Prionospio alexandrae, 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 : 492-497

Prionospio alexandrae sp. nov.

( Figures 26–28 )

Type material. Brazil. Espírito Santo Basin. Holotype: Amb 3 G9, 19°3’13,43” S, 37°45’37,49” W, 02 Dec 2011 to 02 Feb 2012, 2426m, MNRJ-2768. Paratypes: Amb4 F10, 20°46’23,65” S, 38°17’17,65” W, 02 Dec 2011 to 02 Feb 2012, 3004m, MNRJP-2769 (9 ind) .

Additional material examined. Amb3 G9, 19°3’13,43” S, 37°45’37,49” W, 2426m (27 ind); Amb3 G10, 19°3’55,8” S, 37°45’8,27” W, 2993m (12 ind); Amb4 A9, 21°9’35,19” S, 38°52’4,93” W, 2502m (2 ind); Amb4 A10, 21°11’4,9” S, 38°28’2,78” W, 3006m (4 ind); Amb4 B8, 20°41’33,45” S, 39°35’14,76” W, 1914m (8 ind); Amb4 B10, 21°4’40,47” S, 38°26’13,68” W, 3007m (3 ind); Amb4 C10, 20°59’0,28” S, 38°28’36,56” W, 2997m (3 ind); Amb4 D10, 20°53’33,64” S, 38°21’17,35” W, 3004m (19 ind); Amb4 E9, 20°35’50,48” S, 38°27’7,64” W, 2494m (29 ind); Amb4 E10, 20°49’23,58” S, 38°17’11,07” W, 2997m (13 ind); Amb4 F7, 20°4’8,18” S, 38°31’27,32” W, 1302m (2 ind); Amb4 F8, 20°16’35,72” S, 38°27’18,98” W, 1902m (23 ind); Amb4 F9, 20°29’3,31” S, 38°23’15,5” W, 2504m (30 ind); Amb4 F10, 20°46’23,65” S, 38°17’17,65” W, 3004m (17 ind); Amb5 A8, 21°6’30,57” S, 39°38’36,43” W, 1889m (9 ind); Amb5 A9, 21°9’40,3” S, 38°52’25,04” W, 2498m (7 ind); Amb5 B6, 20°36’2,03” S, 39°51’35,37” W, 1000m (2 ind); Amb5 B7, 20°36’42,03” S, 39°49’25,36” W, 1333m (5 ind); Amb5 B9, 20°54’44,14” S, 38°56’10,72” W, 2519m (21 ind); Amb5 C6, 20°15’36,86” S, 39°46’15,05” W, 1040m (2 ind); Amb5 C7, 20°17’41,07” S, 39°42’38,02” W, 1358m (14 ind); Amb5 C8, 20°25’16,2” S, 39°27’20” W, 1918m (11 ind); Amb5 C9, 20°48’39,87” S, 38°45’23,86” W, 2496m (9 ind); Amb5 D7, 19°54’5,01” S, 39°22’20,04” W, 1335m (3 ind); Amb5 D8, 20°8’42,82” S, 39°7’29,5” W, 1922m (29 ind); Amb5 D9, 20°34’36,32” S, 38°40’53,6” W, 2460m (7 ind); Amb5 E8, 20°15’59,97” S, 38°40’53,86” W, 1887m (17 ind); Amb6 CANWN7 , 19°58’11,44” S, 39°31’38,29” W, 1300m (2 ind); Amb8 E7, 19°47’5,96” S, 39°3’11,96” W, 1258m (5 ind); Amb8 G7, 19°3’29,3” S, 37°48’39,27” W, 1302m (2 ind); Amb8 G8, 19°3’45,82” S, 37°47’28,26” W, 1928m (24 ind); Amb11 A7, 21°4’43,08” S, 40°4’12,96” W, 1295m (3 ind); Amb11 A8, 21°6’38,26” S, 39°38’31,44” W, 1889m (14 ind); Amb11 A9, 21°9’39,38” S, 38°52’7,25” W, 2502m (6 ind); Amb11 A10, 21°10’59,11” S, 38°28’4,99” W, 2987m (3 ind); Amb11 B7, 20°36’48,64” S, 39°49’32,61” W, 1324m (2 ind); Amb11 B8, 20°41’33,93” S, 39°35’22,06” W, 1908m (9 ind); Amb11 B9, 20°54’43,79” S, 38°56’10,85” W, 2520m (14 ind); Amb11 B10, 21°4’33,4” S, 38°26’19,34” W, 3001m (8 ind); Amb11 C7, 20°17’37,38” S, 39°42’36,72” W, 1355m (19 ind); Amb11 C8, 20°25’13,22” S, 39°27’19,49” W, 1920m (6 ind); Amb11 C9, 20°48’37,26” S, 38°45’28,85” W, 2465m (18 ind); Amb11 C10, 20°57’57,99” S, 38°27’52,41” W, 2996m (7 ind); Amb11 D8, 20°8’45,23” S, 39°7’31,74” W, 1926m (30 ind); Amb11 D9, 20°34’41,91” S, 38°40’57,73” W, 2496m (9 ind); Amb11 D10, 20°53’28,94” S, 38°21’21,75” W, 3000m (14 ind); Amb11 E8, 20°15’55,63” S, 38°40’45,57” W, 1892m (17 ind); Amb11 E9, 20°35’51,99” S, 38°27’13,04” W, 2501m (9ind); Amb11E10, 20°49’19,95” S, 38°17’8,76”W, 2994m (12 ind); Amb11 F7, 20°4’9,68” S, 38°31’29,01” W, 1295m (5 ind); Amb11 F8, 20°16’38,17” S, 38°27’26,52” W, 1904m (25 ind); Amb11 F9, 20°29’3,85” S, 38°23’18,56” W, 2507m (27 ind); Amb11 F10, 20°46’17,79” S, 38°17’16,01” W, 3002m (13 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 (9 ind); Amb12 E6, 19°40’1,46” S, 39°7’21,99” W, 1050m (1 ind); Amb12 E7, 19°47’2,44” S, 39°3’14,62” W, 1250m (3 ind); Amb12 G7, 19°3’30,62” S, 37°48’46,66” W, 1347m (1 ind); Amb12 G8, 19°3’39,78” S, 37°47’39,35” W, 1867m (23 ind); Amb12 G9, 19°3’10,76” S, 37°45’34,37” W, 2770m (33 ind); Amb12 G10, 19°3’10,22” S, 37°45’28,45” W, 2950m (31 ind); Amb12 CANWN7 , 19°58’12,82” S, 39°31’42,22” W, 1316m (5 ind) .

Diagnostic features: Palps bearing small papillae, cirriform branchiae on chaetigers 2 and 3 only, postchaetal lamellae enlarged on chaetiger 3, lack of dorsal crests, lack of pygidial cirri.

Description. A small-sized Prionospio species, largest complete specimen 7 mm long, 0.25 mm wide at widest part for 52 chaetigers; holotype 5 mm long, 0.15 mm wide at widest part for 40 chaetigers. Body slightly dorsoventrally flattened throughout, tapering towards pygidium. Body color whitish in alcohol ( Fig. 26 ).

Prostomium rectangular, narrow, anteriorly truncated, extending posteriorly as a narrow keel reaching anterior margin of chaetiger 2 ( Figs 26 ; 27 A–D). U-shaped nuchal organs reaching posterior margin of chaetiger 1. Prostomial peaks absent. Eyes absent. Peristomium surrounding prostomium and partially fused to chaetiger 1, lateral wings absent ( Figs 26 ; 27 A–D). Grooved palps reaching up to chaetiger 6, lost in most specimens. Palps bearing minute papillae along groove margin ( Fig. 27 E–F).

Chaetiger 1 with only a few chaetae on both rami, shorter than chaetae on succeeding chaetigers. Postchaetal lamellae absent on both rami. Prechaetal lamellae absent ( Fig. 28A ).

Notopodial postchaetal lamellae foliaceous from chaetiger 2 to chaetigers 6–10 (depending on specimen size) ( Figs 27 A–D; 28B–D), longest on chaetiger 3 (twice as long as surrounding lamellae) and rounded afterwards, gradually reducing in size, present as a low flap from middle region onwards. Notopodial prechaetal lamellae absent. Dorsal crests absent.

Neuropodial postchaetal lamellae rounded from chaetiger 2, elongated on chaetiger 3 and rounded from chaetiger 4 to chaetigers 8–10 ( Fig. 28 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 lightly granulated capillaries ( Fig. 28E, F ). On chaetigers 2–4, neuropodial capillaries extremely long, up to twice as long as capillaries from chaetiger 5 ( Fig. 28G ). On remaining chaetigers, neuropodial chaetae slightly shorter than notopodial chaetae. Towards posterior region, capillaries progressively become elongate, non-limbate, non-granulated, thinner and less numerous ( Fig. 28H ).

Hooks in notopodia starting from chaetigers 26–46, up to six per fascicle, accompanied by 1–6 non-limbate capillaries ( Fig. 28I ). Hooks in neuropodia starting from chaetigers 10–20, up to nine per fascicle, accompanied, by 1–8 non-limbate capillaries. All hooks multidentate, with secondary teeth arranged in two rows above main tooth ( Fig. 28J ). Secondary hood absent. Sabre chaetae absent throughout.

Branchiae present on chaetigers 2 and 3 only, up to twice as long as notopodial lamellae on chaetiger 2 and shorter than notopodial lamellae on chaetiger 3. Both branchiae cirriform, apinnate and sparsely ciliated, slightly wrinkled on chaetiger 2 and smooth on chaetiger 3 ( Figs 27 B–D; 28K–L).

Pygidium rounded, lacking cirri.

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

Remarks. Prionospio alexandrae sp. nov. is unusual for having only two pairs of branchiae, which is uncommon among Prionospio species, observed only in P. hermesia , P. kaplani and P. solisi , although species can be distinguished by branchial morphology and distribution—on chaetigers 2–3, slightly wrinkled on chaetiger 2 and smooth on chaetiger 3 in P. alexandrae sp. nov., on chaetigers 2–3, smooth to slightly wrinkled and cylindrical in P. hermesia , digitiform on chaetiger 2 and conical on chaetiger 3 in P. kaplani and on chaetigers 3–4, both pairs robust and flattened in P. solisi . Prionospio alexandrae sp. nov. also differs from the aforementioned species in lacking sabre chaetae (also absent in P. hermesia and apparently absent in P. kaplani ) and in lacking dorsal crests (also lacking in P. solisi ) ( Paterson et al. 2016).

Among the species discussed above, P. alexandrae sp. nov. is most similar to P. hermesia in lacking sabre chaetae, greatly enlarged notopodial postchaetal lamellae on chaetiger 3 and an elongated neuropodial postchaetal lamellae on chaetiger 3, although species can be distinguished based on the prostomial morphology—rectangular in P. alexandrae sp. nov. and oval in P. hermesia , presence of elongated neuropodial capillaries on chaetigers 2–4 in P. alexandrae sp. nov., present only in chaetiger 3 in P. hermesia ; starting chaetiger of notopodial hooded hooks—chaetigers 26–46 in P. alexandrae sp. nov. and chaetiger 48 in P. hermesia , starting chaetigers of neuropodial hooded hooks—chaetigers 10–20 in P. alexandrae sp. nov. and chaetigers 13–14 in P. hermesia , hood mor-phology—all multidentate in P. alexandrae sp. nov. and bi- to multidentate in P. hermesia , and lack of secondary hood on the hooded hooks of P. alexandrae sp. nov.

Prionospio alexandrae sp. nov. exhibits unusual palp morphology, being the only known species to bear papillae along groove margin ( Fig. 27 E–F). The function of these papillae is unknown.Although this is a useful character to identify this species, palps are unfortunately lost in most specimens.

The pygidium morphology is also unusual because both cirri and lobes were not observed.Although Blake et al. (2017) diagnosis of the genus Prionospio includes a pygidium in which dorsal cirrus and ventral cirri are fused, this does not seem to be the case, as the pygidium ends abruptly, lacking elongated structures. Since over 50 complete specimens were examined, all with the same pygidium morphology, we believe our observations to be correct.

Four specimens were found in samples collected along the 400m isobath and were removed from this work, as these specimens occurred on shallower depths when compared with other records and their identity cannot be confirmed at the moment. These specimens will be set aside for the time being and reexamined in the future.

This species was also observed in samples collected in the continental slope of Sergipe and Alagoas states, northeastern Brazil, on similar depths (pers. obs.) .

Etymology. The specific epithet, alexandrae , is an homage to Dr. Alexandra E. Rizzo, a fellow polychaete researcher and a friend.

Habitat: Medium silt to clay, 1000–3007m depth.

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

Figures

FIGURE 26. Prionospio alexandrae sp. nov., showing characteristic color in ethanol (MNRJP-2768, holotype). Abbreviations: br, branchiae; pe, peristomium; pr, prostomium.

FIGURE 27. SEM of Prionospio alexandrae sp. nov. A. Anterior end and mid-body chaetigers, dorsal view. B. Anterior end, dorsal view. C. Anterior end, dorsolateral view. D. Close-up of anterior end, dorsal view. E. Anterior end and mid-body chaetigers, lateral view. F. Palp, lateral view. Abbreviations: br, branchiae; nola, notopodial lamella; pa, palp; pe, peristomium; pp, palp papillae; pr, prostomium.

FIGURE 28. Prionospio alexandrae 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. Row of long neurochaetae from chaetigers 2–4. H. Posterior capillary chaetae. I. Companion capillary chaetae. J. Hooded hook. K. Branchia from chaetiger 2. L. Branchia from chaetiger 3. M. Posterior-most chaetigers and pygidium.