Macrodasys macrurus, 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 : 16-18

Macrodasys macrurus sp. n. Figure 7

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

Diagnosis:

Adult Lt being described 590 µm; PhJIn at U36. Head ovoid, with a narrow band of circumcephalic cilia at U02 and pestle organs at U03; trunk broad throughout, narrowing gradually along the rear intestinal region to the long caudum. Glands inconspicuous. TbA 11 per side, in arcs that insert directly on the body; TbL 4-5 per side, with 1-2 along the fore and 0 along the rear pharynx, 3 in the rear intestinal region, and 0 behind the anus; TbD 4 per side, of similar size and spacing, in the rear half of the body from U53 to U75; TbV 17 per side, nearly even in size and spacing, with 3 along the rear pharynx, the remainder in the intestinal region, and 0 behind the anus; TbP 7 per side symmetrically along the long caudum. Locomotor ciliature: a single field from the TbA to the tip of the caudum, unciliated in spots surrounding ventral openings. Mouth terminal, of narrow width; shallow buccal cavity is lightly cuticularized, expanding with depth; pharyngeal pores sub-basal; intestine broadest in front, narrowing quickly along the mid- to hind-gut, then bending around the caudal organ; anus ventral at U83. Hermaphroditic; testes begin just before the PhJIn, vasa differentia join beneath the frontal organ; ova develop rear to front; frontal organ elongate ovate, its nozzle in close contact with the ovum, with a beak-like cavity lying on the left that has a ventral pore and an accessory chamber behind; short, thick caudal organ has spiral muscles throughout, except for the rearmost glandular sac, the fore half appearing glandular, the rear half bearing an internal canal; caudal organ barely overlapping the accessory cell of the frontal organ.

Description:

Adult being described Lt 590 µm (others Lt 477-620); LPh 192 µm (others LPh 195-203) to PhJIn at U36 (others PhJIn at U33-U41) (Fig. 7). Body medium in length as an adult, ventrally flattened, dorsally vaulted; head ovoid, bearing a narrow band of circumcephalic cilia at U02 and pestle organs at U03; trunk broad throughout, narrowing gradually along the rear intestinal region to the long caudum. Widths at pestle organs /PhJIn /trunk /anus /caudum, and locations along the length of the body are as follows: 45 /51 /58 /24 /11-7 µm at U03 /U36 /U47 /U83 /U85-U98, respectively. Glands not conspicuous.

Adhesive tubes: TbA 11 per side (L 7-9 µm), in arcs that insert directly on the postoral body surface at U02 and project from forward to obliquely outward; TbL 4 -5, of similar size, with 1-2 along the fore and 0 along the rear pharynx, 3 in the rear intestinal region, and 0 behind the anal aperture; TbD 4 per side, of similar size and spacing, all in the rear half of the body from U53 to U75; TbV 17 per side, nearly even in size and spacing (L 8-12 µm), with 3 along the rear pharynx, the remainder in the intestinal region, and 0 behind the anus; TbP 7 per side (L 9-10 µm) symmetrically along the caudum.

Ciliation: Sensory hairs (L 16-20 µm) occur on either side of the mouth and on the head; a band of cilia surrounds the forehead (L 13-15 µm) at U02; other sensory hairs arise in four columns on either side of the body: lower ventrolateral (L 9-12 µm), upper ventrolateral (L 9-12 µm), lateral (L 12-14 µm) and dorsolateral (L 20-24 µm), with about 30-32, 30-32, 28 and 24 per column. Ventral locomotor ciliature forms a single field that lies from the TbA back between the TbL/V series back to the tip of the tail, with bare spots surrounding the ventral openings.

Digestive tract: Mouth terminal, narrow (9 µm diameter), surrounded by sharp tooth-like projections; shallow buccal cavity expands from oral opening to its base and is lightly cuticularized; pharynx has sub-basal pharyngeal pores at U26; intestine is broadest in front, narrowing quickly at the mid- to hind-gut and bending around the caudal organ; anus is ventral at U83.

Reproductive tract: Hermaphroditic; testes beginning just before the PhJIn, containing pulses of sperm, and extending as vasa deferentia back to the rear of the frontal organ, though their termini were not seen; ova develop from rear to front, the largest (52 × 36 µm in size) lying above the rear fore-gut; frontal organ elongate ovoid, its nozzle in close contact with the ovum, with a beak-like cavity lying on the left that has a ventral pore, and an accessory chamber to the rear; sperm not seen internally; short, thick caudal organ has spiral muscles throughout, except for the rearmost glandular sac, the fore half appearing glandular, the rear half bearing an internal canal; caudal organ barely overlapping the accessory chamber of the frontal organ.

Ecology:

Occasional in frequency of occurrence (10-30% of samples), scarce to prevalent in abundance (3 to greater than 30% of a sample; often a sub- [sdom], co- [cdom], or dominant [dom]); littoral in fine, well sorted to coarse-very coarse, poorly to very poorly sorted, coralline sand with small amounts of detritus, at low water neap to extreme low water, 0-15 cm depth; sublittoral in fine to coarse, medium well to very poorly sorted coralline sand and coral debris at 1-14 m water depth, sometimes between coral platforms or between patches of fringing reef.

Geographical distribution:

RED SEA:EGYPT:{Marsa Bareika N [sdom], Daghashland [video], Far Garden [dom] [video], Giftun Island SE [cdom] [3-videos]/SS, ^Giftun Village Spit Outside (27°10'N, 33°49'E) [video], Middle Garden, Moon Beach, Sharm el-Naga [cdom], Sharm el-Sheikh, Tip Ras Mohamed NP [video]}.

Remarks:

There are seven video sequences of Macrodasys macrurus sp. n., all from the upper Red Sea in Egypt. Five of these are available as MPEG 2 (and MPEG 1) from Hummon (2009): #1172 a mature adult of Lt=620 µm (LPh=203 µm) from Far Garden, S. Sinai, Egypt; #1167 a mature Lectotype adult of Lt=590 µm (LPh=207 µm), collected in June 1994 from Giftun Village Spit O, Egypt; #1173 a mature adult of Lt=477 µm (LPh=195 µm) from Daghashland, Egypt; #1170 a subadult of Lt=276 µm (LPh=122 µm) from Giftun Island SE, Egypt; and #1168 a juvenile of Lt=140 µm (LPh=73 µm) also from Giftun Island SE, Egypt.

Etymology:

Macrurus (Greek: macros + oura = meaning long tail) refers to the appearance of a distinctly long tail, enhanced by the relative few TbP that it bears.

Taxonomic affinities:

Macrodasys macrurus sp. n. is the only species in the genus with an ovoid head, a long tail, PhJIn at U33-U41, which also has 11 TbA per side in arcs; a TbL formula of 5=2,0/2,1 (2 along the fore and 0 along the rear pharynx/2 along the rear intestine and 1 behind the anus); a TbD formula of 4=0,0/4,0; a TbV formula of 17=0,3/14,0; and TbP 7 per side. There is no other species in the genus has a beaked frontal organ and a non-overlapping caudal organ, combined with columns of TbV and TbD, and a paucity of TbL.