Prionospio solisi, Peixoto & Paiva, 2019

Peixoto, Antônio João Malafaia & Paiva, Paulo Cesar De, 2019, New Prionospio and Laubieriellus (Annelida: Spionidae) species from Southeastern Brazil, Zootaxa 4577 (3), pp. 529-547 : 532-536

Prionospio solisi sp. nov.

( Figures 2–5 )

Type material. Brazil. Espírito Santo Basin. Holotype: Amb 6 D4R1, 19° 45' 55.39" S 39° 30' 25.74" W, 12/2011 to 02/ 2012, 149m, MZUSP 3390 . Paratypes: Amb6 D4R1, 19° 45' 55.39" S 39° 30' 25.74" W, 12/2011 to 02/ 2012, 149m, MNRJP 1826 (6 ind), MZUSP 3391 (3 ind); Amb6 D4R2, 19° 45' 54.88" S 39° 30' 26.22" W, 12/2011 to 02/ 2012, 142m, MNRJP 1825 (2 ind); Amb6 D4R3, 19° 45' 54.96" S 39° 30' 26.46" W, 12/2011 to 02/ 2012, 144m, MNRJP 1827 (1 ind) .

Additional material examined. Brazil. Espírito Santo Basin. Amb 3 CAND4 , 19° 31' 51.66" S 39° 3' 4.04" W, 171m (114 ind); Amb 3 CAND7 , 19° 42' 18.42" S 39° 5' 52.41" W, 1307m (1 ind); Amb4 B8, 20° 41' 33.45" S 39° 35' 14.76" W, 1914m (1 ind); Amb5 C7, 20° 17' 41.07" S 39° 42' 38.02" W, 1358m (1 ind); Amb6 D4, 19° 45' 55.39" S 39° 30' 25.74" W, 149m (56 ind); Amb6 E4, 19° 36' 5.17" S 39° 10' 32.93" W, 153m (1 ind); Amb11 A5, 21° 4' 4.67" S 40° 13' 6.06" W, 415m (1 ind); Amb11 C7, 20° 17' 37.38" S 39° 42' 36.72" W, 1355m (1 ind); Amb11 E8, 20° 15' 55.44" S 38° 40' 48.23" W, 1892m, (1 ind); Amb11 F8, 20° 16' 38.17" S 38° 27' 26.52" W, 1904m (3 ind); Amb12 CAND4 , 19° 31' 51.68" S 39° 3' 4.79" W, 171m (40 ind); Amb12 CAND6 , 19° 37' 45.14" S 39° 3' 58.75" W, 1050m (12 ind) .

Diagnostic features: Branchiae only on chaetigers 3–4, apinnate; dark yellow pigment present on anterior region.

Description. A small-sized spionid, largest individual about 7.5 mm long, 0.25 mm wide for 81 chaetigers, holotype 7.3 mm long, 0.23 mm wide for 65 chaetigers. Body cylindrical, slightly dorsoventrally compressed after branchial region and tapered towards the pygidium. Body color whitish in alcohol with conspicuous dark yellow pigment inclusions present on dorsal and ventral sides from chaetiger 4 or 5 to chaetigers 8–12 (strongest on chaetigers 8–10), including parapodia ( Fig 2 A–C).

Prostomium anteriorly rounded, extending posteriorly as a narrow keel to the posterior margin of chaetiger 1 ( Figs 2 A–C; 3A; 4A–B). Two pairs of black eyes in trapezoidal arrangement (posterior pair faded in alcohol) present or eyes absent. Prostomial peaks absent. Peristomium surrounding prostomium and partially fused to the first chaetiger, lacking lateral wings. Grooved palps reaching up to chaetiger 8, lost in most individuals.

Chaetiger 1 with only a few short chaetae in both rami. Postchaetal lamellae rounded, reduced. Prechaetal lamellae absent.

Notopodial postchaetal lamellae triangular on chaetigers 2–4, largest on chaetigers 3 and 4, rounded with a pointed tip on chaetiger 5, rounded on chaetiger 6, and reduced to a low flap from chaetiger 7 onwards ( Figs 2 A–C; 3A; 4A–B). Dorsal crests absent. Prechaetal lamellae absent throughout.

Neuropodial postchaetal lamellae triangular with rounded corners on chaetiger 2, rounded on chaetigers 3 and 4 and flaplike from chaetiger 5, drastically reduced in size from chaetiger 7 onwards ( Figs 2 A–B; 3B; 4A); lamellae slightly more developed in both rami on last 4–7 chaetigers. Prechaetal lamellae absent throughout.

Chaetae organized in two rows of unilimbate and sparsely granulated capillaries ( Fig. 5A ). In anterior notopodia, capillaries of posterior rows up to 1.3 times longer than capillaries in anterior row ( Fig. 5B ). Towards the posterior region, capillaries progressively become elongate, non-limbate, thin and less numerous ( Fig. 5C ).

Hooks in notopodia from chaetigers 48–61, up to two per fascicle, accompanied by 1–4 short non-limbate capillaries. Hooks in neuropodia from chaetigers 9–14, up to eight per fascicle, accompanied by 3–6 non-limbate capillaries. Neuropodial hooks slightly curved near the tip. Hooks multidentate, with 8–10 secondary teeth arranged in two rows above main tooth ( Figs 3C ; 5E ). Small secondary hood present ( Fig. 5E ). Hooks accompanied by 3–10 short non-limbate capillaries.

Sabre chaetae with light granulations along the shaft, from chaetiger 9–11 (usually chaetiger 10) ( Figs 3B ; 5D ).

Two pairs of branchiae on chaetigers 3 and 4, of the same length or slightly longer than notopodial postchaetal lamellae (longer on chaetiger 3), completely free from notopodial lamellae. Branchiae triangular, flattened and densely ciliated ( Figs 2A, C ; 3A ; 4 A–B). Branchiae absent on chaetigers 2 and 5 ( Figs 2A, C ; 3A ; 4 A–B).

Pygidium with one long mid-dorsal cirrus and a pair of shorter ventral cirri ( Figs 2D ; 3D ).

Oocytes from chaetigers 11–14, measuring up to 100 µm.

Methyl green pattern: Intense staining on prostomium, dorsal side of peristomium, dorsum of chaetigers 8– 16 and lateral sides of chaetigers 8–20.

Remarks: The placement of this species in any current genus is problematic since, based on branchiae starting on chaetiger 3 and pigmentation of the anterior chaetigers, it resembles Aurospio species. However, the branchiae are morphologically similar to the apinnate branchiae observed in chaetigers 3 and 4 of Prionospio sensu stricto (i.e., robust, flattened, densely ciliated, and free from the notopodial postchaetal lamellae), as well as the presence of a secondary hood on the hooded hooks, places the species closer to the genus Prionospio .

Boundaries between both genera are still discussed, although, according to Blake et al. (2017), in the last years, several Prionospio species have been erroneously attributed to Aurospio ( Sigvaldadóttir 2002; Mincks et al. 2009; Patterson et al. 2016). According to the current valid diagnosis, only species bearing branchiae starting from chaetiger 3 and partially fused to the notopodial postchaetal lamellae and lacking a secondary hood on the hooded hooks should be included in Aurospio , a view also followed in this work. Aurospio pilkena ( Wilson, 1990) , a species with a similar branchial arrangement and morphology, was described as Prionospio pilkena Wilson 1990 and placed in Aurospio by Sigvaldadóttir (1998), although Dagli & Çinar (2011) treat it as Prionospio (Minuspio) pilkena .

An amended diagnosis of the genus Prionospio is proposed in this work to include species with branchiae starting from chaetiger 3 and not fused to the notopodial lamellae, rather than erecting a new taxon within the Prionospio -complex, which is beyond the scope of this work as it would require a review of all related taxa.

Prionospio solisi sp. nov. differs from the remaining Prionospio species by the presence of conspicuous dark yellow pigment inclusions on the anterior region and the presence of only two pairs of branchiae, on chaetigers 3 and 4. According to Radashevsky (2012), late development of branchiae on anterior chaetigers is common in Prionospio , which could suggest that the species represents a juvenile stage. However, the same branchial pattern was observed in all individuals, regardless of size or sexual maturity.

Regarding species recorded in Brazil, Prionospio solisi sp. nov. shares the absence of dorsal crests with P. dubia , P. lighti , P. perkinsi Maciolek, 1985 and P. pygmaeus . Prionospio solisi sp. nov. differs from P. lighti and P. perkinsi by the lack of prostomial peaks, lack of lateral wings, starting chaetiger of notopodial hooded hooks and number of branchial pairs, up to 12 pairs in P. lighti and 10 pairs in P. perkinsi , starting chaetiger of sabre chaetae (in P. lighti ) and absence of sabre chaetae (in P. perkinsi ) ( Maciolek, 1985). Prionospio solisi sp. nov. differs from P. pygmaeus by the prostomial shape, branchial pattern and starting chaetiger of notopodial and neuropodial hooded hooks. The species is most similar to P. dubia , sharing a similar prostomium shape, lack of prostomial peaks and lateral wings, but the species can be distinguished by branchial pattern, the starting chaetiger of neuropodial hooded hooks, and sabre chaetae.

Prionospio solisi sp. nov. is similar to Aurospio dibranchiata Maciolek 1981a and some individuals of A. banyulensis Laubier, 1966 due to the presence of only two pairs of branchiae, on chaetigers 3 and 4. However, P. solisi sp. nov. can be distinguished from A. dibranchiata by the morphology of branchiae—robust and completely free from the notopodial postchaetal lamellae, by the absence of dorsal crests, starting chaetiger of notopodial and neuropodial hooded hooks and presence of a secondary hood on the hooded hooks. Prionospio solisi sp. nov. can be distinguished from A. banyulensis by the starting chaetiger of notopodial and neuropodial hooded hooks, the shape of postchaetal neuropodial lamellae on anterior chaetigers and absence of dorsal crests.

Etymology: The species name, solisi , refers to the dark yellow to orange pigment observed on anterior chaetigers (solis, Latin for sun).

Habitat: muddy sand to mud, 142–1914 m depth.

Distribution: Northeastern Brazil (Alagoas and Sergipe states) and Southeastern Brazil (Espírito Santo and Campos basins).

Figures

FIGURE 2. Prionospio solisi sp. nov., dorsal view (MZUSP 3391, paratypes). A. Anterior chaetigers. B. Anterior chaetigers and mid-body, showing characteristic pigmentation in ethanol. C. Anterior chaetigers stained with Shirlastain A. D. Posterior chaetigers and pygidium. Abbreviations: br, branchia; pe, peristomium; pr, prostomium.

FIGURE 3. SEM of Prionospio solisi sp. nov. A. Anterior chaetigers, dorso-lateral view. B. Mid-body neuropodium, lateral view. C. Posterior neuropodium, dorso-lateral view. D. Pygidium, dorso-lateral view. Abbreviations: br, branchia; hh, hooded hook; py, pygidium, sa, sabre chaeta.

FIGURE 4. SEM of Prionospio solisi sp. nov., dorsal view. A. Anterior chaetigers and mid-body. B. Anterior chaetigers. Abbreviations: br, branchia; bs, branchial scars; nol, notopodial lamella; pe, peristomium; pr, prostomium.

FIGURE 5. Prionospio solisi sp. nov. A. Anterior capillary chaeta from posterior row. B. Anterior capillary chaeta from anterior row. C. Posterior capillary chaeta. D. Sabre chaeta. E. Hooded hook (as seen in light microscopy).