Paraturbanella xaymacana, Zotto, Matteo Dal, Leasi, Francesca & Todaro, M. Antonio, 2018

Zotto, Matteo Dal, Leasi, Francesca & Todaro, M. Antonio, 2018, A new species of Turbanellidae (Gastrotricha, Macrodasyida) from Jamaica, with a key to species of Paraturbanella, ZooKeys 734, pp. 105-119 : 107-110

Paraturbanella xaymacana sp. n. Figs 1, 2, 3

Type locality.

The sediment samples were collected on 24 February 2011 from Duncans Bay, Duncans, Jamaica (18°29'13.05'N, 77°32'03.23"W).

Type specimen.

Holotype: the 542 μm long adult specimen shown in Figures 2, 3, no longer extant (International Code of Zoological Nomenclature, Articles 73.1.1 and 73.1.4), collected on 24 February 2011 (MAT & FL legit).

Examined material.

Two adults (including the holotype) collected by MAT & FL from the type locality; specimens were observed alive and are no longer extant i.e., both physical specimens were inadvertently destroyed during the study. Considering the size and nature of these organisms, the provided drawings, and the original multiple photos of the studied animals, the establishment of a new species-group taxon should be considered valid under the recommendation 73G-J of Declaration 45 - Addition of Recommendations to Article 73 ( ICZN 2017).

Ecology.

Sparse in frequency of occurrence (10 % of samples), scarce in abundance (3-5% of a sample); sub-littoral at a water depth of about 0.5 m in sediment made up of fine, moderately sorted carbonate sand (mean grain size, 0.18 mm; sorting 0.59; kurtosis, 2.52; skewness, 0.43). Values of salinity and temperature of the interstitial water at the time of sampling were 34 ‰ and 26 °C respectively.

Diagnosis.

Body strap-shaped, up to 564 μm in length. Head with a feeble peribuccal swelling, with a slight constriction at U3.7; pestle organs present. PhJIn at U31; body widest from mid-pharynx to mid-intestine, thinning gradually to the caudal base; caudum bilobed, incised from its tips to U95, with a clearly visible medial cone; distance between apices of outermost TbP on either side is 1.3 times the width of the caudal base. About 20-23 glands are distributed along both lateral body margins in a single column per side. TbA six per side, the innermost being the shortest, whereas the adjacent being the longest, occur on fleshy hands that insert at approximately U11; TbV, TbVL, TbL and TbD absent; TbP, six per side, occurring as 4, 1, 1, the outermost being the longest; caudal cone present; accessory adhesive tubes (called also dohrni/ Seitenfüsschen) two per side, posterolaterally directed (longer tube = 21 μm, shorter tube = 14 μm), inserting ventrolaterally just behind the hands at U14. Locomotor ciliature runs from the TbA rearward in two longitudinal bands that trace the lateral body margins, joining after the anus. Mouth terminal, width narrow; buccal cavity medium-sized, mug-shaped; walls heavily cuticularized; pharyngeal pores near the base at U28; intestine straight, broadest in front; anus ventral at U91. Hermaphroditic, paired testes extend rearward from U51, with sperm ducts recurving to the fore at U63 and emptying to the exterior via a common pore at U49; paired ovaries, the largest ovum occurs in the mid-gut region at U51. Frontal organ dorsal to the intestine at U63.

Etymology.

The specific name alludes to the original name of Jamaica: Xaymaca , (adjective: xaymacana ) an Arawak word meaning "land of wood and water".

Description.

Mostly based on the adult holotype, 542 μm in total length. Body strap-shaped; head with a feeble peribuccal swelling and a slight constriction at U04 and then the body proper. Pestle organs, small, at U5; body widest at mid-intestine, thinning gradually to the caudal base; caudum bilobed, deeply incised from its tips to U95, with a visible medial cone; distance between apices of outermost TbP on either side is 1.3 times the width of the caudal base. Widths at outer oral opening/head constriction/mid-pharynx/PhJIn/mid-intestine/furcal base, and their locations along the body length are: 12/26/33/39/45/29 μm at U0/U04/U17/U31/U61/U95. Epidermal glands are in one column per side, scattered along the body margins, up to 20-23 and variable in size (4-7 μm in diameter).

Adhesive tubes.TbA, six per side (7-11 μm in length), all occurring on fleshy hands that insert at approximately U11; the innermost, mimicking a thumb, is the shortest, while the second from the inner side is the longest; TbV, TbVL,TbL, TbD absent; TbP, six per side, occurring as two groups of 4, 1, 1 elements each, along the inner (4 + 1 tube) and distal margin of each lobe (1 tube); the distal tube being the longest (14 μm in length) and the four proximal ones the shortest (6-7 μm in length); a caudal medial cone is present, but it is rather short, 4 μm in length. Accessory adhesive tubes (known also as dohrni tubes or Seitenfüsschen) two per side, posterolaterally directed (longer tube=21 μm, shorter=13.7 μm from their base), arise ventrolaterally just behind the fleshy hands at U14, usually being held close to the body.

Ciliation. Tufts of sparse cilia (11-21 μm in length) occur on lateral and dorsal sides of the head, behind the mouth. Additional sensory hairs, of similar length (13-19 μm), occur along the pharyngeal and intestinal region, organized in lateral, dorsolateral and dorsal columns, with about 20-23 hairs per column. Ventral locomotor cilia (16-20 μm in length) flow from the head constriction rearward in two longitudinal bands that trace the lateral body margins, and join behind the level of the anus.

Digestive tract. Mouth terminal, narrow (9 μm diameter); buccal cavity large, mug-shaped, 18 μm in length and approximately 11 μm in width, with walls heavily cuticularized; Pharynx 153 μm in length, with pharyngeal pores near the base at about U28; PhJIn at U31; intestine straight, broadest in front; anus ventral at U91.

Reproductive tract. Hermaphroditic; paired testes extend posteriorly from U51, with short sperm ducts recurving toward the front at U63, and emptying to the exterior via a common pore located at U49; ovaries paired, with the oocytes occurring from U64 to U68 and maturing from posterior to anterior; a large egg (approximately 70 by 24 μm) was present in the mid-gut region centred at U51. Caudal organ absent; frontal organ, vesicular, dorsal to the intestine centered at about U63; it is ovoid in shape (28 by 26 μm) and contains sparse spermatozoa and secretory material.

Variability and remarks.

The other studied adult specimen was 564 μm in total body length, with 154 μm long pharynx. Number and arrangement of TbA, and of the TbP along the caudal lobes matched those of the holotype. The placement of the testes and the male pore is similar to that of the holotype. Unfortunately the animal got destroyed during the study so no further details could be acquired. The unfortunate event happened while we were trying to confirm the crossing of the ascended and descendent tracts of the sperm ducts observed in the holotype (see Figures 1B, 3A), a trait never recorded before in Gastrotricha. Future studies could indicate whether the crossing is an autapomorphic character of the species or just a feature of the holotype.

Taxonomic affinities.

Prior to the current study there were 22 described species of Paraturbanella ( Hummon 2010b, 2011, Hummon and Todaro 2010, Todaro et al. 2017). P. xaymacana sp. n., in virtue of its testes, located at about mid body instead than at- or near the PhIJ, approaches P. africana Todaro, Dal Zotto, Bownes & Perissinotto, 2017, recently described from the KwaZulu-Natal coast of South Africa ( Todaro et al. 2017). These two species can easily been differentiated based on the following traits which, in our opinion, should be considered in order of importance: i) position of the male pore: located near the PhIJ in P. africana vs at about mid body in P. xaymacana sp. n.; ii) buccal swelling, very clear in P. africana vs almost non-existent in the new species; iii) TbA, number and arrangement: 5 tubes per side and without the innermost short “thumb” in the African species vs 6 tubes per side and with the shortest tube being the innermost one in the Jamaican species; iv) TbP, number and arrangement: 5 tubes, organized as 3, 1, 1 in P. africana vs 6 tubes organized as 4, 1, 1 in P. xaymacana sp. n.