Tetranchyroderma rhopalotum, 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 : 27-29

Tetranchyroderma rhopalotum sp. n. Figure 14

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

Diagnosis:

Adult Lt 344 µm; PhJIn at U30. Head end bluntly rounded, bearing club-shaped, ear-like pestle organs at U04; body narrows along the hind-pharynx; trunk broadens along the mid-gut, narrowing gently to the caudal base; caudal pedicles medium, with a sharply concave margin, indenting medially to U94. Glands 37 per side in medial and lateral columns. Epidermis covered with tetrancres of similar size, but smaller fore and aft; ancres occur in 36-38 rows of 13-15 ancres each, excluding the oral hood, but covering the caudal lobes. TbA 5 per side forming a transverse arc, tubes inserting directly on the postoral body surface; TbVL 12 per side, 1 along the fore pharynx, behind the TbA, 4 along the fore-gut, and 7 closely spaced from anus onto the caudal lobes; TbV 3 per side in a transverse row at U87; TbDL 2 per side at U51 (L 26 µm) and U90 (L 17 µm); TbP 3 per side on the caudal pedicles, forming the fused 'two fingers and a thumb’ typical of the family, without supplemental cirrata-like structure projecting from between the ‘fingers’ or additional tubes in the space between the peduncles. Locomotor ciliature: a single field covers the entire ventral surface from TbA to anus, with a narrower tract continuing beneath the caudum. Mouth subterminal, as broad as the fore end of the body, buccal cavity lightly cuticularized; pharynx narrows to inconspicuous basal pharyngeal pores; intestine narrows fore to aft, anus ventral at U87. Hermaphroditic; testis on left side as seen from below; vas deferens opens near the anus; developing ovum occurs above the midgut, with oocytes bilaterally to the rear; caudal organ small, ovoid and thick-walled, with an interior of refractive material and a central canal; frontal organ broadly oval and hyaline, bearing active sperm.

Description:

Adult Lt 271-344 µm; LPh 102 µm to PhJIn at U39-U30 (Fig. 14). Body length medium, ventrally flattened, dorsally vaulted; head end bluntly rounded, bearing club-shaped, ear-like pestle organs at U04; body narrows along the hind-pharyx; trunk broadens along the mid-gut, narrowing gently to the caudal base; caudal pedicles of medium length (L 22 µm) borne on lobes, with a sharply concave margin separating the two lobes, indenting medially to U94. Widths at pestles /neck /mid-gut /caudal base, and locations along the length of the body are as follows: 48 /38 /56 /26 µm at U04 /U19 /U64 /U96, respectively. Glands 37 per side, 20 (2 µm diameter to 9 × 5 µm) scattered in lateral columns at U13-U87 and 16-17 (5 µm diameter to 9 × 5 µm) scattered in medial columns at U11-U92.

Cuticular armature : Epidermis armored with tetrancres (L 7 W 5 µm) that are of much the same size over much of the body (Fig. 14 B), though somewhat smaller fore and aft; ancres cover dorsal and lateral surfaces in some 36-38 rows of 13-15 ancres each, being absent from the oral hood, but extending the length of the caudal lobes.

Adhesive tubes: TbA 5 per side (L 9 µm), forming a transverse arc, the medial-most differing in shape from the others, all tubes inserting directly on the postoral body surface at U07-U08, radiating from forward to obliquely outward. TbVL 12 per side, 1 in the fore pharyngeal region (L 6 µm) at U10 inserting just behind the TbA, 4 of similar size and spacing along the fore-gut (L 10 µm) at U36-U58, and 7 located at and behind the anus (L 10 µm) closely spaced at U91-U96, the last 3 inserting beneath the caudal lobe; TbV 3 per side (L 10 µm) in a transverse row at U87; TbDL 2 per side at U51 (L 26 µm) and U90 (L 17 µm); TbP 3 per side on the caudal pedicles, forming the fused 'two fingers and a thumb’ typical of the family, (L terminal tubes 8 µm, L tube on the inner margin 6 µm), not supplemented by a blind cirrata-like structure projecting dorsoposteriorly from between the ‘fingers,’ and with no additional tubes in the space between the peduncles.

Ciliation: Many short sensory cilia surround the oral opening (L 6-9 µm), with a number along the fore end of the oral hood (L 10-18 µm) and several laterally (L 12-15 µm) before the pestle organs; other cilia occur regularly along the lateral (L 10-40 µm) and dorsolateral (L 22-40 µm) body surfaces, numbering 12 and 18 per side, respectively. Ventral locomotor ciliature forms a single field of transverse rows from TbA to anus, lying between the TbVL columns, the field narrowing from anus to caudal base; individual cilia are 8-10 µm in length.

Digestive tract: Mouth subterminal, as broad as the fore end of the body (32 µm width); oral hood extends from U00 to U03; buccal cavity is lightly cuticularized; pharynx has inconspicuous basal pharyngeal pores; intestine narrows gradually front to rear; anus is ventral at U87.

Reproductive tract: Hermaphroditic, testis on right side as seen from above (left side as seen from below); vas deferens appears to open into the caudal organ, just before the anus; The largest developing ovum (up to 94 × 37 µm) occurs above the foregut, with ovules bilaterally to the rear; caudal organ large, longitudinally ovoid and thick-walled (47 × 19 µm), with an interior of refractive material and a central canal; frontal organ transversally ovoid and hyaline, often bears active sperm.

Ecology:

Occasional in frequency of occurrence (10-30% of samples), scarce to prevalent in abundance (3% to greater than 30% of a sample, occasionally a co-dominant [cdom]); littoral in fine to very coarse, medium to poorly sorted clean silicious or carbonate sand at low water neap to low water spring, 0-15 cm depth; sublittoral in very fine to medium, well to medium sorted sand at 1-3 m water depth (sometimes in very fine-very coarse, poorly to very poorly sorted coralline sand at the edge of or amid a depression in a coral platform at 1 m water depth).

Geographical distribution:

RED SEA:EGYPT {23km S Ein Sukhna, Sharm el-Arab Outside, Wadi 'Araba [video], Daghashland, Giftun Island SE [2-videos], Giftun Island SS, ^Giftun Village Spit Outside [cdom] (27°10'N, 33°49'E) [4-videos], Hammam Pharaon, Nabq S [video], Ras Nasrani}.

Remarks:

There are eight video sequences of Tetranchyroderma rhopalotum sp. n., all are from the upper Red Sea in Egypt. Five of these are available as MPEG 2 (and MPEG 1) from Hummon (2009): #1494 a mature Lectotype adult of Lt=344 µm (LPh=118 µm), collected in June 1994 from the Giftun Village Spit O, near Hurghada; #1500 a mature adult of Lt=303 µm (LPh=109 µm) from Nabq, S. Sinai; #1501 a mature adult of Lt=271 µm (LPh=107 µm) from Wadi 'Araba, Gulf of Suez; #1497 a subadult of Lt=186 µm (LPh=79 µm) also from the Giftun Village Spit O; and the last, #1499 a juvenile of Lt=123 µm (LPh=57 µm) from Giftun Island SE.

Etymology:

Rhopalotum (Greek: rhopalon + otus = meaning ‘club’ -like ‘ear’) referring to its club-shaped, ear-like pestle organs.

Taxonomic affinities:

Tetranchyroderma rhopalotum sp. n. is the only medium sized species in the genus with club-shaped, ear-like pestle organs, a PhJIn at U39-U30, and tetrancres, which also has TbA 5 per side; TbVL 12 per side, 1 behind the TbA, 4 along the fore half of the intestine, and a set of 7 near the caudum; TbV 3 in a row on each side at U87; TbDL 2 at U51 (longer) and U90 (shorter); TbP 3 per side as 'two fingers and a thumb’ on medium pedicles without a cirrata-like structure inserting between the ‘fingers’ or additional tubes in the space between pedicles. Only two other described species that bear only tetrancres, also have lateral cephalic tentacles and TbV: Tetranchyroderma sanctaecaterinae Todaro, Tongiorgi & Balsamo, 1992 and Tetranchyroderma schizocirratum Chang, Kubota & Shirayama, 2002, the former has its TbV in columns and lacks TbD, while the latter, like Tetranchyroderma rhopalotum sp. n., has its TbV in rows and has TbD; Tetranchyroderma schizocirratum differs from Tetranchyroderma rhopalotum sp. n. in having asymmetrical rather than symmetrical pestle organs and three dorsal cirrata per side, whereas dorsal cirrata are absent in Tetranchyroderma rhopalotum sp. n.