17 thoracic chaetigers (excluding paleal segment), starting from segment III. 14 thoracic uncinigers, starting from segment VI. Elevated or modified notopodia absent. 10 abdominal uncinigers without rudimentary notopodia or glandular pads. Thoracic neuropodia are tori; abdominal neuropodia are pinnuli (uncini at the margin of neuropodia) ( Fig. 4 D). Pinnules without dorsal cirrus. Pygidium of holotype slightly macerated, so that the presence or absence of anal cirri is not clear. Methyl blue staining pattern absent, except for random spots. Tube unknown.

Additional features from paratypes. All other specimens either have paleae or have paleal notopodia from which the paleae have been lost ( Fig. 4 E). A pair of large brown pigmented spots is usually present. Two large nuchal organs in posterior corners of the median lobe ( Fig. 4 H), though they may be completely withdrawn and invisible ( Fig. 4 A, E). Uncini of thoracic uncinigers with numerous teeth in three to four rows, abdominal uncini with five to six rows but the number of teeth in each is less than in the thoracic uncini ( Fig. 4 F, G).

Despite obvious variation in presence/absence of paleae and shape of the lower lip, I consider all specimens to belong to a single species as they have the same number of branchiae and either characteristic brown pigmented spots or paleal notopodia without chaetae. Variation in lower lip shape does not seem to exceed that of Lysippe labiata .

species paleae thoracic uncinigers pairs of branchiae abdominal uncinigers Differential diagnosis. The difference between the new species and previously described species is clear from Table 1 . L. storchi is the most morphologically similar species. It has the same number of thoracic uncinigers and pairs of branchiae but has 11 abdominal uncinigers, while the new species only 10. The difference between the species’ ranges makes it unlikely that they are a single species with wide geographic variation. L. storchi inhabits shallow, tropical waters, while the new species is limited to abyssal depths. Other species differ from the new one by at least two, sometimes three, of the following characters: number of thoracic uncinigers, number of abdominal uncinigers and number of branchiae.

Distribution ( Fig. 4 I). The species has one of the deepest ranges in the family (4180–6210 m) and is widely distributed in the North Pacific and Indian Oceans; its actual range is probably much wider, as such depths are not well known. Wide species distributions, such as this, are quite common amongst Polychaeta ( Kucheruk 1981).

Etymology. The species is named after my late friend Nikita Kucheruk, who was, amongst his other specializations, an ampharetid taxonomist, describing several new species.

Figures

FIGURE 4. Lysippe nikiti sp. nov. A — anterior dorsal view perpendicular to prostomial dorsal surface; B — anterior left view; C — anterior dorso-lateral view; D — last thoracic and 1 st abdominal segments; E — dorsal view; F — uncini of 5 th thoracic unciniger; G — uncini of mid abdomen; H — anterior of worms with everted nuchal organs; I — species range; A – D — holotype, st. 5625; E — paratype, st. 4158; F – H — paratype, st. 6136. A – E — methyl blue staining pattern. Numbers refer to segments: ll — lower lip, ml — median lobe of prostomium, ne — neuropodium; no — nuchal organs; np — nephridiopores; nt—notopodium; pal — paleae.

Tables

TABLE 1. Diagnostic characters of Lysippe. Species are ordered firstly by the number of thoracic uncinigers, then by the number of pairs of branchiae, then by the number of abdominal uncinigers.

L. mexicana	+ 1 2	4	1 1–1 2
L. agulhasensis	+ 1 2	4	1 2
L. labiata	+ 13	4	14–15
L. trichobranchia	– 13	4	16–19
L. nipponica	+ 1 3	4	? (>5)
L. nikiti	± 1 4	3	1 0
L. storchi	- 1 4	3	1 1
L. sexcirrata	+ 1 4	3	1 3
L. annenkovae	- 1 4	3	1 5
L. gurjanovae	- 14	3	17–19
L. hesslei	- 14	3	25–26
L. fragilis	+ 1 4	4	8
L. caeca	+ 1 4	4	1 1
L. annectens	+ 1 4	4	>1 0