Paraprionospio dibranchiata, Delgado-Blas & Carrera-Parra, 2018

Delgado-Blas, Víctor H. & Carrera-Parra, Luis F., 2018, New Phylogenetic Analysis of Paraprionospio Caullery (Polychaeta: Spionidae), with Description of a New Species from the Gulf of Mexico, Zoological Studies 57 (52), pp. 1-20 : 10-13

Paraprionospio dibranchiata sp. nov.

( Figs. 2 A-E; 3A-D)

urn:lsid:zoobank.org:act:B384511A-F4DD-45B0-8B09-0CE375C9C82E

Type material: Holotype, USNM 1187918 , Gulf of Mexico, off Coatzacoalcos , Veracruz, Mexico, 18°39.8'N, 94°13.1'W, E 16, 147 m, mud, coll. F.E. Donath Hernández, 10 August, 1984 . Paratypes: ECOSUR 0198, 5 specimens, off Coatzacoalcos, Veracruz, Mexico, 18°40.2'N, 94°25'W, E 15, 185 m, muddy, coll. F.E. Donath Hernández, 10 August 1984. ECOSUR 0199, 1 specimen, 18°31'N, 94°36'W, E12, 63 m, coll. F.E. Donath Hernández, 10 August 1984.

Additional material: ECOSUR-SEM; E 15, 185 m, 10 August 1984, 18°40.2'N, 94°25'W, muddy, coll. F.E. Donath Hernández.

Description: Holotype incomplete with 29 chaetigers, 7 mm long, 0.4 mm wide. (Paratypes all incomplete with 20-27 chaetigers, 4.5-6 mm long, 0.3-0.4 mm wide). Color in alcohol pale yellow. Prostomium fusiform, frontally truncate to slightly rounded, projecting slightly beyond peristomium ( Fig. 2A ), continuing as a narrow caruncle posterior to chaetiger 1. Eyes absent. Palps lost. Peristomium moderately developed, collar-like, surrounding the prostomium, distinct from chaetiger 1, with small lateral wings ( Fig. 2 A- B), without marginal papillae.

Two pairs of branchiae present on chaetigers 1-2 ( Fig. 3A ); first pair longest, joined basally by a small dorsal ridge, with few and small pinnules plate-like ( Fig. 3A ); the most basal branchial lamellae consisting of one rounded plate, lamellae on middle and distal regions thick, blunt and arranged along the posterior margins of the branchial shaft ( Fig. 3A ); without basal accessory lamellae. Second pair of branchiae cirriform, with smooth surface, and scarce lateral ciliation ( Figs. 2 A-B; 3A), extending to chaetiger 4 (one specimen missing all branchiae). Chaetiger 3 with a long thin filament at base of third notopodial lamellae; filament twice longer than notopodial lamellae and lightly longer that of second pair of branchiae ( Figs. 2 A-C; 3A).

Notopodial postchaetal lamellae on chaetigers 1-4 subtriangular; first smallest; largest on chaetigers 2-3 ( Fig. 2B ); on chaetigers 5-11 becoming smaller, rounded with a small projection at central edge ( Fig. 2C ); from chaetiger 27 lamellae becoming longer, with subtriangular ligules. Thin glandular fields or rings absent. Notopodial lamellae from chaetiger 23 until last segment expanded towards dorsum, forming a small dorsal fold, without dorsal cuticle. Ventral and dorsal edges of notopodial and neuropodial lamellae not touching each other on anterior chaetigers ( Fig. 2C ). Notopodial prechaetal lamellae short in branchial region ( Fig. 2D ), inconspicuous thereafter.

Neuropodial postchaetal lamellae subtriangular on chaetigers 1-3 ( Fig. 2B ); largest on chaetigers 2-3; rounded with small central projection providing a subtriangular appearance on chaetigers 4-5; from chaetiger 6 entirely rounded, diminishing progressively in size, becoming a small round lobe in most posterior chaetigers ( Fig. 2C ). Neuropodial prechaetal lamellae very small ( Fig. 4A ), rudimentary throughout. Interparapodial pouches from chaetigers 6-28 (smallest paratypes, 0.2 mm wide, including parapodia, from chaetigers 5 to 20; in largest paratypes (up to 0.3 mm wide) from chaetiger 7 to about chaetigers 23-25) ( Figs. 2C, E ; 3B ). Ventral crest on chaetiger 8 absent.

Capillary chaetae in anterior region thick, moderately granulated, without limbation, arranged in two rows, chaetae of first row shortest, with fine granulations on shaft. Capillary chaetae of posterior region thin, lacking granulations. Sabre chaetae from chaetiger 9 ( Figs. 2E ; 3C ), small, thin, moderately granulated, without limbation; one per neuropodium ( Fig. 2E ). Neuropodial hooded hooks from chaetiger 9, with 8-9 hooks per neuropodium, alternating with capillary chaetae ( Fig. 2E ); hooded hooks with three pairs of small accessory teeth above main fang, secondary hood striated ( Fig. 3D ). Notopodial hooded hooks not observed in fragments. Shallow furrow on ventral side of body beginning from chaetiger 15 to the end of the fragment.

Pygidium unknown.

Type locality: off Coatzacoalcos, Veracruz, Mexico (18°39.8'N, 94°13.1'W).

Distribution: Paraprionospio dibranchiata sp. nov. occurs in the SW Gulf of Mexico, off Coatzacoalcos, Veracruz, Mexico, from depths of 63-185 m on muddy bottoms.

Etymology: The species name, dibranchiata , refers to the number of pairs of branchiae.

Remarks: The presence of one filament at the base of the third notopodial lamellae is similar to Paraprionospio inaequibranchia and some species described by Yokoyama (2007), with which this species was compared. However, the consistency of taxonomic characters of Paraprionospio dibranchiata sp. nov. over the number and shape of branchiae is different to all other known Paraprionospio species. All specimens of P. dibranchiata sp. nov. have two pairs rather than three pairs of branchiae; the first pair is pinnate and the second one cirriform.

Foster (1971) and Yokoyama (1981) mentioned that in some instances, during the branchial regeneration, branchiae are entirely smooth in Paraprionospio pinnata . Also, Carrasco (1976) reported that the first pair of branchiae is bipinnate and the second pair cirriform in the larval stage of P. pinnata . However, all specimens studied in this study are juvenile or adult specimens. Further, the specimens were collected in three stations from the Gulf of Mexico at different depths (63-185 m), and all specimens have the same shape and number of branchiae regardless of its size. Therefore, we consider that the shape and the number of branchiae of these specimens do not correspond to branchiae in regeneration process or larval specimens.

Figures

Fig. 2. Paraprionospio dibranchiata sp. nov. ECOSUR-SEM. (A) anterior region, lateral view; (B) anterior region, dorso-lateral view; (C) anterior and middle region, dorsal view; (D) anterior region, lateral view; (E) interparapodial pouches. © 2018 Academia Sinica, Taiwan

Fig. 3. Paraprionospio dibranchiata sp. nov. Holotype USNM 1187918. (A) anterior region, lateral view; (B) ventrolateral interparapodial pouches; (C) sabre chaeta; (D) neuropodial hooded hook. Scale bars: A = 200 µm; B = 64.28 µm; C, D = 0.5 µm. © 2018 Academia Sinica, Taiwan

Fig. 4. Paraprionospio inaequibranchia (Caullery, 1914). Lectotype ZMA1688. (A) anterior region, dorsal view; (B) anterior region, dorso-lateral view; Paralectotype ZMA1568. (C) first branchia; (D) second branchia; (E) third branchia and filament; (F) parapodium of chaetiger 1; (G-I) parapodium of chaetigers 2-4; (J-L) parapodium of chaetigers 7-9; (M) parapodium of chaetiger 13; (N) capillary notochaeta, chaetiger 2; (O) capillary neurochaeta, anterior chaetiger; (P) sabre chaeta, chaetiger 10; (Q) neuropodial hooded hook, chaetiger 11; (R) notopodial hooded hook, chaetiger 34. Scale bars: A-I = 571.2 µm; J-L = 571 µm; M = 200 µm; N-R = 50 µm.