Chaetozone grasslei, Blake, 2019

Blake, James A., 2019, New species of Cirratulidae (Annelida, Polychaeta) from abyssal depths of the Clarion-Clipperton Fracture Zone, North Equatorial Pacific Ocean, Zootaxa 4629 (2), pp. 151-187 : 174-177

Chaetozone grasslei new species

Figures 15–16

urn:lsid:zoobank.org:act:3215B796-C25E-4512-8261-2D6BCC792267

Chaetozone sp. A: Wilson & Hessler 1987: 66 Appendix E (in part).

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-5-93, veg. 14, 0–2 cm fraction, 13 Aug 1993, 12°56.566′N, 128°35.408′W, 4870 m, holotype ( USNM 1557550 ) ; Sta. DDT-5-93, veg. 19, 2– 5 cm fraction, 1 paratype ( USNM 1557551 ) ; Sta. DDT-3-93, veg. 11, 0–2 cm fraction, 10 Aug 1993, 12°55.972′W, 128°35.395′N, 4867 m (1, USNM 1557552 ) ; Sta. DDT-7-93, veg. 16, 2– 5 cm fraction, 02 Sep 1993, 12°56.303′W. 128°35.311′N, 4844 m, 1 paratype ( USNM 1557553 ) ; Sta. DDT-11-93, veg. 23, 2– 5 cm fraction, 04 Sep 1993, 12°56.055′N, 128°35.695′W, 4859 m (1, USNM 1557554 ) ; Sta. DDT-8-94, on a nodule, 29 Jul 1994, 12°55.020′N, 128°35.400′W, 4880 m, 1 paratype ( USNN 1557555 ) . — ECHO I, DOMES Site C, R/V Melville cruise, coll. R. Hessler, 0.25 m 2 Sandia box core, Sta. H350, 0–1 cm fraction, 14 Jun 1983, 14°38.1226′N, 125°26.8208′W, 4506 m, 2 juveniles ( LACM-AHF Poly 11282) ; Sta. 356, 0–1 cm fraction, 21 Jun 1983, 14°42.4541′N, 125°24.2664′W, 4518 m, 1 speci- men ( LACM-AHF Poly 112843) ; Sta. H357, 0–1 cm fraction, 23 Jun 1983, 14°42.1404′N, 125°24.2787′W, 4510 m, 1 specimen ( LACM-AHF Poly 11284) ; Sta. H357, top water from box core, 1 juvenile ( LACM-AHF Poly 11285).

Description. An elongate, slender species ( Fig. 16A ). Holotype (USNM 1557550) complete, 3.5 mm long, 0.150 mm wide across anterior setigers, with 36 setigerous segments; paratype (USNM 1557553) in two parts, 4.9 mm long, 0.22 mm wide across anterior segments, with 46 setigerous segments. Anterior 5–6 segments narrow, about three times wider than long ( Fig. 15A ), middle and posterior segments becoming longer, eventually about 1.5 times as long as wide, sometimes appearing oval or moniliform ( Figs. 15B , 16 A–B). Holotype and a few larger paratypes with some individual segments along body enlarged, appearing distended due to concentration of ingested sediment particles in intestine ( Fig. 16 A–B). Dorsum rounded, venter flattened or with shallow groove along much of body. Color in alcohol opaque white, with diffuse reddish pigment on peristomium.

Pre-setiger region relatively narrow, about twice as long as wide ( Fig. 15A ). Prostomium broadly triangular, narrowing to rounded tip ( Fig. 15A ); eyespots absent; nuchal organs not observed. Peristomium divided into two rings, first ring broadly rounded ending at narrower second ring bearing dorsal tentacles and first pair of branchiae ( Fig. 15A ); dorsal crest absent. Dorsal tentacles arising from anterior half of second peristomial ring, immediately followed by first pair of branchiae ( Fig. 15A ). Second pair of branchiae arising in a line posterior to the first branchiae dorsal to notosetae ( Fig. 15A ). Subsequent branchiae arising from similar location; branchiae not observed in middle and posterior segments.

Parapodia reduced, lateral shoulders not developed, distinct podial lobes absent, setae appearing to arise directly from body wall, some anterior setigers with low mound posterior to origin of setae. Posterior segments with spines and capillaries forming cinctures, but these arising from low ridges, not elevated into high membranes ( Fig. 15B ). Anterior setae all capillaries, 3–4 per noto- and neuropodia; additional long natatory capillaries on variable number of anterior and middle segments. Noto- and neuropodial acicular spines from setiger 16 on all larger specimens examined including holotype and a paratype (USNM 1557553). Spines initially numbering 1–2 per podia, increasing to 5–6 spines in notopodia and 6–8 in neuropodia in posterior 10–12 setigers; with up to 11–14 spines on a side; spines alternating with slender capillaries. Individual spines curved, tapering to pointed tip; notoacicular spines longer and thinner ( Figs. 15C , 16D ) than neuropodial spines ( Figs. 15D , 16E ); core of spines clear, weakly striated.

Posterior segments narrow, pygidium with rounded lobe ventral to anal opening ( Figs. 15B , 16C ).

Methyl Green stain. A weak light-green peristomial band posterior to prostomium, otherwise stain not retained.

Etymology. This species is named for the late Dr. J. Frederick Grassle, prominent deep-sea benthic ecologist of the Woods Hole Oceanographic Institution and the Rutgers University Institute of Marine and Coastal Sciences. Dr. Grassle introduced this author to offshore benthos, including how to collect specimens with care and analyze and interpret the results with the most relevant statistical methods. From his numerous deep-sea surveys, he also provided this author and other investigators with numerous polychaetes from vents and other habitats that have resulted in a rich harvest of species new to science.

Remarks. Chaetozone grasslei n. sp. is a long slender species with only a slight widening of the anterior segments. Middle and posterior segments are longer and somewhat rounded, sometimes weakly moniliform. The distension of some body segments is due to concentration of sediment in the intestine. These enlarged segments, when present, are conspicuous owing to the otherwise elongate slender appearance of these worms.

There are no described species of Chaetozone that have the combination of a long, slender appearance to the body and two peristomial rings. See comments for C. truebloodi n. sp. (below).

Habitat & biology. The fine sediment in the gut of these worms suggests a silt-clay habitat. The worms were typically found in the upper 5 cm of the sediment column: two specimens including the holotype were in the 0–2 cm level in the box core and three specimens were at the 2–5 cm level.

Distribution. Abyssal Pacific Ocean, 4844–4880 m.

Figures

FIGURE 15. Chaetozone grasslei n. sp. Holotype (USNM 1557550): A, anterior end, dorsal view; B, posterior end, dorsal view; C, notopodial acicular spine, D, neuropodial acicular spine.

FIGURE 16. Chaetozone grasslei n. sp. Holotype (USNM 1557550): A, entire worm, mostly lateral view; B, anterior end, right lateral view; C, posterior end, dorsal view; D, notopodial acicular spine; E. neuropodial acicular spine (same scale as in D). Stained with Shirlastain A.