Collastoma esotericum, Huston, 2019

Huston, Daniel C., 2019, Collastoma esotericum (Neodalyellida: Umagillidae), a new species of sipunculan-inhabiting rhabdocoel from Queensland, Australia, Zootaxa 4701 (6), pp. 563-573 : 568-569

Collastoma esotericum n. sp.

ZooBank LSID: http://zoobank.org/ urn:lsid:zoobank.org:act:E9CA2D61-C8ED-4BC0-A55D-699BCFE1F91B

Type host. Phascolosoma scolops (Selenka & de Man) .

Site in host. Intestine.

Prevalence. 15 out of 43 (35%).

Type locality. Moreton Bay ; mudflats off Dunwich, Queensland, Australia (27° 29’42”S, 153° 23”56’’ E).

Other localities. Moreton Bay; mudflats off Cleveland, Queensland, Australia (27° 30’38” S, 153° 16’70” E).

Type material. Holotype ( QM G238239 ) and 11 paratypes ( QM G238240–50 ).

Representative DNA sequences. 18S rDNA (GenBank accession number: MN 621251 ).

Etymology. The name is chosen because few are interested in worms and even fewer are interested in worms living within other worms.

Description. Figure 2 . Measurements in Table 2 .

Based on 12 whole-mount specimens. Body ellipsoidal, tapers slightly at posterior end; somewhat dorsoventrally flattened.Tegument ciliated. Mouth small, round, near anterior extremity, opens on ventral surface. Pharynx robust, subglobular. Oesophagus distinct, short. Intestine broad, margins irregular, lined with clear, anuclear, celllike bodies; extends posteriorly as far as ovarian complex.

Testis single, ventral to intestine, elongate, cylindrical, medial, extends from just posterior to oesophagus, narrows towards posterior half of body to unite with seminal vesicle. Seminal vesicle globular, swollen with sperm. Sperm duct thin, weakly sclerotised, tubular, arising at posterior of seminal vesicle, passes more or less straight posteriorly to genital atrium.

Ovaries two, parallel, in posterior fourth of body, ellipsoidal, recurved, each narrows about mid-length, curve ventrally towards longitudinal midline, unite with vitellaria forming short ovovitelloduct, then unite with seminal bursa. Paired vitellaria extend along left and right sides of body, respectively, from level of pharynx to seminal vesicle, each with two or three tandem branches originating in anterior third of body; distal ends narrow, join common ovovitelloduct. Seminal bursa saccular, dorsal to seminal vesicle, sperm duct and uterus, often containing sperm. Ductus communis indistinct, arises ventrally from seminal bursa, passes posteriorly to genital atrium. Vagina arises from dorso-distal portion of seminal bursa, passes posteriorly, unites with genital atrium posterior to union of ductus communis and genital atrium. Uterus blind, extends from genital atrium anterio-ventrally to seminal bursa, thin-walled, surrounds egg-capsule. Egg-capsule robust, golden-tan in colour; distinct stalk originates from posterior extremity of egg-capsule, bifurcates into two filaments, filaments extensively coiled in swollen, distal portion of genital atrium. Paired shell glands indistinct, saccular, on either side of genital atrium. Cement glands distinct, fan-like, posterior to shell glands. Common genital pore subterminal, opens on ventral surface.

Remarks. Collastoma esotericum is the first species of Collastoma described from Australia. It can be differentiated from the other species of the genus using a combination of characters. From Collastoma anderseni Roehl , C. esotericum differs in having a vitellarium with a simple, tandem branching pattern, with branches splitting in the anterior third of the body, versus the wide variety of branching patterns observed in C. anderseni where the branches begin splitting near the genital complex. Furthermore, according to Roehl and Bailey-Brock (2017) the uterus and egg-capsule is situated dorsal to the rest of the genital complex in C. anderseni , unlike all other species of the genus where the uterus and egg capsule are situated ventral to the rest of the genital complex. From Collastoma erimatae Beklemischev , C. esotericum differs in having a long, cylindrical testis which reaches the seminal vesicle rather than a short pyriform testis situated in the anterior of the body which reaches the seminal vesicle via a long, thin sperm-duct. Collastoma esotericum also has a vitellarium with 2–3 tandem branches per side rather than 3–6 parallel branches in C. erimatae . Lastly, C. erimatae has a pyriform body shape versus the elongate ellipsoidal body shape of C. esotericum . From Collastoma kozloffi Westervelt , C. esotericum differs in having a branched rather than unbranched vitellarium and a much smaller egg-capsule (~ 120 µm versus ~ 500 µm). Additionally, in C. kozloffi the testis is shorter, and the seminal vesicle is situated more anteriorly in the body relative to that of C. esotericum . From Collastoma minutum Wahl , C. esotericum differs in having a branched vitellarium rather than an unbranched one, a longer egg-capsule stalk, a longer and less robust testis and a longer and more distinct oesophagus. From Collastoma monorchis Dörler , and Collastoma pacifica Kozloff , C. esotericum differs in having ovovitelloduct ducts which enter the seminal bursa rather than the ductus communis and in having a branched, rather than an unbranched vitellarium. C. esotericum can be further differentiated from C. monorchis in having a sclerotised sperm duct rather than a non-sclerotised one. From Collastoma wahli Ponce de León & Mañé-Garzón , C. esotericum differs in having a vitellarium with a relatively simple, tandem branching pattern with branches extending along the left and right side of the body, versus the extensive, antler-like branching pattern of C. wahli . In C. wahli the egg capsule is situated further posteriorly, below the cement glands, versus above in C. esotericum . The testis of C. wahli is also depicted as much narrower than in C. esotericum , and the seminal vesicle does not overlap the testis in C. wahli as it does in C. esotericum .

Figures

FIGURE 2. Collastoma esotericum n. sp. A) Holotype. B) Holotype, genital complex. Abbreviations: cg, cement glands; dc, ductus communis; eg, egg-capsule; fi, filament; ga, genital atrium; gp, genital pore; in, intestine; mo, mouth; oe, oesophagus; ov, ovary; ph, pharynx; sb, seminal bursa; sd, sperm duct; sg, shell gland; sv, seminal vesicle; te, testis; ut, uterus; vg, vagina; vi, vitellarium. Scale bars: A) 500 µm; B) 200 µm.