Pachyprocerastea, Nygren, Arne, 2004

Nygren, Arne, 2004, Revision of Autolytinae (Syllidae: Polychaeta)., Zootaxa 680, pp. 1-314 : 100-102

Pachyprocerastea gen. n.

Linnean name definition. Type species Procerastea hydrozoicola Hartmann­Schröder, 1992 .

PhyloCode definition. No name definition provided.

Apomorphies. Supported by a single morphological apomorphy ( Fig. 4 ), nuchal epaulettes extend to beginning, half of tentacular segment (character 8); character state change is a parallelism.

Etymology. The greek word pachy means thick, and alludes to the thick body shape of Pachyprocerastea .

Pachyprocerastea hydrozoicola (Hartmann­Schröder, 1992) comb. n. (Fig. 45A–F) Procerastea hydrozoicola Hartmann­Schröder, 1992a: 97 –99, fig. 3A–D.

Material examined. New Caledonia: holotype MNHN UC 231, 1 paratype MHNH UC 230, Mont Musorstom auf der Rippe der Îles Loyauté, 21°60'S 167°54.7'E, 300m, associated with a calcified hydrocoral, 22 Feb 1989; 2 paratypes ZMH P­ 20631, Banc Aztèque off Norfolk­Rippe, 23°17.4'S 168°04.8'E, 315 m, on calcified hydrozoans, 14 Sept 1989.

Diagnosis. Procerini with a chaetal arrangement of compounds, simple fused chaetae, and a thick, distally dilated, bayonet chaeta with distal denticulation; cylindrical dorsal cirri on all chaetigers.

Description. Holotype incomplete, length 5.7 mm for 27 chaetigers; width, excluding parapodial lobes, 0.4 mm at level of proventricle. Paratype MHNH UC 230 is the rear fragment of the holotype, length 3 mm for 30 chaetigers. The two paratypes in ZMH P­20631, are from the same individual; it is the anterior fragment and its detached male stolon. Anterior fragment measures 5.6 mm for 13 chaetigers. Preserved material yellowish without colour markings.

Body shape, excluding parapodial lobes, cylindrical in transection, stout, venter flattened, body width fairly constant. Ciliation not assessed. Anterior half of body annulated (Fig. 45A, B). Three antennae developing behind chaetiger 13 (Fig. 45C) in holotype.

Prostomium rounded rectangular, wider than long (Fig. 45A). Four eyes, with lenses, present in trapezoid arrangement, anterior pair larger. Eyes separated (Fig. 45A); eye spots absent. Palps in dorsal view projecting 1/3–1/4 of prostomial length (Fig. 45A), fused. Nuchal epaulettes small, inconspicuous, difficult to see, extending over anterior part of tentacular segment (Fig. 45A). Median antenna lost. Lateral antennae reaching chaetiger 4–5. Tentacular cirri curled, ventral pair 1/3–1/2 as long as dorsal pair; first dorsal either lost or broken. Alternation in direction of cirri not assessed. Dorsal cirri from chaetiger 2, of equal length (Fig. 45A), c. 1/5 of body width. Cirrophores on tentacular cirri and first dorsal cirri present (Fig. 45A); cirrophores otherwise absent. All appendages cylindrical.

Parapodial lobes rounded–conical, small to medium in size. Chaetiger 27 with 2 aciculae. Chaetal fascicle with 15–20 chaetae in anterior chaetigers, 10 in posterior; 2 or 3 of these are compound chaetae ventrally positioned, the others are simple chaetae (Fig. 45D). Simple chaetae have small diffuse denticulation along the "fusion line" (Fig. 45D). Compound chaetae as well as simple chaetae with small distal tooth; serration absent on simple chaetae, sometimes present on compounds. Single thick, distally dilated, bayonet chaetae, with distal denticulation (Fig. 45D), beginning at chaetiger 15.

Pharynx with sinuation anterior to proventricle (Fig. 45E). Trepan in tentacular segment or chaetiger 1. Not possible to assess detailed structure of trepan teeth; infradental spines seem to be absent. Proventricle equal in length to 2–2.5 segments in chaetiger 4–6 with 24–26 rows of square shaped muscle cells (Fig. 45F). Pygidium with 2 anal cirri, length equal to body width at level of proventricle.

Reproduction. Schizogamous reproduction by anterior scissiparity, behind chaetiger 13. The holotype is a budding female, containing eggs, with 3 developing antennae (Fig. 45C), and one of the paratypes is a male with a detached stolon.

Morphology of epitokous stages. Male stolon immature?, length 4 mm for 6+22+4 chaetigers. Regions indicated by the presence of notoaciculae in mid­region; swimming chaetae not developed.

Prostomium rounded rectangular, wider than long, anterior margin concave. Two pairs of eyes, with lenses; eyes situated on ventral and dorsal side of prostomium, ventral pair larger. Nuchal epaulettes not detected.

Median antenna, inserted in posterior part of prostomium, curled, equal to 1/3 of stolon length. Bifid antennae equal to prostomial width, bifid part 1/2 of total length, its rami equal in length. Frontal processes not observed. Tentacular cirri 1 pair. First dorsal cirri, equal in length to median antenna; achaetous knobs absent. Second dorsal cirri situated above chaetiger 1. All dorsal cirri equal, with about same length and shape as in stock. Cirrophores present on first dorsal cirri, otherwise cirrophores absent.

Neuropodial lobes of same size as in stock, notopodial lobes in region b indistinct. 1–2 neuropodial aciculae in all chaetigers; 2–3 anterodorsal, and c. 4 thick and 3 thin posteroventral notopodial aciculae in region b. It is possible that the absence of achaetous knobs and presence of only a single pair of tentacular cirri is due to that the stolon is not fully developed.

Habitat. On calcified hydrocorals and hydrozoans, 300– 315 m.

Distribution. South West Pacific. New Caledonia. Only known from type locality.

Remarks. Pachyprocerastea hydrozoicola is unique in its combination of equal cylindrical dorsal cirri on all chaetigers together with its chaetal arrangement. In Virchowia spirifer , a similar combination of compound, simple, and bayonet type of chaetae is found, but in V. spirifer the cirri alternate in both shape and length, and the nuchal organs are located on curled outgrowths. Hartmann­Schröder states that the nuchal organs reach as far as the end of second chaetiger in P. hydrozoicola . This could not be confirmed and the structure she refers to as the nuchal organs are the cirrophores of the first dorsal cirri (Fig. 45A).

Figures

FIGURE 4. Character transformations. Symbols as follow: black box, only one most parsimonious reconstruction (MPR) exists; white box, more than one MPR exist; X reversal; = parallelism; character later reversed within clade; character further changed within clade;? unknown character state for one or several taxa within clade.