Paucibranchia, Molina-Acevedo, 2018

Molina-Acevedo, Isabel C., 2018, Morphological revision of the Subgroup 1 Fauchald, 1970 of Marphysa de Quatrefages, 1865 (Eunicidae: Polychaeta), Zootaxa 4480 (1), pp. 1-125 : 6-8

Paucibranchia n. gen.

Type species. Eunice bellii Audouin & Milne-Edwards 1833 .

Etymology. The name of the new genus is formed by the combination of the prefix Pauci- (Latin) that means few or small number of, and the word branchia. These combined names refer to the branchiae restricted to a few chaetigers, which is one of the main features of the group.

Gender. Feminine

Diagnosis. Prostomium entire or bilobed; five prostomial appendages without articulations; eyes present or absent. Peristomium without peristomial cirri. Maxillary apparatus with four paired maxillae (left and right sides) plus an unpaired one (placed on left side); maxillary carriers with rectangular anterior region, posterior end triangular, with a pair of oval wings situated at the lateral margins of maxillary carriers; MI with falcal arch developed, rounded; with the outer edge of the base straight and with a curvature in the basal inner edge where the base of maxillae II is supported ( Fig. 1D ), without attachment lamella; MII without attachment lamella; MIII curved, forming part of distal arc, with attachment lamella rectangular or irregular shape, situated at the center of posterior edge of maxilla; MIV with attachment lamella circular or rectangular. Branchiae restricted to a short anterior region; branchial filaments tapered ( Fig. 5C ). Dorsal cirri, without articulation, longer than ventral cirri; in branchial region, elongated, thicker or the same size as the basal branchial filaments; in postbranchial region slender, as long ( Fig. 5A, E ) or longer ( Fig. 13A, C ) than in prebranchial chaetigers; postchaetal lobe well developed, in branchial region longer than pre-branchial region ( Fig. 5A–C ); ventral cirri with a swollen base only in anterior region, oval, poorly developed ( Fig. 5A–C ). Aciculae dark or translucent. Supracicular chaetae include limbate; two types of pectinate chaetae: isodonts narrow, with long and slender teeth in anterior region ( Fig. 6D ), isodonts narrow, with short and slender teeth in posterior region ( Fig. 6E ), both type of pectinate chaetae with distal edge either transverse or oblique. Subacicular chaetae include compound falcigers, spinigers or both. Compound chaetae with blades of different sizes in the same chaetigers or only one size. Subacicular hook, bidentate or unidentate; with color reddish basally, translucent or amber distally, only translucent or only amber. Pygidium with two pairs of anal cirri, without articulation.

Remarks. Paucibranchia n. gen. includes 21 species which share in common the following features: branchiae restricted to few anterior chaetigers; maxillae I with falcal arch developed, rounded, with the outer edge of the base straight and with a curvature in the basal inner edge ( Fig. 1A, D ), dorsal cirri longer in branchial region, in median-posterior region slender, as long or longer than in pre-branchial chaetiger; postchaetal lobe well developed with wide base and tapered end in branchial region; and ventral cirri with a swollen base developed only in the anterior region.

This set of features constitute a distinct morphological pattern from that of Marphysa because the latter has the branchiae distributed along the body and the maxillae I has a rectangular falcate arch, with the outer edge of the base arch lacking a curvature in the basal inner edge ( Fig. 1B, E ). Also, in Marphysa the dorsal cirri are reduced in size towards the posterior region, and the ventral cirri with a swollen base are developed in more than half of the chaetigers.

Paucibranchia n. gen. shares with Treadwellphysa the absence of peristomial cirri and the curvature at the basal inner edge of maxillae I ( Fig. 1C, F ). However, as in Marphysa , it differs because Treadwellphysa has branchiae distributed along the body and the maxillae I have a rectangular falcate arch, with the outer edge of the base arched. Also, the base of maxillae II has a small rounded projection which fit with the curvature of the inner edge of maxillae I ( Fig. 1C, F ). In addition, the species of Treadwellphysa have poorly developed postchaetal lobes and compound spinifalciger chaetae, whereas in Paucibranchia n. gen. the postchaetal lobes are well developed and the compound spinifalciger chaetae are absent. Finally, the species of Marphysa and Treadwellphysa have anodont pectinate chaetae in the median and posterior chaetigers, while in Paucibranchia n. gen. they are absent.

Within Eunicidae , the branchiae have been a controversial feature since some genera have been established by the absence of this structure (e.g., Nicidion Kinberg, 1865 and Paramarphysa Ehlers, 1887 , the latter a junior synonym of Marphysa ). However, some authors have dismissed the value of this absence to establish new genera ( Fauchald 1992; Carrera-Parra & Salazar-Vallejo 1998). However, branchial distribution along the body has been shown to be a morphologically important feature (e.g., Kinberg 1865; MacIntosh 1885) and phylogenetically informative ( Zanol et al. 2014). In a recent phylogenetic analysis of the Eunicidae based on morphological and molecular evidence, Marphysa was found to be composed of two clades ( Zanol et al. 2014, Fig. 2 ). In one of the clades (number 47), all species included have branchiae restricted to anterior chaetigers, whereas in the other clade (number 46) all species have branchiae distributed along the body. Despite no analysis of these clades was provided, their phylogenetic tree supports the branchial distribution as an important and useful characteristic to split the genus.

Another taxonomically important feature of Paucibranchia n. gen. is the architecture of the maxillary apparatus, which has already been used to differentiate families and genera in Eunicida ( Kielan-Jaworowska 1966; Orensanz 1990; Carrera-Parra 2006). For example, the sharp teeth on maxillae III, IV and V is typical of Euniphysa Wesenberg-Lund, 1949 ( Lu & Fauchald 2000) and the shape of maxillae I and II was important to establish the genus Treadwellphysa ( Molina-Acevedo & Carrera-Parra 2017) .

There are two available genus names which were erected with species belonging to the subgroup 1 ( Fauchald 1970). The first one is Nausicaa Kinberg, 1865 ; this genus was proposed with one species ( N. striata Kinberg, 1865 ) from San José Island, Panama, which was briefly characterized with bilobed prostomium, peristomial cirri absent, and branchiae restricted to the anterior region, but as a single filament. Unfortunately, the type material of N. striata , which was deposited in the Swedish Museum of Natural History (SMNH) is lost, the vial is empty except for some fragments of parapodia in alcohol (Lena Gustavsson - SMNH, e-mail comm. to L.F. Carrera-Parra). Further, the species was never recorded after its description, and I was unable to find additional material for its redescription. However, if new specimens are found even from the type locality, it would not be possible to determine if they belong to the same species, because the original description was brief and did not contain all the diagnostic characters of the species. Therefore, N. striata is considered an indeterminable species, leaving the name Nausicaa unavailable.

A second genus, Macduffia McIntosh, 1885 , was also proposed for only one species ( M. bonhardi McIntosh, 1885 ) collected from the West Indies to a depth greater than 700 m. The species was described with branchiae restricted to the anterior region of the body. Unfortunately, the author only studied a small fragment of an incomplete specimen (L10: 3.1 mm, holotype BMNH 1885.12.1.210), that is currently in poor condition, as it has only 33 chaetigers with all chaetae broken, and the maxillary apparatus is lost ( Fig. 2 A– C ). In the holotype, the branchiae are present in chaetigers 6 to 9 with up to four filaments; however, the branchiae look underdeveloped and the branchial filaments are digitiform-shaped, the postchaetal lobe is not developed, and the dorsal cirri are digitiform and shorter in the branchial region. This diagnosis does not match with the Paucibranchia n. gen. species, which have all branchiae well developed, with longer and tapered branchial filaments (even in species with few filaments such as P. fallax ( Marion & Bobretzky, 1875) n. comb.), the postchaetal lobe is well developed both in the pre-branchial and in the branchial region, and the dorsal cirri is always elongated in the branchial region. Although McIntosh drew the maxillary apparatus ( McIntosh 1885, p.303, Fig. 60 ), it is not possible to determine in which genera this species belongs to due to the inaccuracy of the drawing. This evidence indicates that M. bonhardi does not belong to Paucibranchia n. gen. and its correct identification will depend mainly on finding topotypic material.

The new genus includes 13 species that were previously classified in Marphysa : Paucibranchia adenensis ( Gravier, 1900) n. comb., P. bellii ( Audouin & Milne-Edwards 1833) n. comb., P. cinari (Kurt- Sahin, 2014) n. comb., P. conferta ( Moore, 1911) n. comb., P. disjuncta ( Hartman, 1961) n. comb., P. fallax ( Marion & Bobretzky, 1875) n. comb., P. gemmata ( Mohammad, 1973) n. comb., P. kinbergi ( McIntosh, 1910) n. comb., P. oculata ( Treadwell, 1921) n. comb., P. purcellana ( Willey, 1904) n. comb., P. sinensis ( Monro, 1934) n. comb., P. stragula ( Grube, 1878) n. comb. and P. totospinata ( Lu & Fauchald, 1998) n. comb.. Another six are regarded as new species: P. andresi n. sp., P. carrerai n. sp., P. gathofi n. sp., P. gilberti n. sp., P. miroi n. sp. and P. patriciae n. sp.; whereas two species were not formally named: Paucibranchia sp. 1 and Paucibranchia sp. 2.

Figures

FIGURE 1. Maxillary apparatus. A. Paucibranchia disjuncta n. comb. (Hartman, 1961), LACM-AHF POLY 6447, dorsal view; B. Marphysa viridis Treadwell, 1917, ECOSUR-P2678, dorsal view; C. Treadwellphysa yucatanensis Molina-Acevedo & Carrera-Parra, 2017, ECOSUR-P2811, dorsal view; D. Left MI-II-III-IV-V of P. disjuncta n. comb., dorsal view; E. Left MI- II-III-IV-V of M. viridis, dorsal view; F. Left MI-II-III-IV-V of T. yucatanensis, dorsal view. Scale bars: A, D, 0.4 mm; B, E, 0.45 mm; C, F, 0.25 mm. Dark and thin lines in D, E and F indicate the different forms in the MI of the apparatus of each species. fa= falcal arch, boe= basal outer edge, bie= basal inner edge, rp= rounded projection in base of MII.

FIGURE 2. Marphysa bonhardi McIntosh, 1885, holotype BMNH 1885.12.1.210. A. Anterior end, dorsal view; B. Anterior end, ventral view; C. Aciculae, anterior chaetigers. Scale bars: A, 0.8 mm; B, C, 0.67 mm.

FIGURE 5. Paucibranchia adenensis (Gravier, 1900) n. comb., non-type MNHN-A148. A. Parapodium 3; B. Parapodium 11; C. Parapodium 26; D. Parapodium 70; E. Parapodium 158; F. Parapodium 216. All in anterior view. Scale bars: A–F, 0.7 mm.

FIGURE 6. Paucibranchia adenensis (Gravier, 1900) n. comb., non-type MNHN-A148. A. Compound falciger, long blade, chaetiger, 11; B. Compound falciger, median blade, chaetiger, 11; C. Compound falciger, short blade, chaetiger, 216; D. Isodonts pectinate narrow with long and slender teeth, chaetiger 3; E. Isodonts pectinate narrow with short and slender teeth, chaetiger 216; F. Subacicular hook, distal end, chaetiger 158. Scale bars: A, 12.5 µm; B, 20 µm; C, F, 9.8 µm; D, 14 µm, E, 4.9 µm.

FIGURE 13. Paucibranchia bellii (Audouin & Milne-Edwards, 1833) n. comb. A. Parapodium 3; B. Parapodium 29; C. Parapodium 46; D. Parapodium 93; E. Parapodium 138. All in anterior view. A, E from non-type MNHN-A39; B–D from lectotype MNHN TYPE 568. Scale bars: A, 140 µm; B, 180 µm; C, 160 µm; D, 111 µm; E, 230 µm.

FIGURE 60. Paucibranchia purcellana (Willey, 1904) n. comb., holotype BNHM 1911.2.1.13. A. Anterior end with branchiae, lateral view; B. Anterior end, ventral view; C. Anterior end with branchiae, dorsal view; D. Pygidium. Scale bars: A, C, 3.6 mm; B, D, 1.8 mm.