INTRODUCTION
The amphinomid genus Paramphinome Sars, Reference Sars1872 includes small deep-water species which are often very abundant in quantitative deep-sea studies (eg. Hartman & Fauchald, Reference Hartman and Fauchald1971; Narayanaswamy et al., Reference Narayanaswamy, Nickell and Gage2003). This genus is worldwide distributed, mainly in deep waters and is characterized by the presence of one, two or three pairs of small notopodial hooks on each side of first chaetiger.
The genus Paramphinome was proposed by Sars (Sars, Reference Sars1872) to include P. pulchella from the Norwegian coasts, as the replacement name for Paramphinome pulchella Sars, 1869, which are nomina nuda. In 1930, Paramphinome australis Monro, Reference Monro1930 from off Signy Island (sub-Antarctic) was described based on one specimen. Gustafson (Reference Gustafson1930) briefly described two other species: P. grandis from Japan and P. splendens from the Gilbert and Ellis Islands, western Pacific. Hartman (Reference Hartman1964) recognized and briefly redescribed P. australis while P. grandis was considered doubtful by Imajima & Hartman (Reference Imajima and Hartman1964) because it was known only from an illustration of a fragmented individual without indication for the presence of the first chaetigers hooks. Fauvel (Reference Fauvel1932) described P. indica from the Arabian Sea, which differed from P. pulchella in body size and number of branchiate chaetigers.
Hartman (Reference Hartman1965) redescribed Paramphinome jeffreysii (McIntosh, 1868) and made a new combination from Hipponoa jeffreysii McIntosh, 1868. She considered P. jeffreysii as a senior synonym of P. pulchella.
Up to now there are approximately eight valid species in the genus: P. jeffreysii (McIntosh, 1868); P. oculifera (Augener, 1913); P. australis Monro, Reference Monro1930; P. grandis Gustafson, Reference Gustafson1930; P. splendens Gustafson, Reference Gustafson1930; P. indica Fauvel, Reference Fauvel1932; P. trionyx Intes & Le Loeuff, Reference Intes and Le Loeuff1975 and P. pacifica Fauchald & Hancock, Reference Fauchald and Hancock1981.
This study describes a new Paramphinome species from southern Brazil. This new species differs from all other described species by the lower number of branchiate chaetigers, branchiae starting in a posterior region on the body, shorter body size and a much reduced caruncle.
MATERIALS AND METHODS
Specimens were collected in the Campos Basin (southern Brazil, Rio de Janeiro state coast, between 21°18 S and 23° S) during a survey made by PETROBRAS (Brazilian Petroleum Company) under the scope of the project ‘Campos Basin Deep-sea Environmental Project’ coordinated by CENPES/PETROBRAS. Sediment samples were collected using a box-corer. The sediment collected was separated in three strata: 0–2 cm; 2–5 cm and 5–10 cm. After this the sediment of each stratum was sieved (0.5 mm mesh-size) and fixed in 10% formalin. We used an analysis of variance (Sokal & Rohlf, Reference Sokal and Rohlf1995) to test the difference of specimen density among the different strata.
The new species holotype was deposited at the polychaete collection of the Zoology Department of Universidade Federal do Rio de Janeiro, Brazil (IBUFRJ) together with ten paratypes. Ten paratypes were also deposited at Centro de Estudos do Mar of Universidade Federal do Paraná, Brazil: (MCBM-BPO) and the other ten were deposited at the Museu de História Natural of ‘Universidade Estadual de Campinas’ (MNH-BPO).
MATERIAL EXAMINED
Holotype (IBUFRJ-0588): complete, 5 mm long, 0.6 mm wide, 25 chaetigers, 22 May 2003, 22° 04′ S–39° 47′ W, 1600 m deep. Paratypes: (IBUFRJ-0608; MCBM-BPO 1315; MNH-BPO 16/1–5): 1.0–7.0 mm long, 0.3–0.8 mm wide, 10–29 chaetigers, collected between 2002 and 2003 in many stations around the geographical coordinates cited above, between 900 and 2000 m deep.
DESCRIPTION OF THE HOLOTYPE
Holotype with 27 chaetigers, 5 mm length, 0.6 mm width.
Anterior part of the body inflated. Body yellowish, without colour patterns. Eyes and caruncle absent. Mouth surrounded by large round prostomial buccal cushion. Sac-like pharynx eversible. Prostomium with three antennae and two palps, median antenna placed in the prostomial posterior half, lateral antennae anterior (Figure 1A, M). Palps and lateral antennae similar in length, longer than median antennae. Dorsal and ventral cirri of first chaetiger three times longer than those of posterior chaetigers. Along the whole body ventral cirri longer than dorsal ones (Figure 1A, F & C). Parapodial rami well separated. All notopodial lobes short, blunt, dorsal cirri long, posteriorly attached; neuropodia more prominent, usually truncate; with ventral cirri longer than chaetal lobe (Figure 1C). Branchia dichotomously branched with up to ten filaments (Figure 1E); holotype with 3 pairs (see variation of this character below). Notochaetae of three types: (1) hooks directed forward (Figure 1A, M & O), present only in first notopodia (extremely difficult to observe in optical microscope); (2) stout spines (in number of 2, 3 or 4) (Figure 1G); and (3) slender, longer, smooth ribbon-shape setae (Figure 1J). Neurochaetae of three types: (1) a few thick, subdistally swollen spines (Figure 1H, N); (2) several slender marginally serrated chaetae (Figure 1I, P); and (3) some slender, long, smooth ribbon-shape chaetae (Figure 1J). Anus terminal, with median oval papilla (Figure 1B).
Paramphinome posterobranchiata sp. nov. (A) Anterior end in dorsal view; most chaetae of chaetiger 1 were omitted; (B) posterior end in ventral views; (C) parapodia of chaetiger 15; (D,O) hook; (E) branchiae; (F) anterior region in lateral view; (G) notopodial spine; (H,N) neuropodial spine subdistally inflated; (I,P) neuropodial slender marginally serrated chaetae; (J) notopodial and neuropodial slender, smooth capillaries; (L) a paratype in lateral view; (M) prostomium.
Variation
Branchia is absent in specimens with less than 14 chaetigers, starting in chaetiger 6 in specimens with more than 14 chaetigers (Figure 1A, F). Larger specimens can present up to three pairs of branchiae, but always starting in chaetiger 6 (Figure 2). It is noteworthy that specimens having 21 chaetigers might have one, two or three pairs of branchiae. The number of notopodial hooks on the first chaetiger might vary from one (holotype) to two (some paratypes).
A growth curve is presented in Figure 3. It shows a strong correlation between total number of chaetigers and body length of specimens, indicating that growth in this species is accomplished by the increase of new segments in a linear fashion.
Regression of number of branchiate chaetigers on number of chaetigers. Number of branchial pairs = −1.33 + 0.145 × number of chaetigers; R = 0.92.
Regression of body length on number of chaetigers. Body length = −2.57 + 0.30 × number of chaetigers; R = 0.83.
REMARKS
Paramphinome posterobranchiata sp. nov. is unique for having a posterior start of the first branchiae despite its small body size. In all other species of Paramphinome, branchiae starts in chaetiger 3 or chaetiger 4, while in P. posterobranchiata sp. nov., they start in chaetiger 6. Therefore, this species cannot be regarded as a juvenile of any other already known species, once ontogenetic variation in this species is expressed in the increment of branchiae in an anterior–posterior fashion (Figure 2). The ontogenetic variation in the number of branchiate chaetigers is very important for delineating the new species since branchial patterns are usually used as a taxonomic character in this genus and also in other genera of Amphinomidae (e.g. Linopherus). Furthermore, its body size, number of chaetigers and number of branchiate chaetigers are reduced when compared to all other Paramphinome species.
Another difference between P. posterobranchiata and other species of Paramphinome is its much reduced or even fused caruncle which may be related to a miniaturization process. The caruncle in Paramphinome is usually Y-shaped and extremely reduced, and has been considered by Gustafson (Reference Gustafson1930) as the most primitive for the family Amphinomidae.
It is rather difficult to consider such ‘reduced’ characteristics (small body size, small number of chaetigers and pairs of branchia and fused caruncle) in P. posterobranchiata as either plesiomorphic or apomorphic character states within Paramphinome when no phylogeny of the genus is available.
A new species of Paramphinome from the Brazilian continental shelf was noticed in a MSc thesis (Temperini, Reference Temperini1981); it was never formally published, although having been recorded in several later studies (Paiva, Reference Paiva1993; Amaral & Nonato, Reference Amaral and Nonato1994; Brasil & Silva, Reference Brasil and Silva2000). Nevertheless, the undescribed species is larger (6–13 mm), has more chaetigers (35–45), more branchiate chaetigers (5), starting in more anterior chaetiger (4) and has been found in shallower depths (160 m).
A comparison of the character states of the four most referred species of Paramphinome and the new species herein described is presented in Table 1.
Character variation and current distribution of the most referred Paramphinome species and P. posterobranchiata sp. nov.
ECOLOGICAL REMARKS
Of 100 specimens collected, 69 were in the upper 2 cm, 28 in 2–5 cm and only 3 were found in 5–10 cm. The average number of individuals per litre of sediment was 1.38, for the 0–2 cm strata; 0.88, for the 2–5 cm strata and 0.23 for the lower strata (5–20 cm). Differences among the three strata were significant (ANOVA, F = 22.4, P < 0.001). Paramphinome posterobranchiata is probably a surface dweller, that could be a predator, as other members of the family, or a deposit-feeder using the sac-like pharynx to get the organic matter deposited on sediment.
ETYMOLOGY
This specific name refers to the posterior start of the branchiae when compared to all other species of the genus Paramphinome.
ACKNOWLEDGEMENTS
We thank CENPES/PETROBRAS for providing the studied samples and financial support and CNPq (Process No. 471886/2004-1) for financial support. We are also grateful to Joana Zanol, Paulo da Cunha Lana, Vasily Radashevsky, Sergio Salazar-Vallejo and an anonymous referee for their valuable comments and suggestions.
