Prionospio quadrilamellata, 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 : 500-504

Prionospio quadrilamellata sp. nov.

( Figures 32–34 )

Type material. Brazil. Espírito Santo Basin. Holotype: Amb 5 C6, 20°15’36,86” S, 39°46’15,05” W, 02 Dec 2011 to 02 Feb 2012, 1040m, MNRJP-2772. Paratypes: Amb11 C7, 20°17’37,38” S, 39°42’36,72” W, 06 Jun 2013 to 17 Jul 2013, 1355m, MNRJP-2773 (5 ind) .

Additional material examined. Amb3 E6, 19°40’8,03” S, 39°7’22,1” W, 1035m (1 ind); Amb3 CAND6 , 19°37’50,08” S, 39°3’56,16” W, 970m (1 ind); Amb4 F6, 19°52’56,9” S, 38°35’8,88” W, 1022m (1 ind); Amb5 A6, 21°4’43,84” S, 40°8’31,76” W, 1024m (2 ind); Amb5 A7, 21°4’51,67” S, 40°4’14,88” W, 1300m (3 ind); Amb5 B6, 20°36’2,03” S, 39°51’35,37” W, 1000m (4 ind); Amb5 B7, 20°36’42,03” S, 39°49’25,36” W, 1333m (1 ind); Amb5 C6, 20°15’36,86” S, 39°46’15,05” W, 1040m (2 ind); Amb5 C8, 20°25’16,2” S, 39°27’20” W, 1918m (1 ind); Amb5 D7, 19°54’5,01” S, 39°22’20,04” W, 1335m (1 ind); Amb8 E7, 19°47’5,96” S, 39°3’11,96” W, 1258m (1 ind); Amb8 G6, 19°3’32,9” S, 37°49’4,82” W, 988m (2 ind); Amb11 B6, 20°36’1,61” S, 39°51’39,15” W, 1003m (1 ind); Amb11 B7, 20°36’48,64” S, 39°49’32,61” W, 1324m (2 ind); Amb11 C5, 20°14’17,95” S, 39°48’34,35” W, 395m (3 ind); Amb11 D8, 20°8’45,23” S, 39°7’31,74” W, 1926m (1 ind); Amb11 F7, 20°4’9,68” S, 38°31’29,01” W, 1295m (2 ind); Amb12 D6, 19°50’6,01” S, 39°26’34,62” W, 1050m (2 ind); Amb12 D7, 19°54’4,77” S, 39°22’29,46” W, 1335m (1 ind); Amb12 E6, 19°40’1,46” S, 39°7’21,99” W, 1050m (1 ind); Amb12 F5, 19°34’20,47” S, 38°41’19,8” W, 449m (1 ind); Amb12 CANWN7 , 19°58’12,82” S, 39°31’42,22” W, 1316m (2 ind) .

Diagnostic features: Notopodial postchaetal lamellae quadrangular from chaetiger 2 to chaetigers 4–6, dorsal crests low from chaetiger 9 to chaetiger 13, four pairs of apinnate branchiae.

Description. A small-sized Prionospio species, largest complete specimen 5 mm long, 0.2 mm wide at widest point for 43 chaetigers; holotype 3.5 mm long, 0.15 mm wide at widest point for 33 chaetigers. Body slightly dorsoventrally flattened on anterior region and cylindrical on middle and posterior regions ( Figs 32 ; 33B ), tapering towards pygidium. Body color whitish in alcohol ( Fig. 32 ).

Prostomium rectangular, narrow, rounded on anterior margin, extending posteriorly as a narrow keel reaching the posterior margin of chaetiger 1 ( Figs 32 ; 33A, C ). U-shaped nuchal organs reaching anterior margin of chaetiger 1. Prostomial peaks absent. One or two pairs of small eyes present. Peristomium surrounding prostomium and partially fused to chaetiger 1, lateral wings absent ( Figs 32 ; 33 A–C). Palps lost in all specimens.

Chaetiger 1 with only a few chaetae on both rami, shorter than chaetae on succeeding chaetigers. Postchaetal lamellae rounded on notopodium and digitiform in neuropodium, both much smaller than lamellae on succeeding chaetigers, especially in neuropodium. Prechaetal lamellae absent ( Fig. 34A ).

Notopodial postchaetal lamellae quadrangular from chaetiger 2 to chaetigers 4–6 (depending on specimen size) ( Fig. 34 B–D), triangular from chaetigers 5–7 to chaetigers 6–9 and rounded afterwards, gradually reducing in size, present as a low flap from middle region onwards. Notopodial prechaetal lamellae absent. Dorsal crests low from chaetiger 9 to chaetiger 13 ( Fig. 33 A–B).

Neuropodial postchaetal lamellae rounded from chaetiger 2 to chaetigers 5–7 ( Fig. 34 B–D), abruptly reduced to a low flap afterwards. Neuropodial prechaetal lamellae absent.

Chaetae from notopodia and neuropodia organized in two rows of narrowly unilimbate and granulated capillaries. Notopodial chaetae ( Fig. 34E ) slightly longer than neuropodial chaetae ( Fig. 34F ). Towards the posterior region, capillaries progressively become elongate, non-limbate, non-granulated, thinner and less numerous ( Fig. 34G ).

Hooks in notopodia starting from chaetigers 20–32, up to five per fascicle, accompanied by 1–5 non-limbate capillaries ( Fig. 34H ). Hooks in neuropodia starting from chaetigers 9–13, up to seven per fascicle, accompanied by 1–7 non-limbate capillaries. All hooks multidentate, with secondary teeth arranged in two rows above main tooth ( Figs 33D ; 34I ). Secondary hood absent. Sabre chaetae starting from chaetigers 9–11 ( Fig. 34J ). Sabre chaetae nonlimbate and granulated throughout length, robust on first 2–3 chaetigers and thinner on remaining chaetigers ( Fig. 33D ).

Branchiae present on chaetigers 2–5, about same length of notopodial lamellae on chaetigers 2–4 and slightly shorter than notopodial lamellae on chaetiger 5. All branchiae apinnate, robust and flattened ( Fig. 34K ).

Pygidium bearing a single thin and long dorsal cirrus and two short ventral cirri ( Fig. 34L ).

Variation: In juveniles bearing less than 20 chaetigers, neuropodial postchaetal lamellae absent on chaetiger 1.

Methyl green staining pattern: No pattern observed, whole specimen weakly stained.

Remarks. Prionospio quadrilamellata sp. nov. is similar to P. fauchaldi , P. corrugata sp. nov., P. alexandrae sp. nov., P. vallensis , P. kaplani and P. amarsupiata in bearing a rectangular prostomium, although species can be distinguished based on branchiae morphology and distribution—four pairs of flattened and apinnate branchiae in P. quadrilamellata sp. nov., up to six pairs of apinnate branchiae in both P. fauchaldi and P. corrugata sp. nov., two pairs of apinnate branchiae in both P. alexandrae sp. nov. and P. kaplani , four pairs of wrinkled branchiae in P. vallensis and four pairs of branchiae, first (pinnate) and fourth (apinnate) pairs cirriform in P. amarsupiata ( Maciolek 1985; Paterson et al. 2016).

The species also differs from the aforementioned species in the distribution of dorsal crests—on chaetigers 9–13 in P. quadrilamellata sp. nov., on chaetigers 8–11 in P. fauchaldi , from chaetigers 8–9 to chaetigers 14–15 in P. corrugata sp. nov., absent in P. alexandrae sp. nov., from chaetiger 6 to beyond chaetiger 20 in P. vallensis , on chaetigers 7–17 in P. kaplani and on chaetigers 5–20 in P. amarsupiata . Species can be further distinguished based on the starting chaetiger of sabre chaetae—from chaetigers 9–11 in P. quadrilamellata sp. nov., not mentioned in P. fauchaldi , from chaetigers 10–17 in P. corrugata sp. nov., absent in P. alexandrae sp. nov., chaetiger 10 in P. vallensis , not observed in P. kaplani and from chaetigers 18–19 in P. amarsupiata . Unfortunately, characters such as the starting chaetiger of notopodial and neuropodial hooded hooks presented a considerable overlap among species, not being particularly useful in separating species ( Maciolek 1985; Paterson et al. 2016).

Prionospio quadrilamellata sp. nov. is also similar to P. cinthyae sp. nov. and P. biancoi sp. nov. in bearing four pairs of apinnate branchiae, although species can be easily distinguished due to prostomium shape—rectangu-lar in P. quadrilamellata sp. nov. and P. biancoi sp. nov. and triangular in P. cinthyae sp. nov. and branchial mor-phology—all pairs flattened in P. quadrilamellata sp. nov., first and fourth pairs wrinkled in P. cinthyae sp. nov. and first and fourth pair cirriform in P. biancoi sp. nov. Species also differ on the starting chaetiger of notopodial hooded hooks, in case of P. biancoi sp. nov. —chaetigers 20–32 in P. quadrilamellata sp. nov. and chaetiger 67 in P. biancoi sp. nov.; starting chaetiger of neuropodial hooded hooks, in case of P. biancoi sp. nov. —chaetigers 9–13 in P. quadrilamellata sp. nov. and chaetigers 16–22 in P. biancoi sp. nov. and starting chaetiger of sabre chaetae—chaetigers 9–11 in P. quadrilamellata sp. nov., consistently from chaetiger 10 in P. cinthyae sp. nov. and chaetigers 14–20 in P. biancoi sp. nov.

Etymology. The specific epithet, quadrilamellata , refers to the shape of notopodial postchaetal lamellae from the anterior region (quadri is term for quadrangular, while lamellata refers to the lamellae).

Habitat: Coarse silt to fine silt, 395–1926 m depth.

Distribution: Brazil (Rio de Janeiro, Espírito Santo, Sergipe and Alagoas states), Atlantic Ocean.

Figures

FIGURE 32. Prionospio quadrilamellata sp. nov., showing characteristic color in ethanol (MNRJP-2772, holotype). Abbreviations: br, branchiae; pe, peristomium; pr, prostomium.

FIGURE 33. SEM of Prionospio quadrilamellata sp. nov. A. Anterior end, dorsal view. B. Whole fragment, dorsal view. C. Close-up of anterior end. D. Mid-body chaetigers, dorsolateral view. Abbreviations: dc, dorsal crest; hh, hooded hook; nola, notopodial lamella; pe, peristomium; pr, prostomium; sa, sabre chaetae.

FIGURE 34. Prionospio quadrilamellata sp. nov. A. Chaetiger 1. B. Chaetiger 2. C. Chaetiger 3. D. Chaetiger 4. E. Notochaetae from anterior region. F. Neurochaetae from anterior region. G. Posterior capillary chaetae. H. Companion capillary chaetae. I. Hooded hook. J. Sabre chaetae. K. Branchia. L. Posterior-most chaetigers and pygidium.