DISTRIBUTION OF BENTHIC INVERTEBRATES IN THE BEAGLE CHANNEL, ARGENTINA

Bathymetric and spatio-temporal distributions of both abundance and biomass as well as secondary production of benthic invertebrates in the Beagle Channel were determined. The sampling stations were seasonally placed in three different areas in the Beagle Channel at two depth ranges, 15-40 m and 70-259 m. A total of 32,686 specimens distributed in 30 taxonomic groups were identified. In addition, 4 taxa were quantified only in terms of biomass. The invertebrate abundance and biomass were different with depth. Secondary production at this range was 0.59 ±0.51 kJ·m-2 year¹ whereas it decreased to 0.09 ±0.08 kJ·m-2 year¹ at 70-259 m. In contrast to secondary production, P/B ratio showed a positive increment with depth. Furthermore, seasonal variations were not observed in secondary production of the macrozoobenthos. Parameters directly associated with depth could be involved in structuring the macrobenthic assemblages in the Beagle Channel

Thysanozoon brocchii Risso 1818

Thysanozoon brocchii (Risso 1818) (Figures 4–6) Examined material. Voucher: 8.0 μm sagittally sectioned specimen, mounted on 81 slides. Collected by M.J. Albano, 9 May 2008, North Breakwater of the Mar del Plata harbour. On a mussel and ascidians community, 1–2 m depth. MACN-In 38206. Morphology. Large, oval, 26 mm long by 15 mm wide alive, 23 mm by 14 mm preserved. Marginal tentacles formed by foldings of the fore margin, conspicuous, oriented dorsally and directed backwards, distally enlarged, with no pigmentation. Ground colour is light brown, delicately translucent in the margins, centrally yellowish brown. Round black spots cover the dorsal surface, especially in a wide marginal area. Dorsal surface covered with big bulky conical dark brown papillae, which are longer and more densely distributed to the sides of the dorsal bulge, but scattered on the bulge itself, and declining in length and number to the margins, leaving the margin free of papillae. A second area free of papillae extends from the cerebral eyes up to between the tentacle bases (figures 4 A– 4 B). Though the presence of blunt dorsal papillae gives the animal a solid appearance, the body itself is very delicate and frail. The dorsal tentacular eyespots are numerous on the dorsal surface, distributed in a single row; they are scattered ventrally. The cerebral eyespots form two separated triangular clusters. Pharynx ruffled, 320 µm long. The mouth opens at 7.2 mm from anterior margin, in the middle of the pharynx cavity. The main gut opens in the middle of the pharynx cavity roof and runs distally up to short behind the female system. Intestinal ramifications are conspicuous and numerous, running parallel to the body surface and giving out extensions into every dorsal papilla (figure 6 D). Ventral sucker at 13 mm from the fore margin of the body (figure 4 C). Dorsal body wall 50 µm high. The ciliated cellular epidermis has rhabdites and granular pigmentation. The cilia are very short, and the rhabdites and pigmentation are abundant and more densely packed on the papillae, but they are scattered on the dorsal epidermis. Beneath the epidermis a frail layer of circular muscle fibres is present, followed by a longitudinal muscle layer. The granular pigmentation is present in the epidermis and the circular muscle layer. Ventral body wall 70 µm high. The cilia are numerous and longer than those on the dorsal epidermis. Ventral surface with scarce rhabdites and no granular pigmentation. Beneath a well defined basement membrane, a thin layer of circular muscle fibres is underlain by a layer of loose longitudinal muscle fibres. The testes are latero-ventrally distributed but especially greatly accumulated in the rear part of the body (figure 4 C, 6 C), beyond the uteri. The ovaries are dorsal; the uteri are short, filled with small and few mature cells. The male reproductive system is double. Each male copulatory organ consists of a true seminal vesicle, free prostatic vesicle and penis papilla armed with a stylet (figure 5). The swollen vas deferens runs ventrally before entering the elongated seminal vesicle. The seminal vesicle is curved and dorsal to the male prostatic vesicle and stylet; it has a well-developed muscular wall and its lumen is narrow. The rounded prostatic vesicle has a muscular wall and a very high, smooth glandular inner lining. The ciliated ejaculatory duct describes a tortuous trajectory up to reach the penis papilla, having a well-developed muscular layer. The prostatic duct is short and straight, joining the ejaculatory duct beyond the point where the stylet is attached. The stylet is conical and elongated, 330 µm long and slightly curved. The penis sheath is ciliated, short and narrow (figure 6 A). The spacious male atrium is ciliated and directed forwards, opening to a male gonopore located 7.6 mm from the fore end. The second male copulatory organ is similar to the one already described. The female reproductive system is single (figure 5). The oviducts enter the vagina separately from the rear end. The canal is proximally swollen, later narrowing and turning ventrally, to finally enlarge distally. The fore and middle tract of the vagina is immersed in an eosinophilic glandular mass (figure 6 B). There are no cement glands either distally to the vagina or surrounding the elongated female atrium. Without an apparent cement pouch, the vagina and atrium are completely ciliated, underlain by a frail layer of circular muscle fibres. The female atrium opens to a female gonopore ventrally in the midline of body. Taxonomical discussion. Species in genus Thysanozoon are identifiable by their papillated dorsal epidermis, each species showing a definite body shape, a particular distribution of the papillae and a specific colour pattern. The studied specimen of T. brocchii from Mar del Plata matched the detailed descriptions of this species made by Lang (1884) and Stummer-Traunfels (1895). Under the current frame of morphological identification, the crucial characters that discriminate T. brocchii from its relatives are the dorsal surface covered with large bulky conical dark brown papillae, with the margin and cerebral areas free of papillae; its ground colour light brown, delicate translucent in the margins, and the internal anatomy being consistent with the descriptions of the T. brocchii specimens described for Brazil, Curaçao and Patagonia (Marcus 1949, 1952; Marcus & Marcus 1968; Brusa et al. 2009). Marcus (1949) described T. lagidium from the coast of Brazil; later on, after comparing the anatomy with the specimen from Curaçao and Europe, he synonymised T. lagidium with T. brocchii (Marcus & Marcus 1968). These descriptions were accurate enough for Brusa et al. (2009) to identify the specimen from Patagonia as T. brocchii and the specimen from Mar del Plata as well. Thysanozoon brocchii has been described inhabiting Indopacific waters, the Mediterranean, and the Atlantic coast of South America, from the Caribbean to Patagonia. Such a worldwide distribution is curious, especially since water temperature has been considered a limiting factor for the distribution of polyclad species. Prudhoe (1985) proposed that the presence of dorsal papillae in the genera Acanthozoon and Thysanozoon could be related with their flotation capacity as a mean of dispersion, but from personal observation, T. brocchii possess a benthonic life habit, crawling over rocks and into cracks between short swimming periods. Faubel (1984) published a list of pelagic polyclad species collected during different expeditions to South and Central Atlantic Ocean and Sargasso Sea. The unpapillate polyclads collected by these expeditions, were not in accordance to Prudhoe’s (1985) hypothesis. We agree with Brusa et al. (2009) in that the presence of the papillae should be associated with increasing the surface of gas exchange and digestion. The cosmopolitan dispersion of T. brocchii over the South American Atlantic coasts could be associated with the Brazilian ocean current, especially at larval stage. However, because the traditional taxonomy of the Pseudocerotidae is mostly based on external morphological characters, it does not necessarily reflect their phylogenetic relationships. There is still no molecular evidence to discuss if the South American T. brocchii is genetically identical with the morphologically similar specimens collected from the Indopacific waters and Mediterranean coasts.Published as part of Bulnes, Verónica N., Albano, Mariano J., Obenat, Sandra M. & Cazzaniga, Néstor J., 2011, Three Pseudocerotidae species (Platyhelminthes, Polycladida, Cotylea) from the Argentinean coast, pp. 30-44 in Zootaxa 2990 on pages 35-38, DOI: 10.5281/zenodo.20231

Thysanozoon mirtae Bulnes, Albano, Obenat & Cazzaniga, 2011, sp. nov.

Thysanozoon mirtae sp. nov. Figures 7–9 Diagnosis. Pseudocerotidae with papillated surface, ground colour greenish yellow covered with rounded black spots, more densely distributed on a mid dorsal band. The papillae are elongated, reddish brown; with a marginal band and cerebral area free of papillae. Conspicuous marginal, colourless tentacles. Two cerebral eye clusters present. The tentacular eyes extend from the fore margin, where they are arranged in a single marginal band, backwards up to the base of the tentacles where they are scattered. Male copulatory apparatus double with conspicuous spermiducal vesicles, a single true seminal vesicle, free prostatic vesicle and a slightly asymmetric stylet. The ejaculatory duct joins the prostatic duct proximally at the base of the penis stylet. Male atrium short, narrow and ciliated. Vagina ciliated, without a cement pouch. Female atrium small and ciliated. Separated gonopores. Ventral sucker in the fore body half. Type material. Holotype: 9.0 μm sagittally sectioned specimen, mounted on 180 slides. Collected by M.J. Albano, 21 February 2009 from the Club Náutico de Mar del Plata. On a mussel and ascidians community, 1–2 m depth. MACN-In 38207. Etymology. The specific name is dedicated to the memory of Mariano Albano´s mother, Mrs. Mirta R. Elías. Description. Large, elongated, 36.5 mm long by 20 mm wide alive, 35 mm by 18.4 mm preserved. Marginal tentacles formed by foldings of the fore margin. Dorsal surface covered with elongated reddish brown papillae which are longer and more thickly placed in the centre, declining in length and number to the margins, leaving a marginal band free of papillae. Ground colour is greenish yellow covered with rounded black spots, more densely distributed on a mid dorsal band. With an interrupted reddish brown marginal band. Marginal tentacles without pigmentation, extending between the tentacle bases and reaching the brain dorsally (figures 7 A– 7 B). The dorsal tentacular eye spots are numerous, distributed dorsally in a single row and ventrally scattered. The cerebral eyespots form two separated triangular clusters joining anteriorly. Frontal eyes scattered (figure 7 D). Pharynx ruffled, 5.5 mm long (figure 7 C). The mouth opens at 14 mm from fore margin, behind the pharynx cavity. The main gut opens in the middle of the pharynx cavity roof and runs distally up to short behind the female system. The intestinal ramifications give out extensions into the dorsal papillae (figure 9 C). Dorsal body wall 103 µm high. The ciliated cellular epidermis bears rhabdites and granular pigmentation. The elongated rhabdites are densely packed on the epidermis of the papillae and are readily seen as small red small rods even in living specimens. The granular pigmentation is distributed mostly in the epidermis free of papillae. Beneath the epidermis a layer of circular muscle fibres is present, followed by a longitudinal muscle layer. Ventral body wall 110 µm high, without rhabdites but with granular pigmentation. Beneath the basement membrane, there are a layer of circular muscle fibres and an innermost layer of longitudinal muscle fibres. The ventral epidermis is higher than the ventral one, the ventral circular layer is thinner than the dorsal one, and the ventral longitudinal layer is much higher and dense than the dorsal one. Body parenchyma immersed in a dense net of parenchymatic muscle fibres, giving the body a strong appearance (figure 9 D). The testes are small, widely spaced and ventrally arranged beyond the uteri. The uteri are dorsal to the testes, but ventral to the gut. They are well developed, filled with numerous eggs and located behind the spermiducal vesicles. The male copulatory system is double. Each copulatory organ consists of a true seminal vesicle, free prostatic vesicle and penis papillae armed with a stylet (figure 8). The vas deferens runs ventrally from the rear. After it passes the ventral sucker, the vas deferens distends to form a few voluminous spermiducal vesicles (figure 9 E) before entering the elongated seminal vesicle. The seminal vesicle has a well developed muscular wall and is arranged dorsally to the male prostatic vesicle and stylet. The rounded prostatic vesicle shows a muscular wall and a very high, smooth glandular inner lining. The ciliated ejaculatory duct follows a short trajectory until reaching the penis papillae, its muscular wall being well developed. The prostatic duct is short and straight, joining the ejaculatory duct at the basis of the penis papilla. The stylet is conical and elongated, 760 µm long, slightly asymmetric and sharp. The male atrium is short and narrow, ciliated and directed backwards, opening to a male gonopore located 12 mm from the fore margin (figure 9 B). The second male copulatory organ is similar to the one already described. Both male copulatory organs are symmetrically arranged left and right of the longitudinal body axis. The female reproductive system is single (figure 8). The oviducts enter separately the vagina from the rear, turning ventrally to open distally into a small female atrium and a median gonopore. The canal is about the same diameter along the whole trajectory. The vagina is surrounded by scarce cement glands. There is no cement pouch. The vagina and atrium are completely ciliated. Taxonomical discussion. Thysanozoon mirtae sp. nov. is the only known species having slender, elongated dorsal papillae of reddish brown colour on a greenish yellow body covered with rounded black spots with a reddish brown marginal band; the marginal tentacles and cerebral area devoid of pigment complete an exclusive colour pattern. The presence of slender papillae was described for Thysanozoon skottsbergi Bock, 1913 and T. distinctum Stummer-Traunfels, 1895, while T. minutum Stummer-Traunfels, 1895 has a similar ground body colour. However, the dorsal papillae of T. mirtae sp. nov. differ from the papillae of T. skottsbergi because of the absence of darker pigmentation. The margin of T. distincutum is golden yellow and that of T. minutum is white, sharply different from the reddish brown marginal band of T. mirtae sp. nov. The spermiducal vesicles are thin-walled expansions of the vas deferens serving as storage of sperm (Faubel 1983, p. 21) different from the spermiducal bulbs, which are more muscularized structures, presumably assisting the propulsion of sperm. The apparent spermiducal vesicles and the strongly developed parenchymatic musculature are two main features characterizing the new species T. mirtae. It differs readily from the only species of Thyzanozoon with which it was recorded in sympatry, T. brocchii (Risso 1818), both in colour and anatomy. While T. mirtae is dorsally greenish yellow, covered with translucent, slender reddish brown papillae, with spermiducal vesicles and a well developed mesenchymatic musculature; T. brocchii is dorsally light-brown, covered with, solid, blunt dark brown papillae, without spemiducal vesicles and few mesenchymatic muscle fibres.Published as part of Bulnes, Verónica N., Albano, Mariano J., Obenat, Sandra M. & Cazzaniga, Néstor J., 2011, Three Pseudocerotidae species (Platyhelminthes, Polycladida, Cotylea) from the Argentinean coast, pp. 30-44 in Zootaxa 2990 on pages 39-41, DOI: 10.5281/zenodo.20231