Prionospio kinbergi, 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 : 465-470

Prionospio kinbergi sp. nov.

( Figures 8–10 )

Type material. Brazil. Espírito Santo Basin. Holotype: Amb 2 Foz 7, 19º 49’ 50.65” S, 39º 52’ 22.92” W, 12 Jul 2011 to 18 Jul 2011, 28m, MNRJP-2750. Paratypes: Amb7 A2, 21º 3’ 26.62” S, 40º 23’ 0.67” W, 02 Dec 2011 to 02 Feb 2012, 36 m, MNRJP-2751 (4 ind); Amb12 CAND4 , 19º 31’ 51.68” S, 39º 3’ 4.79” W, 06 Jun 2013 to 17 Jul 2013, 163 m, MNRJP-2752 (5 ind); Amb14 C2, 20º 11’ 25.75” S, 40º 2’ 15.87” W, 06 Jun 2013 to 17 Jul 2013, 33m, MNRJP-2753 (5 ind) .

Additional material examined. Amb1 Foz7, 19º 49’ 54.12” S, 39º 52’ 11.79” W, 29m (3 ind); Amb1 Foz10, 19º 35’ 11.01” S, 39º 38’ 37.65” W, 29m (1 ind); Amb1 Foz14, 19º 42’ 32.21” S, 39º 38’ 57.36” W, 35m (1 ind); Amb1 Foz16, 20º 1’ 3.73” S, 39º 50’ 13.76” W, 48m (1 ind); Amb1 Foz17, 19º 55’ 44.66” S, 39º 45’ 38.7” W, 46m (1 ind); Amb2 Foz1, 19º 52’ 15.25” S, 39º 59’ 42.87” W, 19m (1 ind); Amb2 Foz7, 19º 49’ 50.65” S, 39º 52’ 22.92” W, 28m (11 ind); Amb2 Foz11, 19º 57’ 30.39” S, 39º 53’ 35.28” W, 46m (10 ind); Amb2 Foz14, 19º 42’ 28.53” S, 39º 39’ 4.25” W, 36m (6 ind); Amb2 Foz16, 20º 1’ 1.92” S, 39º 50’ 18.19” W, 49m (1 ind); Amb2 Foz17, 19º 55’ 43.7” S, 39º 45’ 39.68” W, 43m (2 ind); Amb2 Foz18, 19º 50’ 16.34” S, 39º 40’ 10.8” W, 46m (3 ind); Amb3 CAND4 , 19º 31’ 51.66” S, 39º 3’ 4.04” W, 140m (1 ind); Amb6 D4, 19º 45’ 54.96” S, 39º 30’ 26.46” W, 121m (2 ind); Amb7 A2, 21º 3’ 26.62” S, 40º 23’ 0.67” W, 36 m (11 ind); Amb7 A3, 21º 4’ 1.29” S, 40º 18’ 50.11” W, 46m (2 ind); Amb7 A4, 21º 4’ 4” S, 40º 14’ 15.31” W, 142m (1 ind); Amb7 B2, 20º 34’ 46.54” S, 40º 11’ 30.67” W, 35m (1 ind); Amb7 B3, 20º 34’ 53.69” S, 40º 6’ 27.35” W, 45m (8 ind); Amb7 C2, 20º 11’ 25.35” S, 40º 2’ 16.02” W, 35m (5 ind); Amb7 C3, 20º 12’ 20.26” S, 39º 57’ 59.7” W, 44m (1 ind); Amb7 F1, 18º 42’ 56.07” S, 39º 31’ 28.8” W, 20m (1 ind); Amb7 F2, 18º 52’ 32.61” S, 39º 8’ 42.82” W, 34m (47 ind); Amb7 F3, 18º 53’ 29.72” S, 39º 6’ 23.3” W, 43m (6 ind); Amb7 G2, 18º 36’ 31.68” S, 39º 9’ 33” W, 30m (10 ind); Amb12 E4, 19º 36’ 3.57” S, 39º 10’ 33.64” W, 142m (1 ind); Amb12 CAND4 , 19º 31’ 51.68” S, 39º 3’ 4.79” W, 163 m (7 ind); Amb13 G2, 18º 36’ 31.38” S, 39º 9’ 33.56” W, 28m (1 ind); Amb13 G3, 18º 40’ 57.41” S, 38º 55’ 39.92” W, 44m (7 ind); Amb14 A4, 21º 4’ 4.81” S, 40º 14’ 13.86” W, 147m (1 ind); Amb14 B1, 20º 34’ 29.6” S, 40º 20’ 54.56” W, 21m (5 ind); Amb14 B3, 20º 34’ 53.05” S, 40º 6’ 27.68” W, 43m (1 ind); Amb14 B4, 20º 35’ 26.19” S, 39º 54’ 59.91” W, 156m (2 ind); Amb14 C2, 20º 11’ 25.75” S, 40º 2’ 15.87” W, 33m (10 ind); Amb14 E2, 19º 18’ 8.36” S, 39º 23’ 24.69” W, 33m (3 ind); Amb14 F2, 18º 52’ 32.42” S, 39º 8’ 41.41” W, 33m (22 ind); Amb14 F3, 18º 53’ 33.65” S, 39º 6’ 20.73” W, 43m (17 ind) .

Diagnostic features: First and last pairs of branchiae cirriform, remaining branchiae flattened; low dorsal crests from chaetiger 12 to chaetigers 15–18.

Description. A large-sized Prionospio , largest complete specimen 12 mm long, 0.45 mm wide at widest part for 94 chaetigers; holotype 10 mm long, 0.4 mm wide at widest part for 74 chaetigers (incomplete). Body dorsoventrally flattened in branchial region and cylindrical afterwards, tapering towards pygidium. Body color whitish to yellow in alcohol ( Fig. 8 ).

Prostomium rounded anteriorly, extending posteriorly as a narrow keel reaching anterior margin of chaetiger 2. U-shaped nuchal organs reaching posterior margin of chaetiger 1 ( Fig. 9 –B ). Prostomial peaks absent. One pair of small eyes or eyes absent. Peristomium surrounding prostomium and partially fused to chaetiger 1, low lateral wings present. Palps lost in all specimens.

Chaetiger 1 with only few chaetae in both rami, especially on the notopodium, shorter than chaetae on succeeding chaetigers. Postchaetal lamellae rhomboid and shifted dorsally on the notopodium, and rounded on neuropodium, both much smaller than lamellae on succeeding chaetigers ( Figs 9B ; 10A ). Prechaetal lamellae absent.

Notopodial postchaetal lamellae foliaceous on chaetigers 2–15 ( Fig. 10 B–D), rounded afterwards and drastically reduced in size, present as a low flap in posterior region. Notopodial prechaetal lamellae small and rounded from chaetiger 2 to chaetigers 15–21 (depending on specimen size). Low dorsal crests from chaetiger 12 to chaetigers 15–18, incomplete crests for about 10 more chaetigers ( Fig. 9A, C ).

Neuropodial postchaetal lamellae rounded from chaetiger 2 to chaetiger 20 ( Fig. 10 B–D), abruptly reduced to a low flap afterwards. Neuropodial prechaetal lamellae small and rounded from chaetiger 2 to chaetiger 15.

Chaetae from notopodia and neuropodia organized in two rows of narrowly unilimbate and granulated capillaries ( Fig. 10 E–F). Chaetae from posterior row up to 1.5 times longer than chaetae from the anterior row; neuropodial chaetae slightly shorter than notopodial chaetae. Towards posterior region, capillaries become progressively elongate, non-limbate, non-granulated, thinner and less numerous ( Fig. 10G ).

Hooks in notopodia starting from chaetigers 21–41, up to four per fascicle, accompanied by 1–5 short nonlimbate capillaries ( Fig. 10H ). Hooks in neuropodia starting from chaetigers 12–19, up to eight hooks per fascicle, accompanied by 1–7 short non-limbate capillaries.All hooks multidentate, with 14 secondary teeth organized in two rows above main tooth ( Figs 9D ; 10I ). Secondary hood present ( Fig. 10I ). Sabre chaetae starting from chaetigers 10–14. Sabre chaetae unilimbate, with sparse light granulations along shaft ( Fig. 10J ).

Up to 10 pairs of smooth branchiae, cirriform on first and last chaetigers (rarely cirriform also on the penultimate chaetiger) and robust and flattened on remaining chaetigers ( Figs 9 A–C; 10K–L). Branchiae starting from chaetiger 2, up to two times longer than notopodial lamellae, not significantly reduced in length towards last branchial pair. First and last pairs of branchiae sparsely ciliated, remaining pairs of branchiae densely ciliated throughout its length (except tip). All branchiae completely free from notopodial postchaetal lamellae ( Fig. 9 A–C).

Pygidium bearing a single long dorsal cirrus and two short ventro-lateral cirri ( Fig. 10M ).

Oocytes from chaetiger 10, measuring up to 150 µm.

Variation: In specimens with fewer than 10 pairs of branchiae, the last pair is always cirriform, regardless of the chaetiger on which they occur. In juveniles, the ventral pygidial cirri were not observed and the pygidium possessed a single dorsal cirrus.

Methyl green staining pattern: Anterior margin of the prostomium, dorsal and lateral sides of the peristomium and ventral midline intensely stained, postchaetal lamellae from the branchial region slightly stained.

Remarks. Prionospio kinbergi sp. nov. is unusual in having a combination of cirriform and flattened branchiae, a character observed only in P. cirrifera , P. elongata Imajima, 1990b , described from Japan and P. aluta Maciolek, 1985 , described from Massachusetts ( USA).

All four species share a similar hook morphology (seven pairs of secondary teeth in P. kinbergi sp. nov., six to seven pairs of secondary teeth in P. elongata , five to six pairs in P. cirrifera and six pairs in P. aluta ) and an overlap in the starting chaetiger of neuropodial hooded hooks (chaetigers 10–20 in P. kinbergi sp. nov., chaetiger 19 in P. elongata , chaetigers 10–17 in P. cirrifera and chaetigers 14–17 in P. aluta ).

However, species with similar branchial and hook morphology to P. kinbergi can be separated based on the starting chaetiger of sabre chaetae (chaetigers 10–14 in P. kinbergi sp. nov. and P. aluta , chaetiger 16 in P. elongata and chaetiger 10 in P. cirrifera ), distribution of dorsal crests (from chaetiger 12 to chaetigers 15–18 in P. kinbergi sp. nov., from chaetiger 14 to several chaetigers [distribution not mentioned] in P. elongata and from chaetiger 10 almost the end of the body in P. cirrifera ; and dorsal crests present at least in chaetiger 15 in P. aluta ).

The same group of similar species can also be distinguished based on the shape of postchaetal lamellae from chaetiger 1 (rhomboid on the notopodium and digitiform on the neuropodium in P. kinbergi sp. nov., foliaceous on both rami in P. elongata , triangular on the notopodium and rounded on the neuropodium in P. cirrifera and rounded on both rami in P. aluta ),branchial distribution (10 pairs in P. kinbergi sp. nov., 13 pairs in P. elongata , six to eight pairs in P. cirrifera [ Mackie 1984; Maciolek 1985] and six pairs in P. aluta ) and branchial morphology (first and last pairs cirriform in P. kinbergi sp. nov. and P. cirrifera , first and last four pairs cirriform in P. elongata and only first pair cirriform in P. aluta ).

Apart from the characters discussed above, P. kinbergi sp. nov. can be readily distinguished from P. aluta due to the absence of interparapodial pouches, a character rarely observed among Prionospio species.

Prionospio kinbergi sp. nov. is similar to P. acuta sp. nov. and P. mutata sp. nov. in having robust flattened branchiae, although these species bear only robust branchiae and not a combination of cirriform and flattened branchiae, as in P. kinbergi sp. nov. All three species share a similar distribution of dorsal crests (from chaetigers 10–11 to chaetigers 15–17 in P. acuta 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.), although P. kinbergi sp. nov. can be distinguished by the prostomial shape (rounded in P. mutata sp. nov. and P. kinbergi sp. nov. and triangular in P. acuta sp. nov.), the presence of sabre chaetae appearing abruptly (absent in P. acuta sp. nov. and appearing gradually in P. mutata sp. nov.) and the presence of incomplete crests after the last complete dorsal crest, from chaetiger 25 to chaetiger 28.

In specimens of Prionospio kinbergi sp. nov. with fewer than 10 pairs of branchiae, the last pair is always cirriform, regardless of the chaetiger on which they occur. This suggests a gradual transformation of branchiae from cirriform to tapered, as those on the penultimate chaetigers are sometimes also cirriform, but more robust than the last branchial pair.

According to Radashevsky (2012), in the majority of species from the Prionospio -complex, the number of branchiae is constant and species-specific, increasing only to a certain point, when new branchial pairs will not develop regardless of specimen growth. The sequence of branchial development in P. kinbergi sp. nov., however, is not clear, since branchiae from chaetiger 2 remain cirriform in adults, while the remaining branchiae gradually transform into flattened branchiae—except for the last branchial pair, which also remains cirriform in adults.

Etymology. The specific epithet, kinbergi , is a tribute to Johan G. H. Kinberg (1820–1908), who was the first to describe a Brazilian spionid, Laonice brevicornis Kinberg, 1866 .

Habitat: Medium to fine sand, 19–163 m depth.

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

Figures

FIGURE 8. Prionospio kinbergi sp. nov., dorso-lateral view (MNRJP-2750, holotype), showing characteristic color in ethanol. Abbreviations: Cbr, cirriform branchia; dc, dorsal crest; Fbr, flattened branchia; pe, peristomium; pr, prostomium.

FIGURE 9. SEM of Prionospio kinbergi sp. nov., dorsal view. Anterior end and mid-body chaetigers. B. Close-up of the anterior end. C. Anterior end and mid-body chaetigers. D. Hooks (hoods removed).Abbreviations: br, branchia; dc, dorsal crest; ho, hook; nol, notopodial lamella; pe, peristomium; pr, prostomium.

FIGURE 10. Prionospio kinbergi sp. nov. A. Chaetiger 1. B. Chaetiger 2. C. Chaetiger 3. D. Chaetiger 4. E. Anterior capillary chaeta from anterior row. F. Anterior capillary chaeta from posterior row. G. Posterior capillary chaetae. H. Companion capillary chaetae. I. Hooded hook. J. Sabre chaetae. K. Flattened branchiae. L. Cirriform branchiae. M. Posterior-most chaetigers and pygidium.