Acanthascus (Acanthascus) alani microdiscoctasterus, Tabachnick & Menshenina & Ehrlich, 2023

Tabachnick, K. R., Menshenina, L. L. & Ehrlich, H., 2023, Rossellidae (Porifera: Hexactinellida) from the Bering Sea and off Bering Island, Invertebrate Zoology 20 (1), pp. 57-89 : 60-62

Acanthascus (Acanthascus) alani Ijima, 1898 Acanthascus (Acanthascus) alani microdiscoctasterus ssp.n.

Figs 1 , 2 ; Suppl. Tab. 1.

MATERIAL. Holotype: IORAS 5 /2/3805. RV ‘ Akademik M.A. Lavrentyev’ – 75, ROV ‘ Comanche’, sta. 18, spec. 5-2, 55.4352° N 167.2668° E, 1420 m.

DESCRIPTION. BODY. Funnel-like body with smooth dermal and atrial surfaces, about 500 mm

high with 2 oscula about 80 mm in diameter. The sponge was attached to rocky substratum; its basal part is about 100 mm in diameter. Some irregular prostalia diactins are observed, they are generally oscularia but some of these spicules are lateralia. The walls of this specimen are up to 25–30 mm in thickness. Only a portion, about 100x 100 mm and 10–25 mm in thickness, from the upper part of this sponge was sampled, a largest portion of the holotype specimen was left on the bottom alive. The collected material was reduced to many lamellate fragments during the fixation and transportation.

SPICULES. MEGASCLERES. Choanosomal spicules are diactins with stout, smooth shafts, and rounded, rough outer ends. These diactins are 1.4–4/ 0.004 –0.013 mm. Several hypodermal pentactins with smooth and spiny tangential rays were found among the spicule preparations, they likely belong to other representatives of Acanthascus numerously distributed around this specimen. Dermalia and atrialia are very similar, both consisting of pentactins, hexactins, some stauractins and rare diactins with short-spiny rays and rounded outer ends. Most pentactins and some stauractins have tuberculated rudiments of the absent rays. The only difference between dermal and atrial spicules is the dominance of pentactins in the dermal sides of the colony and hexactins in the atrial sides. Dermal pentactins have tangential rays 0.081 –0.196 mm long (n=25, avg: 0.150 mm, std: 0.029 mm), the proximal rays 0.104 – 0.233 mm long (n=25, avg: 0.169 mm, std: 0.032 mm), and rudiments of the distal ray if present 0.007 –0.019 mm long (n=19, avg: 0.011 mm, std: 0.002 mm). The diameter of these rays is 0.009 – 0.015 mm. Dermal hexactins have rays of equal length 0.159 –0.252 mm long (n=3, avg: 0.201 mm, std: 0.047 mm). Stauractins have tangential rays 0.137 –0.189 mm long (n=3, avg: 0.158 mm, std: 0.027 mm), their rudimental tubercles if present are 0.007 –0.015 mm long (n=3, avg: 0.012 mm, std: 0.004 mm). Some unique diactins have rays about 0.222 mm long with a widening in the middle. Atrial pentactins have tangential rays 0.085 –0.178 mm long (n=13, avg: 0.144 mm, std: 0.024 mm), the ray directed inside the body is 0.074 –0.204 mm long (n=13, avg: 0.145 mm, std: 0.033 mm), the rudiment of the distal ray if present is 0.007 –0.019 mm long (n=13, avg: 0.010 mm, std: 0.003 mm), the diameter of these rays is 0.010 –0.011 mm. Atrial hexactins have rays 0.104 –0.326 mm long (n=26, avg: 0.170 mm, std: 0.046 mm). Atrial stauractins have tangential rays 0.111 –0.144 mm long (n=3, avg: 0.132 mm, std: 0.018 mm), their rudimental tubercles if present are 0.011 –0.015 mm long (n=4, avg: 0.013 mm, std: 0.002 mm).

MICROSCLERES. Discoctasters are common and rare discomultiasters are present in this species. Unlike discohexasters, discomultiasters have more than 8 tufts of secondary rays — up to 11, sometimes these additional secondary rays have a single secondary ray, but usually they have 2–8 secondary rays in a tuft. The secondary rays of discoctasters have spiny shafts. Some discoctasters have a specific shape with 4 secondary ray tufts located in one plane distributed at about 90 degree to each 4 other secondary ray tufts which are similar to the former ones are situated below it. Some discoctasters without developed secondary rays were found. The discohexasters are 0.036 –0,079 mm in diameter (n=25, avg: 0.061 mm, std: 0.010 mm), their primary rosette is 0.025 – 0.050 mm in diameter (n=25, avg: 0.038 mm, std: 0.007 mm). Spherical discohexasters with numerous secondary rays are 0.023 –0.036 mm in diameter (n=20, avg: 0.028 mm, std: 0.003 mm), their primary rosette is 0.006 –0.014 mm in diameter (n=20, avg: 0.009 mm, std: 0.002 mm). An occasional spherical discohexaster is 0.065 mm in diameter with primary rosette 0.011 mm in diameter. A unique stellate discohexaster was also found with 3–4 secondary rays 0.054 mm in diameter with the primary rosette 0.027 mm in diameter. Oxyoidal microscleres are very fragile and in the spicule preparations they were usually broken with their primary rosettes and secondary rays separated. The secondary rays (1–3 in number, but sometimes up to 7) have finest part at base what provides the effect described above, they are covered by numerous spines directed towards the spicular center especially at their basal part. Many oxyoidal microscleres have secondary rays of different length. The oxyoidal microscleres included oxyhexasters,oxyhemihexasters (mostofthesetwoforms should be rather called anysooxyhexasters and anysooxyhemihexasters) and hexactins. The oxyhexasters and oxyhemihexasters are 0.067 –0.281 mm in diameter (n=26, avg: 0.139 mm, std: 0.035 mm), their primary rosette is 0.008 –0.022 mm in diameter (n=20, avg: 0.013 mm, std: 0.003 mm). A unique oxyhexaster was 0.027 mm in diameter with primary rosette 0.009 mm in diameter. The oxyhexactins are 0.126 –0.154 mm in diameter (n=7, avg: 0.154 mm, std: 0.025 mm).

REMARKS. In the presence of the set of dermal spicules and fragile oxyoidal microscleres when such spicules easily split to primary and secondary rays the new subspecies is similar to two previously described subspecies: A. (Acanthascus) alani alani Ijima, 1898 and A. (Acanthascus) alani profundus Koltun, 1967 . The differences are in the sizes of discoctasters, the presence of discomultiasters and in the similarity between dermal and atrial spicules in the new subspecies (in previously described subspecies atrialia are generally hexactins). Hypodermal pentactins with smooth and spiny tangential rays found in the new subspecies are considered to have allochthonous origin but meantime they point the close affinities between tree subgenera of Acanthascus which taxonomic status was downgraded by Tabachnick (2002b). It is very likely, that these subspecies should be raised to the species level but due to the historical tradition and comfort in identification of multispecific taxon Acanthascus its taxonomic position is preserved at the moment. A question of rising of the status of all the described subspecies to specific level requires futher investigations.

ETYMOLOGY. The subspecies name reflects the characteristically small size of discoctasters.

DISTRIBUTION. Currently found only at the Piip Volcano slope, Bering Sea, at 1420 m depth.

Figures

Fig. 1. Acanthascus (Acanthascus) alani microdiscoctasterus ssp.n. Complete specimen before ROV ‘Comanche’ sampling. Рис. 1. Acanthascus (Acanthascus) alani microdiscoctasterus ssp.n. Целый ЭкЗемплЯр перед вЗЯтием обраЗца подводным роботом “Comanche”.

Fig. 2. Spicules of Acanthascus (Acanthascus) alani microdiscoctasterus ssp.n., holotype. A — dermal stauractin. B — dermal hexactin. C — dermal pentactin. D — dermal diactin. E–F — choanosomal diactins and their outer ends. G–J — discoctasters. K — primary rosette of discoctaster, secondary rays not developed. L — secondary ray of discoctaster. M–N — spherical microdiscohexasters. O — stellate microdiscohexaster. P–T — oxyoidal microscleres. U — primary rosette and secondary ray of oxyoidal microsclere. Рис. 2. Спикулы Acanthascus (Acanthascus) alani microdiscoctasterus ssp.n., голотип. A — дермальнаЯ стаурактина. B — дермальнаЯ гексактина. C — дермальнаЯ пентактина. D — дермальнаЯ диактина. E–F — хоаносомальные диактины и их концевые Элементы. G–J — дискоктастры. K — первичнаЯ роЗетка дисоктастра, вторичные лучи не раЗвиты. L— вторичные лучи дискоктастра. M–N — сферические микродискогексастры. O — ЗвеЗдчатый микродискогексастр. P–T — оксиоидные микросклеры. U — первичнаЯ роЗетка и вторичные лучи оксиоидной микросклеры.