Macrodasys scleracrus, 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 : 21-24

Macrodasys scleracrus sp. n. Figures 1011

Macrodasys EgyG and ShmA Hummon (2009) [E Med & Red Seas, and Other Databases].

Diagnosis:

Adult being described Lt 635 µm; PhJIn at U46. Head stepped, narrowing toward the mouth, with a narrow band of circumcephalic cilia at U02 and pestle organs in the step at U03; trunk of similar breadth throughout, narrowing quickly in the hind-gut region to the medium caudum. Glands inconspicuous. TbA 7-9 per side, in arcs that insert directly on the postoral body surface at U02-U04 and project forward to obliquely outward; TbL 11, of similar size, with 0 along the fore half and 2 along the rear half of the pharynx, 9 in the intestinal region, and 0 behind the anal aperture; TbV 14 per side, similar in size, but giving the impression of linear pairs, all in the intestinal region, with 0 behind the anus; TbP 11-12 per side symmetrically around the caudum. Locomotor ciliature: paired lateral bands lie between the TbV series back to the tip of the tail, with additional sparse cilia running medially to U73. Mouth terminal, of medium width; buccal cavity lightly cuticularized, expanding with depth; pharyngeal pores sub-basal; intestine narrows gradually front to rear; anus ventral at U91. Hermaphroditic; testes begin before the PhJIn, vasa differentia join beneath the frontal organ; ova develop rear to front, with a large ovum above the fore-gut and smaller ovules to the rear; frontal organ pyriform, its nozzle, having a thick refractive cuticular cap, and lying in close contact with the developing ova, bearing sperm internally; caudal organ of medium length, its fore half appearing glandular, its rear half having an internal canal and a spiral muscular covering, except for the rearmost sac; the caudal organ barely overlaps the rear of the frontal organ, and not at all in younger specimens.

Description:

Adult being described Lt 635 µm (others 394-800); LPh 290 µm (others 159-300) to PhJIn at U46 (others to PhJIn at U29-U47) (Fig. 10). Body medium in length as an adult, ventrally flattened, dorsally vaulted; head stepped, narrowing toward the mouth, with a narrow band of circumcephalic cilia at U02 and pestle organs in the step at U03; trunk of similar breadth throughout, narrowing quickly in the hind-gut region to the gradually delineated caudum of medium size. Widths at pestle organs /at U05 /PhJIn /anus /caudum, and locations along the length of the body are as follows: 45 /57 /54 /32 /13-10 µm at U03 /U05 /U46 /U91 /U92-U97, respectively. Glands inconspicuous.

Adhesive tubes: TbA 7-9 per side (L 7-9 µm), in arcs that insert directly on the postoral body surface at U02-U04 and project from forward to obliquely outward; TbL 11, of similar size (L 12-18 µm), with 0 along the fore half and 2 along the rear half of the pharynx, 9 in the intestinal region, and 0 behind the anal aperture; TbV 14 per side, similar in size (L 7-8 µm), but giving the impression of linear pairs, all in the intestinal region, with 0 behind the anus; TbP 11-12 per side (L 9-12 µm) symmetrically around the caudum.

Ciliation: Sensory hairs (L 10-20 µm) occur on either side of the mouth; a band of cilia surrounds the forehead (L 24-26 µm) at U02; other sensory hairs (L 8-16 µm) arise in three columns on either side of the body: lateral, dorsolateral, and dorsal, with about 30 per column. Ventral locomotor ciliature forms paired lateral bands that lie between the TbV series from the TbA back to the tip of the caudum, with additional cilia running in the medial space back to U73.

Digestive tract: Mouth terminal, of medium width (16 µm diameter), surrounded by sharp tooth-like projections; buccal cavity expands from oral opening to base and is lightly cuticularized; pharynx is covered by circular muscles (visible under DIC) and has sub-basal pores at U36; intestine is broadest in front, narrowing to the rear and bending around the base of the caudal organ; anus is ventral at U91.

Reproductive tract: Hermaphroditic; testes beginning just before the PhJIn, and extending as vasa deferentia back to the rear of the frontal organ, the termini not seen, though sperm can be seen in the vasa deferentia lateral to the frontal organ; ova develop from rear to front, with a large developing ovum (104 × 37 µm in size) above the fore-gut and ten smaller ovules to the rear; frontal organ asymmetrically pyriform (Fig. 10 a-c), its nozzle having a thick refractive cuticular cap, and lying in close contact with the largest developing ovum, and bearing sperm internally; caudal organ (Fig. 10 a) is of medium length, its fore half appearing glandular, and reducing in size proportionately with age (Fig. 10 c), its rear half having an internal canal and a spiral muscular covering, except for the rearmost sac; caudal organ barely overlaps the rear of the frontal organ, and not at all in older specimens.

Ecology: Common in frequency of occurrence (30-60% 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, medium sorted to very fine-very coarse, poorly sorted silicious to coralline sand, with coral debris, at mean low water to extreme low water, 0-15 cm depth, occasionally occurring on a tombolo; sublittoral in fine, medium-well sorted to very fine-very coarse, very poorly sorted silicious to coralline sand, with coral debris at 1-15 m water depth, sometimes occurring in troughs and bars, between patches of healthy or unhealthy fringing reef, between coral platforms or in depressions in coral platforms.

Geographical distribution:

MED SEA:EGYPT {Betash 'Agami [video], Marsa Matruh, Sidi Abd al-Rahman [video]}. RED SEA:EGYPT:{Abu Ramada 1, Abu Ramada 2 [2-videos], Abu Ramada 3, Sharm el-Arab Outside, Wadi 'Araba, Marsa Bareika N, ^Marsa Bareika W [dom] [video], Daghashland, Ein Sukhna, Giftun Island SE [video], Giftun Island SS [sdom], Main Beach Ras Mohamed NP [video], Mugawish [dom], Na’ama Bay N [dom], Na’ama Bay S [3-videos], Nabq [dom], Nabq S [sdom] [3-videos], Sharm el-Naga [cdom], Ras Nasrani, Nuweiba, Princess, Ras Qanti, Safaga, Ras Sudr [video], Tareef el-Reeh, 'Uyun Musa, West Gate Ras Mohamed NP [dom] [video]}; ISRAEL: {Coral Beach M3 [3-videos] & M4, Coral Beach S [video], North Beach [2-videos], Snuba DS} PACIFIC NE:HAWAIIAN ISLANDS: {Oahu: Hālona, Ka’a’awa [2-videos], Kaiona [sdom] [video], Penalu’u [video]}

Remarks:

There are 25 video sequences of Macrodasys scleracrus sp. n. most from the upper Red Sea in Egypt and Israel, but some as well from the eastern Mediterranean Sea and from Oahu in the Hawaiian Islands. Ten of these are available as MPEG 2 (and MPEG 1) from Hummon (2009), seven from Egypt and three from Hawaii (collected by the author in 1994 and 2000/2003, respectively): from Egypt are #1320 a mature adult of Lt=800 µm (LPh=300 µm) from Abu Ramada, near Hurghada; #1315 a mature Lectotype adult of Lt=635 µm (LPh=207 µm), collected in July 1994 from Nabq S, S. Sinai; #1314 a mature adult of Lt=540 µm (LPh=159 µm) from West Gate, Ras Mohamed NP, S. Sinai; #1311 a mature adult of Lt=438 µm (showing reproductive organs) from Na’ama Bay, S. Sinai; #1316 a barely mature adult of Lt=394 µm (LPh=161µm) also from Nabq S; #1319 a subadult of Lt=215 µm (LPh=110µm) also from Abu Ramada, near Hurghada; and #1321 a juvenile of Lt=135 µm (LPh=70 µm) from Ras Sudr. From Hawaii are #2550 a mature adult of Lt=553 µm (LPh=262 µm) from Ka’a’awa Beach, Oahu; #2565 a subadult of Lt=407 µm (LPh=213 µm) from Penaluu Beach, Oahu; and #2551 a juvenile of Lt=135 µm (LPh=70 µm) from Ka’a’awa Beach, Oahu. This is the only new species of Macrodasys that occurs both on the Red Sea (IndoPacific Ocean) side and on the Mediterranean Sea side of the Suez Canal; it might be a Lessepsian migrant, since each of its Mediterranean occurrences occurs west of the openings of the Suez Canal, the direction of prevailing currents.

Etymology:

Scleracrus (Greek: scleros + akros = meaning 'hard, tough summit, peak’) refers to the refringent cuticular nozzle cap on the frontal organ.

Taxonomic affinities:

Macrodasys scleracrus sp. n. is the only species in the genus with a stepped anterior, with pestle organs in the step, a medium tail, and a PhJIn of U29-U47, which also has TbA=7-8 per side in arcs; a TbL formula of 11=0,2/9,0 (0 along the fore half and 2 along the rear half of the pharynx/9 along the rear intestine and 0 behind the anus); a TbV formula of 14=0,0/14,0; and TbP=11-12 per side, with TbD absent.

Several species have frontal organs that are tipped by a small cuticular nozzle: Macrodasys achradocytalis Evans, 1994; Macrodasys cunctatus Wieser, 1957; Macrodasys fornerisae Todaro & Rocha, 2004; Macrodasys gerlachi Papi, 1957; Macrodasys imbricatus sp. n., Macrodasys syringodes Hummon, 2010; and Macrodasys thuscus Luporini, Magagnini & Tongiorgi, 1973, but only Macrodasys sp. A of Schmidt (1974: Figs. 5, 6) shows an animal that has a full cuticular cap (Schmidt: Fig. 6D, not Fig. 5D). Todaro (personal communication) has seen specimens from Santa Cruz, one of the Galapagos islands from which Schmidt reported Macrodasys sp. A., which he holds "can without a doubt be attributed to that species", notwithstanding that Schmidt erred in his contention that testes originated well forward in the pharygeal region rather than at the pharynx-intenstinal junction where they usually occur. Todaro holds that Macrodasys scleracrus cannot be Schmidt’s Macrodasys sp. A because of differences in the shape of the caudal organ and the shape of the nozzle of the frontal organ, and differences between the two species with regard number and arrangment of the adhesive tubes of the TbL series. While I have not seen specimens from Schmidt’s collecting areas, I note that his TbL arrangement is confused by the composite habitus drawing of Schmidt that does not distinguish dorsal from ventral features, that the caudal organ in Macrodasys scleracrus sp. n. is somewhat variable, and that the new species was found several times on Oahu in the Hawaiian Islands. In my estimation, the reproductive similarities of the frontal organ outweighs other differences, and argues that Macrodasys sp. A may be a variant of Macrodasys scleracrus sp. n.