Prionospio delta Hartman 1965

Prionospio cf. delta Hartman, 1965

(Figures 23–25)

Prionospio (Minuspio) delta Hartman, 1965: 151.

Minuspio minor Fauchald & Hancock, 1981 fide Maciolek, 1985

Prionospio longibranchiata Reish, 1968 fide Maciolek, 1985

Prionospio delta in Pardo & Peixoto (in press)

Material examined. Amb3 E5, 19º 36’ 26.24” S, 39º 10’ 17.35” W, 352m (7 ind); Amb3 F5, 19º 34’ 20.51” S, 38º 41’ 18.75” W, 438m (4 ind); Amb3 CAND5, 19º 33’ 20.99” S, 39º 2’ 36.2” W, 374m (10 ind); Amb5 B5, 20º 35’ 16.23” S, 39º 53’ 47.1” W, 382m (2 ind); Amb5 C5, 20º 14’ 19.45” S, 39º 48’ 36.67” W, 416m (2 ind); Amb5 D6, 19º 50’ 4.42” S, 39º 26’ 33.42” W, 1053m (2 ind); Amb6 D5, 19º 46’ 31.83” S, 39º 30’ 3.38” W, 402m (5 ind); Amb6 CANWN4, 19º 49’ 10.21” S, 39º 36’ 10.05” W, 124m (1 ind); Amb6 CANWN5, 19º 49’ 37.21” S, 39º 35’ 41.25” W, 352m (47 ind); Amb11 A5, 21º 4’ 4.67” S, 40º 13’ 6.06” W, 383m (2 ind); Amb11 B5, 20º 35’ 15.33” S, 39º 53’ 45.22” W, 382m (2 ind); Amb11 C5, 20º 14’ 17.95” S, 39º 48’ 34.35” W, 418m (8 ind); Amb12 D5, 19º 46’ 32.84” S, 39º 30’ 3.65” W, 431m (7 ind); Amb12 E5, 19º 36’ 30.6” S, 39º 10’ 19.39” W, 349m (5 ind); Amb12 CAND5, 19º 33’ 23.09” S, 39º 2’ 35.67” W, 446m (1 ind); Amb12 CANWN4, 19º 49’ 6.26” S, 39º 36’ 9.34” W, 181m (1 ind); Amb12 CANWN5, 19º 49’ 36.9” S, 39º 35’ 42.69” W, 363m (16 ind); Amb14 A4, 21º 4’ 4.81” S, 40º 14’ 13.86” W, 147m (1 ind).

Comparative material examined. USNM 80299 (1 ind); USNM 80300 (1 ind).

Diagnostic features: Single median prostomial peak, lack of dorsal crests, up to eight pairs of thin strap-like branchiae and sabre chaetae consistently from chaetiger 12.

Description. A large-sized Prionospio, largest complete specimen 16 mm long, 0.45 mm wide at widest part for 82 chaetigers. Body dorsoventrally flattened throughout, especially in branchial region, tapering towards pygidium. Body color yellow to whitish in alcohol (Fig. 23).

Prostomium triangular, inflated in mid-region, widening towards anterior margin, extending posteriorly as a narrow keel reaching posterior margin of chaetiger 1. Median prostomial peak present. One or two pairs of eyes present in most specimens. Peristomium surrounding prostomium and partially fused to chaetiger 1, lateral wings absent. Grooved palps reaching up to chaetiger 14 (Figs 23; 24 A–B).

Chaetiger 1 with only a few chaetae in both rami, shorter than chaetae on succeeding chaetigers. Postchaetal lamellae absent on notopodium and digitiform on neuropodium, greatly reduced and barely visible (Figs 24 A–B; 25A). Prechaetal lamellae absent.

Notopodial lamellae foliaceous from chaetiger 2 to chaetigers 11–13 (depending on specimen size) (Fig. 25 B–D), rounded afterwards and gradually reduced in size towards posterior region, present as a low flap on last chaetigers. Notopodial prechaetal lamellae absent throughout. Dorsal crests absent.

Neuropodial postchaetal lamellae rhomboid on chaetiger 2 and elliptical from chaetiger 3 (Fig. 24 B–D), gradually reduced in size towards posterior region, present as a low flap on last chaetigers. Neuropodial prechaetal lamellae absent throughout.

Chaetae from notopodia and neuropodia organized in two rows of unilimbate and granulated capillaries (Fig. 25E). Chaetae from both rows of equal length, although neuropodial chaetae slightly shorter than notopodial chaetae. Towards posterior region, capillaries progressively become elongate, non-limbate, non-granulated, thinner and less numerous (Fig. 25F).

Hooks in notopodia starting from chaetigers 23–39, up to five per fascicle, accompanied by 1–4 short non-limbate capillaries (Fig. 25G). Hooks in neuropodia starting from chaetigers 14–22, up to seven per fascicle, accompanied by 1–6 short non-limbate capillaries. All hooks multidentate, with eight secondary teeth organized in two rows above main tooth (Figs 24D; 25H). Secondary hood absent. Sabre chaetae consistently from chaetiger 12. Sabre chaetae broadly unilimbate, with dense dark granulations along shaft (Fig. 25I).

Up to eight pairs of smooth, slightly wrinkled and strap-like branchiae. Branchiae from chaetiger 2, up to 10 times longer than notopodial lamellae, slightly reduced in length towards last branchial pair. Branchiae bear short cilia (except at base) (Figs 24 A–C; 25J). All branchiae completely free from notopodial postchaetal lamellae (Fig. 24 A–B).

Pygidium bearing one thin dorsal cirrus and two short ventral lobes (Fig. 25K).

Gametes not observed.

Methyl green staining pattern: prostomium, peristomium, postchaetal lamellae from chaetiger 2 up to chaetigers 15–20 intensely stained; ventral side of branchial region slightly stained.

Remarks. Prionospio cf. delta is easily recognized among Brazilian apinnate Prionospio species by its cirriform, strap-like branchiae and triangular prostomium, with an inflated mid-region. Our specimens are similar to the original description (Hartman 1965) and its redescription (Maciolek 1985), differing in the development of peristomial wings, the number of branchiae and the number of secondary teeth on the hooded hooks.

While in the descriptions of P. delta (Hartman 1965; Maciolek 1985) specimens had up to six pairs of branchiae, our specimens bore eight pairs of branchiae, although the last pairs of branchiae could have been lost or had not yet developed in specimens examined by other authors. As for the number of secondary teeth, three pairs in the previous descriptions and four pairs in our specimens, the last pair of teeth could have been overlooked using light microscopy, due to their small size. Additionally, while Hartman (1965) did not mention the peristomium morphology, Maciolek (1985) described a peristomium bearing moderate lateral wings, lacking in specimens examined in this work.

In addition, branchiae from our specimens possess small wrinkles, a character that could not be observed during light microscopy examination. SEM micrographs revealed sculptured branchiae, just as branchiae found in Prionospio fauchaldi and P. corrugata sp. nov. (Figs 21 A–B; 22K), but these species differ in the branchial number (eight pairs of strap-like branchiae in P. cf. delta, four pairs in P. fauchaldi and up to six pairs in P. corrugata sp. nov., shape of the prostomium (triangular in P. cf. delta and rectangular in P. fauchaldi and P. corrugata sp. nov.), the presence of typical sabre chaetae in P. cf. delta and lack of long row of neurochaetae on chaetiger 3 in P. cf. delta. At first, branchial wrinkles were treated as artifacts during sample preparation for SEM, but latter it was noticed that wrinkles were present on all specimens examined using SEM. It is unclear if such wrinkles are present on material from the type-locality. Due to the discrepancies from Hartman (1965) and Maciolek (1985) descriptions, it was decided to adopt the “cf.”.

Only a few species possess branchiae of similar morphology, such as Prionospio pulchra Imajima, 1990a, described from Japan, P. elegantula Imajima, P. perkinsi, P. anatolica Dagli & Çinar, 2011, described from the Levantine Sea, Turkey, and P. yuriel Wilson, 1990, described from Australia, all which possess a similar branchial distribution (eight pairs in P. cf. delta, up to 10 pairs in P. pulchra and P. perkinsi, seven pairs in P. anatolica and up to nine pairs in P. yuriel), except for P. elegantula, which possess only four pairs of branchiae. Interestingly, all mentioned species (except for P. perkinsi) lack notopodial postchaetal lamella on chaetiger 1.

Prionospio cf. delta can be quickly distinguished from P. perkinsi by the prostomial shape—triangular with a single median prostomial peak in P. cf. delta and rounded with several small peaks in P. perkinsi, starting chaetigers of notopodial hooded hooks (from chaetigers 23–39 in P. cf. delta and from chaetigers 16–23 in P. perkinsi and by the presence of sabre chaetae in P. cf. delta.

Although P. cf. delta shares some similarities with P. yuriel and P. anatolica —including an overlap on the starting chaetiger of sabre chaetae (chaetiger 12 in P. cf. delta, chaetigers 11–13 in P. yuriel and chaetiger 11 in P. anatolica), the starting chaetiger of hooded hooks (chaetigers 23–39 in notopodia and chaetigers 14–22 in neuropodia in P. cf. delta, chaetigers 34–42 in notopodia and chaetigers 14–19 in neuropodia in P. yuriel and chaetigers 27–39 in notopodia and chaetigers 14–15 in neuropodia in P. anatolica), the morphology of the hooded hooks (four pairs of secondary teeth in P. cf. delta and P. anatolica and four to five pairs in P. yuriel) and a similar number of branchiae, these species can be distinguished from P. cf. delta by the prostomial shape—which is triangular and inflated in the mid-region in P. cf. delta, narrow and elongated anteriorly in P. yuriel and inflated, and rounded anteriorly in P. anatolica) (Wilson 1990; Dagli & Çinar 2011).

Prionospio cf. delta is also similar to P. pulchra, but these species can be readily distinguished by the prostomial shape—which is triangular and inflated in the mid-region in P. cf. delta and subtriangular in P. pulchra and by the number of prostomial peaks—five peaks in P. pulchra, while P. cf. delta has a single median peak (Imajima, 1990a).

Habitat: Muddy sand to mud, 124–1053 m depth.

Distribution: Southeastern Brazil (Espírito Santo and Campos basins), Atlantic Ocean. According to Maciolek (1985), P. delta has been recorded from Northwestern Atlantic Ocean (USA), Central America (Mexico), Southwestern Atlantic Ocean (Suriname, type locality), Southeastern Atlantic Ocean (Namibia and Angola) and Northeastern Pacific Ocean (USA and Mexico).