Urodasys toxostylis, 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 : 24-26

Urodasys toxostylis sp. n. Figure 12

Urodasys EgyA Hummon (2009) [E Med & Red Seas Database].

Diagnosis:

Trunk of adult specimen being described Lt 440 µm, Lt tail 1100 µm; PhJIn at U40 of the trunk. Head bluntly ovate, with a narrow band of circumcephalic cilia and broad pestle organs at U05; neck constriction slight; trunk broadest along the mid-gut, narrowing gradually in the hind-gut region to the elongate tail. Glands 15-16 per side. TbA 7 per side, 3 in transverse rows at U07, which project obliquely forward, and 4 in longitudinal columns at U08-U17, which project obliquely outward, all inserting directly on the postoral body surface; TbL 4 per side, similar in size, all in the intestinal region; TbVL 4 per side, similar in size, 2 along the fore and 0 along the rear pharynx, and 2 in the rear intestinal region; TbD 5 per side, similar in size, 1 along the fore and 0 along the rear pharynx, and 4 in the intestinal region; TbV absent; TbP 10 or more per side, asymmetrical along the tail, depending on its length. Locomotor ciliature: paired lateral bands run from the TbA back to the rear of the caudal organ, with more sparse cilia medially from the TbA to U49. Mouth terminal, narrow; buccal cavity lightly cuticularized, expanding with depth; pharyngeal pores sub-basal; intestine narrowing gradually front to rear, lacking an anus. Probably hermaphroditic, though testis was not seen; ova develop from rear to front, with two bilateral ova in the mid-gut region of recently mature specimens, much larger in fully mature specimens (video #1904); frontal organ not seen; caudal organ, appearing enclosed in an oval capsule, has a hyaline bulblet in the rear, with an internal canal, that cycles around to include a darkish mass on the left and a stylet on the right, which is curved in the rear, widening and straightening toward the front, where it has an asymmetrical bulb that has a symmetrical opening at the end.

Description:

Trunk of adult specimen being described Lt 440 µm (others Lt 413-480); Lt tail 1100 µm (others Lt 588-1620); LPh 174 µm (others LPh 161-173) to PhJIn at U40 (others PhJIn at U34-U40) (Fig. 12 A, B). Trunk medium in length as an adult, ventrally flattened, dorsally vaulted; head bluntly ovate, with a narrow band of circumcephalic cilia and broad pestle organs at U05; neck constriction slight; trunk broadest along the mid-gut, narrowing gradually in the hind-gut region to the elongate tail. Widths at pestle organs /pharyngeal pores /PhJIn /front, rear of caudal organ, and locations along the length of the body are as follows: 46 /48 /50 /54,30 µm at U03 /U33 /U46 /U72,97, respectively. Glands 15-16 per side (4-7 µm), larger in front than behind.

Adhesive tubes: TbA 7 per side (L 12 µm), 3 in transverse rows at U07, which project obliquely forward, curving laterally to form longitudinal columns of 4 at U08-U17, the latter projecting obliquely outward, all inserting directly on the postoral body surface; TbL 4 per side, similar in size (L 15 µm), all in the intestinal region at U54, U62, U75 and U88; TbVL 4 per side, similar in size (L 14-16 µm), 2 along the fore and 0 along the rear pharynx, and 2 in the rear intestinal region as the caudal base narrows; TbD 5 per side (also L 15-20 µm), 1 along the fore and 0 along the rear pharynx pores, and 4 in the intestinal region; TbV absent; TbP 10 or more per side (L 10-12 µm) asymmetrically about the tail, depending on its length.

Ciliation: Numerous sensory hairs (L 10-16 µm) occur around the head; a band of cilia surrounds the forehead (L 28-30 µm) at U05; other sensory hairs (L 25 µm) arise in two columns on either side of the body: lateral and dorsolateral, with about 30 per column. Ventral locomotor ciliature forms paired lateral bands that run from the TbA back to the rear of the caudal organ, with more sparsely placed cilia filling the space between from TbA to U49.

Digestive tract: Mouth terminal, narrow (6 µm diameter); buccal cavity expands from oral opening to base and is lightly cuticularized; pharynx has sub-basal pharyngeal pores at U33; intestine is broadest in front, narrowing to the rear, but lacks an anus.

Reproductive tract: Probably hermaphroditic, though testis was not seen; ova develop from rear to front, with two bilateral ova (74 × 24 and 55 × 19 µm in size) in the mid-gut region of recently mature specimens, and a much larger ovum (138 × 98 µm in size) appears in fully mature specimens (video #1904); frontal organ not seen; caudal organ, appearing enclosed as an oval capsule, has a hyaline bulblet in the rear, with an internal canal, that circles around to include a darkish mass on the left and a curved stylet on the right (Fig. 12 C), which is thin and curved in the rear, widening and straightening toward the front, where it has an asymmetrical bulb that has a symmetrical opening at the end.

Ecology:

Occasional in frequency of occurrence (10-30% of samples), scarce to prevalent in abundance (3% to greater than 20% of a sample, sometimes a sub- dominant [sdom]); occasionally littoral in fine, medium-well sorted silicious sand, at mean low water to extreme low water, 0-15 cm depth; mostly sublittoral in fine, medium well sorted to very fine-very coarse, very poorly sorted silicious to corraline sand, with coral debris at 1-14 m water depth, sometimes in troughs, between patches of fringing reef, between coral platforms, in depressions in coral platforms or at the base of seagrass beds.

Geographical distribution:

RED SEA:EGYPT:{Marsa Bareika N, Abu Ramada 1, Sharm el-Arab [sdom], Daghashland, ^Giftun Island SS [video], Main Beach Ras Mohamed NP, Middle Garden [video], Mugawish, Na’ama Bay S [video], Nabq S, Sharm el-Sheikh, Ras Sudr, Tareeh el-Reeh S, 'Uyun Musa};ISRAEL: {Coral Beach M2, M3 [2-videos] & M5, Coral Beach N1 [2-videos], Princess Hotel [video]}.

Remarks:

There are eight video sequences of Urodasys toxostylis sp. n., all from the upper Red Sea in Egypt and Israel. Six of these are available as MPEG 2 (and MPEG 1) from Hummon (2009): #1904 a mature adult of L trunk=480 µm (LPh=164, L tail=1200 µm) from the Coral Reserve (Eilat), Israel; #931 a mature adult of L trunk=438 µm (LPh=174, L tail=972 µm) from Na’ama Bay, S. Sinai, Egypt; #932 a mature Lectotype adult of L trunk=430 µm (LPh=173, L tail=1100 µm), collected in June 1994 from Giftun Island SE, near Hurghada, Egypt; #930 a mature adult of L trunk=413 µm (LPh=161, L tail=590 µm) from Middle Garden, S. Sinai, Egypt; #1909 a subadult of L trunk=387 µm (LPh=152, L tail=1620 µm) also from the Coral Reserve (Eilat); and #1923 a juvenile of L trunk=140 µm (LPh=70, L tail= 588, mm) also from the Coral Reserve (Eilat), Israel. The tail may reach 4 × the length of the trunk, but is sometimes broken to lengths even shorter than that of the trunk.

Etymology:

Toxostylis (Greek: toxo + stylos = meaning 'bow shaped column’) referring to the bowed shape of the reproductive stylet in the caudal organ.

Taxonomic affinities:

Urodasys toxostylis sp. n. is the only species in the genus with an bluntly ovate head, pestle organs, a tail up to 4 times the length of the trunk, and a PhJIn of U32-U46, which also has TbA 7 per side in transverse rows and longitudinal columns; a TbL formula of 4=0,0/4 (0 along the fore and 0 along the rear pharynx and 4 along the intestine); a TbVL formula of 4=2,0/2; a TbD formula of 5=1,0/4; and TbP=10 or more per side, depending on the tail length, with TbV absent. There are several stylet-bearing species that are morphologically close to Urodasys toxostylis sp. n., all western Atlantic. Urodasys cornustylis Schoepfer-Sterrer, 1974 differs from Urodasys toxostylis sp. n. in having a stylet with an asymmetrical opening; Urodasys nodostylis Schoepfer-Sterrer, 1974 differs in having a stylet with a sharp nearly perpendicular angle at its base; Urodasys calicostylis Schoepfer-Sterrer, 1974 differs in having a stylet that lacks a bulb and narrows too quickly from its conical end-piece; and Urodasys remostylis Schoepfer-Sterrer, 1974 has a stylet that bears a false bulb, though the outer surface does not really indent.