Figure 47
Material examined. Off Western South America, central Chile, USNS Eltanin Cr. 4, Sta. 203, 31 Aug 1962, 35.65°S, 73.13°W, Petersen grab, 436 m, holotype ( USNM 56074).
Description. A small species, holotype complete, 5.4 mm long, 0.4 mm wide for 72 setigerous segments. Color in alcohol light tan to brown, lacking any distinctive body pigment. Body elongate, narrow, widest in middle segments, narrowing posteriorly; 12–15 posterior setigers formed into distinct cinctures with high membranes bearing spines ( Fig. 47B). Dorsum rounded, without dorsal groove; venter somewhat flattened, with shallow ventral groove present from about setiger 15, deepening in middle body segments, not apparent posteriorly.
Prostomium triangular, narrowing to a blunted anterior margin ( Fig. 47A); eyespots absent; small slit-like nuchal organ present laterally on posterior margin, not pigmented; peristomium with three nearly equal annular rings, surmounted dorsally by a raised ridge without annular grooves, extending to anterior margin of setiger 1 ( Fig 47A). Dorsal tentacles arising from posterior margin of raised peristomial ridge ( Fig. 47A); first pair of branchiae lateral and slightly posterior to tentacles, on anterior margin of setiger 1; second pair of branchiae on posterior edge of setiger 1, dorsal to notosetae ( Fig. 47A); subsequent setigers with branchiae in similar location.
Setiger 1 of approximately same size as following segments; podial lobes reduced to inconspicuous ridges in anterior setigers; inflated and conspicuous in middle setigers, greatly enlarged with elevated ridges and conspicuous armature in posterior setigers ( Fig. 47B); posterior segments separated by deeply cut intersegmental furrows. Noto- and neurosetae from setiger 1 all capillaries; notosetae 8–10 per fascicle, neurosetae 7–9 per fascicle; each capillary thickened, but with no distinct fibrils apparent along edge; setigers 25–50 with long, natatory-like notosetae. Acicular spines first present from about setiger 50 in both noto- and neuropodia; spines numbering 1–3 at first, accompanied by an equal number of thin capillaries; in far posterior setigers notopodial spines numbering 7–8 and neuropodial spines numbering 6–7, forming nearly complete cinctures with spines numbering 13–15 on a side and accompanied by alternating thin capillaries ( Fig. 47B); spines with relatively straight shaft, weakly curved apically, with sharply pointed tip that curves back and adheres to shaft, thus superficially resembling blunted tip ( Fig. 47 C–G); one spine observed with double tip, with one tip projecting forward and the other curved back and fused the shaft ( Fig. 47F); shaft with weak node or notch at point of emergence from podial lobe.
Last few cinctured setigers narrowing to posterior end; pygidium a simple achaetous segment with terminal anus and ventral bi-lobed disk ( Fig. 47B).
Methyl Green stain. No pattern.
Etymology. This species is named for Dr. Gesa Hartmann-Schröder, retired annelid curator of the Zoological Museum of Hamburg, in recognition of her major works on polychaetes of Western South America and Antarctica. Her species, Chaetozone curvata, was the first Chaetozone discovered with the distinctive spines having a sharply pointed tip that curves back and adheres to the shaft ( Hartmann-Schröder 1965).
Remarks. Chaetozone gesae n. sp. is the seventh species to be described having spines with the unusual sharply pointed tip that curves back and adheres to the shaft. The following species are previously known: C. curvata, from coastal waters of Chile; C. commonalis Blake, 1996 from California shelf depths; C. allanotai Blake, 2006, from California deep-water slope depths; C. anasima Doner & Blake, 2006 from offshore New England; C. camasetosa Blake, 2015 from the Puget Sound; and C. nicoyana Dean & Blake, 2007 from the Pacific coast of Costa Rica. Chaetozone curvata and C. commonalis have the first pair of branchiae on setiger 1, whereas C. allanotai, C. anasima, C. camasetosa, C. gesae n. sp., and C. nicoyana have an extra pair of branchiae just lateral and posterior to the dorsal tentacles on the anterior margin of setiger 1, as well as a pair on the posterior margin of the same setiger, effectively having two branchiae on setiger 1, suggesting that a segment has been lost or two segments have been fused. Chaetozone anasima lacks distinct peristomial rings, including any demarcation or annulation between the peristomium and setiger 1; whereas, C. allanotai, C. camasetosa, C. gesae n. sp., and C. nicoyana have two or three distinct peristomial rings. Of these, C. nicoyana is unusual in having both long and short spines in posterior cinctures that number up to 19–20 spines on a side. Chaetozone gesae n. sp. is the only species to have a raised peristomial ridge that merges with setiger 1. Further, C. gesae n. sp. has fewer spines in the posterior cinctures and does not exhibit any Methyl Green staining reaction, unlike that described for C. allanotai and C. camasetosa ( Blake 1996, 2015).
Distribution. Offshore Chile, 436 m.