Tetranchyroderma xenodactylum, Hummon, William D., 2011

Hummon, William D., 2011, Marine Gastrotricha of the Near East: 1. Fourteen new species of Macrodasyida and a redescription of Dactylopodola agadasys Hochberg, 2003, ZooKeys 94, pp. 1-59 : 32-34

Tetranchyroderma xenodactylum sp. n. Figure 16

Tetranchyroderma EgyE Hummon (2009) [E Med & Red Seas Database]

Diagnosis:

Adult being described Lt 246 µm; PhJIn at U35. Body short, robust; head end rounded, without pestle organs, tentacles or lobes; neck a slight narrowing at the PhJIn; trunk broadening in the mid-gut, before narrowing gently then quickly to the caudal base; cirrata dorsolateral, 3 per side; caudal pedicles medium, naked, with a narrow concave margin separating the pedicles, incising medially to U92. Glands 9 per side scattered in lateral columns at U24-U85. A strange sub-cylindrical finger-like structure occurs laterally at U34. Epidermis covered with curved pentancres three times as long as wide, slightly smaller fore and aft; ancres occur in 46 rows of 14-15 ancres each, on dorsal and lateral surfaces, extending onto the middle of the oral hood and onto the caudal base. TbA 4 per side, 1 medially and 3 laterally, all projecting forward or obliquely outward, tubes inserting directly on the postoral body surface at U09-U10; TbVL 11 per side, 1 along the fore half of the pharynx at U14, 7 along the intestine at U39-U75, and 3 at and behind the anus at U88-U92; TbV 3 per side in a transverse row at U80; TbL per se/TbD absent; TbP 3 per side on the caudal pedicles, forming the fused 'two fingers and a thumb’ typical of the family, supplemented by the last of the dorsal cirrata, with 2 additional tubes in the space between the peduncles. Locomotor ciliature: a single field covers the ventral surface from TbA to the anus and behind. Mouth subterminal, as broad as the fore end of the body; buccal cavity lightly cuticularized; pharynx medium throughout, with inconspicuous basal pores; intestine narrows fore to aft, anus ventral at U88. Hermaphroditic; testis on left side as seen from below; vas deferens appears to open in front of the anus; developing ovum occurs above the hindgut; caudal organ spherical; frontal organ oblong, hyaline, partly embedded in the rear of the ovum.

Description:

Adult being described Lt 246 µm (others 197-322); LPh 87 µm (others 79-128) to PhJIn at U35 (others to PhJIn at U40) (Fig. 16). Body short, robust, ventrally flattened, dorsally vaulted; head end rounded, without pestle organs, tentacles or lobes; neck a slight narrowing at the PhJIn, broadening along the mid-gut, before narrowing gently along the hind-gut and then quickly behind the anus to the caudal base; cirrata 4 per side (L 7-11 µm), dorsolateral at U22, U50, U72 and U96; caudal pedicles medium (L 13 µm), naked (without lobes), with a broad concave margin separating the two pedicles, incising medially to U92. Widths at mouth /mid-pharynx /PhJIn /mid-gut /caudal base, and locations along the length of the body are as follows: 41 /44 /39 /47 /22 µm at U06 /U19 /U34 /U66 /U93, respectively. A strange sub-cylindrical finger-like structure (L 7 µm) occurs at U34, being hollow but occluded at its outer end. Glands 9 per side (4 µm diameter to 6 × 9 µm) scattered in lateral columns at U24-U85.

Cuticular armature: Epidermis armored with slightly curved pentancres (L 6, W 2.5 µm), much taller than wide, all 5 tines of the same length, ancres of much the same size over most of the body, but slightly smaller fore and aft; ancres cover dorsal and lateral surfaces in some 46 rows of 14-15 ancres each, extending onto the middle of the oral hood and onto the caudal base.

Adhesive tubes: TbA 4 per side, 1 medially (L 4 µm) projecting forward and 3 laterally (L 6-8 µm), projecting obliquely to the side, all inserting directly on the postoral body surface at U09-U10. TbVL 11 per side, 1 (L 4 µm) along the fore half of the pharynx at U14, just behind the TbA, 7 (L 7-12 µm) along the intestine at U39-U75, and 3 (L 7-12 µm) at and behind the anus at U88-U92; TbV 3 per side (L 7, 11, 7 µm) in a transverse row at U80; TbL per se and TbD are absent; TbP 3 per side on the caudal pedicles, forming the fused 'two fingers and a thumb’ typical of the many members of the family, (L terminal tubes 4-5 µm, L tube on the inner margin 9 µm), supplemented by the last of the dorsal cirrata, with 2 additional tubes (L 7-8 µm) in the space between the peduncles.

Ciliation: Short sensory cilia surround the oral opening (L 4 µm), with a number of also on the oral hood: 6 (L 14-17 µm) projecting directly or obliquely forward and 13-15 (L 7-14 µm) trailing to the rear; other cilia (L 10-18 µm) occur regularly along the lateral and dorsolateral body surfaces, numbering 12-13 each. Ventral locomotor ciliature forms a single field of transverse rows from TbA to behind the anus, lying between the TbVL columns; individual cilia are 5-6 µm in length.

Digestive tract: Mouth subterminal, as broad as the fore end of the body (34 µm width); oral hood extends from U00 to U07; buccal cavity lightly cuticularized; pharynx of medium breadth throughout, with inconspicuous basal pores; intestine narrows gradually front to rear; anus is ventral at U88.

Reproductive tract: Hermaphroditic, testis on right side as seen from above (left side as seen from below); vas deferens appears to open in front of the anus; developing ovum (up to 29 × 16 µm), appearing somewhat shrivled, occurs above the hindgut; caudal organ spherical (7 µm diameter); frontal organ oblong (20 × 14 µm) and hyaline, without active sperm, partly embedded in the rear of the ovum.

Ecology:

Sparse in frequency of occurrence (fewer than 10% of samples), scarce to numerous in abundance (3% to 20% of a sample, sometimes a sub-dominant [sdom]); littoral in fine, well sorted sand at low water spring in a shallow tombolo, 0-5 cm depth; sublittoral in fine to medium-fine, well to medium-well sorted sand at 1-5 m water depth.

Geographical distribution:

RED SEA:EGYPT {Marsa Bareika W, ^Nabq [sdom] (28°05'N, 34°35'E) [2-videos], Sharm el-Sheikh, Wadi 'Araba [video]}.

Remarks:

There are three sequences of Tetranchyroderma xenodactylum sp. n., all from the upper Red Sea in Egypt. These three are available as MPEG 2 (and MPEG 1) from Hummon (2009): #1517 a mature adult of Lt=332 µm (LPh=128 µm) from the Wadi 'Araba, on west side of the Gulf of Suez, Egypt; #1514 a mature Lectotype adult of Lt=246 µm (LPh=91 µm), collected in July 1994 from Nabq, S. Sinai, Egypt; and #1515 a mature adult of Lt=197 µm (LPh=79 µm) also from Nabq.

Etymology:

Xenodactylum (Greek: xenos + daktylos, meaning 'strange finger’) is named after the strange finger-like appendage that protrudes laterally in all specimens from the rear of the pharyngeal region.

Taxonomic affinities:

Tetranchyroderma xenodactylum sp. n. is the only small species in the genus without pestle organs, tentacles or lobes, a PhJIn at U40-U35 and slightly curved pentancres, with tines of similar size, which also has TbA 4 per side, 1 medial and 3 lateral, TbVL 11 per side, 1 along the fore half of the pharynx at U14, 7 along the intestine at U39-U75, and 3 at and behind the anus at U88-U92; TbV 3 per side in a transverse row at U80; TbP 3 per side on the caudal pedicles, with the fused 'two fingers and a thumb’ typical of much of the family, supplemented by the last dorsal cirratum, with 2 additional tubes between the peduncles, TbL per se and TbD being absent. There is no other species in the genus, regardless of their ancres, that bears such a sub-cylindrical finger-like structure as is found at the base of the pharynx in Tetranchyroderma xenodactylum sp. n.