Rhabdocalyptus trichotis, Reiswig, 2018

Reiswig, Henry M., 2018, Four new species of Hexactinellida (Porifera) and a name replacement from the NE Pacific, Zootaxa 4466 (1), pp. 124-151 : 137-141

Rhabdocalyptus trichotis n. sp.

( Figs 7 & 8 , Table 4)

Material examined. Type material: Holotype: RBCM 016-00227-001 , FV Ocean Agressor, Set 0 0 8, 12 May 2016, Bowie Seamount , 180 km W of Haida Gwaii (Queen Charlotte Islands), British Columbia, Canada, 53°17.4’N, 135°44.5’W, 714 m.

Species diagnosis. Rhabdocalyptus with long prostal diactins all around body; veil of raised pentactin hypodermalia limited to the area a few cm wide around the terminal osculum. Both dermalia and atrialia are mostly rough pentactins.

Description. Body form of the holotype is that of an ovoid tun, with a body length of 96.8 mm and width of 55.4 mm; the long axis intersects the attachment to small cobbles basally and the 19 mm diameter osculum apically. The entire body is densely covered by a layer of diactine prostalia ( Fig. 7A ) that radiate from low conules in small groups of 2–5 for an emergent length of 18–47 mm. A veil of raised pentactine hypodermalia extend apically from the low conules around the osculum and down the lateral body for 10.6 mm ( Figs 7B–C ) but below that area the pentactine hypodermalia are sparsely present but not raised. The dermal surface is formed by a lattice of loose pentactine and stauractine dermalia raised over the subdermal spaces and supported by diactine and pentactine hypodermalia ( Fig. 7D ). On lateral surfaces of the atrium, the atrial lattice supported by diactine hypoatrialia is closely adherent to the underlying choanosome ( Fig. 7E ), without an intervening subatrial space. Exit apertures of exhalant canals are uncovered on the walls of the atrium. The types of spicules composing the atrial lattice are pentactins and stauractins, or in some places, diactins ( Fig. 7F ). Body wall thickness is 7.9–10.6 mm. Color is light tan. The known distribution of the species is so far only that of the type location on Bowie Seamount, off Haida Gwaii, 714 meters depth..

Megascleres (for measurements see Table 4) consist of prostal diactins, hypodermal pentactins, choanosomal diactins, dermalia (mostly pentactine and stauractine plus rare tauactine and paradiactine) and atrialia (mostly pentactine plus stauractine, diactine, paratetractin, tauactine and hexactine). Prostal diactins ( Fig. 8A ) are large spicules usually with a smooth surface but some very small spines may be present subterminally; ray tips are sharply pointed and there is no detectable central swelling. About 10-11 mm of each prostal diactin lies within the body wall, irrespective of the length of the emergent part. Hypodermal pentactins ( Fig. 8B ) are regular or irregular and crucial or paratropal in shape. Among 136 raised ones, 93% are entirely smooth and 7% have robust thorns on the distal face of tangential rays; among 46 unraised spicules all are smooth and without thorns. Ray tips are bluntly pointed or rounded. Choanosomal diactins ( Fig. 8C ) are highly variable in size but size classes are not evident in size-frequency analysis. These are mostly smooth spicules with rough ends, often rounded or even inflated; a swollen centrum is often small but always detectable. Dermalia ( Fig. 8D ) are mostly rough regular pentactins (68% of 493 counted) and stauractins (28%) with a few tauactins, paratetractins, bent diactins (together 6%) and no hexactins; ray tips are rounded. Atrialia ( Fig. 8E ) assessed at 5 locations, are consistently mainly rough regular pentactins (69.7% of 885 counted) but the second most abundant is either stauractins (12.1% overall) or diactins (10.5% overall); less abundant are tauactins (3,6%), paratetractins (2,5%) and hexactins (1.6%). Ray tips are rounded. Only pentactins, stauractins and diactins have been measured for Table 4.

Microscleres (for measurements see Table 4) are discoctasters, oxyhexasters, hemioxyhexasters, oxyhexactins and microdiscohexasters. Discoctasters ( Fig. 8F ) are highly variable in size but classes are not demonstrated in frequency histograms; the dermal ones are generally smaller than the atrial ones (180 vs 212 µm mean diameters) but there is complete overlap of ranges. Both primary and terminal rays are rough but the centrum is smooth. Terminal rays number 1– 4.4 –7 (n = 98) on each primary ray; they end in small button hemispherical discs not wider than the terminal ray shaft. Terminal rays often originate abnormally on the sides of primary rays and short curved processes project from the sides of the primary ray bases. Oxyoid microscleres consist of about 70% hemihexasters, 10% full hexasters, and about 20% hexactins. Oxyhexasters and hemioxyhexasters ( Fig. 8G ) are thin spicules with very short, usually smooth, primary rays bearing 1–3 rough, straight terminal rays ending in very sharp points. Oxyhexactins ( Fig. 8H ) are similar to the oxyhexaster but lack ray branching and are about 13% larger. Microdiscohexasters ( Figs 8I –J ) are minute compact spicules with each primary ray bearing ~20 terminal rays ending in hemispheric discs with ~6 marginal teeth. At resolution of the SEM available, both primary and secondary rays appear smooth and nearly the same length, the secondary rays only ~17% longer than primary rays.

Etymology. The species name is derived from the Greek word, trichotos, meaning "hairy".

Remarks. By the presence of both smooth and thorned pentactine hypodermalia as undoubted proper spicules, this specimen is assignable to the genus Rhabdocalyptus . Of the 17 accepted valid species, seven have dermalia as mostly or significantly pentactins as found here: R. dawsoni ( Lambe, 1893) , R. asper Schulze, 1899 , R. nodulosus Schulze, 1899 , R. tener Schulze, 1899 and R. tenuis Schulze, 1899 , and R. borealis Okada, 1932 and R. heteraster Okada, 1932 . However, all seven of these are unlike the present form in having atrialia as mainly or significantly hexactins (vs atrialia as mainly pentactins and hexactins being rare here). The combination of pentactin dermalia with pentactin atrialia is new for the genus and sets this specimen apart from all Rhabdocalyptus members. It is here considered to be the first known member and holotype of a new species, here named Rhabdocalyptus trichotis .

Figures

FIGURE 7. Rhabdocalyptus trichotis n. sp., holotype body. A. The holotype in lab. B. External view of distal end with conules and veil. C. Internal view of distal end with turned-in margin and veil. D. Dermal (outer) surface showing remnants of the dermal lattice. E. Atrial (inner) surface showing uncovered exhalant canals and atrial lattice directly applied to the underlying tissues and thus invisible. F. Atrial peel containing pentactins and diactins.

FIGURE 8. Rhabdocalyptus trichotis n. sp., holotype spicules. A. Prostal diactin, whole and two close-ups. B. Hypodermal pentactins, two whole smooth ones, lateral view of thorned one and close-up of thorned segment of tangential ray. C. Choanosomal diactins including four whole spicules, three magnified ends and a center segment showing insignificant center swelling. D. Dermalia, including whole pentactin, stauractin, tauactin, paradiactin and magnified ray tip. E. Atrialia, pentactin and diactin. F. Discoctaster, whole and close-ups of center, tuft of terminal rays and one terminal ray. G. Oxyhexaster and hemioxyhexaster with close-ups of spicule center and terminal ray. H. Oxyhexactin. I Microdiscohexaster at same scale as other whole microscleres. J. Microdiscohexaster enlarged to show detail.