Taeniogyrus tantulus O'Loughlin 2007, sp. nov.

Taeniogyrus tantulus O’Loughlin sp. nov. Figures 4c,d, 6, 7 Material examined. Holotype: Victoria, East Gippsland, Ninety Mile Beach, off McGaurans Beach, 800 m offshore, 10 m, fine sand, strong currents, LVWSB: SWOP 1, stn 7, Site 2, 31 Dec 1979, data from J. Carey and J. Watson, NMV F59198. Paratypes: Type locality and date, F59199 (11, with many microscope slides). Other material. Type locality and date, F82710 (many); stn 6, 31 Oct 1979, F80938 (many). Description. Up to 11 mm long, 2 mm diameter at oral and anal ends (preserved); preserved form commonly with oral and anal ends swollen, mid-body contracted and narrow, anterior dorsal body and tentacles overhang ventral body and tentacles; tentacles digitate, 10, each with 4–5 pairs of digits, longest pair distally, shortest pair proximally; calcareous ring with 5 radial 5 interradial plates fused to form narrow ring; radial plates low, with anterior narrow indentation between 2 low rounded projections, shallow concave posterior indentation; interradial plates with anterior indentation with 1 lateral low rounded projection, shallow concave posterior indentation; single dorsal stone canal, madreporite; 1 polian vesicle, ventral; narrow band of ciliated funnels along mid-dorsal interradius, on both sides of mesentery attachment; 2 unbranched gonad tubules, 1 on each side of dorsal mesentery, joined dorsally at shared gonoduct. Body wall ossicles wheels, sigmoid hooks: wheels adjacent to longitudinal muscles in interradii of body wall, sparse in ventral interradii, wheels only ossicles anteriorly, wheels with rounded hexagonal form, 6 spokes, inner margin of rim parallel to outer margin, inner margin with continuous teeth, wheel diameters 40–104 μ m; sigmoid hooks absent anteriorly, scattered throughout interradii in mid-body, more numerous and slightly smaller than wheels, outer curved side of some hooks with spinelets, hook lengths 60–80 μ m. Tentacles with rod ossicles: rods not swollen centrally, ends with short lobed branches, rods lacking side branches or denticulations, rods 40–64 μ m long. Colour (preserved). White, translucent. Distribution. Eastern Victoria, East Gippsland, offshore sediments; 11 m. Etymology. From the Latin tantulus (so small), referring to the very small size of specimens of this species. Remarks. T. tantulus sp. nov. is distinguished in the key (above) from the other species of Taeniogyrus Semper in southern Australia. It is a very small holothuroid, extremely abundant in the off-shore sublittoral sediments of east Gippsland. Data from Jan Watson (pers. comm.) gives estimated populations at Stns 6 and 7 of 13,870 per square m. Jan noted (pers. comm.) that nearby sites had only a few individuals. There was no evidence of internal brood-protection or fissiparity in the many individuals examined, but such reproductive strategies could be seasonal. The only material examined here was collected in mid-summer.Taeniogyrus tantulus O’Loughlin，新种 图版4c、d，图6、7 检视标本：正模标本采自维多利亚州东吉普斯兰地区九十英里海滩麦高恩斯海滩外海，离岸800米，水深10米，细沙底质，强流环境，采集信息为LVWSB: SWOP 1，站位7，位点2，1979年12月31日，数据源自J. Carey与J. Watson，馆藏号NMV F59198。 副模标本：模式产地与采集日期同正模，馆藏号F59199（11号标本，附带多张显微镜玻片）。 其他标本：模式产地与采集日期同正模，馆藏号F82710（多份）；站位6，1979年10月31日，馆藏号F80938（多份）。 形态描述：保存标本体长可达11mm，口端与肛端直径约2mm；保存标本的口端与肛端常呈膨大状态，体中部收缩变窄；背面前部及触手覆盖于腹面体壁与触手之上；触手呈指状，共10支，每支具4~5对指状小枝，最长的一对位于远端，最短的一对位于近端；石灰环（calcareous ring）由5块辐板（radial plates）与5块间辐板（interradial plates）愈合形成窄环；辐板低平，两低圆突起间具前侧窄凹陷，后侧具浅凹缺；间辐板的前侧凹陷具1个外侧低圆突起，后侧具浅凹缺；具单个背侧石管（stone canal）与筛板（madreporite）；1个波里氏囊（polian vesicle），位于腹侧；沿背中部间辐区、在系膜（mesentery）附着两侧，具一窄带纤毛漏斗；2条不分枝的生殖管（gonad tubules），位于背系膜两侧，以共同的生殖管（gonoduct）在背侧汇合。 体壁骨片包括轮形体（wheels）与S形钩（sigmoid hooks）：轮形体分布于体壁间辐区的纵肌附近，腹侧间辐区较为稀少，体前部仅存轮形骨片；轮形体呈圆角六边形，具6根辐条，环的内缘与外缘平行，内缘具连续的齿状结构，轮径40~104μm；S形钩在体前部缺失，散布于体中部的间辐区，数量略多于轮形体且尺寸稍小，部分钩的外侧弯曲面具小棘突，钩长60~80μm。 触手骨片为杆状体（rod ossicles）：杆状体中部不膨大，末端具短的分叶状分枝，无侧枝或齿状突起，杆长40~64μm。 保存体色：白色，半透明。 分布：维多利亚州东部东吉普斯兰海域离岸沉积物中，水深11m。 词源：源自拉丁语tantulus（意为“极小的”），指代本种标本体型极其微小。 讨论：本新种T. tantulus sp. nov.可通过前述检索表与澳大利亚南部的细枝海参属（Taeniogyrus Semper）其他物种区分。本种为体型极小的海参类，在东吉普斯兰的近岸亚潮带沉积物中极为丰富。据Jan Watson的个人交流数据，站位6与7的种群密度估计为13870个/平方米。Jan还提及（个人交流），邻近位点仅采集到少量个体。本次检视的大量标本均未发现体内育幼或裂体生殖的证据，但这类生殖策略可能具有季节性。本次仅检视了仲夏采集的标本。