Pseudostomella dolichopoda, Todaro, M. Antonio, 2012

Todaro, M. Antonio, 2012, A new marine gastrotrich from the State of Sao Paulo (Brazil), with a key to species of Pseudostomella (Gastrotricha, Thaumastodermatidae), ZooKeys 223, pp. 39-51 : 42-48

Pseudostomella dolichopoda sp. n. Figures 2-4

Type locality.

Brazil, State of São Paulo, Praia Grande of Ubatuba (23°23'04.4"S; 45°03'49.9"W). At Mid-Water Mark, in fine (mean grain size, 0.160 mm) moderately well sorted (sorting, 0.70 mm) siliceous sand, and at 1.5 m water depth in fine (mean grain size, 0.153 mm), moderately sorted (sorting, 0.54 mm), siliceous sand. Values of salinity, temperature and pH of the interstitial water at date of sampling 35.1 psu, 26.3° C and 7.92 respectively; from the same beach additional specimens were collected on 7 September 2003. Other location in the State - Ubatuba: praia Prumirim (sl=sublittoral) also in 2003, Ilha do Prumirim (2003, l=littoral), praia do Tenório (2003, sl); São Sebastio: praia de Guaecá (sl), praia de Santiago (sl), praia do Saí (l, sl), praia Preta e Conchas (sl); Ilhabela: praia de Castelhanos (sl) (see Fig. 1 and also Todaro and Rocha 2004 for additional details on these localities).

Type specimens.

Holotype, the 358 μm long adult specimen shown in Figure 3.

Material examined.

Fifteen adult specimens(including the holotype) collected by the author from different localities (see below); ten specimens were observed alive and are not longer extant, while five were prepared for SEM survey and are kept in the meiofauna collection of the author (Ref. n. 2002-BR-01-05).

Ecology.

Frequency of occurrence - common in sediment of the northern sites, usual in southern sites but occasional in locations facing the São Sebastião channel and on Ilhabela. Abundance - prevalent to numerous in sub-littoral sediment, scarce in littoral sediments where found.

Diagnosis.

A Pseudostomella with an adult length to 425 μm; pharynx length to 90 μm, with pharyngeal pores at base. Pharyngeo-intestinal junction (PhIJ) at U32; body slender, with graceful lines and elongate, furcate caudum. Head with mid-sized fleshy preoral palps curving around forward; palps showing few sensory hairs and provided with 5 and 8 papillae on the dorsal and ventral border respectively. Sensory hair sparce but evenly spaced on the body, forming lateral columns from about U12.5 to U85; glands barely visible, asymmetrically scattered along most of the length of the body. Cuticular armature of small, delicate pentancres on whole dorsal and ventrolateral surface, except for a bare, roughly T-shaped area posterior to the palps. Adhesive tubes: TbA, 2 per side in a row U7.8; TbDL, 1 per side, robust, inserting on lateral margin of the posterior trunk region at U83.5; TbVL, 11 per side, 2 smaller ones in the anterior pharyngeal region, roughly at U16, 7 of slightly variable size, irregularly spaced in the intestinal region from U33.5 to U71.5, the remainder 2 originate from a common base at U76.2; TbP, 4 per side, 2 + 1 at the end of each foot of the furcated caudum and the other one flanking each foot medially. Ventral locomotor cilia: a continuous field of transverse rows covering sparsely the entire surface from U12 to U35; the field splits in the anterior intestinal region to form paired lateral tufts that extend onto the ano-genital area at U84. Reproductive system: testis on the right body side, caudal organ inverted pyriform, at U78; frontal organ bladder-like, at U74.5; maturing eggs mid-dorsally above the posterior half of the intestine.

Etymology.

The specific name alludes to the extraordinary length of the caudal pedicles ( dólicos Gr., long, and poús, podos Gr., foot).

Description.

The description is mainly based on the adult specimen, 358 µm in total length, shown in Figure 3. Body somewhat slender, little swollen in the posterior pharyngeal region and at the base of the 43 µm-long caudal pedicles. Pharynx 81 µm in length, measured from the ventral border of the oral opening to the pharyngeo-intestinal junction; pharyngeal pores near the base, at U29.5; pharyngeo-intestinal junction at U32; widths of neck\PhIJ\trunk\caudal base 30\29.5\40\31 µm at U15\U31\U51\U82, respectively. Head with well developed, fleshy preoral palps, incurving ventromedially; the dorsal border projecting just beyond the ventral. Sensory hairs and papillae occur on dorsal and ventral borders of the preoral palps; hairs are scattered on the dorsal, lateral and ventral surface of the palps; dorsally there are five papillae, nearly same in length (8-10 µm), symmetrically arranged along the inner border of the palps in a 2 + 1 + 2 pattern; ventrally, there are eight papillae, 5-8 µm in length, symmetrically arranged more centrally about the inner border of the palps in a 4 + 4 pattern; all papillae bearing one or two, short sensory hairs at their tip; other hairs form lateral columns that are evenly spaced from U12.5 to U85; individual hairs are 12-15 µm in length. Glands barely visible, variable in shape (oval to oblong) and size (4-8 µm in diameter), asymmetrically scattered along most of the length of the body.

Cuticular armature. Small sized pentancres with delicate, curved grasping tines, as tall as wide (3 × 3 µm - 5 × 5 µm) on whole dorsal and ventrolateral surface, except for a bare, roughly T-shaped area posterior to the palps; posteriorly most ancres extend onto the caudum.

Adhesive tubes. TbA, 2 per side (7-8 µm in length) in a row at U7.8; TbDL, 1 per side (15-18 µm in length), robust, inserting on the lateral margin of the posterior trunk region at U83.5; TbVL, 11 per side, 2 smaller ones (9-11 µm in length) in the anterior pharyngeal region, roughly at U16, 7 of slightly variable size and length (11-16 µm in length), irregularly spaced in the intestinal region from U33.5 to U71.5, the remainder 2, of unequal length (10 and 14 µm), originate from a common base at U76.2; TbP, 4 per side, 2 + 1 (5-6 µm in length) at the end of each foot of the furcated caudum and the other one (10 µm in length) flanking each foot medially.

Ventral locomotor cilia. A continuous field of transverse rows covering sparsely the entire surface from U12 to U35; the field splits in the anterior intestinal region to form paired lateral tufts that extend onto the ano-genital area at U84. Reproductive system: testis on the right body side, caudal organ inverted pyriform (11 × 22 µm), at U78; frontal organ bladder-like (9 µm in diameter), at U74.5; maturing eggs mid-dorsally above the posterior half of the intestine.

Measurement and variability. Body length of 15 living specimens ranged from 340-425 µm (mean = 388 µm, SD = 25.4 µm) all of them were mature (i.e., showed at least the testicles filled with sperm). Strange enough all of the SEM prepared specimens resulted of smaller size (i.e., less then 300 µm) even though only specimens appearing larger under the dissecting microscope were selected for this scope; these measurements are well below the 5.5% length reduction allowed for fixed specimens (cf. Clausen 2004a). The adhesive tubes of the TbVL series showed some variability in number, depending on individuals, ranging 11-15; however, the one borne on a common base numbered invariably two per side. Three specimens, 415-425 µm in total body length, collected in September 2003 from praia do Tenório and praia Grande showed 3-4 tubes of “cirrata” type along each dorsolateral side of the trunk region; cirrata tubes where never observed in specimens collected during the 2002 campaign. The meaning of these differences is unknown.

Taxonomic affinities.

Prior to the present study, the total number of Pseudostomella species known was 15 including one described by Valbonesi and Luporini (1984) but not formally named (cf. Hummon and Todaro 2010). Records come from a variety of locations including India and the Andaman Sea (e.g., Rao 1970, Rao 1993, Priyalakshmi et al. 2007); east Malaysia ( Renaud-Mornant 1967); Somalia ( Valbonesi and Loporini 1984); Portugal, Atlantic coast of France and north Sea (e.g., Swedmark 1956, Clausen 2004b, Hummon 2008); Mediterranean Sea (e.g., Hummon et al. 1993, Todaro et al. 2003); Atlantic and Gulf of Mexico coasts of the US ( Ruppert 1970, Todaro et al. 1995); moreover, the recent addition of new taxa from Australia ( Hochberg 2002), South Korea ( Lee and Chang 2002) and South Africa (Todaro et al. 2011) testify the cosmopolitan distribution of the genus. By contrast, Pseudostomella species appear to have a relatively restricted geographic range, at least compared to the wide distribution or even the cosmopolitan nature of many other gastrotrichs (cf. Todaro et al. 1996, Curini-Galletti et al. 2012, Kanneby et al. 2012, Kieneke et al. 2012).

Gastrotricha Thaumastodermatidae , including species of Pseudostomella , are characterized by peculiar cuticular armatures made up of sculptured plates, spines or a combination of both. Species of the genera Acanthodasys , Pseudostomella , Tetranchyroderma and Thaumastoderma bear peculiar pronged scales called ancres: uniancres, triacres, tetrancres and pentancres depending on number of prongs.

Acanthodasy and Thaumastoderma species bear ancres of a single type only, uniancres and tetrancres respectively whereas Pseudostomella and Tetranchyroderma bear tri- tetra- or pentancres depending on species. In the latter two taxa the type of pronged cuticular armature has been regarded as the single most important taxonomic trait to classify species (e.g., Todaro 2002; Lee and Chang 2002, but see Todaro et al. 2011); consequently, within the genus Pseudostomella three basic species groups are envisioned based on type of pronged spines i.e., species characterized by triancres: Pseudostomella faroensis Clausen, 2004, Pseudostomella klauserae Hochberg, 2002, Pseudostomella megapalpator Hochberg, 2002, Pseudostomella plumosa Ruppert, 1970 and Pseudostomella triancra Hummon, 2011 (5 species). Forms that bear tetrancres: Pseudostomella andamanica Rao, 1993, Pseudostomella indica Rao, 1970, Pseudostomella koreana Lee & Chang, 2002, Pseudostomella longifurca Lee & Chang, 2002, Pseudostomella malayica Renaud-Mornant, 1967 and Pseudostomella roscovita Swedmark, 1956 (six species). Taxa that possess pentancres: Pseudostomella cataphracta Ruppert, 1970, Pseudostomella cheraensis Priyalakshmi, Menon & Todaro, 2007, Pseudostomella etrusca Hummon, Todaro & Tongiorgi, 1993, and Pseudostomella sp1 of Valbonesi and Luporini (1984) (four species).

Based on the type of ancres, the new species approaches the latter four taxa. However, Pseudostomella cataphracta , is unique in that it shows a group of four ventral adhesive tubes per side that is missing in the other species, while Pseudostomella etrusca is peculiar in thatit possesses a robust dorsal adhesive tubes inserted at base of each oral palp, a trait lacking in the other taxa. Pseudostomella dolichopoda sp. n. differs from Pseudostomella cheraensis mainly in virtue of its larger size (up 425 µm vs. up to 295 µm), presence of two adhesive tubes in the anterior pharyngeal region and on the presence of two adhesive tubes originated from a common base located in the posterior intestinal region; finally, Pseudostomella dolichopoda sp. n. differs from Pseudostomella sp1 because, among others, it has larger size (425 µm vs. 350 µm), possesses longer caudal pedicles (43 µm vs. 23 µm), bears two pairs of anterior adhesive tubes vs. a single pair present of Somali species, and because of the presence of the two adhesive tubes originate from a common base located in the posterior intestinal region.

Taxonomic key.

Hochberg (2002) and Lee and Chang (2002) in describing their new taxa, two species each, provided useful taxonomic keys; however, because two species were omitted in their analyses (i.e., Pseudostomella andamanica Rao, 1993 omitted in Hoch berg, 2002 and Pseudostomella sp. 1 Valbonesi & Luporini, 1984 omitted in Chang and Lee 2002) and other taxa have been described in the meanwhile (see above), a revised key seems necessary. The key will hopefully prove useful not only to gastrotrich specialists but also to marine ecologists who find these peculiar metazoans in the course of research on interstitial meiobenthos.