Themiste ( Themiste ) pyroides ( Chamberlin, 1920 )

Themiste ( Themiste) pyroides ( Chamberlin, 1920) View in CoL

Fig. 6H View Fig

Dendrostoma pyroides Chamberlin, 1920: 3 ( type locality: Laguna Beach, California; intertidal).

Dendrostoma pyroides – Fisher 1952: 406–409, pl. 27 figs 1–2, pl. 28 fig. 2, pl. 29 (Ensenada and San Quintin Bay, Baja California).

Themiste pyroides View in CoL – Adrianov et al. 2006: 577–579, figs 1c–d, 7–10 (Vostok Bay, Sea of Japan).

Material examined

MEXICO – Baja California Sur • 1 spec.; La Paz Bay , El Caimancito Beach ; 24°12ʹ10.43ʺ N, 110°18ʹ01.09ʺ W; 28 Nov. 1986; depth 2 m; SSV leg.; under rocks; ECOSUR-S0251 GoogleMaps • 8 specs; La Paz Bay , El Caimancito Beach ; 24°12ʹ15ʺ N, 110°18ʹ02.96ʺ W; 29 Feb. 2004; depth 1 m; PSS and MTH leg.; inhabiting Porites sp. ; ECOSUR-S0252 GoogleMaps • 1 spec.; La Paz Bay , Calerita Beach ; 1 Mar. 2006; DHP et al. leg.; UMAR-SIPU 130 . – Sinaloa • 1 spec.; Mazatlan, Pinitos Beach ; 23°12ʹ28.022 N, 106°25ʹ32.69ʺ W; 3 Feb. 2004; depth 1 m; PSS and MTH leg.; associated with sabellariid tubes; ECOSUR-S0258 GoogleMaps .

Description ( UMAR-SIPU 130)

Trunk 12 mm in length, pyriform, caudal region pointed; smooth, light brown body wall, with small, flat oval papillae. Introvert as long as 0.75 of trunk length, with pigmented collar and tentacular crown base; tentacular crown with four stems divided into two branches, stems of ventral pair slightly longer than those of dorsal pair; each branch with eight terminal tentacles. Small, dark, claw-like hooks at posterior introvert.

Longitudinal musculature continuous; two retractor muscles attached to body wall at 50% of trunk length; contractile vessel with 15 tubules. Two nephridia, of 25% of trunk length; nephridiopores before anus. Spindle muscle present, attached to intestine anteriorly and to trunk posteriorly.

Habitat

Intertidal to subtidal ( 1–2 m); under rocks, inhabiting Porites sp. , and associated with sabellariid tubes.

Distribution

Eastern Pacific: from California to the Gulf of California.

Remarks

Themiste ( T.) pyroides may be confused with T. ( T.) blanda ( Selenka & de Man, 1883) ; however, the main difference between the species concerns the tentacular crown. Themiste ( T.) blanda has the branches symmetrically divided, in addition to bearing tentacles along the inner face of the stems and branches, whereas T. ( T.) pyroides only has terminal tentacles and the branches are not divided symmetrically. According to Cutler (1994), T. ( T.) pyroides is distributed in the eastern Pacific, from southern Alaska ( Frank 1983) to the western coast of Baja California ( Fisher 1952); however, the Alaska record should be reviewed, because the temperature range tolerance for this species has not been investigated and it seems unlikely that a subtropical species such as T. ( T.) pyroides would occur at such low temperatures. Furthermore, there are no records of this species farther north than its type locality, apart from Frank’s record ( Frank 1983). In the northwestern Pacific of Mexico, T. ( T.) pyroides extends its distribution from the west coast of Baja California to the Gulf of California ( Sinaloa).

Themiste ( T.) pyroides has also been recorded from the Sea of Japan ( Adrianov et al. 2006, 2008); however, the latter study was based on a molecular analysis and concluded that the eastern and western populations are two distinct clades at the molecular level ( Schulze et al. 2012). This may suggest that both populations could be part of a species complex, which should be addressed using morphological and molecular evidence.