Tharyx tierralobos, Blake, 2018

Blake, James A., 2018, Bitentaculate Cirratulidae (Annelida, Polychaeta) collected chiefly during cruises of the R / V Anton Bruun, USNS Eltanin, USCG Glacier, R / V Hero, RVIB Nathaniel B. Palmer, and R / V Polarstern from the Southern Ocean, Antarctica, and off Western South America, Zootaxa 4537 (1), pp. 1-130 : 110-112

publication ID

https://doi.org/ 10.11646/zootaxa.4537.1.1

publication LSID

lsid:zoobank.org:pub:169CBE5C-3A6E-438B-8A81-0491CBFBAC85

DOI

https://doi.org/10.5281/zenodo.3798492

persistent identifier

https://treatment.plazi.org/id/03A2CB16-FF98-A225-FF36-FB36FB91FEFB

treatment provided by

Plazi

scientific name

Tharyx tierralobos
status

sp. nov.

Tharyx tierralobos View in CoL new species

Figures 60–61 View FIGURE 60 View FIGURE 61

Material examined. Off northern Peru, Isla Lobos de Tierra , SEPBOP, R / V Anton Bruun, Cr. 16, Sta. 635-A, coll. 05 Jun 1966, 06°27ʹS, 80°56ʹW, trawl, 160 m, holotype ( USNM 1490757 About USNM ) and 3 paratypes ( USNM 1490758 About USNM ) GoogleMaps .

Description. A small species, holotype complete, 7.1 mm long, 0.5 mm wide across anterior segments, with approximately 115 setigerous segments; one complete paratype smaller, 3.4 mm long, 0.3 mm wide across anterior segments, with 110 setigerous segments. All segments short, crowded throughout, not becoming longer in middle body ( Figs. 60A View FIGURE 60 , 61 View FIGURE 61 A–B). Body generally dorsoventrally flattened, especially in posterior half; anterior segments with dorsum weakly elevated and rounded over lateral parapodial shoulders ( Fig. 60A View FIGURE 60 ); venter flattened with midventral groove extending along entire body ( Fig. 61B View FIGURE 61 ); venter of far posterior segments with broad shallow groove into which neurosetae project ( Fig. 61C View FIGURE 61 ). Color in alcohol: light tan, no body pigment present on holotype; one paratype with dusky pigment on peristomium and at interface with setiger 1.

Prostomium triangular, tapering to narrow tip ( Figs. 60A View FIGURE 60 , 61A View FIGURE 61 ); eyespots absent; nuchal organs narrow slits on posterior lateral margins. Peristomium with three weakly developed rings with grooves not crossing dorsum ( Fig. 60A View FIGURE 60 ); with prominent dorsal crest extending onto setiger 1 ( Fig. 60A View FIGURE 60 ). Dorsal tentacles on posterior margin of peristomium, lateral to posterior extension of dorsal crest ( Fig. 60A View FIGURE 60 ). First pair of branchiae on setiger 1, dorsal to notosetae ( Fig. 60A View FIGURE 60 ); subsequent branchiae in similar position; branchiae present on all segments of first one-third of body, irregularly present on middle and posterior segments.

Noto- and neuropodia moderately separated from one another, most noticeably in middle and posterior segments; anterior notopodia forming distinct dorsal shoulders in anterior segments ( Fig. 60A View FIGURE 60 ), less distinct shoulders posteriorly; neuropodia less well developed. In middle and posterior segments, setae arising from low ridge. Anterior setae all capillaries, numbering about 5–6 per fascicle. Neuropodial hooks first present from setiger 28, numbering 1–2 at first with 2–3 thin capillaries, increasing to 3–4 hooks in middle and posterior segments with 2–3 thin capillaries; neuropodial hooks short, geniculate, tapering to rounded weakly expanded tip, appearing hollow internally ( Fig. 60 View FIGURE 60 B–C, inset). Notosetae all capillaries through middle segments replaced in posterior segments by 3–4 long geniculate setae that taper to narrow pointed tip ( Fig. 60D View FIGURE 60 ); these accompanied by 3–4 long, thin capillaries.

Pygidium with about 6–8 glandular papillae surrounding anal opening.

Methyl Green stain. Stain retained on dorsum and venter of prostomium and peristomium producing distinct pattern, best seen on holotype ( Fig. 61A View FIGURE 61 ). No stain retained on individual segments.

Etymology. The name tierralobos is derived from the name of the island “Lobos de Tierra” near the collecting site off northern Peru.

Remarks. Tharyx tierralobos n. sp. differs from most of its congeners by having a relatively thick body with numerous short segments throughout and with the tips of the neuropodial geniculate hooks expanded, but with a rounded tip instead of the sub-bidentate or irregular knobby tip characteristic of most Tharyx species. Based on the body shape and details of the noto- and neuropodial hooks, T. tierralobos n. sp. is most similar to T. robustus Blake & Göransson, 2015 , from northern Europe. The two species differ in that T. robustus has the first pair of branchiae on the peristomium posterior to the base of the dorsal tentacles whereas T. tierralobos n. sp. has the first branchiae arising directly on setiger 1. Additional differences are that (1) T. robustus has characteristic pigment spots on the posterior lateral margins of the prostomium that are absent in T. tierralobos n. sp.; (2) both species have relatively flattened bodies, but T. tierralobos n. sp. has a prominent ventral groove along most of the body that is not welldeveloped in T. robustus , which instead has a distinct mid-ventral ridge; and (3) the notopodial acicular hooks of T. robustus consist of both short and long curved setae, whereas the notopodial hooks of T. tierralobos n. sp. are limited to long, geniculate hooks that taper to a point.

It is noted that the noto- and neuropodia of T. tierralobos are moderately separated from one another, especially in middle and posterior segments, a characteristic of species of Caulleriella . However, by lacking any evidence of bidentate hooks, this species has been assigned to Tharyx , but is clearly an outlier and deserves further study.

Distribution. Known only from off Peru, near Isla Lobos de Tierra, 160 m.

R

Departamento de Geologia, Universidad de Chile

V

Royal British Columbia Museum - Herbarium

Kingdom

Animalia

Phylum

Annelida

Class

Polychaeta

Order

Terebellida

Family

Cirratulidae

Genus

Tharyx

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