Paraprionospio treadwelli ( Hartman, 1951 )

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 : 15-19

Paraprionospio treadwelli ( Hartman, 1951)

( Fig. 5 A-I)

Prionospio plumosa Treadwell 1931: 3-5 , fig. 3. non Sars M. in Sars G.O. 1872.

Prionospio treadwelli Hartman 1951: 84-85 (new name for P. plumosa Treadwell, 1931 ).

Type material: Holotype Prionospio plumosa, USNM 19598, sta. 8881, Chesapeake Bay .

Additional material: Topotypes specimens, 7 specimens from the same station of holotype; 1 specimen, sta. 8882, in bad condition (anterior fragment with 12 chaetigers).

According to Treadwell (1931), the material was collected ranging through the lower middle bay from the mouth of the Patuxent River to the mouth of the Rapphannock River, in depths of from 7.32 to 47.58 m, August 22 to October 19, 1920.

Redescription: Holotype incomplete with 46 chaetigers, 15 mm long, 0.6 mm wide. Median and posterior chaetigers in bad condition. Topotype specimens incomplete, with 38-62 chaetigers, 7-16 mm long, 0.5-0.8 mm wide. Color in alcohol dark. Prostomium spindle-shaped, small, frontally rounded ( Fig. 5A ), with two small peaks on ventrolateral position (one specimen with four peaks), one on each side of prostomium ( Fig. 5B ). The prostomium extends posteriorly as a low raised ridge until chaetiger 1 ( Fig. 5A ). Eyes not visible in holotype, some specimens with two pairs of dark-brown eyes in trapezoidal arrangement. Palps lost. Peristomium not fused with chaetiger 1; extending dorsally as a pair of lateral wings of moderate size, which partially enclose the prostomium, ( Fig. 5C ). Posterior margins of peristomial wings without pigment spots neither marginal papilla.

Branchiae present on chaetigers 1-3, all with flabellate lamellae ( Fig. 5A, C ); because of the condition of holotype, the description is based on topotype specimens. First pair largest, joined basally by a small dorsal ridge, without processes along anterior edge neither slender filament.

Notopodial postchaetal lamellae of chaetigers 1-3 elongate, triangular ( Fig. 5C ); longest on chaetiger two; lamellae of chaetigers 4-7 subtriangular ( Fig. 5C ), gradually reduced on the following segments, becoming rounded ( Fig. 5D ) near to the end of the fragments. Dorsal crests on chaetigers 21-28 (in holotype those chaetigers in bad conditions), accompanied by a semitransparent dorsal cuticle. On anterior chaetigers, ventral edge of notopodial lamellae does not touch the dorsal edge of neuropodial lamellae ( Fig. 5C ). Notopodial prechaetal lamellae short in branchial region, inconspicuous thereafter.

Neuropodial postchaetal lamellae small, rounded through ( Fig. 5C ), except on chaetigers 1-2, subtriangular ( Fig. 5C ); becoming wider, rounded ( Fig. 5C ) on chaetigers 3-10, decreasing progressively in size, thereafter becoming as a small rounded lobe ( Fig. 5D ). Neuropodial prechaetal lamellae very small on anterior chaetigers ( Fig. 5C ), inconspicuous on median and posterior chaetigers. Interparapodial pouches and ventral crest on chaetiger 8 absent.

Capillary chaetae in anterior region thick, densely granulated ( Fig. 5 E-F); arranged in two rows, chaetae of first row shortest, with granulations on shaft; notochaetae unilimbated ( Fig. 5E ), and more granulated than neurochaetae; neurochaetae alimbates ( Fig. 5F ). Capillary chaetae of posterior region long, thin, without limbations neither granulations; neurochaetae shorter and thinner than notochaetae. Sabre chaetae from chaetiger 9, stout, heavily granulated, without limbation ( Fig. 5G ); with up to 2 per neuropodium. Neuropodial hooded hooks ( Fig. 5H ) from chaetiger 9, with up to 10 hooks per neuropodium, accompanied with small and thin capillary chaetae; hooded hooks with 2-3 pairs of small accessory teeth above main tooth ( Fig. 5H ). Notopodia hooded hooks ( Fig. 5I ) from chaetiger 45 (topotypes specimens 41-45), accompanied with long capillary chaetae, without granulations and alimbated; hooded hooks with 2 pairs of small accessory teeth above main fang ( Fig. 5I ). All hooks with main hood striated ( Fig. 5 H- I), neuropodial hooks with main hood bigger than notopodial hooks, covering more than half of the hooks shaft; all hooks without secondary hood.

Pygidium unknown.

Distribution: Chesapeake Bay, USA. From 7 to 48 m depth.

Remarks: Treadwell (1931) described Prionospio plumosa based on specimens collected from the Chesapeake Bay. Hartman (1951) gave a new name for this species as Prionospio treadwelli because the specific name was preoccupied by Prionospio plumosa M. Sars in G.O. Sars, 1872. However, she described the species based on specimens collected from Louisiana, Gulf of Mexico, and stated the presence of four pairs of branchiae on those specimens. As we noted above and previously other authors ( Foster 1971; Yokoyama 2007) the species only have three pairs of branchiae. Because of the presence of four pairs of branchiae on Hartman’s specimens, these specimens correspond to a different species of Prionospio . Yokoyama (2007) considered Paraprionospio treadwelli similar to Paraprionospio alata in that both have three pairs of branchiae and a membranous dorsal crest on chaetigers 21-28. Due to these similarities, he suggested that both species are conspecific. However, P. treadwelli differs from P. alata in many features, as was noted above in the remark section of P. alata and table 3.

Phylogenetic analysis

The Branch-Bound search yielded one most parsimonious tree of 191 steps, with a consistency index (CI) of 0.45, excluding uninformative characters, and a retention index (RI) of 0.54 ( Fig. 6 ).

Our result shows Paraprionospio characterized by a prostomium spindle-shaped, Peristomial wings conspicuous; notochaetae and neurochaetae of first segment absent; Postsetal lamellae of first segment well developed; Notopodial lamellae of middle segments triangular; with three pairs of branchiae (excepting P. dibranchiata sp. nov.); Pinnules branchial on segment 2 flabellated; Ridge between branchial bases on segment 2; with dorsum with transverse series of slightly raised ridges; Caruncle reach segment 1; peristomial wings present; peristomium and segment 1 completely fused. All characters, except the last three, are non-homoplastic.

In the analysis, the basal species is P. dibranchiata sp. nov., which is mainly characterized by having two pairs of branchiae, the first pair with unifoliated branchial pinnules, and notopodial lamellae of middle segments subtriangular; all these characters are autapomorphies. The following species is P. pinnata followed by a major clade including all other Paraprionospio species. The major clade is characterized by having dorsal crest posterior to segment 21, and with up to 3 pairs of secondary teeth in notopodial hooks. This clade is subdivided into another two subclades; the first one, identified by two homoplastic characters (triangular neuropodial lamellae on segment 3, and neuropodial capillaries on segment 10 limbate) include the species P. africana , P. lamellibranchia , P. patiens , P. alata and P. tamaii . In this group of species, P. africana , P. lamellibranchia , and P. patiens constitute a clade with P. africana basal to the sister species P. lamellibranchia and P. patiens ; while, P. alata and P. tamaii constitute a clade characterized by having one non-homoplastic character, the notopodial lamellae segment 5 reniform.

The second subclade is characterized by one non-homoplastic character (triangular notopodial lamellae of segment 3), and three homoplastic characters (triangular notopodial lamellae of s e g m e n t 2 a n d 4, s u b t r i a n g u l a r n o t o p o d i a l lamellae of segment 5). This subclade is divided in another two clades, the first one including the species P. treadwelli as basal species of the sister species P. coora and P. yokoyamai . The second one, identified by two homoplastic characters (lanceolate neuropodial lamellae of segment 3 and filament of segment 4 present) includes P. cristata as the basal species followed by P. inaequibranchia as sister species of P. cordifolia and P. oceanensis .

The result of this analysis confirms our idea that P. treadwelli , P. tamaii and P. yokoyamai are not synonymies of P. alata as Yokoyama suggested (2007). We found that the shape of noto- and neurolamellae are very useful features for recognizing the species.

Figures

Fig. 5. Paraprionospio treadwelli (Hartman, 1951). Holotype USNM 19598 (C), Topotype (A-B, D-I). (A) anterior region, dorsal view; (B) prostomium, lateral view; (C) anterior region, lateral view; (D) middle region, lateral view; (E) capillary notochaeta, anterior chaetiger; (F) capillary neurochaeta, anterior chaetiger; (G) sabre chaeta, chaetiger 10; (H) neuropodial hooded hook, chaetiger 11; (I) notopodial hooded hook, chaetiger 46. Scale bars: A, C, D = 500 µm; B = 90 µm; E-I =0.5 µm.

Fig. 6. Most parsimonious tree. Numbers in plain text are the characters and the superscript number is the character state occurring at the internode; filled rectangles represent no homoplasy, blank rectangles represent homoplasy, double lines represent reversal. © 2018 Academia Sinica, Taiwan