Pseudexogone helmuti, Salazar-Vallejo & Bailey-Brock & Dreyer, 2007

Salazar-Vallejo, Sergio I., Bailey-Brock, Julie H. & Dreyer, Jennifer C., 2007, Revision of Pseudexogone Augener, 1922 (Annelida, Polychaeta, Syllidae), and its transfer to Pilargidae, Zoosystema 29 (3), pp. 535-553 : 544-547

Pseudexogone helmuti n. sp.

( Fig. 5 )

TYPE MATERIAL. — Southern Indian Ocean. Off Saint-Paul Island, Marion Dufresne, campagne MD50 JASUS, stn 20-DC 91, 38°47’67”S, 77°27’11”E, 17.VII. 1986, 975 m, very compacted fine sand, holotype ( MNHN-1482 ) ; paratypes (12 in MNHN, 6 in ECOSUR, including SEM specimen) .

TYPE LOCALITY. — Off Saint-Paul Island, southern Indian Ocean, in deep water.

ETYMOLOGY. — This species is named after Helmut Zibrowius, author of many important publications on serpulid polychaetes, and who participated in several cruises, including the one on which the specimens of this new species were collected.

DISTRIBUTION. — Only known from the type locality, off the Saint-Paul Island, southern Indian Ocean, in about 1000 m depth.

DESCRIPTION

Holotype complete, transparent; body tapering posteriorly, 7.5 mm long, 0.25 mm wide, with 42

chaetigers. Prostomium subtriangular, about as long as wide, slightly narrower than peristomium (corrugated in SEM specimens). Three antennae, all cirriform of about the same size; laterals placed by the prostomial middle, median placed over the posterior prostomial margin. Eyes not visible. Palps tapering, separated distally, in SEM specimens distorted, free from each other ( Fig. 5 A-C), each provided with a ventrolateral papilla ( Fig. 5B, C ), as long as antennae, placed about the half of the palp length. Tentacular cirri cirriform, dorsal cirri slightly longer; ciliary bundles eroded ( Fig. 5B ).

Parapodia uniramous in chaetigers 1-6, thereafter biramous. Parapodial cirri cirriform throughout body. Anterior parapodia with two denticulate capil- laries, one pectinate, and one furcate neurochaetae ( Fig. 5D ). Notopodia with large sigmoid bidentate spines starting in chaetiger 7, continued to last chaetiger. Neuropodia includes furcates in anterior chaetigers, pectinates and denticulate capillaries, most broken.Furcates with unequal tines, longer tine with a flaring blade not reaching the blunt digitate smaller tine. Median chaetigers ( Fig. 5E ) with slightly emergent notospines, parapodial cirri digitate, dorsal cirri larger than ventral cirri. Chaetal lobe conical, with 2 denticulate capillaries and 1 or 2 pectinates. Bidentate curved notospines more exposed in posterior chaetigers ( Fig. 5F ), each with rounded larger subdistal tooth, and a smaller, probably eroded, apical tooth. In median and posterior chaetigers, broken pectinates resemble furcates but they differ.

Posterior end tapering. No achaetous segments. Pygidium conical, blunt, with two lateral anal cirri. Anus terminal. Pharynx not everted, as long as first 4 chaetigers in length.

VARIATION

The complete paratypes were 5.0- 5.8 mm long, 0.15-0.25 mm wide, with 34-40 chaetigers.The start of notospines was in chaetiger 7. One with unbroken chaetae had two of each: furcates, pectinates and denticulate capillaries. There were no prepygidial achaetous segments. One paratype had its pharynx everted; it is made of two muscular rings with an apparently smooth margin.

REMARKS

Pseudexogone helmuti n. sp. is the only described species of the genus living in almost 1000 m depth. It resembles P. dineti n. comb. by lacking eyes but they differ in the relative development of the blade of furcates; it is straight in P. helmuti n. sp. while it is curved in P. dineti n. comb.

Figures

FIG. 5. — Pseudexogone helmuti n. sp.: A, anterior end in dorsal view; B, another specimen, anterior end in lateral view; C, same, showing antennae; D, furcate and pectinate chaetae from an anterior chaetiger; E, median chaetiger, showing a notospine slightly exposed; F, notospine broken, from a posterior chaetiger. Abbreviations: see p. 536. Scale bars: A, 20.0 µm; B, 20.5 µm; C, 33.3 µm; D, 4.0 µm; E, 11.1 µm; F, 2.05 µm.