Prionospio mutata, Peixoto & Paiva, 2020

Peixoto, Antônio João Malafaia & Paiva, Paulo Cesar, 2020, New apinnate Prionospio (Annelida: Spionidae) species from southeastern Brazil, Zootaxa 4853 (4), pp. 451-508 : 475-477

Prionospio mutata sp. nov.

( Figures 14–16 )

Type material. Brazil. Espírito Santo Basin. Holotype: Amb 5 B6, 20º 36’ 2.03” S, 39º 51’ 35.37” W, 02 Dec 2011 to 02 Feb 2012, 991m, MNRJ-2758. Paratypes: Amb5 B6, 20º 36’ 2.03” S, 39º 51’ 35.37” W, 02 Dec 2011 to 02 Feb 2012, 991m, MNRJP-2759 (3 ind); Amb12 E7, 19º 47’ 2.44” S, 39º 3’ 14.62” W, 06 Jun 2013 to 17 Jul 2013, 1242m, MNRJP-2760 (2 ind) .

Additional material examined. Amb3 E5, 19º 36’ 25.08” S, 39º 10’ 20.15” W, 352m (2 ind); Amb3 E6, 19º 40’ 5.6” S, 39º 7’ 15.87” W, 1010m (12 ind); Amb4 F7, 20º 4’ 8.18” S, 38º 31’ 27.32” W, 1288m (2 ind); Amb5 B5, 20º 35’ 15.16” S, 39º 53’ 46.36” W, 382m (1 ind); Amb5 B6, 20º 36’ 2.03” S, 39º 51’ 35.37” W, 991m (24 ind); Amb5 B7, 20º 36’ 41.55” S, 39º 49’ 24.15” W, 1315m (2 ind); Amb5 C5, 20º 14’ 22.9” S, 39º 48’ 33.06” W, 416m (5 ind); Amb5 C6, 20º 15’ 34.21” S, 39º 46’ 15.69” W, 1031m (2 ind); Amb5 C7, 20º 17’ 35.61” S, 39º 42’ 35.67” W, 1309m (1 ind); Amb5 D6, 19º 50’ 1.87” S, 39º 26’ 30.04” W, 1053m (1 ind); Amb5 D8, 20º 8’ 43.27” S, 39º 7’ 22.23” W, 1905m (1 ind); Amb11 B6, 20º 35’ 57.27” S, 39º 51’ 38.12” W, 994m (4 ind); Amb11 B7, 20º 36’ 49.74” S, 39º 49’ 29.01” W, 1327m (6 ind); Amb11 C5, 20º 14’ 19.79” S, 39º 48’ 36.57” W, 418m (6 ind); Amb11 C7, 20º 17’ 37.38” S, 39º 42’ 36.72” W, 1347m (1 ind); Amb12 A5, 21º 4’ 8.5” S, 40º 13’ 7.35” W, 383m (1 ind); Amb12 D7, 19º 54’ 4.77” S, 39º 22’ 29.46” W, 1330m (1 ind); Amb12 E6, 19º 40’ 1.68” S, 39º 7’ 23.79” W, 1018m (1 ind); Amb12 E7, 19º 47’ 2.44” S, 39º 3’ 14.62” W, 1242m (11 ind); Amb11 E8, 20º 15’ 53.31” S, 38º 40’ 53.51” W, 1886m (1 ind); Amb12 F5, 19º 34’ 20.47” S, 38º 41’ 19.8” W, 445m (1 ind); Amb12 G7, 19º 3’ 31.11” S, 37º 48’ 42.65” W, 1361m (1 ind); Amb12 CANWN5 , 19º 49’ 36.4” S, 39º 35’ 41.77” W, 363m (1 ind) .

Diagnostic features: Peristomium slightly inflated, low dorsal crests from chaetiger 10 to chaetigers 18–20; sabre chaetae appearing as a gradual transformation of capillary chaeta.

Description. A small-sized Prionospio , largest complete specimen 2 mm long, 0.15 mm wide at widest part for 34 chaetigers; holotype 5 mm long, 0.2 mm wide at widest part for 45 chaetigers (incomplete). Body dorsoventrally flattened in branchial region and cylindrical afterwards, tapering towards pygidium. Body color whitish in alcohol ( Fig. 14 ).

Prostomium elongated, rounded anteriorly, widening towards anterior margin and extending posteriorly as a narrow keel reaching anterior margin of chaetiger 2. U-shaped nuchal organs reaching anterior margin of chaetiger 2 ( Fig. 15 A–B). Prostomial peaks generally present in adults. Eyes absent. Peristomium moderately developed, slightly inflated, well-separated from prostomium by a furrow and partially fused to chaetiger 1, lateral wings moderately developed. Grooved palps reaching up to chaetiger 8, lost in most specimens.

Chaetiger 1 with only a few chaetae in both rami, especially in the notopodium, shorter than chaetae on succeeding chaetigers. Postchaetal lamellae rounded on notopodium and digitiform on neuropodium, both smaller than lamellae on succeeding chaetigers ( Fig. 16A ). Prechaetal lamellae absent.

Notopodial postchaetal lamellae foliaceous on chaetigers 2–10 ( Fig. 16 B–D), square-shaped with a pointed tip on chaetigers 11–12, and broadly rounded from chaetiger 13, reduced to a low flap after chaetigers 22–25 (depending on specimen size). Notopodial prechaetal lamellae absent throughout. Dorsal crests low from chaetiger 10 to chaetigers 18–20 ( Fig. 16A , C–D).

Neuropodial postchaetal lamellae rhomboid in chaetiger 2 and broadly rounded in chaetigers 3–11 ( Fig. 16 B–D), elliptical from chaetiger 12 to chaetigers 20–23 (depending on specimen size), drastically reduced in subsequent chaetigers, present as a low flap. Neuropodial prechaetal lamellae absent throughout ( Fig. 15A, C ).

Chaetae from notopodia and neuropodia organized in two rows of unilimbate (narrow limbation) and sparsely granulated capillaries ( Fig. 16E ). Chaetae from both rows of almost equal length, with neuropodial chaetae slightly shorter than notopodial chaetae. Towards the posterior region, capillaries progressively elongate, non-limbate, nongranulated, thinner and less numerous ( Fig. 16F ).

Hooks in notopodia starting from chaetigers 26–34, up to three per fascicle, accompanied by 1–4 short nonlimbate capillaries ( Fig. 16G ). Hooks in neuropodia starting from chaetigers 13–19, up to seven per fascicle, accompanied by 2–6 short non-limbate capillaries. All hooks multidentate, with 10 secondary teeth organized in two rows above the main tooth ( Fig. 16H ). Secondary hood present ( Fig. 16H ). Sabre chaetae starting from chaetigers 12–17, appearing as a gradual transformation of inferior-most capillary chaeta from 2–3 previous chaetigers. Sabre chaetae non-limbate, with dense light granulations along the shaft ( Fig. 16 I–K).

Up to 11 pairs of smooth, robust, cirriform branchiae, tapered at the tips. Branchiae starting from chaetiger 2, up to two times longer than notopodial lamellae, gradually reduced in length towards last branchial pair. Branchiae densely ciliated throughout length (except the tip), completely free from notopodial postchaetal lamellae ( Figs 15 A–D; 16L).

Pygidium bearing one dorsal cirrus and two short digitiform ventro-lateral lobes ( Fig. 16M ).

Oocytes from chaetiger 12, measuring up to 100 µm.

Methyl green staining pattern: Prostomium, dorsal and lateral sides of the peristomium intensely stained, postchaetal lamellae from chaetigers 2–5 slightly stained.

Remarks. The gradual transformation of capillary chaetae into sabre chaetae has never been reported in Prionospio . According to Radashevsky (2012), it is known only in Microspio Mesnil, 1896 and Spio Fabricius, 1785 , genera that belong to the subfamily Spioninae Söderström, 1920 . Sabre chaetae have been reported lacking in only few species— Prionospio perkinsi , P. hermesia , P. cerastae , P. fosterae sp. nov., P. alexandrae sp. nov. and P. acuta sp. nov., while in the remaining Prionospio species they are present and appear abruptly.

The presence of up to 11 pairs of cirriform branchiae is reported for Prionospio mutata sp. nov., P. fosterae sp. nov. and P. hartmanae sp. nov., but these species can be distinguished based on the presence of dorsal crests from chaetiger 10 to chaetigers 18–20 in P. mutata sp. nov. and the shape of lamellae on chaetiger 1 (rounded on the notopodium and digitiform on the neuropodium of P. mutata sp. nov., rounded on both rami in P. fosterae sp. nov. and rounded with a pointed tip on the notopodium and digitiform on the neuropodium of P. hartmanae sp. nov.). Additionally, sabre chaetae are absent in P. fosterae sp. nov., appearing abruptly in P. hartmanae sp. nov. and appearing gradually in P. mutata sp. nov.

Prionospio mutata sp. nov. is similar to P. fosterae sp. nov., P. hartmanae sp. nov. and P. kinbergi sp. nov. in having a rounded prostomium, but P. mutata sp. nov. can be separated from these species based on the presence of prostomial peaks and presence and distribution of dorsal crests (absent in P. fosterae sp. nov. and P. hartmanae sp. nov., from chaetiger 10 to chaetigers 18–20 in P. mutata sp. nov. and from chaetiger 12 to chaetigers 15–18 in P. kinbergi sp. nov.). Species can also be distinguished based on branchial characters—branchial number and morphology (up to 11 pairs of cirriform branchiae in P. fosterae sp. nov. and P. hartmanae sp. nov. and up to 10 pairs of branchiae, cirriform on the first and last pairs and flattened on the remaining pairs in P. kinbergi sp. nov.).

Etymology. The specific epithet, mutata , refers to the gradual transformation of the inferior-most capillary chaeta into sabre chaetae ( mutata, Latin for change; alteration).

Habitat: Mud to silt, 352–1905 m depth.

Distribution: Southeastern Brazil (Espírito Santo and Campos basins), Atlantic Ocean.

Figures

FIGURE 14. Prionospio mutata sp. nov., dorsal view (MNRJP-2759, paratype), showing characteristic color in ethanol. Abbreviations: br, branchia; pe, peristomium; pr, prostomium.

FIGURE 15. SEM of Prionospio mutata sp. nov., dorsal view. A. Anterior end and mid-body chaetigers. B. Close-up of the anterior end. C. Anterior chaetigers and mid-body. D. Close-up of the mid-body. Abbreviations: br, branchia; dc, dorsal crest; nol, notopodial lamellae; pe, peristomium; pr, prostomium.

FIGURE 16. Prionospio mutata sp. nov. A. Chaetiger 1. B. Chaetiger 2. C. Chaetiger 3. D. Chaetiger 4. E. Anterior capillary chaeta. F. Posterior capillary chaetae. G. Companion capillary chaetae. H. Hooded hook. I–J. Gradual transformation of capillary chaetae into sabre chaetae. K. Sabre chaetae. L. Sabre chaetae. M. Posterior-most chaetigers and pygidium.