Dendrodasys rubomarinus, 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 : 12-13

Dendrodasys rubomarinus sp. n. Figure 5

Dendrodasys EgyA Hummon (2009) [E Med & Red Sea Database].

Diagnosis:

Adult 272 µm; PhJIn at U20. Body slender; head has crescent-shaped anterior, with protruding mouth and laterally directed lobes that have rounded tips, with a knob-shaped pestle organ on each side lying largely exposed beneath the rear of the head lobes; neck constriction slight, marking the pharyngeal pore openings; trunk parallel-sided, narrowing gradually in the rear, ending in a long, narrow caudal peduncle, with a bifurcate apex that indents medially to U90; pharynx short, pharyngeal pores basal; intestine narrows fore to aft; anus ventral at U68. Glands 7 per side, with another medially in the caudal peduncle; longitudinal muscles are striated. TbA 1 per side, with a duo-gland tube extending forward from a tapering base; TbL absent; TbP 3 per side, the longer one, arising from the caudal base, and the shorter two, arising from the bifurcate tip of the caudum. Mouth diameter narrow, protruding forward from anterior head curvature; small goblet-shaped buccal cavity moderately cuticularized; pharyngial pores located at the level of the neck constriction, and only detected with maturity; intestine broader in front, narrower behind, its lumen fringed by actively-beating cilia; anus ventral at U68. Locomotor ciliation forms paired longitudinal bands from the TbA rearward, joining behind the anus and continuing as a unified band onto the caudal peduncle, with a patch lying just before the bifurca. Hermaphroditic; paired testes lie along the fore-gut and paired ovaries along the rear mid-gut, eggs maturing rear to front; an ovoid frontal organ bearing active sperm occurs opposite the largest ovum on the right side.

Description:

Adult Lt 244-272 µm; LPh 48-53 µm to PhJIn at U20 (Fig. 5). Body flattened ventrally, vaulted dorsally, comprised of head that is crescent-shaped anteriorly, with laterally directed lobes that have rounded tips and a protruding mouth, with a knob-shaped cephalic pestle organ (L 7 µm) on each side that lies largely exposed beneath the rear of the head lobes; neck constriction slight, marking the pharyngeal pore openings; neck constriction slight; the trunk is parallel-sided trunk, narrowing gradually in the rear, ending in a long, narrow caudal peduncle, with a bifurcate apex that indents medially to U90. Width of head /lobes /neck /trunk /caudal base are as follows: 28 /38 /21 /26-28 /7 µm at U08 /U04 /U18 /U31-U55 /U73, respectively. Glands are of two types, one with 4 per side, oval in shape (diam 4-6 µm) at U05 /U13 /U26 /U62 and a solitary medial gland on the caudal peduncle at U87, the other with 3 per side, ragged in shape and more refringent (diam 3 µm) at U21 /U42 /U65.

Adhesive tubes: TbA 1 per side (L 18 µm), comprising a long (6 µm) duo-gland tube extending forward from a heavy tapering base that inserts directly on the body surface, tubes being highly mobile and able to project laterally; TbL are absent; TbP 3 per side: one longer (L 12 µm) arising proximally from the caudal peduncle, and two shorter (L 5 & 9 µm) arising from the bifurcate tips of the 80 µm long pedunculated caudum.

Ventral ciliation: Head lobes bear a transverse row of cilia ventrally (L 8µm); head bears numerous cilia (L 10-25 µm) frontally, laterally and dorsally; sensory hairs 7 each per side occur in lateral (L 8-10 µm) and dorsal (L the first 26-28, others 14-16 µm) columns, lateral cilia occurring singly, dorsal cilia occurring in pairs, all spaced more or less evenly from U08 to U70, behind which are single lateral hairs on either side at U76 and U90 on the caudal peduncle. Locomotor ciliation runs in paired longitudinal bands from the TbA rearward, joining behind the anus and continuing as a unified band onto the caudal peduncle, with a patch lying just before the bifurca.

Digestive tract: Mouth diameter narrow (2 µm), protruding forward from the anterior head curvature; a goblet-shaped buccal cavity is moderately cuticularized; pharynx narrow, its basal pores located at the level of the neck constriction, and only detected with maturity; intestine narrow, broader in front, narrowing markedly half way along its length, but with a bulge around the anus, its lumen being fringed by actively-beating cilia; anus ventral at U68.

Reproductive tract: Simultaneous hermaphrodites; testes paired, but uneven in origin, along the fore-gut, its vasa deferentia extending rearward, but their termini not seen; sperm (L 25 µm) show half a spirally thickened head and half a flagellum; ovaries, with several (3-7) immature ovules, are located along the rear mid-gut, with the most mature ova developing medially forward between ovary and testes; an ovoid frontal organ bearing active sperm occurs opposite the largest ovum on the right side.

Ecology:

Occasional (10-30% of samples) in frequency of occurrence, scarce to prevalent (3% to more than 30% of a sample, the latter sometimes a co-dominant [cdom]) in abundance; littoral in clean fine to coarse, well- to poorly sorted coralline sands at low water neap to low water spring; sublittoral in medium-fine to medium, well to medium sorted, clean coralline sands, often mixed with shell and coral gravel, at 1-5 m water depth.

Geographical distribution:

RED SEA:EGYPT: {Sharm el-Arab Inside, Marsa Bareika N, ^Giftun Island SE (27°10'N, 33°57'E) [cdom] [video], Main Beach Ras Mohamed NP [2-videos], Nabq [video]}.

Remarks:

There are four video sequences of Dendrodasys rubomarinus sp. n., all from the Red Sea in Egypt. All four are available as MPEG 2 (and MPEG 1) from Hummon (2009): #797 a mature Lectotype adult of Lt=272 µm (LPh=53 µm), collected in June 1994 from Giftun Island SE, near Hurghada, Egypt; #800 a mature adult of Lt=258 µm (LPh=51 µm) from Main Beach Ras Mohamed National Park, S. Sinai, Egypt; #799 a mature adult of Lt=244 µm (LPh=48 µm) also from Main Beach; and the other #798 a subadult of Lt=152 µm (LPh=35 µm) from Nabq, Egypt, also on the S. Sinai. The hind-gut is often found bearing diatom frustules.

Etymology:

Rubomarinus (Latin: ruber + marinus = meaning 'red sea’) refers to the body of water in which it was found, the Red Sea.

Taxonomic affinities:

Dendrodasys rubomarinus sp. n. is the only member of the genus with rounded head lobes and pestle organs that are knob-like, that also has the neck constriction occurring at the pharyngeal pores, rather than behind the pharyngeal pores, and has bi-lateral testes. Two of the other four species closely resemble Dendrodasys rubomarinus , but differ in detail: Dendrodasys gracilis Wilke, 1954 has rounded head lobes, pyriform pestle organs and bi-lateral testes, while Dendrodasys affinis Wilke, 1954 [see also Hummon et al. (1998)] has rounded head lobes, lobiform pestle organs, and uni-lateral testes.