Doconesthes robinsoni, Goodwin, Claire E., Berman, Jade, Janussen, Dorte, Göcke, Christian & Hendry, Katharine R., 2016

Goodwin, Claire E., Berman, Jade, Janussen, Dorte, Göcke, Christian & Hendry, Katharine R., 2016, Hexactinellida (Porifera) from the Drake Passage (Southern Ocean) with a description of three new species, Zootaxa 4126 (2), pp. 207-220 : 211-212

Doconesthes robinsoni sp. nov.

Type material. Holotype: MNHNCL POR–15002 Dried sample, small sub-sample rehydrated with Decon–90, tissue section and spicule preparation on slides. Sub–sample of above deposited as BELUM.Mc2015.345 (spicule preparation only). Cruise sample number NBP1103–T0104–sponge20. 31 st May 2011 Sars Seamount 59° 43.43’S 68° 45.38’W, 570–820m, Otter Trawl.

Etymology. Named after Dr Laura Robinson who was a principal scientist on RVIB Nathaniel B Palmer Cruise NBP11–03 on which these sponges were collected.

External morphology ( Figure 3 A–C). The single specimen is a flattened sac, cream to light brown in colour (both when fresh and preserved). The sponge was dried after collection and it has only been possible to examine the dried and rehydrated specimen so details of living form may have been lost. The end of the sponge had been removed for preservation in alcohol and has completely disintegrated. The overall form is an oval sac 10 cm in length and 8 cm wide with a thickness of around 2 cm. At the top of a sponge is a single large osculum which opens to a large atrium. Because the specimen has been damaged it is not possible to see the exact form of this but the atrium appears to have a maximum diameter of 5 cm with one thin wall (~ 4 mm) and one thicker wall (1.5 cm). Presumably the sponge was originally attached at one of the narrow ends of its oval body, but the sample has been detached from its substrate by the trawl. There is no visible root tuft and attachment was basiphytous, directly onto the body. The consistency of the preserved specimen is fairly soft and it fragments easily.

Skeleton. Confused mass of diactins with a dermal layer of pentactins and rough diactins and an atrial layer of hexactines and pentactines.

Spicules. Hypodermal pentactins ( Figure 3 D): Pentactins with four long tangential rays and a short proximal ray. From the tip to about 1/3 of the way up the ray is slightly spined. Proximal ray 53–(98)–203 by 22.1–(33.8)– 58.7 µm, tangential rays 323–(463)–652 by 16.8–(38.8)–56.3 µm. Hypoatrial pentactines of a similar form but smaller size – proximal ray 33–(63)–128 by12–(24)–31 µm tangential rays 231–(304)–355 by 17–(22)–27 µm.

Atrial hexactines ( Figure 3 E). Spined for about ½ to 2/3 of their length. Ray length 197– (312) –467/20– (25) – 33 µm.

Dermal diactins ( Figure 3 G): Entirely spined diactins with rounded ends. Centrum marked by a large swelling indicating that spicules are probably derived from hexactins. 206–(251)–295 by 10.0–(13.6)–20.3 µm.

Choanosomal diactins ( Figure 3 F): Large diactins which are slightly spined at their tips. Tips sometimes tapered and sometimes coming to a fairly abrupt point. Centrum often slightly tylote. 1110–(2118)–3084 by 13.3– (20.7)–28.8 µm.

Oxyoidal microsceleres ( Figure 3 H): Oxyhemihexasters. The majority have six unbranched rays but in a few spicules one or more of the rays is divided in two. The spicules are slightly ornamented with small spines. Total length of rays (measured from centrum) 48–(59)–74 µm.

Strobiloplumicomes ( Figure 3 I): Total diameter 65.6–(81.5)–97.7 µm; Diameter across centrum 1.8–(2.5)–4.0 µm; Calyx diameter 17.0–(20.2)–22.7 µm; ray length 18.8–(29.2)–39.6 µm.

Diagnosis. As strobiloplumicome microscleres are present, this specimen is assigned to the subfamily Lanuginellinae . Within the family genera are divided between those which possess only one type of hypodermal pentactin and those which have a second, short toothed, anchorate, category ( Tabachnick 2002). As this specimen lacks a second category of hypodermal pentactins and pinular hexactins, pinular pentactins or discohexasters we have assigned it to the genus Doconesthes . The genus is poorly known and until recently was represented only by Doconesthes sessilis Topsent, 1928 . An additional species Doconesthes dustinchiversi Reiswig 2015 has recently been recorded from the north-east Pacific. Doconesthes sessilis was originally described from a basal fragment so its full complement of spicules may not be represented in the description. Specimens provisionally assigned to this species have also been recorded from the northern mid–Atlantic ridge ( Tabachnick & Collins 2008; Tabachnick & Menshenina 2013), however, as noted by Reiswig (2015), there are significant differences in spiculaton between the type and these two specimens (e.g. each has a different size class of dermal diactins) and a re-evaluation of their status may be warranted.

Our specimen differs from the type of D. sessilis in having smaller dermal and choanosomal diactins, smaller oxyoidal microscleres and strobiloplumicomes almost twice the size of those of the holotype D. sessilis and other recorded specimens. Our specimen differs from D. dustinchiversi Reiswig 2015 in having smaller oxyhemihexasters and lacking pinular hexactins (Table 1).

Figures

FIGURE 3. Doconesthes robinsoni sp. nov. Type specimen MNHNCL POR – 15002. A. Freshly collected specimen, scale in cm; B. Rehydrated specimen, scale in cm; C. Atrium of rehydrated specimen, scale in cm; D. Hypodermal pentactin, illustration traced from light microscope image, scale 100 µm; E. Atrial hexactine, illustration traced from light microscope image, scale 100 µm F. End of choanosomal diactin, scale 200 µm, light microscope; G. Dermal diactin, scale 100 µm, light microscope; H. Hemioxyhexaster, scale 10 µm, SEM; I. Strobiloplumicome, scale 10 µm, SEM, the frontal ray is missing.