Chaetozone adunca, Blake, 2022

Blake, James A., 2022, New species and records of Caulleriella, Chaetocirratulus and Chaetozone (Annelida, Cirratulidae) from continental shelf and slope depths of the Western North Atlantic Ocean, Zootaxa 5113 (1), pp. 1-89 : 31-37

Chaetozone adunca new species

Figures 15–16

urn:lsid:zoobank.org:act:0936557E-257C-466D-8857-A24CF9309413

Chaetozone sp. 11 : Blake et al. 1987: 61, 68, C-2; Maciolek et al. 1987b: D-2; Blake & Grassle 1994: 850, 855; Blake & Hilbig 1994: 883–884, 896; Hilbig 1994: 940.

Chaetozone sp. B: Maciolek et al. 1987b: D-2 (in part).

Chaetozone sp. 1 : Maciolek et al. 1987b: D-2 (in part).

Material examined. (407 specimens) Off Cape Hatteras , North Carolina , US South Atlantic ACSAR Program, coll. J.A. Blake, Chief Scientist. Sta. 9: Cruise SA-3, Rep. 1, 22 Jul 1984, 35°28.30′N, 74°47.70′W, 579 m , holotype ( USNM 1660944 ) , 7 paratypes ( USNM 1660945 ); Rep. 2, 22 Jul 1984, 3°28.40′N, 74°47.50′W, 614 m , 18 paratypes ( USNM 1660946 ); Rep. 3, 22 Jul 1984, 35°28.30′N, 74°47.60′W, 598 m , 32 paratypes ( USNM 1660947 ); Cruise SA-4, Rep. 1, 24 May 1985, 35°28.41′N, 74°47.44′W, 640 m , 23 paratypes ( USNM 1660948 ); Rep. 2, 24 May 1985, 35°28.41′N, 74°47.56′W, 603 m , 9 paratypes ( USNM 1660949 ); Rep. 3, 24 May 1985, 35°28.28′N, 74°47.52′W, 623 m , 25 paratypes ( USNM 1660950 ); Cruise SA-5, Rep. 1, 25 Sep 1985, 35°28.41′N, 74°47.46′W, 629 m , 18 paratypes ( USNM 1660951 ); Rep. 2, 25 Sep 1985, 35°28.41′N, 74°47.47′W, 629 m , 23 paratypes ( USNM 1660952 ).— MMS Cape Hatteras Survey , August 1992, coll. J.A. Blake, Chief Scientist. Sta. SA-9: 35°28.36′N, 74°47.42′W, 620 m (57, USNM 1660953 ) ; Sta. CH-1: 35°42.47′N, 74°46.58′W, 804 m (15, USNM 1660954 ) ; Sta. CH-3, 35°37.08′N, 74°46.12′W, 812 m (7, USNM 1660955 ) ; Sta. CH-18: 35°30.01′N, 74°47.61′W, 530 m (1, USNM 1660956 ) ; Sta. CH-19: 35°29.79′N, 74°46.59′W, 812 m (13, USNM 1660957 ) ; Sta. CH-34: 35°25.10′N, 74°48.35′W, 775 m (8, USNM 1660958 ) ; Sta. CH-41: 35°22.19′N, 74°52.31′W, 590 m (6, USNM 1660959 ) ; Sta. CH-42: 35°21.28′N, 74°50.64′W, 785 m (1, USNM 1660960 ) . — Off Cape Lookout , North Carolina, ACSAR, Sta. 2: Cruise SA-3, Rep. 1, 15 Jul 1984, 34°14.50′N, 75°43.90′W, 984 m (1, USNM 1660961 ) ; Rep 3, 15 Jul 1984, 34°15.00′N, 75°43.70′W, 1002 m (2, USNM 1660962 ) .— Off Charleston , South Carolina, ACSAR Sta. 14: Cruise SA-4, Rep. 3, 20 May 1985, 32°23.67′N, 77°01.12′W, 803 m (1, USNM 1660963 ) .— Off New England, U.S. North Atlantic ACSAR Program, coll. G.W. Hampson, Chief Scientist. Sta. 4: Cruise NA-2, Rep. 1, 28 Apr 1985, 40°21.23′N, 67°32.32′W, 563 m (3, USNM 1660964 ) ; Rep. 2, 28 Apr 1985, 40°21.23′N, 67°32.33′W, 572 m (6, USNM 1660965 ) . Sta. 7: Cruise NA-1, Rep. 1, 10 Nov 1984, 40°27.54′N, 67°40.34′W, 560 m (19, USNM 1660966 ) ; Rep. 2, 10 Nov 1984, 40°27.49′N, 67°40.29′W, 560 m (21, USNM 1660967 ) ; Rep. 3, 10 Nov 1984, 40°27.52′N, 67°40.36′W, 560 m (1, USNM 1660968 ) ; Cruise NA-2, Rep. 1, 28 Apr 1985, 40°27.50′N, 67°40.27′W, 560 m (10, USNM 1660969 ) ; Rep. 2, 28 Apr 1985, 40°27.46′N, 67°40.22′W, 560 m (22, USNM 1660970 ) ; Rep. 3, 28 Apr 1985, 40°27.44′N, 67°40.19′W, 558 m (4, USNM 1660971 ) ; Cruise NA-3, Rep. 1, 06 Jul 1985, 40°27.47′N, 67°40.26′W, 556 m (22, USNM 1660972 ) ; Rep. 2, 06 Jul 1985, 40°27.50′N, 67°40.22′W, 555 m (12, USNM 1660973 ) ; Rep. 3, 06 Jul 1985, 40°27.48′N, 67°40.21′W, 560 m (18, USNM 1660974 ) ; Sta. 12: Cruise NA-2, Rep. 2, 04 May 1985, 39°54.26′N, 70°55.07′W, 555 m (1, USNM 1660975 ) ; Cruise NA-5, Rep. 2, 06 May 1986, 39°54.27′N, 70°55.17′W, 548 m (1, USNM 1660976 ) ; Cruise NA-6, Rep. 2, 30 Jul 1986, 39°54.26′N, 70°55.07′W, 559 m (1, USNM 1660977 ) ; Cruise NA-6, Rep. 3, 30 Jul 1986 ,, 39°54.24′N, 70°55.09′W, 563 m (1, USNM 1660978 ) .

Description. A moderately sized species, holotype with 75 setigers, 10.25 mm long, 0.5 mm wide across setiger 1, increasing over swollen anterior segments to 1.1 mm wide, and then decreasing posteriorly to 0.5 mm wide. Body variable in shape, larger specimens with a swollen thoracic region ( Fig. 15A ); most specimens with thorax only slightly enlarged ( Fig. 16A–B ). Individual segments short, narrow, about five times wider than long at first, with some middle thoracic segments 6–8 times wider than long in some specimens; posterior cinctured segments about twice as wide as long ( Figs. 15B , 16F ). Venter with shallow groove along most of body, absent in posterior cinctured segments. Dorsum with narrow groove in mid-body segments ( Fig. 15A ), reduced posteriorly. Posterior cinctured segments with deep intersegmental grooves ( Figs. 15B , 16F ) and a low elevated membrane from which capillaries and acicular spines emerge ( Fig. 16B ). Color in alcohol light tan; no apparent pigmentation.

Pre-setiger region long, narrow, smooth, about as long as first ten setigers ( Fig. 15A ). Prostomium long, narrow, triangular, pointed anteriorly, merging seamlessly with peristomium ( Fig. 15A ); eyespots absent; nuchal organs narrow slits. Peristomium triangular, not divided into rings, with weakly developed shallow lateral grooves visible on some specimens; dorsum narrow, producing weakly developed dorsal crest ( Fig. 15A ). Peristomium merging seamlessly with setiger 1; dorsal tentacles arising from posterior margin with first pair of branchiae lateral to tentacles ( Fig. 15A ); second pair of branchiae dorsal to notosetae on setiger 1 and posterior to position of first branchiae; subsequent branchiae from setiger 2 in same location dorsal to notosetae; present along most of body, but most missing and reduced to stubs or scars.

Parapodia of anterior and middle segments reduced to low ridges or mounds from which setae arise; posterior parapodia swollen, with low raised membrane from which setae arise forming prominent segmental cinctures on last 20–25 setigers. Setiger 1 and thoracic segments with 9–12 capillaries in notopodia and neuropodia; capillaries mostly of moderate size; a few long, natatory-like capillaries present or absent, but not associated with sexual maturity. Acicular spines first present in holotype from setiger 58 in notopodia and setiger 55 in neuropodia; spines 1–2 at first, increasing posteriorly, transitioning into full cinctures with 14 spines in notopodia and 13 neuropodia, up to 27 spines on a side ( Fig. 16C ); spines alternating with capillaries as long as or slightly longer than spines; cinctures with only narrow dorsal, lateral, and ventral gaps between noto- and neuropodial fascicles providing a prominent armature ( Fig. 16C–D ). Notopodial spines clearly longer than neuropodial spines ( Fig. 16C ). Individual spines with basal manubrium at emergence from podial lobes; spines curving and tapering gradually to narrow blunted tip at first ( Figs. 15C, E–G , 16D–E ); more posterior spines with narrow hooked tip ( Fig. 15H–J ); last 3–5 cinctures bearing spines where tip of hook curves back and merges with shaft ( Figs. 15D, K ).

Body narrowing sharply in last few cinctured segments, terminating in simple pygidium with a small, semicircular disk ventral to anal opening ( Figs. 15B , 16F ).

Methyl green staining. A distinct MG pattern present ( Fig. 16G ), with the entire pre-setiger region staining intensely, with only the tip of prostomium and a diagonal transverse band between the prostomium and peristomium not staining; about 9–10 anterior segments also retaining stain laterally and ventrally; rest of body only staining weakly, with no pattern; de-stains rapidly; pre-setiger and anterior segmental stain retained well after return to alcohol.

Remarks. Chaetozone adunca n. sp. belongs to the C. curvata group and represents the eighth species to be reported with acicular spines having a narrow tip that curves back and merges with the shaft. Chaetozone adunca n. sp. differs from others in this group by having a smooth pre-setiger region that is not divided into separate rings and with most segments having the acicular spines narrowing to a blunt or curved tip, with the spines having recurved tips limited to the posteriormost cinctured segments. This transition from blunt-tipped spines to the recurved type has not been previously reported in the genus. Two other species in group are also reported in the present paper: C. anasima and C. brychiata n. sp. (see below). All known species in the C. curvata group are compared in Table 3 .

Biology. Chaetozone adunca n. sp., as Chaetozone sp. 11, was reported as among the dominant species off Cape Hatteras, North Carolina, during the ACSAR surveys ( Blake et al. 1987, Blake & Grassle 1994) and the separate Cape Hatteras Survey ( Blake & Hilbig 1994). Station 9 is an ACSAR upper continental slope station located at a depth of about 600 m in an area that exhibits high sedimentation rates and is influenced by the Western Boundary undercurrent (WBUC) and Gulf Stream ( Blake & Grassle 1994). Perhaps because of the high sedimentation rates, infaunal densities at Station 9 at an average of 46,255 individuals per m 2 were the highest found at any location along the entire U.S. Atlantic continental slope ( Blake et al. 1987; Blake & Grassle 1994). Similarly high densities were reported by Blake & Hilbig (1994) at stations (SA-9 and CH-1, CH-3, CH-18, CH-19, CH-34, CH-41 and CH-42) in the 500–800 m range as part of the separate Cape Hatteras survey.

At total of 145 species of benthic invertebrates were identified as Station SA-9 from nine samples collected on three surveys as part of the ACSAR program ( Blake & Grassle 1994). Chaetozone adunca n. sp. (as C. sp. 11) ranked 11 th out of 20 dominant species at Station 9. The five most abundant annelids identified at this site in order of abundance were Cossura longocirrata Webster & Benedict, 1887, Scalibregma inflatum, Rathke, 1843, Limnodriloides medioporus Cook, 1969, Tubificoides intermedius ( Cook, 1969) and Aricidea quadrilobata Webster & Benedict, 1887.

Chaetozone adunca n. sp. also occurred at several upper slope stations in the North Atlantic ACSAR program, but was never among the dominant species ( Maciolek et al. 1987b).

Etymology. The epithet is from the Latin, aduncus, for bent inward, in reference to the inwardly curved tip of some of the acicular spines of this species.

Distribution. U.S. Atlantic continental slope, 530–1003 m.

Figures

FIGURE 15. Chaetozone adunca n. sp. Holotype (USNM 1660944): A, anterior end, dorsal view; B, posterior end, dorsal view. Paratypes (USNM 1660947): C, neuropodial acicular spine with narrow blunted tip; D, neuropodial acicular spine from far posterior setiger with recurved tip; E–I, acicular spines with blunted tips; J–K, acicular spines with curved (J) and recurved (K) tips.

FIGURE 16. Chaetozone adunca n. sp. Paratypes (USNM 1660947):A, anterior end, left lateral view; B, same specimen, dorsolateral view; C, posterior segment, anterior view with full cinctures of 27 spines on a side and narrow dorsal and ventral gaps; D, detail of notopodial acicular spines and capillaries; E, neuropodial acicular spine; F, posterior end, dorsal view; G, anterior end, left lateral view, arrows denote MG. A–D, F stained with Shirlastain A; G, stained with MG.