Caulleriella bathytata Blake 2019, new species

Caulleriella bathytata new species

Figures 11–12

urn:lsid:zoobank.org:act: 030AB8AA-E468-47B1-86C0-9E5E877E8EE7

Caulleriella sp. A: Wilson & Hessler 1987: 66, Appendix E.

Material examined. North Equatorial Pacific Ocean, abyssal plain, Clarion-Clipperton Fracture Zone. NOAA

BIE Project site, coll. D.D. Trueblood, Sandia box corer, Sta. DDT-9-94, 0–2 cm fraction, 29 Jul 1994, 12°54.980′N, 128°35.440′W, 4877 m, holotype (USNM 1557546); Sta. DDT-1-93, 08 Sep 1993, 12°56.042′N, 128°35.940′W, 4824 m, 1 specimen (USNM 1557549); Sta. DDT-2-93, veg. 16, 0–2 cm fraction, 10 Aug 1992, 12°565.166′N, 128°35.520′W, 4869 m, 1 paratype (USNM 1557545); Sta. DDT-9-93, veg. 25, 0–2 cm fraction, coll. 03 Sep 1993, 12°56.280′N, 128°35.440′W, 4860 m, 1 paratype (USNM 1557547); Sta. DDT-1-94, veg 1, 0–2 cm fraction, 25 Jul 1994, 12°55.788′N, 128°35.843′W, 4851 m, 1 specimen (USNM 1557548).— ECHO I, DOMES Site C, R/V Melville cruise, coll. R. Hessler, Sta. Sta. H348C, 1–5 cm fraction, 13 Jun 1983, 14°38.0720ʹN, 125°38.0720ʹW, 4504 m, 1 specimen (LACM-AHF Poly 11275); Sta. H361N, 1–5 cm fraction, 18 Jun 1983, 14°42.0775ʹN, 125°25.8565ʹW, 4567 m, 1 specimen (LACM-AHF Poly 11276).

Description. A long, narrow, threadlike species. Holotype complete, with long, slender body, 8.2 mm long, 0.20 mm across anterior and some middle segments, 0.10 mm across far posterior segments, with 51 setigers; not expanded anywhere along length. One complete paratype (USNM 1557547) 12 mm long, 0.21 mm wide across anterior setigers, with 49 setigers. Anterior segments 1–7 narrow, about twice as wide as long; subsequent segments becoming elongate, up to two or three times as long as wide in about 30 middle segments (Fig. 12D), with some much longer, 5–6 times as long as wide, becoming elongate, but not moniliform; posterior segments rounded, shorter (Figs. 11C, 12E). Body generally cylindrical in cross section, with no dorsal or ventral grooves. One paratype (USNM 1557545) with 3–4 middle segments distended due to large ova measuring 60–70 µm in diameter (Fig. 12A, C). Color in alcohol: opaque white, no pigmentation.

Pre-setiger region elongate, narrow, about twice as long as wide (Figs. 11 A–B). Prostomium triangular, weakly separated into anterior and posterior sections, narrowing to pointed tip (Figs. 11 A–B, 12A–B); eyespots absent; nuchal organs elevated mounds on posterior lateral margins (Fig. 11B). Peristomium generally smooth with no distinct lateral grooves, annulations or dorsal crest, merging almost seamlessly with anterior margin of setiger 1 (Fig. 11 A–B). Dorsal tentacles arising from near posterior margin of peristomium (Figs. 11 A–B, 12B); first pair of branchiae arising directly posterior to dorsal tentacles (Fig. 11 A–B). Second pair of branchiae on setiger 1, arising posterior to first pair dorsal to notosetae; subsequent branchiae in similar location (Fig. 11B). Branchiae present on few middle segments, not observed in posterior segments.

Noto- and neuropodia reduced to low mounds from which setae arise; podial lobes somewhat larger in farthest posterior segments. Setae all capillaries along most of body; bidentate acicular spines appearing in last 5–6 segments on 51-setiger holotype (setigers 45–46), but somewhat more anteriorly on 49-setiger paratype (USNM 1557547): neuroaciculars (setiger 31), notoaciculars (setiger 39). Capillaries of first ten setigers elongate, with broad blades bearing thin fringe of fibrils along one edge, numbering about 7–8 per fascicle; capillaries of subsequent segments narrower, with thinner blades, reduced to 4–5 per fascicle along most of body until far posterior segments where capillaries increase to 5–6 before being replaced by acicular hooks over last few segments. Paratype (USNM 1557547) with a few long natatory-like setae on 7–12 anterior setigers. Bidentate acicular hooks up to 4–5 per noto- and neuropodium in farthest posterior setigers, with notopodial hooks (Fig. 11 D–E) about twice as long as neuropodial hooks (Fig. 11 F–G). Individual hooks with curved shaft tapering to a main fang at about a 45° angle to shaft on concave side and surmounted by a minute apical tooth (Fig. 11 D–G). A short transparent hood extends from main fang, merging with shaft (Fig. 11 D–G); no hood or crest apparent on the convex side.

Pygidium a simple achaetous segment with terminal anus and large, rounded ventral lobe (Fig. 11C); a pair of minute dorsal papillae observed on one specimen dorsal to ventral lobe (Fig. 12E).

Variability. Small specimens with the acicular hooks beginning more anteriorly than on the holotype but limited to posterior one-third of body. Long natatory-like notosetae present or absent.

Methyl Green stain. Stain retained on dorsal and lateral surface of pre-setiger region, but somewhat diffuse. No stain retained elsewhere on body.

Etymology. The epithet bathytata, is from the Greek bathys for deep sea.

Remarks. To date, only three of the 38 previously known species of Caulleriella, are known from depths of 1000 m or greater; these are all from around Antarctica (Blake 2018): C. antarctica Hartman, 1978 (1120 m), C. fimbriata Blake, 2018 (1884 m), and C. kacyae Blake, 2018 (1035 m). Occurring at a depth of more than 4800 m, Caulleriella bathytata n. sp. is the deepest recorded species of the genus discovered to date and like its Antarctic deep-water congeners has a small, fragile, threadlike body. Other undescribed deep-water species of Caulleriella occur in the North Atlantic (Blake unpublished).

The very long, threadlike body of the largest specimens of C. bathytata n. sp. extends for up to 12 mm with a width that is so narrow that the specimens tend to break easily upon handling. It is remarkable that three of the specimens are complete and survived the sample processing intact (a testament to the careful sample handling by Drs. Trueblood and Hessler).

Caulleriella bathytata n. sp. differs from its congeners in having bidentate hooks with a transparent hood extending from the main fang to the concave side of the shaft. Such a hood has not been previously recorded in the Cirratulidae and as such is highly diagnostic for this species. However, a microscope with high magnification (1000 x) is required to clearly observe the hood. Some Caulleriella species, however, do have a hood or crest on the convex side of the shaft, which extends forward forming or otherwise being part of the apical tooth (e.g., C. antarctica: Blake 2018: Fig. 19F).

Habitat & biology. All BIE specimens were collected from the 0–2 cm depth fraction of the box core, suggesting they reside at or just under the sediment-water interface. Some specimens of C. bathytata n. sp. have 3–4 enlarged segments between the anterior and middle body segments that are distended due to large ova (Fig. 12A, C).

Distribution. Abyssal Pacific Ocean, Clarion-Clipperton Fracture Zone, 4504–4877 m.