Loxosomella decorata, Nielsen, Claus, 2017

Nielsen, Claus, 2017, Loxosomella decorata n. sp., a new solitary entoproct from San Juan Island, WA, USA, Zootaxa 4238 (4), pp. 594-596 : 594-596

Loxosomella decorata n. sp.

Holotype: Specimen found in the tubes of the maldanid polychaete Axiothella rubrocincta (Johnson, 1901) from an intertidal sandy-muddy bottom, False Bay, San Juan Island, WA , USA, July 2007, collected by Dr Tim Wollesen . SEM preparation deposited in The Natural History Museum of Denmark, University of Copenhagen: ZMUC-ENT-27. Fig. 1 A,D.

Paratypes: SEM preparations are deposited at The Natural History Museum of Denmark: ZMUC-ENT- 28, -29, -30 ( Fig. 2 B), -31 ( Fig. 2 C). The COI gene of other specimens was partially sequenced and the 710 bp sequence deposited in GenBank (acc. # JQ614997 ) ( Merkel et al. 2012).

Etymology: The specific epithet decorata refers to the crenelated latero-posterior edges of the attachment organs of the foot.

Description: A medium sized species total length (from the upper edge of the tentacle membrane to the ‘heel’ of the foot) up to about 950 µm. Twelve long tentacles in the adults and ten in the large buds. The width of the tentacle membrane is up to about 400 µm. The body is widest at the median part of the body, up to about 300 µm. From there, the body tapers gradually towards the foot; the lateral parts of the body below the stomach are thin ‘lateral wings’. The foot is up to about 275 µm long. It has a conspicuous foot gland, a foot groove with accessory gland cells, and a pair of rounded adhesive organs at the tip ( Fig. 2 B). Two cells of different appearance are associated with each adhesive organ, indicating a duo gland system ( Hermans 1983). The adhesive organs are thin with scalloped lateroposterior edges. Buds develop from a pair of latero-frontal zones level with the upper wall of the stomach. Up to two buds on each side have been observed. The largest bud had a total length of about 400 µm; it had ten tentacles. Up to 20 small eggs/embryos, diameter about 50 µm, have been observed in the atrium ( Fig. 2 A). The larvae are clearly of the small, planktotrophic type found for example in L. atkinsae ( Fuchs & Wanninger 2008) and L. elegans ( Nielsen 1971) .

Discussion: About 120 species have been referred to the genus Loxosomella s.l. ( Nielsen 2010; Varela et al. 2011). There is a wide variation of morphology, but a number of characters distinguish groups of species, which are sometimes treated as genera ( Iseto & Hirose 2010). The most important characters are found in the morphology and fate of the differentiated foot of the buds, the defining character of the genus ( Iseto & Hirose 2010). The attachment of the buds to the parent can be either with the tip of the foot or with the back side of the body. The foot can persist after attachment or be lost after having secreted the cement attaching the specimen permanently to the substratum (variable in a few species, see ( Nielsen 1964; Nielsen & Jespersen 1997)). The foot can have a pointed tip or it can have two or four small attachment organs at the tip, or papillae all the way around the foot; it may also have lateral, wing-like expansions. The number of tentacles seems to be rather constant in species with eight or ten tentacles, but to vary in species with higher numbers of tentacles. However species with 12 tentacles in the adults usually attain a stage with 10–12 tentacles already in the large buds, whereas species with higher numbers of tentacles appear to add new tentacles after settling of the buds.

The new species has 12 tentacles in the adult and 10 in the large buds. Its buds are attached to the parent with the tip of the foot, which is retained in the adults. The foot is of a type close to that described from Loxoxomella s.str. ( Iseto & Hirose 2010; Nielsen & Jespersen 1997), and it shows a pair of characteristic attachment organs at the tip ( Fig. 2 B). The foot lacks lateral wings. Among the previously described species, this combination of characters is found only in two species: L. elegans and L. vancouverensis ( Rundell & Leander 2012) . L. elegans has a prominent Y-shaped row of large cells on the posterior side if the body lacking in the new species and both species lack the characteristic scalloped lateroposterior edges of the attachment organs.

Figures

FIGURE 1. Loxosomella decorata. SEM (The body of the animal has shrunk during the dehydration). A, Holotype in frontal view. B, Paratype in right view. C, Paratype with a large and three small buds, frontal view. D, Foot of the holotype.

FIGURE 2. Loxosomella decorata. A, Half contracted specimen in frontal view, with a large and two smaller buds. B, Foot of a large specimen showing details of the structure (Nomarski contrast); the arrowheads indicate the two cells of the putative duo-gland adhesive system. Photos courtesy of Dr Julia Merkel (Johannes Gutenberg University, Mainz).