Chaetozone

Key to 12 Chaetozone species from the North Atlantic Ocean

(Note: Recent published descriptions of Chaetozone caputesocis and C. zetlandica do not fully agree with the definition of Chaetozone and are not included in the following key; MG = Methyl Green).

1 Anterior body with distinctly enlarged fusiform segments anterior to abdominal segments............................2

- Anterior body segments only slightly enlarged, gradually tapering posteriorly......................................3

2 Anterior body segments enlarged dorsally into hump-backed configuration; peristomium not divided into rings, dorsal tentacles arising from posterior margin of peristomium; posterior parapodia with partial cinctures, up to 8 spines on a side; MG pattern not tested................................................................................. C. gibber

- Anterior segments enlarged forming distinct fusiform shape; peristomium with two distinct rings, dorsal tentacles arising from smaller second peristomial ring; posterior parapodia with complete cinctures, up to 16 spines on a side; elaborate MG staining pattern throughout body.................................................................... C. elakata n. sp.

3 First complete body segment asetigerous; first branchiae on asetigerous segment; eyes absent; long natatory-like capillaries present or absent...................................................................................... 4

- First complete body segment setigerous; first branchiae either on posterior margin of peristomium or setiger 1; eyes present or absent; long natatory-like capillaries absent.................................................................7

4 Peristomium with dorsal crest; dorsal tentacles in notch between peristomium and setiger 1; long natatory-like setae on all segments from setigers 18–21; deep groove present along venter; MG stains peristomial area, stripes on anterior thoracic segments, and posterior cinctured segment.............................................................. C. setosa

- Peristomium without dorsal crest; dorsal tentacles arising from posterior margin of peristomium; long natatory setae present or absent; ventral groove present or absent; MG pattern present or absent...........................................5

5 Body pigmented; neuropodial spines first present from anterior one-third of body (setigers 5–25 in 80-setiger specimens); long natatory-like capillaries present on sexually matures specimens or absent; MG pattern present or absent.................6

- Body not pigmented; neuropodial spines from mid-body, setiger 25 in 50-setiger specimen; long natatory setae from setiger 2 to about setiger 25; MG pattern not tested........................................................... C. jubata

6 Body heavily pigmented with numerous brown to black pigment speckles over entire body; with a prominent mid-ventral ridge along entire length of body formed of ventromedial bulges on each segment; with weak mid-dorsal groove in middle body segments; neuropodial spines from setigers 5–26; posterior cinctures reduced, with 13‒19 spines on a side; no MG pattern................................................................................................ C. pigmentata

- Body with anterior segments with diffuse black pigment, not discrete speckles, limited to certain areas of the body, not all over; mid-ventral ridge low, not conspicuous; posterior cinctures well developed, with elevated membranes with 20‒22 spines on a side; with distinct MG staining pattern, with all of prostomium staining except tip and most of peristomium staining, forming “mask” over the head region..................................................................... C. bathyala

7 First pair of branchiae on setiger 1; eyespots present..........................................................8

- First pair of branchiae on posterior margin of peristomium; eyespots present or absent...............................9

8 Peristomium with dorsal crest; neuropodial spines from setiger 6–9; anterior neuro- and notopodial spines short, curved, pointed; posterior spines long, straight, pointed.................................................... C. carpenteri

- Peristomium without dorsal crest; neuropodial spines from setiger 30; neuro- and notopodial spines, short, curved with blunt tip.......................................................................................... C. christiei

9 Peristomium with prominent dorsal crest; prostomial eyespots present; neuropodial acicular spines from setiger 1; notopodial acicular spines from setiger 1–8; prominent MG stain on prostomium and peristomium....................... C. corona

- Peristomial crest absent; prostomial eyespots absent; neuropodial and notopodial spines from middle and posterior segments....................................................................................................10

10 Bidentate hooks and acicular spines in posterior cinctures............................................. C. diodonta

- Bidentate hooks absent................................................................................ 11

11 Acicular spines with sharp tips curving back and fusing with shaft, from posterior one-third (setigers 50–55 in neuropodia and 45–50 in notopodia); cinctures with 16–24 spines on a side; MG stains prostomium......................... C. anasima

- Acicular spines short, straight, thick with blunt tips, from mid-body (setigers 40–45 in neuropodia and 45–50 in notopodia); cinctures with 12–14 spines on a side; no MG pattern............................................... C. hystricosa