Identification key to Streblospio species

1. Dorsal papilla on chaetiger 1 present...................................................................... 2

- Dorsal papilla on chaetiger 1 absent....................................................................... 7

2. Dorsal crests present.................................................... S. eunateae Martínez & Adarraga, 2019

- Dorsal crests absent.................................................................................... 3

3. Sabre chaetae beginning on chaetigers 2–3................................................................. 4

- Sabre chaetae beginning on chaetigers 6–7................................................................. 5

4. With eyes; sabre chaetae beginning on chaetiger 3; hooks with 5 pairs of teeth above the main tooth; hooks with secondary hoods; without glands on the body.................................................... S. japonica Imajima, 1990

- Without eyes; sabre chaetae starting from chaetiger 2; hooks with 3–4 pairs of teeth above the main tooth; hooks without secondary hoods; numerous papillae scattered throughout the body............................... S. papillaris sp. nov.

5. Notopodial lamellae present on posterior chaetigers; large peristomium covering more than half the length of the prostomium; posterior chaetigers with 8–12 hooks; pygidium simple or bilobed............................................... 6 Notopodial lamellae absent on posterior chaetigers; small peristomium covering the first half of the prostomium; posterior chaetigers with up to 6 hooks; pygidium with one pair of lappets......................... S. eridani Munari et al., 2020

6. Neuropodial lamellae on segment 2 rounded; posterior neuropodial lamellae absent; branchiae with transverse bands; pouched brood structures................................................................... S. benedicti Webster, 1879

- Neuropodial lamellae on segment 2 flap-like; posterior neuropodial lamellae present; branchiae without transverse bands; branchiate brood structures............................................... S. gynobranchiata Rice & Levin, 1998

7. Dorsal collar membranous, bilobed; palps with transverse bands; notopodial lamellae rounded on chaetiger 2; parapodial lamellae disappearing from chaetigers 17 (notopodial), 20 (neuropodial); neuropodial hooks with two pairs of teeth above the main tooth; pygidium simple.................................................... S. shrubsolii (Buchanan, 1890)

- Dorsal collar membranous, entire; palps without transverse bands; notopodial lamellae subtriangular on chaetiger 2; parapodial lamellae disappearing from chaetigers 11–13 (notopodial), 10 (neuropodial); hooks with five pairs of teeth above the main tooth; pygidium with lappets............................................ S. padventralis Delgado-Blas et al., 2018