Hydroids (Cnidaria, Hydrozoa) of the Danish expedition to

More documents

Recommendations

Info

216 Fig. 63. Nemertesia indivisa (Allman, 1883); Samalon Island. A. Colony silhouette. B. One stem internode seen from above, showing arrangement of hydrocladia in four lateral rows. C. Hydrocladial segment. D. Lateral nematotheca. – Scales: A = 2 cm; B = 0.5 mm; C = 0.1 mm; D = 50 µm. Description Colonies with several unbranched or occasionally branched stems, 5–15 cm high, stems clustered, with laterally held hydrocladia all along most of the stem length giving impression of stems being pinnate. Stems thick, usually with distinct nodes but nodes may be indistinct in some regions, majority of internodes with four hydrocladia, less frequently two, six, or more. Hydrocladia originating on relatively short apophyses, each apophysis associated with up to four nematothecae and 1–2 or more close to apophysis. Coenosarc of stem canaliculated. Hydrocladia short in comparison to stem length, in four longitudinal rows but directed P. SCHUCHERT towards sides, in opposite pairs. Basal parts of younger stems may have only two lateral rows of hydrocladia, being thus truly pinnate, in distal parts the hydrocladia can be arranged around the stem in whorls comprising three hydrocladia each. Hydrocladia homomerously segmented by slightly oblique nodes, internodes quite short (0.4–0.5 mm), each with one hydrotheca and three nematothecae: one median inferior, tow laterals. Internal ribs absent. Median inferior nematotheca on slight elevation or not so. Hydrotheca cylindrical, depth 0.2–0.26 mm, diameter about 0.1 mm, adcauline wall completely adnate, adcauline and abcauline wall quite straight and nearly parallel, opening-plane perpendicular to internode axis, rim somewhat lowered on adcauline side. Lateral nematothecae 60 µm high, close to hydrothecal margin, ovoid to conical, upper and lower chamber nearly of same height, wall of upper chamber slightly incurved, rim emarginated on outer and inner side, emarginations on inner side much deeper, reaching bottom of upper chamber. Median inferior nematothecae longer, conical, rim not incurved, rim lowered on adcauline side only. Gonothecae not observed, according to Billard (1913) about 1 mm, irregularly lobed, flattened, with numerous nematothecae. Remarks The arrangement of the hydrocladia of Nemertesia indivisa (Allman, 1883) shows quite some variation. The majority of them are in four longitudinal rows and they are directed sideways. But also truly pinnate sections and sections with verticillate arrangement occur. Nemertesia indivisa with its mostly laterally held hydrocladia, the deep hydrothecae, and the lobed gonothecae furnished with nematothecae is somewhat unusual among it congeners. The peculiar gonotheca induced Allman (1883) to place this species in the new genus Sciurella, which has, however, not found general acceptance. Distribution Northern Australia, Indonesia. Type locality: Somerset Island, Cape York, Torres Strait, Australia, 9–18 m.
HYDROIDS OF THE DANISH EXPEDITION TO THE KEI ISLANDS Sibogella erecta Billard, 1911 Fig. 64. Sibogella erecta Billard, 1911a: 108. – Billard 1913: 61, fig. 51, pl. 3: fig. 32. – Billard 1929b: 72. – Vervoort 1941: 222. – Hirohito 1969: 27, fig. 18. – Hirohito 1995: 282, fig. 97g. Stechowia armata Nutting, 1927: 230, pl. 44: figs 1–2. Material examined: Kei Islands Expedition station 18. Description Colony comprising several erect stems, up to 10 cm high. Stem monosiphonic, composed of a trunk with spirally arranged side-branches, branches bearing hydrocladia. Main stems unsegmented, with numerous nematothecae in three rows. Side-branches homomerously segmented by transverse nodes, segments without hydrotheca, with a subterminal apophysis for hydrocladium, apophysis with a nematotheca and a mamelon, in middle of segment a further nematotheca. Hydrocladia alternate, segmented by transverse nodes, only one hydrotheca per hydrocladium, distal part modified into flexible process. First segment of hydrocladium simple (intersegment), with one nematotheca. Second segment long, bearing at distal end hydrotheca and three nematothecae: one median inferior far below hydrotheca, two laterals near margin of hydrotheca. Distal to hydrothecate segment several simple segments, each with one or two nematothecae thin, jointed flexibly and forming a tendril-like appendage. Hydrotheca cup-shaped, shallow, abcauline side 50 µm, diameter 70 µm, adcauline side adnate, rim even. Nematothecae all movable and two-chambered, conical, lower chamber longer than upper chamber, wall of upper chamber lower on one side. Gonothecae not observed, according to Billard (1913) pyriform, 0.3–0.34 mm long, in upper axil of apophyses of hydrocladia Remarks The flexible, modified distal hydrocladia with up to 12 segments (Billard 1913) make this species quite unique and immediately recognizable. It would be interesting to learn more about 217 Fig. 64. Sibogella erecta Billard, 1911. A. Colony silhouette. B. Part of side-branch with one hydrocladium. – Scales: A = 2 cm; B = 0.1 mm. its function, which is presumably defensive. Billard (1927) described the arrangement of sidebranches as in three longitudinal rows. In the present material, this arrangement is better described as spiral. Occasionally it is also pinnate.
Page 1 and 2:
HYDROIDS OF THE DANISH EXPEDITION T
Page 3 and 4:
Page 5 and 6:
Page 7 and 8:
Page 9 and 10:
Page 11 and 12:
Page 13 and 14:
Family Solanderiidae HYDROIDS OF TH
Page 15 and 16:
Page 17 and 18:
Page 19 and 20:
Page 21 and 22:
Page 23 and 24:
Page 25 and 26:
Page 27 and 28:
Page 29 and 30: HYDROIDS OF THE DANISH EXPEDITION T
Page 79: HYDROIDS OF THE DANISH EXPEDITION T
show all

Hydroids (Cnidaria, Hydrozoa) of the Danish expedition to

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?