Thelepus cincinnatus (Fabricius, 1780), s. str.

Jirkov, Igor, 2018, Three new species of Thelepus Leuckart, 1849 from Europe and a re-description of T. cincinnatus (Fabricius, 1780) (Annelida, Terebellidae), ZooKeys 759, pp. 29-56 : 29

Thelepus cincinnatus (Fabricius, 1780), s. str. Figs 2, 3, 11, 12

Thelepus cincinnatus : type locality Greenland (probably Frederikshâb), type material probably never designated ( Holthe 1986):? Fauvel 1927: 271-272, fig. 95 i–m; Pettibone 1954: 327-328, fig. 37e, f; Zatsepin 1948: 154, table XXXVIII, 7 (partim);? Hartmann-Schröder 1996: 528-530, Abb. 258; Holthe 1986: 140-142, fig. 63, map 62 (partim); Jirkov 2001: 526-527 (partim).

Material

(Table 1): 413 specimens from 33 stations collected at 8-1350 m, bottom temperature -1.53-7.37 °C. Ten specimens from Alaid station 6 deposited at MNCN: 16.01/17777.

Additional material.

Thelepus antarcticus ZIN IV.1.2 (5 specimens)

Description.

Largest specimen 140 mm in length and 5 mm in width, although some fragments distinctly larger (up to 7 mm width); maximum size estimated at over 200 mm; larger specimens had been collected at shallow depths, less than 100 m. Number of segments increased with body size; number in investigated specimens: 113.

Buccal tentacles numerous, equal to body length, grooved. Eyespots rounded subepithelial spots, black or dark brown, numerous, usually in several transverse rows on back of upper lip (Fig. 2A, B). Even smallest specimens (<0.5 mm width R/V Sevastopol st. 1769) with numerous eyespots. Specimens from deepest sample (R/V Sevastopol, st. 1580, 1350 m) also with numerous eyespots.

Branchial filaments numerous, long and tangled (Fig. 2A, C–G). Due to tangling it was impossible to count number of branchial filaments in large worms (>5-6 mm width) without removing them one by one. Maximum number of BS1 filaments ca. 20-30, extending laterally to a point level with midpoint or lower edge of row of U1 uncini; outermost filaments usually 2-3 times shorter than those most developed. BS2 with a maximum of 15-20 filaments. One specimen (from Alaid 30.13) had four filaments on BS3 on right hand side of body; length of these was equal to notopodia of same segment. Filaments attached to a transverse elevated stump in 1-2 irregular rows depending on number of filaments. Number of filaments increases with body size; small worms (1-2 mm width) have fewer than 10 filaments on BS1. Smallest specimen (Sevastopol 1769, width <0.5 mm) with no filaments. Extension of filaments laterally depends upon worm size, with filaments extending only to level of upper margin of uncinal row in small worms. Wide medial gap separating left and right groups of filaments. Lateral lobes absent. Dorsum with warts or subepithelial honeycomb, forming more or less regular rows (Fig. 2C, F); number of rows increases with size of segments and worm. Segmentation distinct. Ventrum glandular, more so with increased “wrinkling” (Fig. 2H). Poorly visible, small nephridial papillae on S4-S7 above neuropodia; those on S5-S7 largest and usually only ones visible (Fig. 2D, F, arrowed).

Notopodia commence from BS2, with anterior notopodia large and transverse. Notopodia raised on body surface or flattened, depending on whether fixation occurs whilst within or outside of tube. Notopodia of BS2 equal to or only slightly smaller than those most developed. Notopodia numerous and present on almost all segments except 10-20 posteriormost developing segments; in investigated material present on up to 106 segments. Last notopodia poorly developed, several times shorter than those most developed and almost without rami, with only a few notochaetae; last neuropodia also reduced (Fig. 2I). Part of worm without notopodia not exceeding 10% of whole body length. Notochaetae in few (ca.10) anterior segments in two transverse rows: posterior row with long chaetae, distal half (winged part) becomes stained with methylene blue, anterior row with short chaetae; other notopodia with a single row of notochaetae. Notochaetae with narrow brims (Fig. 11B).

Neuropodia from C3, tori increasing in size to U10, then becoming progressively shorter. Uncini in a single row with well-developed prow and crest and one tooth in profile (Fig. 3); within a neuropodium main fang develops first, crest develops later (Fig. 3D).

Pygidium with crenulated margin, without cirri or papillae.

Differential diagnosis.

Morphologically, T. cincinnatus is closest to T. antarcticus Kinberg, 1866. The original description of T. antarcticus is very brief. The most complete re-description is by Benham (1921). It looks very similar to T. cincinnatus ; however, I do not believe that it is the same species, since direct comparison of material from the northern and southern hemispheres is necessary to find differences. For the present time it can be stated that, although both species are of equal size (up to 200 mm length and 7 mm in diameter), T. cincinnatus has at least twice as many branchial filaments as T. antarcticus . The five specimens investigated (length up to 5 cm) have no more than 15 branchial filaments on BS1, distinctly fewer eyespots and slightly different uncini, with a hump (Fig. 3E).

Thelepus cincinnatus differs from other new species described herein as indicated: from T. davehalli sp. n. by the presence of eyespots and the absence of numerous completely developed posterior segments without notopodia; from T. marthae sp. n. by the absence of eyespots and by the higher number of branchial filaments and segments with notopodia; and T. parapari sp. n. has a crest of uncini on TU1 with two rows in profile, while T. cincinnatus has only one. Other species of Thelepus with two pairs of branchiae and eyespots have at least three times fewer branchial filaments and all but T. parapari sp. n. have half the number of segments with notopodia (Table 2).

Remarks.

The investigated material included almost 2000 specimens (from more than 100 stations) from the high Arctic to the Mediterranean, from depths between 2 m and almost 2 km. The type locality of T. cincinnatus is outside the ranges of all investigated species, but T. cincinnatus s. str. investigated specimens perfectly agree with the description of topotypes ( Pettibone 1954). It is supposed that Pettibone’s description is that of the true T. cincinnatus .

In some samples, specimens lacked eyespots; however, this is likely to be due to fading because specimens in same samples (with several specimens present) have eyespots, but they are paler, smaller and less numerous than is typical. This fading seems to depend on preservation method: all material with faded eyespots had been stored in formalin for over ten years. The age of samples does not influence fading significantly; although all specimens without eyespots were collected over 50 years ago, other specimens collected a century ago and kept in alcohol had retained eyespots. So absence of eyespots should not be considered to be a characteristic of this species.

Three subspecies (varieties according to original descriptions) of T. cincinnatus have been described ( Bellan 2008) and, based on the discussion below, none are considered valid.

Thelepus cincinnatus var. andreanae McIntosh, 1922. McIntosh wrote "dorsal cephalic collar with eye-specks"; as all other Thelepus with two pairs of branchiae from the area near the type locality also lack eyespots, this name should be accepted as a junior synonym of T. cincinnatus s. str. as believed by Bellan (2008).

Thelepus cincinnatus var. canadensis McIntosh, 1885; has eyespots according to the original description. Type locality: 43°04'N, 64°05'W, 51 fms. Specimens collected near the type locality of this subspecies (R/V “Persey-3” see Table 1) did not show differences from other specimens, confirming Hartman’s (1959) acceptance of T. cincinnatus var. canadensis as a junior synonym of the stem subspecies.

Thelepus cincinnatus var. profundus Roule, 1896. The description is too short to be informative: 'Un seul individu, différant du type par sa taille e plus petite, par son tube plus mince et couvert extérieurement d’un enduit peu épais formé de vase grise, et par la forme de ses plaques onciales; ces dernières sont plus étroites, et leurs trois dents plus espacées’. No figures are given so it is impossible to determine which species he was describing and as no type material was deposited in Paris ( Solís-Weiss et al. 2004) this subspecies should be treated as a nomen dubium.

Other literature reports of Thelepus cincinnatus include:

Fauvel (1927) reported for T. cincinnatus ; "nombreux points oculiformes"; however, most or all the area covered by the "Faune de France" seems to lie outside the range of T. cincinnatus , but includes the range of T. parapari sp. n. with eyespots, so he probably observed T. parapari sp. n.

Zatsepin (1948) and Holthe (1986); despite their descriptions agreeing well with T. cincinnatus s. str., they probably observed the other species described here, because these species’ ranges fall within those covered by their papers. The same is true for our papers ( Jirkov 2001; Jirkov and Leontovich 2013), where we overlooked T. marthae sp. n., T. davehalli sp. n., and T. parapari sp. n. but, in this case, it is supported by re-investigation of the material.

Hartmann-Schröder (1996) reported eyespots for T. cincinnatus (Abb. 258), but her figures showed too few branchial filaments and no visible eyespots (they cannot be confirmed or observed in the figure shown). Either the specimen in the figure is too young (there is no scale) or she was studying a different species.