Phisidia Saint­Joseph, 1894

Nogueira, João Miguel De Matos & Alves, Tarsila Montrezoro, 2006, Two new terebellid polychaetes (Polychaeta: Terebellidae) from the state of São Paulo, southeastern Brazil, Zootaxa 1205, pp. 31-54 : 41-43

Phisidia Saint­Joseph, 1894 , emended

Type species: Leaena oculata Langerhans, 1880 designated by Saint­Joseph (1894).

Diagnosis

Upper lip short and rounded, lower lip restricted to oral area, usually swollen. Basal part of prostomium bearing eyespots in most species. Lobes on anterior segments absent, but some taxa with anterior margins of some anterior segments thickened and raised from integument; segments 1–4 usually dorsally inflated. Branchiae absent. Notopodia from segment 4, usually extending for 14 segments. Each notopodium with two rows of chaetae, chaetae on posterior row distinctly longer than chaetae on anterior row. On anterior notopodia, anterior row of notochaetae as serrated capillaries, posterior row as smooth, limbate capillaries; on posterior notopodia, anterior row of notochaetae as serrated capillaries, posterior row of notochaetae as medially limbate capillaries with serrated tips (= flail­tipped capillaries). Neuropodia from segment 5 until near pygidium, in double rows from segments 10–11 until end of thorax or more posteriorly. Uncini higher than long, with short heel, developed prow and dorsal button away from anterior margin, at about midlength of the distance between base of main fang and end of prow.

Remarks

One of the first attempts to organize the taxa of abranchiate terebellines into genera was made by Malmgren (1866), who erected the genera Leaena Malmgren 1866 , Lanassa Malmgren 1866 and Laphania Malmgren 1866 , which are distinguished mainly by the number of pairs of notopodia present.

In the original description of P. oculata, Langerhans (1880) stated that according to the criteria proposed by Malmgren (1866), a new genus should be erected to accommodate his new species, as none of the genera known at that time had 14 pairs of notopodia. Langerhans, however, did not consider this character important enough as to distinguish between genera and proposed that all abranchiate terebellines should be assigned to a single genus, which he suggested to be Leaena , under which he described his new species ( Langerhans 1880).

Subsequently, Saint­Joseph (1894) described Phisidia to accommodate the abranchiate terebellines with 14 pairs of notopodia and nominated L. oculata as the type­species, following the criteria established by Malmgren (1866).

The genus currently contains seven known species, but it is poorly defined generically. According to Saint­Joseph (1894), the number of pairs of notopodia, together with the absence of branchiae, should be the most distinctive features, however three of the species currently assigned to Phisidia have a different number of pairs of notopodia: Phisidia aurea Southward, 1956 has 13 pairs – although one of the specimens studied for the original description had 14 pairs of notopodia ( Southward 1956) – while P. castanea Hartmann­Schröder and Rosenfeldt, 1989 and P. sanctaemariae Hilbig, 2000 have both 16 pairs of notopodia.

Southward (1956) described her species as Phisidia because it had separate nephridia, two types of notochaetae present from segment 4, neuropodia from segment 5 and lacked branchiae. On the other hand, P. sanctaemariae was described as Phisidia because, in spite of having 16 pairs of notopodia, Hilbig (2000) considered that Lanassa , which is the only abranchiate genus of Terebellinae with 16 pairs of notopodia, possesses only one type of notochaetae, while Phisidia has two types, as does P. sanctaemariae . Accordingly, Hartmann­Schröder and Rosenfeldt (1989) said that the “short notochaetae” (= chaetae of the anterior row of notochaetae) of P. castanea were serrated capillaries similar to those of Lanassa , but the authors preferred to describe their new species as Phisidia , possibly because it had “long notochaetae” (= chaetae on the posterior row of notochaetae) as smooth, limbate capillaries.

The types of notochaetae present in Phisidia , must also be considered. In the original description of P. oculata, Langerhans (1880) stated that all notochaetae were smooth, with long tips. Hessle (1917), however, said that in P. oculata and P. sagamica Hessle 1917 both types of notochaetae were distally serrated, with those on the anterior row of notochaetae having stouter teeth and broader blades. Similar descriptions were provided by subsequent authors for the anterior row of notochaetae of the other species of Phisidia described subsequently ( Southward 1956, Hutchings and Glasby 1988, Hartmann­ Schröder and Rosenfeldt 1989, Hilbig 2000), but the chaetae on the posterior row of notochaetae were sometimes described as limbate ( Hutchings and Glasby 1988) or medially limbate and distally serrated ( Southward 1956, Hartmann­Schröder and Rosenfeldt 1989, Hilbig 2000), which could represent a specific character.

None of the authors above, however, seem to have noticed that, similarly to what occurs in several other genera of Terebellinae , Phisidia shows a change in the type of notochaetae present on the posterior row of notochaetae, from anterior to posterior thoracic chaetigers. This was studied in at least three species of Phisidia investigated so far by one of us (JMMN) for a forthcoming phylogenetic paper (Nogueira and Hutchings in prep.), P. e c h u c a Hutchings and Glasby, 1988, P. rubra sp. nov. and P. sp., the latter an undescribed species from New Zealand. In all of these species, as seen under light microscope, chaetae of the posterior row of notochaetae on anterior thoracic chaetigers are limbate, with the limbation extending to tips, while on posterior thoracic chaetigers they are medially limbate and finely serrated distally.

Under the SEM, however, it is possible to follow this transition in Phisidia rubra sp. nov. On anteriormost chaetigers, chaetae of the posterior row of notochaetae are limbate, with the limbation ending subdistally and a short tip, with one lateral row of fine hairs ( Figs. 7 A, C). However, on segments 4–11, the alimbate tips become progressively longer and the “hairs”, progressively stouter and sharper, resulting in medially limbate, distally serrated chaetae from segment 11 until the end of thorax.

At this stage it is unknown if this change of the type of chaetae on posterior rows of notochaetae also occurs in the type­species of the genus, as the type­material for the genus appears to have been lost ( McHugh 1995) and no further material from the type­locality is available.

In addition to the types of notochaetae, all three species of Phisidia so far examined have segments 1–4 dorsally inflated, forming a distinct “hump” ( Figs. 5 A, 6A–B, D, F). It is possible that this is due to an artifact of fixation, however similar dorsal swellings have been observed in some other taxa of terebellines and this may represent an additional character available for systematic studies.

Figures

FIGURE 5. Phisidia rubra sp. nov .. A: holotype (MZUSP 16927), lateral view; B: long notochaeta, segment 7; C: short notochaeta, segment 7; D: uncinus, segment 11; E: abdominal uncinus; F: long notochaeta, segment 15; G: short notochaetae, segment 15. Scale bars: A: 0.5 mm; B – G: 10 µm.

FIGURE 7. Phisidia rubra sp. nov .. A: notochaetae, segment 6; B: serrated (short) notochaetae, segment 5; C: tip of limbate (long) notochaetae, segment 6; D: limbate (long) notochaetae, segment 4; E: notochaetae, segment 13; F, H: Higher magnification of notochaetae of segment 13; G: notochaetae, segment 15. Scale bars: A: 5 µm; B, D, H: 4 µm; C: 2 µm; E: 9 µm; F, G: 6 µm.