Collastoma anderseni Roehl, 2017

Roehl, William R. & Bailey-Brock, Julie H., 2017, Collastoma anderseni sp. nov. (Rhabdocoela: Umagillidae: Collastominae), an endosymbiont from the intestine of the sipunculan Themiste lageniformis, Journal of Natural History 51 (15 - 16), pp. 843-852 : 844-849

publication ID	https://doi.org/ 10.1080/00222933.2017.1303549
publication LSID	lsid:zoobank.org:pub:5C7F80E0-0712-4159-9894-FABL8101E001
persistent identifier	https://treatment.plazi.org/id/03CB87F0-FFFE-2976-99A1-B8FA0D7A1F51
treatment provided by	Carolina
scientific name	Collastoma anderseni Roehl
status	sp. nov.

Treatment

Collastoma anderseni Roehl , sp. nov.

( Figures 1 – 4 View Figure 1 View Figure 2 View Figure 3 View Figure 4 )

Type material

Holotype. Whole mount, dorsal view

Holotype. length: 0.885 mm

Holotype width. 0.280 mm

Paratypes. Whole mounts, dorsal and ventral view

Host. Themiste lageniformis

Site of infection. Intestine

Locality. Hawai ’ i, O ’ ahu: Hawai ’ i Kai, intertidal zone; January and February 2016 Etymology. Collastoma anderseni sp. nov. is named after the late Danish author Hans Christian Andersen.

Full endosymbiont description. The body shape of Collastoma anderseni sp. nov. is ovoid and elongate with a thinner and tapering posterior end in live specimens. Body colour ranges from light pink in larger live specimens to translucent or opaque white in smaller living material. The pink colouration is similar to that of the sipunculan eggs and coelomic fluid observed in the body cavities of many individuals of the host T. lageniformis . Of the 25 live C. anderseni specimens measured, length ranged from 0.113 mm to 0.924 mm and was on average 0.588 mm (± 0.21). Width of specimens ranged from 0.051 mm to 0.289 mm and was on average 0.20 mm (± 0.605). The dorsal side of the body is completely covered in cilia and the ventral side appears to be partially ciliated.

In the anterior region of the worm near the mouth are subdermal unpigmented spots. These spots may be eyespots or the remnants of such and are easily observed in live specimens under dissection microscopes. The mouth is circular and ventrally oriented, and connects directly to the gut sac via a short pharynx. The margins of the gut sac are difficult to visualise even when stained, and as such the shape is not described here.

The single median testis, a defining characteristic of the genus Collastoma ( Stunkard and Corliss 1951) , originates from the seminal vesicle and extends past the anterior ends of the vitellaria to terminate just posterior to the mouth. The testis is rounded and elongate with a slightly granular texture and extends along one- to two-thirds the length of the body ( Figure 1 View Figure 1 ). In live specimens, part of the length of the testis appears filamentous; this feature was not seen in the preserved specimens. The seminal vesicle is ovoid to bean shaped and connects the testis to the genital atrium via a thin tubular sperm duct ( Figure 1 View Figure 1 ).

The paired vitellaria extend along the length of the worm and lie on either side of the testis. They extend anteriorly from a connection to the seminal bursa. The parallel ‘ V ’ shaped vitellaria are key distinguishing features of this species and most specimens have a principal bifurcation which originates near the seminal bursa. Vitellaria have variable shapes:

i. simple bifurcation ( Figure 4a View Figure 4 );

ii. secondary bifurcations; these may occur along one or both of the primary branches ( Figure 4b View Figure 4 );

iii. incomplete secondary bifurcation of one branch ( Figure 4c View Figure 4 );

iv. branch patterns in which a secondary bifurcation has occurred and the secondary branches have twisted around each other ( Figure 4d View Figure 4 );

v. large secondary bifurcation resulting in an overall trifurcated appearance ( Figure 4e View Figure 4 ); vi. incomplete secondary bifurcation yielding a club-like lobe ( Figure 4f View Figure 4 ).

Vitellaria may branch after the primary bifurcation as seen in the holotype ( Figure 2 View Figure 2 ): the holotype displays branching pattern (ii) with the medial branches of each vitellarium bifurcating a second time. Branches farther towards the anterior end of the vitellaria tend to be short and most frequently occur along the anterior-most tips of the organ. The medial branch of each vitellarium tends to be longer than its distal counterpart. In live samples, branches were not observed to terminate facing the posterior end of the animal. Ducts which presumably connect the vitellaria to the gut were observed in some specimens.

Connections between the vitellaria, ovaries and seminal bursa can be hard to distinguish, and it is not clear whether these organs are connected by a duct or by attachment muscles. The egg capsule and uterus, which are positioned dorsal to the seminal bursa, often obscure these features. The vitellaria appear to attach to the seminal bursa through a thin filament at the caudal base of the ‘ V ’ shape. A direct connection between the vitellaria and the adjacent ovary is sometimes observed and is termed the ovarian-vitelline connection (ov. in Figure 1 View Figure 1 ) for the purposes of this work. The paired ovaries are distal to the seminal bursa and often caudal to the vitellaria; however, in some preserved specimens ovaries may lie between and parallel to the vitellaria and the body wall. Each ovary connects to the seminal bursa and is filled with large visibly nucleated egg cells; egg cells increase in size with proximity to the ovarian ducts. The seminal bursa lies ventral to the egg capsule and is a round chamber which is sometimes filled with moving filaments of what is presumably sperm.

The seminal bursa connects to a tube which leads to the genital atrium ( Figure 1 View Figure 1 ). The sperm duct connects to a dorsal region of the genital atrium. The uterus connects to the length of the genital atrium between the genital pore and the sperm duct. Within the uterus of mature specimens, an egg capsule is present. The egg capsule is yellow to orange in both live and stained specimens, and appears chitinous ( Figure 3 View Figure 3 ). Attached to the caudal end of the egg capsule is an attachment filament which bifurcates into two loosely coiled strands. These strands may overlap, or in some specimens they are two distinct bundles which sit in a region anterior to the genital pore. The genital pore is a small opening that looks to be somewhat ventrally oriented.

On either side of the genital atrium, between the egg capsule filament bundles and posterior to the egg capsule, are the cement glands. The cement glands stain a dark pink and have a feathery and fan-like appearance. What appear to be shell glands were also observed in some live specimens (omitted in Figure 1 View Figure 1 ) when examined from a ventral view; shell glands appeared ventral to and on either side of the egg capsule.

Description of host. Host Themiste lageniformis ranged in length from 8.265 mm to 27.14 mm and were on average 15.87 mm (± 5.44) long and 4.84 mm (± 1.51) wide. Live worms were beige to whitish, lacked hooks on the introvert, and had the species-specific purple to dark blue pigment band at the anterior end of the introvert just before the tentacular crown.

Nineteen of the 21 sipunculans collected had the new species of Collastoma in the gut. The number of parasites in infested hosts ranged from 1 to as many as 21 worms. The average number of parasites per host was 7.04 (± 5.72). Nematodes were also observed in the guts of T. lageniformis , many of which were alive upon dissection of the host.