Microspio Mesnil, 1896

Fonseca-González, Idalyd, Londoño-Mesa, Mario H. & Delgado-Blas, Víctor H., 2022, Redescription of Microspio moorei (Gravier, 1911) (Annelida: Spionidae) with inclusion of a taxonomic key for all the species of the genus, Zootaxa 5120 (3), pp. 334-344 : 336-342

Genus Microspio Mesnil, 1896

Microspio Mesnil, 1896: 116 , 119; type species: Spio mecznikowianus Claparède, 1869 , (type by subsequent designation ( Söderström, 1920)).

Mesospio Gravier, 1911: 313 ; type-species: Mesospio moorei Gravier, 1911 , by monotypy. Fide Foster, 1971.

Diagnosis. Prostomium anteriorly rounded; or broadly rounded, only weakly incised; or conical or bilobed or bifid (deeply incised along anterior margin, producing two widely diverging lobes), frontal or lateral horns absent; eyespots present or absent; occipital antenna present or absent. Peristomium reduced or well developed, not forming lateral wings. Nuchal organ with short median and long lateral ciliary bands, extending to chaetiger 2 or 3, sometimes an oval or U-shaped ciliated groove; metameric dorsal ciliated organs often present. Transverse ciliary bands present between bases of branchiae on some species. Branchiae from chaetiger 2, limited to anterior region of body or continuing to posterior end, partly fused or free to bases of anterior postchaetal notopodial lamellae and free on posterior lamellae. Ventral epidermal glands present or absent. Intensely pigmented with brown patches on prostomium, peristomium and branchiae, or/and spots scattered on dorsum continuing laterally and ventrally, or absent. Notopodium of chaetiger 1 present or absent; chaetiger 1 with or without notochaetae; with or without additional superior fascicle of long, capillaries from chaetiger 1 and continuing to middle chaetigers; notochaetae and anterior neurochaetae all capillaries. Neurochaetae include capillaries, hooded hooks; ventral sabre chaetae on middle and posterior chaetigers or absent. Hooded hooks bi-, tri-, or multidentate; hooks with a fang surmounted by unpaired or paired teeth; hooks with the hood closed, or completely or partially open. Pygidium with 2–4 anal cirri.

Remarks: Microspio was erected by Mesnil (1896) in order to include Spio mecznikowianus Claparède, 1869 . Mesospio was erected by Gravier (1911b) to include Mesospio moorei Gravier, 1911 ; later, Mesospio was synonymyzed with Microspio by Foster (1971). Microspio is very closely related to Spio , they are distinguished mainly by having branchiae present from the chaetiger 2 in Microspio and from chaetiger 1 in Spio . Currently, the genus is recognized as having 21 species. The last revision of Microspio was made by Maciolek (1990), who recognized 15 species as valid. Blake (1996) and Zhou et al. (2009) added two species, M. spinosa Blake, 1996 and M. multidentata Zhou, Ji & Li, 2009 . Recently, Maciolek & Blake (2021) described three new species, M. fischeri , M. lydonia and M. ariena , including comparative notes for all species in the genus.

Characters regarded as useful based on current information are the shape of the anterior margin of prostomium, presence or absence of caruncle, paired nuchal organs and occipital antenna, pigmentation in any part of the body, presence or absent of noto-lamellae and notochaetae on chaetiger 1, the starting and structure of hooded hooks, the shape of the nuchal organs, presence or absent of sabre chaetae, and the shape of pre- and postchaetal lamellae ( Reish 1959; Blake & Kudenov 1978; Blake 1983, 1984, 1996; Maciolek 1990, Zhou et al. 2009; Bick & Meissner 2011; Maciolek & Blake 2021). Nevertheless, all characters mentioned above have not been described for some species. Therefore, it would be useful to redescribe them using type material or material from type locality or close to, using both morphological and molecular characters but this is beyond the scope of this study.

Identification key to Microspio species

1. Prostomium rounded or straight on anterior margin; or broadly rounded, only very weakly incised in front; or conical..... 2

- Prostomium bilobed or bifid (deeply incised along anterior margin, producing two widely diverging lobes) on anterior margin .................................................................................................. 13

2. Prostomium conical on anterior margin................................................... M. maori Blake, 1984

- Prostomium rounded or straight, slightly flared on anterior margin.............................................. 3

3. Chaetiger 1 with notochaetae............................................................................ 4

- Chaetiger 1 without notochaetae........................................................................ 10

4. Eyes absent; four pairs branchiae present........................................ M. tetrabranchia Maciolek, 1990

- Eyes present; branchiae continuing nearly to the end of the body................................................ 5

5. Hooded hooks with two teeth............................................................................ 6

- Hooded hooks with three or more teeth.................................................................... 7

6. Prostomium rounded, slightly expanded at anterolateral margin; hooded hooks beginning on chaetigers 18–23..................................................................................... M. kussakini Chlebovitsch, 1959

- Prostomium anteriorly tapered; hooded hooks beginning on chaetigers 14–17.................. M. moorei (Gravier, 1911)

7. Hooded hooks with a fang surmounted by two unpaired teeth............................. M. hartmanae Blake, 1983

- Hooded hooks with a fang surmounted by paired teeth........................................................ 8

8. Prostomium broad anteriorly, with curved, slightly incised margin; posterior notopodia include only long capillaries...................................................................................... M. elegantula Blake, 1984

- Prostomium rounded or truncate; posterior notopodia with numerous needle-like capillaries providing a distinct spinous appearance to the posterior end............................................................................ 9

9. Prostomium rounded; hooded hooks with two single teeth surmounted by three pairs of apical teeth; pygidium with four anal cirri......................................................................... M. pigmentata ( Reish, 1959)

- Prostomium truncate; hooded hooks with 2–3 single teeth surmounted by 1–2 pairs of apical teeth; pygidium with poorly developed cirri, if any....................................................... M. lydonia Maciolek & Blake, 2021

10. Eyes absent; hooded hooks multidentate beginning on chaetiger 26................. M. multidentata Zhou, Ji & Li, 2009

- Eyes present; hooded hooks uni-, bi-, or tridentate beginning on chaetiger 9–11................................... 11

11. Occipital antenna present................................................ M. occipitalis Hartmann-Schröder, 1983

- Occipital antenna absent............................................................................... 12

12. Hooded hooks tridentate.......................................................... M. rolasiana Augener, 1918

- Hooded hooks uni-, and bidentate...................................................... M. spinosa Blake, 1996

13. Chaetiger 1 with notochaetae........................................................................... 14

- Chaetiger 1 without notochaetae........................................................................ 15

14. Branchiae long and straplike; branchiae present on chaetigers 8–11; up to eight hooded hooks per fascicle............................................................................................ M. profunda Maciolek, 1990

- Branchiae short, elliptical, densely packed with large elongate glands; branchiae missing on chaetigers 8–11; up to four hooded hooks per fascicle......................................................... M. ariena Maciolek & Blake, 2021

15. Occipital papilla present; notopodial lamellae on chaetiger 1 with two lobes......... M. granulata Blake & Kudenov, 1978

- Occipital papilla absent; notopodial lamellae on chaetiger 1 with one lobe....................................... 16

16. Caruncle present..................................................................................... 17

- Caruncle absent or indistinct........................................................................... 18

17. Notopodial lamellae on chaetiger 1 present; hooded hooks multidentate; anterior hirsute capillaries.................................................................................................. M. microcera ( Dorsey, 1977)

- Notopodial lamellae on chaetiger 1 absent; hooded hooks bidentate; anterior not hirsute capillaries............................................................................................ M. fischeri Maciolek & Blake, 2021

18. Neuropodial lamellae on chaetiger 1 absent................................................................ 19

- Neuropodial lamellae on chaetiger 1 present............................................................... 20

19. Prostomium bifid (deeply incised along anterior margin, producing two widely diverging lobes); thickened capillaries arranged in a U shape on chaetigers 4–5 and notched notopodial capillaries present..................... M. paradoxa Blake, 1983

- Prostomium bilobed on anterior margin; thickened capillaries arranged in a U shape on chaetigers 4–5 and notched notopodial capillaries absent...................................................... M. minuta ( Hartmann-Schröder, 1962)

20. Prostomium slightly incised on anterior margin; hooded hooks beginning on chaetiger 11; pygidium with two cirri............................................................................. M. mecznikowiana ( Claparède, 1869)

- Prostomium bilobed on anterior margin; hooded hooks beginning on chaetiger 9; pygidium with four cirri.......................................................................................... M. atlantica ( Langerhans, 1880)