Isopods of the genus Arcturella ( Valvifera : Arcturidae ) from the expedition FAUNA I ( S Spain ) , with description of a new species *

The genus Arcturella Sars, 1897 is currently represented in the Atlantic and the Mediterranean by fifteen species (Table 1): A. bispinata Menzies and Kruczynski, 1983, A. brevipes Barnard, 1920, A. carlosoteroi Reboreda, Wägele and Garmendia, 1994, A. cornuta Koehler, 1911, A. damnoniensis (Stebbing, 1874), A. dilatata (Sars, 1883), A. dollfusi Monod, 1925, A. lineata (Stebbing, 1873), A. lobulata Barnard, 1925, A. longipes Barnard, 1920, A. poorei Castelló, 1997, A. pustulata Barnard, 1920, A. sawayae Moreira, 1973, A. senegalensis (Koehler, 1911) and A. spinata Menzies and Kruczynski, 1983. One additional species is known from the Pacific, A. nodosa (Dana, 1849) from the Philippines. Many of these species are known for only one specimen (e.g. A. carlosoteroi, A. cornuta, A. nodosa, and A. poorei). This paper is the third of a series of contributions dealing with the marine isopod fauna of Spain (Hedo and Junoy, 1999; Rodríguez Sánchez et al., in press) as result of the examination of collections of the oceanographic expedition “FAUNA I” along the south coasts of the Iberian Peninsula (see Templado et al., 1993), and deals with the three specimens of the genus Arcturella collected. Two specimens are assigned to a new species, Arcturella estherae sp. nov. This new species differs from the others in several aspects, and are therefore considered new to science. Type material is deposited in the collections of the Museo Nacional de Ciencias Naturales (MNCN), Madrid, Spain. The third specimen resembles Arcturella carlosoteroi, but shows certain anatomical differences whose taxonomic significance cannot at present be assessed. SCI. MAR., 66 (1): 33-41 SCIENTIA MARINA 2002

This paper is the third of a series of contributions dealing with the marine isopod fauna of Spain (Hedo and Junoy, 1999;Rodríguez Sánchez et al., in press) as result of the examination of collections of the oceanographic expedition "FAUNA I" along the south coasts of the Iberian Peninsula (see Templado et al., 1993), and deals with the three specimens of the genus Arcturella collected. Two specimens are assigned to a new species, Arcturella estherae sp. nov. This new species differs from the others in several aspects, and are therefore considered new to science. Type material is deposited in the collections of the Museo Nacional de Ciencias Naturales (MNCN), Madrid, Spain. The third specimen resembles Arcturella carlosoteroi, but shows certain anatomical differences whose taxonomic significance cannot at present be assessed. The oceanographic expedition FAUNA I was carried out in the Gulf of Cadiz, on both sides of the Strait of Gibraltar, Sea of Alborán and Bajos of Motril (S Spain) in July 1989. The objective of this expedition was to capture a representation of all sea fauna and, because of this, both pelagic and benthic samples were taken from various depths between 12 to 1250 m. (see Templado et al., 1993 for sampling details). All sampling material was sorted out in the Museo Nacional de Ciencias Naturales (Madrid) and isopods were later sent in alcohol to the senior author (J.J.) of this paper.
The present specimens were caught with the beam trawl described in Templado et al. (1993), preserved in 70% ethanol and dissected in glycerine with minute needles. The microscopic preparations were kept in a drop of glycerine as mounting medium, and sealed with paraffin.

Genus Arcturella Sars, 1897
The identification of species of the family Arcturidae is extremely difficult because many genera are inadequately or sometimes inexactly defined. No consensus seems to exist as for characters that must be used to differ the genera of this family (e.g. Stebbing, 1908;Koehler, 1911;Kussakin, 1972;Kensley, 1978;Menzies and Kruczynski, 1983;Brandt, 1990).
The poorly defined genus Arcturella Sars, 1897, shares several features with other genera of the family. Arcturella was created by Sars (1897) to receive specimens different to genus Astacilla Cordiner, 1795. Both Astacilla and Arcturella have been separated using different characters, such as length and shape of pereonite IV, general shape of the body, number of oostegites and morphology of pereopod I (e.g. Sars, 1897;Koehler, 1911;Barnard, 1920;Monod, 1925;Bocquet and Duchet-Bertin, 1967;Castelló, 1997). However, the separation between these two genera is not clearly established, since some characters have been described contradictorily in the literature. For example, with respect to the morphology of pereopod I, Kussakin (1972) and Kensley and Schotte (1984) note that both Arcturella and Astacilla present a strong dactylar claw on pereopod I; Reboreda et al. (1994) note that Arcturella has no claw and Castelló (1997) notes that Arcturella can be distinguished from Astacilla by the presence of a claw in the latter and its absence in the former.
The diagnoses of Sars (1897) and subsequent authors (e.g. Barnard, 1920;Bocquet and Duchet-Bertin, 1967;Moreira, 1973;Kensley, 1978;Menzies and Kruczynski, 1983;Castelló, 1997) are consistent in that the principal character for distinguishing the two genera is the size and shape of pereonite IV of females, a character that have leads us to include our specimens, with suitable reservations, in the genus Arcturella.  Etymology: The species is dedicated to Esther Serna Sanz in appreciation of her collaboration in this paper and of her friendship.
Diagnosis: Body elongated, thin but expanding level of pereonite IV. Dorsal sculpture formed by 3 little prominences near the posterior margin of cephalon; 3 protuberances on pereonite I; 5 protuberances arranged in rows over pereonites II and III; middorsal protuberance on pereonite IV. Dactylus of pereopods V-VII with one large terminal claw and one very small false claw.
Description: Body elongated (Fig. 1), 9 times longer than pereionite V in dorsal view excluding antennae, thin but expanding level pereonite IV, wider than the rest of pereonites. Length: 5-5.5 mm. Colour: Pale yellow in alcohol. Cephalon: as wide as long, fused with pereonite I, with 3 little prominences on cephalic surface, near posterior margin of cephalon; eyes relatively prominent and red. Antennula ( Fig. 2A) reaches half the third basal article of antenna; peduncle of three articles, article 1 wider than the other two with creased surface, fla-gellum of one article bearing in distal part two aesthetascs and two little setae. Antenna (Fig. 2B) length equivalent to the length between anterior margin of cephalon and posterior margin of pereionite IV; five peduncular articles (first peduncular article not shown in Fig. 2B), articles 2 and 3 with creased surface; flagellum of 3 articles, distal article with flattened scale-spines (Fig. 2C) and apical claw. Mandible (Fig. 2D, E) lacking palp; incisor and lacinia mobilis each with 3 teeth, 3 broad spines in spine row, molar process distally truncate in right mandible and acute in left mandible. Maxillule (Fig.  2F): inner lobe with 4 distal spines, outer lobe with 9 stout spines. Maxilla (Fig 2G): trilobate, endopod with 9 circumplumose spines and 4-5 simple spines; inner and outer lobes of exopod with 4 and 2 elongated circumplumose spines respectively. Maxilliped (Fig. 2H): palp 5-articulate, endite with one coupling hook and 4-5 circumplumose spines.
Pereonite I fused with cephalon, fusion line visible, with 3 protuberances arranged in row. Pereonites II-III short, with 5 protuberances each, arranged in rows over the 2 segments. Laterally pro- truding supracoxal plates prominent. Pereonites IV wider and longer than the rest of pereonites, of roughly rectangular shape, with protruding rounded edges; with a middorsal protuberance; lateral margin with wavy contorn. Pereonites V to VII diminishing in length, rounded laterally protruding supracoxal plate, largest on pereonite V (Fig. 1). Pereopods I-IV adapted to filter functions, pereopods V-VII ambulatory. Pereopod I (Fig. 3A) broader and shorter than pereopods II-IV, terminal claw of dactylus absent (Fig. 3B). Pereopods II-IV subsimilar, dactylus and claw absent, setation as in Figure 3C-E. Oostegites lost during the dissection process. Pereopods V-VII with four first articles creased, with sparse setation (Fig. 3F-H). Dactylus with claw and a small false claw in the inner distal angle (Fig. 3I).
Pleotelson (Fig. 1) as long as the pereonites V-VII together, distal part with cone-shaped, tapering to rounded tip, the latter slightly curved dorsally. All segments of the pleon are fused, with two fusion lines visible.

Arcturella sp A. (Figs. 5-8)
Material examined: 1 female, length 3.5 mm excluding antennae. Station 38, Estepona (36º18.25´-36º20.20´N, 05º13.25´-05º12.40´W), 60-62 m depth, 16 July 1989, bottom: gravel (Templado et al., 1993. Description: Body elongated (Fig. 5), 9 times longer than pereonite V in dorsal view excluding antennae, thin but expanding level pereonite IV, wider and longer than the rest of pereonites. Length: 3,5 mm. Colour: Pale yellow in alcohol. Cephalon: as wide as long, fused with pereonite I, with an anterior pair of tubercles and one simple tubercle behind; eyes relatively prominent and red. Antennula (Fig. 6A) reaches the beginning of the fourth basal article of antenna; peduncle of three articles (first peduncular article not shown in Fig.  6A) and flagellum of one article bearing in distal part two aesthetascs and two elongated simple setae. Antenna (Fig. 6B)  between anterior margin of cephalon and posterior margin of pereonite IV; five peduncular articles (first peduncular article not shown in Fig. 6B), articles 2 and 3 wide, with the same length, articles 4 and 5 slight and long, with numerous simple setae along inner part; flagellum of 3 articles, each of them with short simple setae, and an apical claw. Mandible (Fig. 6C, D) lacking palp; incisor and lacinia mobilis each with 3 teeth, 3 broad thorny spines in spine row, molar process distally truncate in right mandible and acute in left mandible. Maxillula (Fig. 6E): inner lobe with 3 distal spines and 3 short simple setae in basal part of them, outer lobe with 8 broad spines in apical part. Maxilla (Fig. 6F): trilobate, endopod with 7 circumplumose spines and 4-5 simple spines; inner and outer lobes of exopod with 3 and 2 elongated circumplumose spines respectively. Maxilliped (Fig. 6G): palp 5-articulate, endite with one coupling hook and 3 circumplumose spines. Pereonite I fused with cephalon, fusion line visible, with 3 protuberances arranged in row. Pereonites II-III short, with 3 protuberances each arranged in rows over the 2 segments. Pereonite IV wider and longer than the rest of pereonites, of roughly rectangular shape, with each anterior corner lightly projecting and rounded; with smooth surface except for little lateral prominences. Pereonites V to VII diminishing in length, rounded laterally protruding supracoxal plate, largest on pereonite V (Fig. 5).
Pereopods I-IV adapted to filter functions, pereopods V-VII ambulatory. Pereopod I (Fig. 7A) broader and shorter than pereopods II-IV, terminal claw of dactylus absent (Fig. 7B) (Fig. 7F, H), dactylus and claw (Fig. 7G). The specimen is not complete and pereopod VII is lost. Pleotelson (Fig. 5) lightly longer than pereonites V-VII together, distal part with cone-shaped, tapering to rounded tip, the latter slightly curved dorsally. All segments of the pleon are fused, with two fusion lines visible.
Pleopods 1 and 2 with apical plumose swimming setae (Fig. 8A, B). Pleopods 3, 4 and 5 lost. Uropods (Fig. 8C, D): with 4 circumplumose setae on inner distal angle of peduncle, the longer of the two rami with numerous short simple setae in external lateral margin, shorter ramus with 3 long apical plumose setae and numerous short simple setae in external lateral margin.

DISCUSSION
The species of genus Arcturella are mainly identified by shape and ornamentation of pereonite IV in females, bearing dorsally one (A. lineata, A. sawayae and Arcturella estherae sp. nov.), two (A. bispinata, A. cornuta, A. damnoniensis, A. dilatata, A. dollfusi, A. poorei and A. spinata), or many prominent protuberances or spines (A. pustulata and A. senegalensis), or lacking them (A. brevipes, A. carlosoteroi, A. lobulata and A. longipes). A. estherae sp. nov. can be separated from the other species of the genus by the presence of only one dorsal protuberance in pereonite IV of females, a feature shared with A. lineata and A. sawayae. The elongated and rectangular-shaped pereonite IV and the general ornamentation of the body of A. estherae sp. nov. easily distinguish this species from A. lineata and A. sawayae. It can be further distinguished from A. lineata by the morphology of pereopod I (the latter species having a strong, dactylar claw). These three Atlantic species are known from different areas: A. lineata from South Africa, A. sawayae from Brazil and A. estherae sp. nov. from Spain. Table 2 shows comparative measurements for these three species and for A. carlosoteroi, A. damnoniensis and A. poorei, three species recorded in the neighboring waters.
Arcturella sp. A. resembles A. brevipes, A. carlosoteroi, A. lobulata and A. longipes in lacking dorsal protuberances in pereonite IV of females. The three South African species (A. brevipes, A. lobulata and A. longipes) lack ornamentation in pereonites I-III, whereas the two Spanish species (A. carlosoteroi and Arcturella sp. A) have small tubercles in these pereonites. Arcturella sp. A resembles in general appearance A. carlosoteroi, but may be distinguished by the presence of tubercles in cephalon, by the number of tubercles in pereonites I-III (being 3 in Arcturella sp A. and 5 in A. carlosoteroi), by the shape of pereonites V-VII and pleotelson, and by small details in appendices. These differences could be sufficient to establish a separate species but, the other hand, they could represent variations in char-acters from A. carlosoteroi, a rare species that is known from only one specimen. Additional specimens are required to solve this question.